Technology Day 2001—”Origins and Beyond: Our Place in the Cosmos”


HECHT: One of my
faculty colleagues says you can tell
the kind of class you’re in by the response. If it’s an undergraduate
class, there’s no response. They’re still asleep. If it’s a group of adults, you
get that kind of shout back. If it’s a group of
his graduate students, they write down the
words, good morning. [LAUGHTER] For the two or three of you who
don’t know me, I’m Bill Hecht. And for the last 21 years,
it’s been my privilege to be your executive
vice president. Now, I have done
this for 21 years. But four times during that
time are very special to me because I’m a 1, and most
of you are 6’s or 1’s. So for the best bunch of people,
the 6’s and 1’s, congratulate yourselves. [APPLAUSE] There is a small secret
which I’ll share, which is not a happy
thought, actually. I discovered not too
many years after I took this job that statistically
I was rapidly becoming an older alumnus. I tried to deny
that for many years. But as you can see by the
ribbon, this is our 40th. So I can’t deny it much anymore. Welcome to Saturday classes. Those of you who
are youngsters don’t understand that this used to
happen every Saturday morning. And we went usually
to lab on Saturday morning and worked very
hard over experiments, which we were all convinced
that Michelson and Morley lied, that Millikan had
oil in his glasses, not in his oil-drop experiment. But suffice it to
say, we all survived. And that’s part of what MIT
is about, surviving in style. It’s my great
privilege this morning to introduce you to yet another
spectacular Technology Day program. I must tell you a little secret. For 21 years, at the
end of this program we say, how in God’s name are
we going to equal this year, never mind be better? And each year, the
volunteers and my staff, with the great
collaboration of this unusual and rare and
extraordinary faculty, seem to do better. So it’s my great privilege to
start the morning proceedings by introducing my good friend,
Chuck Vest, President of MIT. [APPLAUSE] VEST: Thank you,
Bill, very much. And good morning to all of you. Welcome back to Cambridge. I think that we all know that
universities study and learn from the past. They have some
level of engagement in the future– in the present. And they have something
vaguely to do with the future. What really sets MIT apart from
most institutions, in my view, is while certainly we
respect and indeed try to learn a bit from the past, we
are really, among universities, very deeply engaged in the
present and, above all, really working very hard
to invent the future. And another characteristic,
I think, of this institution is that we tend to be involved
with big, important things and to ask big,
important questions. Well, today, we are going
to tune this very slightly, and we’re going to
take a look really into the very
distant past, as well as the present and the future. And we certainly are not going
to shy away from big questions. The program for
today’s event was inspired by this highly
characteristic painting by Paul Gauguin, tropical
paradise graced by stately figures who somehow
manage to look simultaneously moody and serene. I’ve seen those expressions
around this campus from time to time. [LAUGHTER] But there’s much
more going on here than in Gauguin’s customary
renderings of Polynesian life, because he chose
to use this panel to pose some of the eternal
questions in its title. Where do we come from? What are we? Where are we going? So you’ll notice that while
Gauguin asks these questions brilliantly, his painting is
very careful not to actually provide the answers. It’s a time-honored technique,
though perhaps more typically reserved for use
on mid-term exams. [LAUGHTER] And of course,
these are questions that genuinely resist being
answered in any simple or final or even definitive way. But today, we’re going to
try anyway, this being MIT. This morning, we’ll hear from
four outstanding scientists who will share insights from
their own lifelong pursuit of great answers about
origins, the origins of our universe, our solar
system, and, in a sense, of ourselves. This afternoon,
three separate panels will give us a
chance to look down the road toward some
thrilling new frontiers– what we are learning about the
development of mind, language, vision, and understanding,
some startling new materials and technologies that
will transform our lives, and the latest reports from
the realm of exploration from the depths of the
ocean to outer space. Gauguin, of course,
was not the only artist to consider fundamental
questions of our existence. For the class that just
graduated yesterday, the class of 2001, inevitably
Stanley Kubrick’s film 2001 has been sort of a mascot
over the last four years. And in fact, that film has
become such a cultural icon that it’s hard to remember that
it itself was based on Arthur C. Clarke’s wonderful book. But we’ve kind of forgotten
what it was really all about. Because for all of its
billing as a space odyssey, I think the deepest lesson is
that the simple truth that some of the most important,
undiscovered territories are to be found within us
in the mysterious recesses of our own hearts and minds. This morning, we’re
going to examine both ends of this
spectrum of inquiry, from the sources of our
universe and our planets, to the origins of
humankind, right down to the level of our own genome. These are exciting
times for discovery. And today promises to
reflect that excitement. We’re going to begin by hearing
from Eric Lander, followed by Claude Canizares. We will then take a brief
break, following which we will hear from Maria Zuber. Stephen Jay Gould
is unfortunately not able to be with us as
planned this morning, but he has asked us to let
you know that he very deeply regrets not being with us. However, we are really
very fortunate to be joined by one of Steven’s
colleagues, Charles R. Marshall. Charles will speak after Maria. Professor Marshall,
we are extremely grateful for your willingness
to join us on such exceedingly short notice. And just to– since this is MIT
we’ll quantify short notice. He’s down putting his slides
in the tray right now. [LAUGHTER] Following Professor
Marshall’s remarks, we’ll have a period for question
and answer back and forth between the audience
and our speakers. Let me begin by introducing the
first two speakers, those who will speak prior to the break. Eric Lander is professor
of biology here at MIT and a member of the Whitehead
Institute for Biomedical Research. He’s the director of
the Whitehead/MIT Center for Genome Research,
which, as you may know, was the largest single
contributor to the Human Genome Project. Last February, that project
published a draft sequence and initial analysis
of the human genome, the set of DNA-encoded
instructions that define an
individual person. Before Eric begins,
I want to tell you that we have something here
at MIT called Campus Preview Weekend. This is a weekend in which
we invite all the young men and women who have
been admitted to MIT but have not yet declared what
university they will attend. And we had here in Kresge this
spring a panel of MIT students so that the prospective students
could ask them questions. And one of the first questions–
one of these bright high school students held up
her hand and said, can you people
somehow characterize what’s it like to be at MIT? What’s good, what’s bad? And a hand immediately
shot up and said, the defining moment
of my time here at MIT was when Eric Lander spoke
to us all in room 10-250 about the final
publication of the sequence of the human genome. That really characterized
what this place is all about, and I think we would
all agree with that. Our second speaker this
morning is Claude Canizares, Bruno Rossi Professor
of Experimental Physics at MIT and Director of the
Center for Space Research. Claude is also Associate
Director of NASA’s Chandra X-ray Observatory Center
and leads the development of Chandra’s high-energy
transmission-grading spectrometer, just one of his
many space astronomy missions. While Eric is, in a sense,
an expert on inner space, Claude’s focus is clearly on
the far reaches of outer space. He’s a specialist in both
X-ray and optical astronomy, meaning that he studies stars,
galaxies, clusters of galaxies, quasars, and other
things which give us important clues to the
structure, evolution history of the universe. We begin with Eric Lander. [APPLAUSE] LANDER: Thanks very much, Chuck. Well, welcome to this day
about origins and beyond. I’m going to start
us off by talking about a variety of kinds of
biological origins, origins of life, origins of
human populations, origins of cancers, all of which
our knowledge about emerges from the work of the
Human Genome Project over the course of
the last 10 years. There’s another
important origin that runs throughout all of
what I’m going to say, which is that the origin of an
awful lot of the Human Genome Project and the data that’s
come out of it is here at MIT. MIT is woven completely
into all of this project, both the intellectual
ideas that got it started, the tremendous amount of
work that got it done, and particularly the
multi-disciplinary approaches involving biology, computer
science, and engineering, that made it possible for
it to happen here in a way that I think it couldn’t
have happened any place else. So let’s talk about origins. For thousands of
years, humans have recognized the tremendous
diversity in our own species and in the species around us. This is my favorite picture
to illustrate diversity, Wilt Chamberlain
and Willie Shoemaker here, showing the wonderful
diversity in our own species with respect to height
and weight and skin color. And to me, it’s also
emblematic of the differences that you don’t see, in
differences of susceptibility to diabetes and hypertension
and cancer, all of which are underlain by the action
of genes working together with environment. But of course, for thousands
and thousands of years, we could do little more
than say that traits tended to transmit in
families, and we really didn’t understand the
origin of this transmission. Well, the major
breakthrough, historically, was the work of
Gregor Mendel in 1865 when he published his one
great classic paper indicating that there were these abstract
particles that he could infer called genes that were
transmitted according to specific laws of
inheritance, in crosses. Now, as you may or may not
know, Gregor Mendel’s paper is a wonderful paper,
but it sank like a stone. It had no impact
on the world at all because the world just
wasn’t ready for it. Mendel, perhaps
somewhat discouraged, really never wrote much more
about genetics and, in fact, went into administration. And that’s pretty
much the last– [LAUGHTER] He became the abbot
of the monastery. [LAUGHTER] In any case, the real
revolution of genetics dates from about 35 years
later, in the opening weeks of the 20th century. In January of the year 1900,
three independent groups around the world rediscovered
Mendel’s laws, so to speak. They went back, and they
started doing crosses. They began to see
these regularities. And then they pulled
out this paper and recognized what its
tremendous importance was. And so the 20th century
started with a bang with the understanding
that there were laws that somehow controlled traits. The first quarter
of the 20th century was spent pinning down those
laws to a cellular structure. By about 1925, we had
a pretty good handle that the cellular origin
of these abstract laws were in the chromosomes. Of course, we didn’t have a
clue what the chromosomes did. Chromosome, just the
word “chromosome” itself is a tribute to
the scientific ability to cover up ignorance
with a fancy name. The only thing that
was really known about the structure
of chromosomes then was that they picked up a
dye when you stained the cells. And so they were
called chromosomes, meaning colored things. [LAUGHTER] It took another 25 years to
work out what these colored things really were. And by mid-century, we
were able to determine that the chromosomes had, as
their molecular basis, the DNA double helix, the work
of Watson and Crick, this iconic double-helical
image with information running on one strand
and a redundant copy on the other strand. Of course, this didn’t tell us
how, in an information theory sense, heredity was
encoded in this polymer. But the next 25 years
was spent working out the genetic code, the
understanding of how the sequence of bases encoded
messages, which went off to little factories in
the cell that turned them into proteins through a
process of translation according to a
genetic code, as well as the tools of recombinant DNA,
including very prominently here in Cambridge. And these tools
of recombinant DNA let us do what the
cell does, that is to say, copy and read out
particular pieces of DNA, and even to modify those pieces. So we got to about 1975
now with an ability to read some DNA sequence. Well, the last
quarter of a century has been a time of
voracious appetite to read everything we
can get our hands on. It started with the reading
of individual genes here and there, then more and more
genes, then small genomes, the entire collections
of genes in an organism, to somewhat larger genomes, to,
by the end of the 20th century, a first-pass reading of the
entire genome of the human being at 3 billion letters. It’s not bad for
a century, to have gone from a recognition
of abstract laws to essentially a comprehensive
read-out of the 3 billion letters underlying that. It’s a pretty good
century, although I think we ain’t seen nothing yet. In the last 10 years, 10 or
15 years of that century, it began to become
clear that we could use this kind of information
about genetic sequence to take a systematic approach
to understanding disease. Now, all through
the 20th century, people worked on disease,
and in some cases, they were very lucky
and were able to get to the basis of a disease. But as you well know,
luck is something you can’t count on
any particular day when you go into the lab. Far better would be to
have a systematic approach that you could apply to every
disease regardless of its type. Whether it was brain
degeneration or bowel irritation, you would like
to have a common approach. Well, that approach was
first laid out here at MIT in about 1980. The notion was a
very simple notion, that if you traced
the inheritance pattern of a
disease in a family, you could see that the disease
appeared to be transmitted according to Mendel’s laws. And if you could just
find a piece of DNA which had a spelling
difference that seemed to have the same
pattern of transmission, then, although that
piece of DNA might not be the cause of
the disease, well, it must lie fairly close by. And that is indeed this
notion of genetic mapping that was laid out for the
human being around 1980 or so and became operational here
in Cambridge in the mid-1980s. And it led to the identification
of many, many particular disease genes. Once you’ve found a marker
that was nearby, of course, you don’t have the gene
itself, what you have is a long work ahead of you. In fact, you have to go through
a very tedious process called chromosome walking,
or more formally, although we don’t call
it in the literature, chromosomal
schlepping, where you would start with the marker,
and then you would schlep along the chromosome, because
it’s incredibly tedious using one piece of DNA to get
the next piece, the next piece, the next piece, the next
piece, the next piece. And then four years later
and $40 million later, you might arrive at
the gene of interest, say cystic fibrosis on
human chromosome number 7. Well, here’s the sequence
of the cystic fibrosis gene. It’s got a lot of letters. It doesn’t look very impressive. But I’ve boxed for you one
particular little feature over there– I
better blow that up. There we go. Those three letters
CTT, those three letters are deleted in the
majority of chromosomes with cystic fibrosis. About 2%, 3% of
the population will carry that particular deletion. And in fact, on the way out
the door, if we wanted to, everyone could spit
in a test tube, and enough buccal
cells would come off from the inside of your cheek
to have enough DNA that we could just take it back across
the street to the lab, amplify it, and
tell you if you were a carrier for that deletion. You don’t have cystic fibrosis
unless you have a double dose, but we could tell you if you
were a heterozygous carrier. Well, not just that,
not just DNA diagnostics emerge from that, but
even more emerges. One can toss the sequence
of the cystic fibrosis gene into a computer and ask the
computer, ever seen anything like this before? And the computer says, oh,
yeah, this looks an awful lot like dozens and dozens of
genes whose products sit at the surface of the
cell and transport things back and forth. Congratulations. You’ve just found a transporter. Now this, of course,
stood on its head the usual way of doing biology. The usual way is when
you make a discovery, you go back to the
lab, and you spend years and years trying to
figure out what this gene does. Now you spend a couple of
seconds hitting the Return button, and the computer,
more often than not, comes back to you
and tells you what your gene does because
somebody somewhere else in the world in
some other organism has studied something
sufficiently similar that you have a
pretty good guess. That kind of
hypothesis generation by connecting all of
biological knowledge has led to a dramatic
explosion of research. Because in the old days, all
bits of biological research were separate from each other. Now they’ve all
been interconnected through this common
lingua franca of sequence. Well, the big
problem with all this was that it was
extremely tedious. It took four years, $40
million, about 200 people to get the cystic
fibrosis gene out. And as we all know, the
productive unit of science is the single, smart
graduate student or postdoc. And they’re not going to sign
up for something like this. This is not a good project. And so the job was to lower
the activation barrier, to level the barriers
to actually doing this, to create the infrastructure
so that a single graduate student or postdoc
would be limited only by her or his ideas, not
by the huge amount of work that was needed. But that meant we had to
engage in big science work to build infrastructure
in the service of that graduate
student and postdoc. And so it was born, the
Human Genome Project, the idea that we would
build genetic maps of polymorphic markers up
and down the chromosomes that would let us trace
inheritance, physical maps of the overlapping pieces
of DNA so we wouldn’t have to engage in
chromosome schlepping, but we could just
go to the shelf and pull down the
relevant piece of DNA. Sequence maps, so we wouldn’t
spend years sequencing out the DNA from a region
to find the gene, but we would just double
click on the region. And annotations of all those
genes and a description of all those genes so that
when one found a gene, one would have a pretty
good guess of what it did. At the time, we expected to
have about 100,000 genes or so. As I’ll tell you in
a moment, it appears that we have rather less. Well, more poetically,
what the project was about was building for biology
what the chemists had in the course of the 20th
century– a periodic table. The chemists had a periodic
table from about 1869 to 1889. Following Mendeleev’s
key insight, the chemists put
together a periodic table that described all of matter
in terms of about 100 building blocks. Those building blocks
were understood. Their relationships
were summarized in these rows and columns
of the periodic table, giving rise to the
chemical industry, giving rise to quantum
mechanics to explain all this. The variants on these elements–
the isotopes were understood. And this is, of course, the
basis of all of chemistry. Biology is now at the point
where it’s putting together its periodic table. There are just a
finite number of genes. May sound like a big
number, tens of thousands, 30,000 genes. But that’s a pretty
small number these days. We will, in relatively
short order, know them all in
pretty good detail, know all their variation,
know what they do. And the biology student
a decade or so from now will start with a pretty
good periodic table of all the components. Now, how is all this done? Well, from about 1985 when the
Human Genome Project was first conceived of, in 1990 when
it was actually launched, we needed to make just dramatic
changes in the way biology was done. Traditionally, the way you
would sequence DNA was you would clone the DNA in a little
piece in a bacterial cell. You would grow up the bacterial
cell on a Petri plate. You’d take a toothpick,
you’d pick it. You’d inoculate a culture. It would grow
overnight till you had enough of that bacterial colony
with that one piece of DNA. You’d centrifuge it down. You’d use organic reagents
to crack it– or you use reagents to crack it
open and organic solvents to be able to separate
the protein from the DNA. Then you’d, et
cetera– oh, god, it was just terrible
and really slow. And it was done one at
a time with pipettes. So a big concern in the period
1985 to 1990 about the Human Genome Project was,
would we consign an entire generation
of graduate students to some kind of servitude– [LAUGHTER] –sequencing DNA? Was this going to
be deadly boring? There was talk about doing
this in criminal institute– in penal facilities. [LAUGHTER] Sentencing people
to 10 megabases– [LAUGHTER] –with time off for accuracy. [LAUGHTER] Well, it didn’t
turn out that way. And it didn’t turn out
that way because biology met engineering. And so just a couple of
blocks away from here, here at MIT’s
Genome Center, this is the equivalent
of the toothpick. The toothpick now is
represented by robotics that run around the clock. They have cameras on them that
identify where the colonies are and 96 pins that go and pick the
colonies, dump them into media, wash themselves,
bake themselves, go pick 96 more, et cetera. And we pick 110,000 distinct
bacterial colonies a day. And all that a person has
to do is put the plates on and walk away. We don’t have to purify
all of these DNAs, set up sequencing
reactions, et cetera. Instead of the army of people
standing around with pipettes, it looks like this. This is the way we do
mini-preps for DNA. And this is very much unlike
a biology lab 10 years ago. What you see are
factory-style conveyor belts with microtiter plates
moving around the laboratory at a pulse rate
of one per minute. 110,000 of these
items being processed through the laboratory, all
the way from DNA purification through the set-up and clean-up
of a sequencing reaction. Once all of that
biochemistry is done, we have to put them
through detectors. There, the commercial
world has served us well by developing detector
machines that we can use. We have a farm of these
sequence detectors. We put on 10 plates on each
sequence detector, walk away, and it runs 24 hours unattended. All told, this whole operation
I’ve described to you, the actual number
of people involved in managing the workflow
there is under about a dozen and a half people managing
all of that workflow. At the end of the day,
this suite of machines turn out about 65
million letters of DNA sequence per day. This is just a tremendous
explosion of information. At the height of the
Human Genome Project, the rate of sequencing was
1,000 letters of new sequence every second. As best I can tell– I don’t
have the actual numbers– but as best I can estimate, I
think that rate has actually doubled since then. Despite the fact that the Human
Genome Project is no longer in the height of the
frenzy, so much capacity has been in place that
I think the rate is continuing to go up. Well, all of this led
to a dramatic explosion. The sequencing of
the human genome was first piloted from
about 1996 to 1999. The pilot period was
when we worked out all this robotics, all the
biological technologies, to be sure that we could
cover the sequence of genomes, et cetera. We then had
scheduled, and it had been scheduled for quite
some time, a ramp-up in the spring of
’99 to try to take on the sequencing of the genome. And lo and behold,
everything was ready for it. The ramp-up was launched. And in the course
of about 12 months, we went from having
about 10% of the genome covered to having nearly 90
of the human genome covered. It looked something like this. That was the sequencing
of the human genome over the course of that month. And it was just– I mean, I just
love looking at that picture there. We’ll do that again. That was just so much fun. There we go. [LAUGHTER] How is the genome
getting filled in? I don’t know. To me, there was a lot of
pain underlying that picture. But sort of like childbirth
or something, in retrospect it’s really just fun
to think about there. In any case, the
product justifies it. This was the product, not
just of MIT, of course. It was the product of an
international consortium of 20 different groups
around the world. Indeed, MIT was the largest
contributor to this effort. We contributed something in
the neighborhood of about 30% of the total sequence,
and it really was quite a big effort here. But there were
also large centers in England, the Sanger
Center in Cambridge, England, and also at Washington
University in St. Louis. But I think it was
equally important that there were laboratories
in many other countries of many different
sizes that contributed to this– the United
States, in the UK, in France, in Germany, in
Japan, and even in China. The group in China joined in
late, but that group in Beijing did a marvelous job. They contributed 1 and 1/2%
of the sequence of the human. And what it said clearly
was that the human genome was indeed the patrimony
of all of humankind and appropriately was worked
out by a large international consortium. The only criterion
for signing up for the Human Genome Project? You had to agree to
make all of your data immediately and freely
available on the web as soon as it was assembled. Within 24 hours of
assembling the data, it went up on the web, no
restrictions whatsoever. All the groups signed up for it. And I think it was
a wonderful thing that they did because it meant
that people could immediately start using this information. When we went to write a
paper about the sequence of the human genome,
well, usually people have to speculate in their paper
about what the consequences of their work will be. We had the absolute joy
of being able to devote a section of our paper to
how our data had already been used to find disease genes. And that was just a very
satisfying aspect to it. So anyway, this whole
Human Genome Project got a fair amount of attention. There was lots of
hoopla in the press, and there were several
visits down to Washington, some celebrations down at
the White House and things. But to the scientific
community, the only thing that really matters is a
peer-reviewed scientific paper. And that occurred in
February with the publication of the largest paper in the
history of the journal Nature on the initial sequencing and
analysis of the human genome. It actually was written
as a friendly paper. And even if you’re
not a biologist or haven’t touched
biology in a long time, you might want to
pick up the paper because there are
whole chunks of it that really were intended to be
friendly enough to be readable. There are other bits
you’ll want to skip over, but they’ll be obvious. So just skip them over. I’m not going to try to
tell you everything that’s in this human genome,
but I’ll mention a few interesting
things, particularly with regard to origins. Interpreting the
sequencing of the genome. We have a fold-out to the
sequence of the human genome. It’s actually two entire
centerfolds on both sides. This is just chromosome number
11 here that I’m demonstrating, and you’ll see the
gene distribution and many other features. You can’t really
see the details. But I’ll call your
attention to the fact that there are some
gene-rich regions and some gene-poor regions–
gene-rich, gene-poor, gene-poor, gene-rich. And interestingly,
this correlates with the visible banding
patterns of the chromosome. This is part of a dark
band on the chromosome. This is a light band on
the chromosome– dark band, light band. So even sitting way back
there in the bleachers, you can see that there’s a
correlation between banding pattern and gene density. And if your eyes really
good, you’ll even see that there’s a correlation between
low gene density and a low proportion of G’s and C’s
in the sequence as compared to A’s and T’s. Anyway, there are many
gross interesting features that are visible at
this high level of view. Of course, this is
not a very good view to take because, well, at least
as it appears in the journal, the scale is about 3
million DNA letters per centimeter, which you have
to really good visual acuity to appreciate. [LAUGHTER] And so instead, there are a
number of genome browsers, freely-available genome
browsers that you can just find on the web. You can look to the
University of California Santa Cruz, the National Center for
Biotechnology Information, to the European
Bioinformatics Institute. Lots of cooperating
genome browsers are there, where you can
zoom in by factors of 10 all the way down
to the base and up all the way to the chromosome. You can scroll over. You can see whatever
annotations you want or hide those you
don’t want want. And it’s a wonderful
thing that we now have a number of these
freely-available browsers that let you inspect the genome. I’ll mention just
one or two facts about the genome
that are kind of fun. Most of your genome does
not consist of genes. In fact, genes are only about
1 and 1/2% of your genome. Most of your genome consists
of repetitive elements that are autonomous, replicating
elements that copy themselves, and on evolutionary time
scales, move around your genome. They hop around. So if this is your
genome here, half of it is filled with these repetitive
elements who are interested only in their own reproduction. They make copies of
themselves into RNA. Those copies are
copied back into DNA, and they get slammed
into the chromosome. See? There we go. They get pushed right
into the chromosome there. And over the course of time,
they account for about half of your total sequence. Now, what’s very interesting
about these repeat elements is whenever
they hop, whenever they do this– they go womp,
womp– they bring with it the sequence of the
ancestral elements from which the copy was made. But when they land there,
they’re usually broken, and so they begin to
build up mutations. That means they’re
a historical relic, and we can tell how old
they are by how much they’ve built up mutations. In fact, we can tell whether two
copies of this repeated element are cousins or close brothers
that were born at the same time because they have the
same distinctive sequence characteristics. In fact, we can build an entire
phylogenetic tree relating the origins of all of
these repeated elements in your genome to tell which
ones are part of a sibship that hopped a million years ago,
or dispersed themselves 20 million years ago, or as far
back as 800 million years ago. All of that is there. So our chromosomes,
we now realize, are a geological record. There are all sorts of
geological fossils, about 3 million geological fossils, all
of which have dates on them. From that, we can, for example,
tell, just the simplest thing, what the rate of
this transposition has been over the
course of time. If we go all the way
back, reaching back beyond half a billion years,
about 3/4 of a billion years, the rate was sort of constant. It shot up around 75
million years ago. And then,
interestingly, the rate at which these elements have
been hopping around our genome has plummeted in the
last 30 million years. This is a major
ecological change. We don’t understand
what’s happened. Why have these things
stopped hopping? This, by the way,
has consequences. Since this accounts
for half your genome, this means that in the
long run our genomes are going to get smaller because
there’s a deletion process that deletes these. And if you’re not
replacing them, the equilibrium size of the
genome’s going to get smaller. Now, don’t worry
too much about it because the time constant
on this is pretty long. The rate of deletion of
useless DNA is about– well, we houseclean our useless
DNA with a half-life of about 800 million years. So this effect will kick in in
the next several billion years or so, but nothing to
get too excited about. But it is very
interesting biologically because this fact
I’m telling you is not true about the mouse. In the mouse, it appears that
the rate of transpositions continue just fine. It’s something different
between the hominid lineage and the rodent lineage. And if I had time, I’d
tell you about a population genetic hypothesis
that explains it in terms of the effective
population size of hominids versus rodents. But we’re understanding
now, first of all, the origin
of half of our genome and a fascinating dynamic
process of these elements. Well, there’s much else you
can tell about the genome by following these passive
evolutionary markers that are just conveniently
scattered across. But I won’t tell you about that. I’ll describe briefly the genes. There’s a lot we can tell
about origins from the genes themselves. There was a great
effort in this paper to try to do the best job we
could of gene identification. It’s by no means
absolutely complete, but I think the vast majority
have been identified. And the first surprise was
there were a lot fewer genes than we had thought. Indeed, I have apologies due to
some members of the audience. I have been lying to the
701 students, the Intro Bio students, for the past
10 years by teaching them that there are 100,000
genes in the human genome. I’m trying to send out
notes to all of them and make sure that– [LAUGHTER] –we correct this. But it appears that
there really are only 35,000 genes in the genome. The 100,000 number, when we
closely checked the literature, a, it turns out to be a
back-of-the-envelope estimate that had really huge error bars
that somehow everybody just latched onto, and
b, in any case, the 100,000 estimate was due
to a colleague at Harvard. [LAUGHTER] So the genes tend to– these
genes are very interesting. They bunch up in
these GC-rich regions. They have more splicing. We have more
alternative splicing, alternative ways
to splice and dice our genes and gene
transcripts, than happen in flies and worms and things. But when we actually look
at the origins of humans, we should ask, are
our proteins very different than other organisms
in terms of the modules they’re made up of? And the answer is no. Maybe 5% or so of
the protein modules, the little architectural domains
that make up our proteins, are innovations
amongst vertebrates. 95% of them were there
before vertebrates. So what’s new about us? Well, the origin of
vertebrates seems to have more to do with
innovation in architectures rather than in the
domains themselves. By architectures, I mean
ways of combining the domains in new combinations
but existing domains. So in point of
fact, our creativity that gave rise to
the vertebrates is somewhat derivative. It’s mixing and matching
of pre-existing parts. In a sense, it’s not that
surprising, of course, because these
pre-existing parts– back in the primordial ooze, you had
time to evolve a new domain, and it didn’t have
to work so well. But as life filled up more
and more of the niches on this planet, it
was necessary in order to compete that a new gene
pretty much work from the get go, and therefore had to be made
out of pre-existing components. And we can see that
very clearly in our DNA that that seems to be the
basis of vertebrate novelty. In addition, the simplest
way to make novel genes is just to duplicate
a pre-existing gene and let it change slightly. Highly derivative,
but very effective. And this has been the basis,
for example, for such things as smell receptors. You have in your genome
1,000 smell receptors, indicating that vertebrates
were very interested in smell. The origin of vertebrates
has a lot to do with smell. But then, unfortunately,
I have to tell you that you have
largely decided that, despite your ancestors’
interest in smell, that you are not so
interested in smell. Hominids have largely let these
smell receptors go to seed. About 2/3 of your smell
receptor genes are broken. They have stop codons. They no longer work. That is not true about a mouse. Mice are much more
interested in smell. They keep their smell receptor
genes in fine working order. We seem to have put all this
energy into making smell receptors, and then we let
them break in favor of sight as a preferred sense for humans. All of this you can
tell from the genome. There are stories about
origins and changes throughout the genome. Well, anyway. Whoops, back. I can’t tell you all
of the wonderful things in the sequence of the genome. There is so much to say
about what’s in there. But what I can tell you is
that it’s just the start. We went into the Human
Genome Project thinking that we had to
build infrastructure in the form of
maps and sequences in order to let people really
do their work, in order so that people would be
limited only by their ideas. We’ve come to understand
that the work of building infrastructure has
only just begun. There is a tremendous
amount of work still to go. I want to just highlight some
of the areas in which that’s going on. Comparative genomics. To really understand the
sequence of the human, to understand medicine,
to understand origins, we need to be able to
compare the human sequence with many other organisms to
see what evolution has kept and what it’s changed. We need to have
comprehensive descriptions of each gene in terms of where
it’s expressed in the body and when it’s expressed
in health and in disease and during development. We need to know the shape of
every one of the proteins, so-called structural genomics. We need to have a chemical
that interacts with and binds to and inhibits, where
possible, every protein. We need to have
diseases classified in terms of the sets of genes
that are turned on and off. And we need to have a
comprehensive description of the variation in
the human population. All of these are giving rise
to genome-style projects of their own to
lay the groundwork for that graduate student
and postdoc of the future. I’ll just touch very briefly
on where all this is going just to give you a sense of the
whirlwind that is starting. If you thought the Human
Genome Project was something, just wait for the next decade
of what’s going to explode. The mouse. A year ago, we had
very little sequence of the mouse, maybe about 1%. As of today, about threefold
random coverage of the mouse has already been generated. It covers about 90%
of the entire genome. It’s freely
available on the web. And it’s been integrated
with the human sequence by matching them up. In fact, 2/3 of this entire
project was done here at MIT, and it is leading to a
tremendous amount of work on mammalian genomics. It’s important because by
lining up mouse and human, we can see the
conservation of elements, and we can spot things
that we might have missed with our computer program. For example, if we
ran a computer program over the human genome
to identify genes, we have a
signal-to-noise problem. Genes are only a little bit
of the overall sequence. By lining up the human
and the mouse together and running a computer program
over both simultaneously, we can kind of do a kind of
coincidence detection, almost a genomic interferometry
of some sort, where we ask, do we see features
present in both genomes? And we get tremendously higher
sensitivity and specificity to identify genes. And not just genes,
but what’s popping out of things that we had never
had a way to see before. Regulatory elements that don’t
encode proteins, but encode the instructions to turn on
here at a certain time we recognize because
of conservation between mouse and human. There is, of course, work
on many other species. In the course of
the past year, we sequenced a very important
and largest fungus studied, Neurospora, a very
important genetic organism. And this was just
a great example. We got a three-year grant from
the National Science Foundation to sequence Neurospora, and
we completed 99 and 1/2% of the Neurospora genome in the
first two weeks of that grant. The last half a percent
will take a while, I admit, and there will be
time spent analyzing it. But the success of this
project here at MIT has led to a consortium
of fungal geneticists to identify 15 different
organisms that they want to study, representing
important medical fungi, commercial fungi, and
fungi that will shed light on evolution and diversity. And so we are hoping, if we
can get the funding to do this, to basically start a Fungus
of the Month Club starting later this year. [LAUGHTER] A model vertebrate,
Tetraodon, the pufferfish. The sequence of this pufferfish
is being generated in Paris and here at MIT. And already, about threefold
coverage of this organism is available. This seemingly unimpressive
filter feeder, a tunicate called Ciona, it just sits
there and filter feeds. Why bother sequencing it? Well, it turns out it has
a brief period in its life when it is a tadpole, and it
has a complete chordate body plan with a notochord
and all the structures in a tiny genome. And so we began sequencing
this beast a few weeks ago. We’ve already got onefold
coverage of its genome, and we expect to have about
tenfold coverage of its genome this year. Onward and onward. Genome sequences will
come spewing out, similarly, comparisons
amongst human beings. There is a tremendous amount of
sequence in the human genome. This is sequence. But there’s not
that much variation. That’s the variation. If you can’t see that,
I’ll circle that for you. There we go. Those were the two
spots of variation. That’s it. One base in 1,300 is the extent
of variation in the genome. It turns out that this
makes perfect sense from some dusty, old formulas
of population genetics. Little populations have a
little bit of variation. We’re actually a very
little population. Although we’re 6
billion people today, we were 10,000 people
in Africa a mere several thousand
generations ago. And that signature of a
little bit of variation a few thousand
generations ago has persisted because a few thousand
generations isn’t enough time to build up more variation. So as a consequence
of that, we predict that most genes should only
have two or three flavors in the population. And when we look,
that’s exactly right. Most genes have
only a few flavors. That has led to a
very exciting idea that every gene has its
isotopes, a few isotopes, and that we could
correlate disease with the variants,
or the isotopes. This common disease/common
variant notion is, I think, becoming
very important. We know some examples–
apolipoprotein E. It comes in three flavors,
lives on chromosome 19, E2, E3, E4. If you have a double
dose of E4, you have a high lifetime risk
of Alzheimer’s disease. We know a few other
examples like that. But our goal is to identify each
and every one of the variants for each and every
one of the genes, that is the common variants,
and correlate them with all major traits. And while this seemed like an
absolutely nutty idea even five years ago, I think
folks are conceding that this is very likely
to happen certainly over the next decade. And it may be that we
have all this variation characterized much
sooner than that. Indeed, the goal was
to detect disease genes using lots of variants. There are two different
ways to do it. I won’t fuss over them. We started with a paper here
at MIT about three years ago, where we reported 4,000
variants in the human genome. We thought that was
a lot at the time. Of course, it now
is a puny number. But what it did was
that particular paper got the world interested in
generating these variants. And an international consortium
was put together in parallel with the human, and it
led to the generation of 1.42 million variants
across the human genome. And this paper was
published in parallel with the human sequence
paper back in February. This, again, was a wonderful
international consortium. And again, it was a consortium
led here at MIT with about half of all of this work
having come from MIT. With it, we are now studying
the nature of these ancestral segments in populations,
and it’s really quite a remarkable thing. The segments that we’re
looking for, they are big. They have a limited
number of forms. And I believe we are
going to be able to get comprehensive descriptions
of all of the ancestral types of all of the genes. And I think that this will
form the basis of a new kind of human genetics. I’m going to skip through
a bunch of slides that just say that in some detail. And come to the end and
say what we are getting is a global
perspective on biology. We started with a
comprehensive project to generate complete sequence. And now we’re
realizing we also have to generate a lot of
other complete things– complete descriptions of
where genes are expressed, what their variations are, what
the structures of the proteins are, what the cell
circuitry looks like, and how we’re going
to clip the wires. It is an extraordinary
decade of building ahead, and it’s going to
transform the way we take on biological problems. It is going to give
us our periodic table. We already have it in
rudimentary form today, but nowhere near as well
annotated as we need to have. I think here at MIT
there are projects leading many of these efforts. We will spend a lot of
time generating these data. But we have also
spent– we will also learn one other thing
from this, and that is some lessons about
how to do science. I think biology was in a
very different state in 1985 than it is today. Back in 1985, biology
was done almost entirely at the lab bench in
small groups with people who focused on single problems,
usually with single skill sets. What the Human
Genome Project has forced us to confront in
biology is something that, of course, has long been known
for physics and for chemistry and for engineering, which
is that we, too, need to work in multi-disciplinary
collaboration, that we need to be
able to work in larger teams with professionals,
that, of course, graduate students and postdocs
are always the backbone of creation and invention. But in order to be able
to get our work done, we have to be able to
put together teamwork. We need to build
international cooperation on many of these projects. Most dramatically, I
think, for understanding human populations we need to
engage the human population. And we’ve also learned
that the traditional model of holding on to your data
until you’ve published is not a necessity. We can, in fact,
make all of our data available as we’re
generating it. All of this is
leading to, I think, restructuring and rethinking
in biomedical research. And I think it is time
to think about new kinds of organizations, new
kinds of institutions to take on the challenges
of biomedical research. Now, of course,
these are new kinds for the typical medical
school out there or biology department. These are not new
kinds to places like MIT, where we
have long appreciated the importance of
multi-disciplinary collaboration, of teamwork,
of putting together efforts that are larger than
any one individual can do. And so my own expectation
is MIT has a huge role to play organizationally
in showing the biological world how
we can combine biology with mathematics,
with computer science, with engineering, with
chemistry in a new kind of biological and
biomedical program. Well, it’s traditional
to end any talk by giving a list of the
names of all the people who participated. That’s going to be
difficult in this case. This was truly quite
a remarkable project. And if we mean not just the
sequencing of the genome, but all these other things
I’ve been talking about, it would take far too long to be
able to run through the names. They are on the web, actually. We, for the Human
Genome Project, got everybody’s name who was
involved with it on the web. But I do want to show one
picture here of the group here at MIT, at the
Whitehead/MIT Center for Genome Research, that did
the work here and led so much of the
effort on sequencing and on human variation and on
many other aspects I haven’t talked about. It’s really just been a
tremendous, tremendous privilege to work with
such an extraordinary group of colleagues here
at this institution. But I should also put up
this credit slide here. This was an example
of a project, and a whole field I
think, that could only have gotten done through
the joint efforts of an entire world
working together. And I think we’re
all tremendously proud of what was accomplished
by all pulling together in one cause. It’s great to tell you
about the origins of life, the origins of humans,
the origins of disease, and the origins of the
Human Genome Project. What a great, fun
Technology Day today. Thanks very much for coming. [APPLAUSE] LANDER: What a run, huh? CANIZARES: Yeah. Can I have the lights
down in the front because my slides aren’t
going to show [INAUDIBLE]? Eric, is this yours? That was wonderful. Am I on the air? Many of you, I’m sure, have
seen the wonderful short film produced many years ago
by Charles Eames and MIT’s own Phil Morrison. It starts with a
still photograph of a man lying on a blanket
after a picnic on a summer day, and then zooms alternately down
deep into the skin of his hand, showing first the skin,
then cells, then atoms. And then turns around and
goes out into the universe, showing the solar system,
the planets, the galaxies, and beyond. This journey today is something
like that one as shown by Charles Eames
and Phil Morrison. But the difference
is that whereas they were talking about a static
picture of the structure of these huge
differences in scales, what we’re talking about
today is an even more difficult question, and that
is the dynamics of how this all came about. How is it that this great
complexity and diversity, which Eric showed so beautifully
in the area of the genome and organisms but also
exists for stars and planets and galaxies, how could this
great complexity and diversity emerge from what we know to
have been an extraordinarily uniform and intensely
hot big bang that began some 13 billion years ago? And furthermore, how is it
that this great complexity and diversity seems to have
emerged on each scale almost as quickly as the laws of
physics would allow? Of course, we don’t have
anything like a complete answer to those questions. But in this entire
range of scales, and you’ve certainly
seen it from Eric in the case of the
genome, we’re in the midst of a tremendous revolution
in our understanding about the origin of the universe
from its very beginnings to the genome. In the last few decades–
in fact, most of this has been in the last
20 years, since, I think, Bill Hecht’s 20th
reunion– that cosmology has gone from a science that
used to be well described by the words of Mark Twain– “a
wholesale return of conjecture from a trifling
investment of fact.” [LAUGHTER] But the new tools
of the last 20 years have changed this
completely, and I have the pleasure of sharing
just a bit of this with you today. The tools, the ones that
I’m particularly involved in I’ll show you in a
moment, but I have to say that this
has been matched, the observational detail
which I will focus on, has been matched by an
equally extraordinary advance in our theoretical
understanding and our ability to do numerical computations,
thanks to Moore’s law, so that we can advance our
deep understanding as well as our catalog of observations. Well, to show you the tools
of the trade first, of course, one of the most extraordinary
has been the Hubble Space Telescope. And this has been a
major contributor, and I’ll show you lots
of images from Hubble. I’m particularly proud
of the mission that Chuck Vest mentioned initially, the
Chandra X-ray Observatory, because half of the scientific
instrumentation for this was built here at MIT,
and we’re deeply involved in using this to
probe the universe. And also, although
a lot of what I do and what Maria will tell you
about is done from space, there’s a lot to be done on the
ground using modern telescopes. And we’re very happy
that MIT and its partners dedicated last December the
first of two large research telescopes in Chile, the
Magellan Telescopes, which are now being used in this as well. So let’s now start our journey
out into space and back in time to look at some of
the things that we’ve learned about the
origin of the universe. We’re starting on Earth,
of course, the home planet. And it’s interesting that,
completely independently, Eric used this image of
the Earth, which is up in the upper corner, in
case you don’t recognize it. The Earth is one
of nine planets. There are only eight if you live
in Manhattan near the Museum of Natural History, but– [LAUGHTER] And that must be where this
slide comes from because they left Pluto off the slide, too. But Professor Zuber
is going to tell you a lot about the
origin of the planet, so I’m going to move fairly
quickly out beyond them. But one of the major
discoveries of the past decade has been the existence
of some two dozen or more ordinary stars
that themselves have planets orbiting around them. This is the culmination of
literally decades, if not centuries, of speculation
about whether or not our solar system is unique,
and we know now that it is not. The detection of those
systems is made indirectly by observing the wobble
of the parent star as the planet tugs on it during
the orbit going back and forth around the planet. And we haven’t yet been able
to make a picture of a planet around another star. But the Hubble Telescope–
and I’m sorry, if we could– I don’t know if there’s a way to
reduce the glare on the screen. If there is– from the
lights– I would appreciate it. This shows a picture taken
with the Hubble Telescope. Here’s a bright star. This streak is just
the artifact of the way the telescope is constructed. It is in focus. And this dot here is
not quite a planet. It’s sort of somewhere in
between a planet and a very small star, but it
is orbiting, and it’s the closest we’ve come so
far to a direct picture. It’s called a brown dwarf. But NASA has plans now, and
the scientific community, for an observatory which
could well fly sometime within the next
one to two decades to try to actually image
planets around other stars. Of course, what we
want to learn about is the process by which
the planets formed. And again, Professor Zuber will
tell you a lot more about that. But I want to start
with this, and then she will end up moving downward. I’m going to start moving
outward in a moment. But this shows one of Hubble’s
very famous and beautiful pictures of a region
in our galaxy. It’s a stellar nursery in which
gas and dust is coming together from the Milky Way, our parent
galaxy, and to form new stars. And as those stars
form, they begin to burn their nuclear
material on the inside. They light up. And then that radiation ends
up pushing on and illuminating and pushing around the
clouds of gas that have yet to form into other stars. These contorted columns
are very beautiful, but they’re also the
indication of where stellar birth and planetary
formation are taking place. You can see this
very clearly here in this picture, which shows
the same region of space. Here it is just
tilted to orient it in the right direction
from its Hubble picture. This is a picture taken
with infrared radiation from the ground,
and you can even see here the sort of hint of
the shadow of these columns. But the infrared radiation
penetrates the dust, and so you can actually
see inside to where the young stars are forming. It is the molecular
hydrogen and other elements that are condensing in these
clouds to form the stars. Now, many of the stars
that form in these systems show the kind of evidence for
formation of planetary systems that had been theorized
for many years, but now we can actually
see in much more detail. This shows four examples
from the Hubble Telescope of young stars,
so-called protostars, that are in various stages
of igniting themselves. And they’re backlit by the
other radiation scattering off those columns I was showing you. This is actually a
different nebula, but it’s the same phenomenon. And you can see
the shadow that’s cast by a disk of material at
the center of which the star has collapsed, but this
remaining disk of material is where planets will
eventually, we think, condense and to make planetary
systems not necessarily that different from that we know
here in the solar system. Well, it may
surprise you to learn that, in addition
to stellar birth, stellar death is just as
important to understanding the origin of the universe
and the origin of life as stellar birth is. The early universe, we
have excellent evidence, essentially consisted of just
hydrogen and helium, and maybe a tiny bit of other
very light elements that were formed just a couple
of seconds into the Big Bang. Barely a trace of
any of the elements, certainly no carbon,
nitrogen, oxygen, the kinds of things
that we need for life. All the rest of the chemical
elements, so far as we know, has to be synthesized–
have to be synthesized in the interiors of stars
through the nuclear processes that make them shine. But then they
remain locked there until the star releases them
to eventually mix in and become one of those clouds that
I just showed you before, one of those nebula from which
new stars and planets can eventually form. It’s a cosmic case of ashes
to ashes and dust to dust, without which, certainly, life
would never have been possible. The way most of
the ejection takes place is that some
fraction of the stars, when they reach the
end of their lives, explode in a massive explosion,
essentially turning themselves inside out and returning all
this newly-synthesized chemical material out to
interstellar space, and we see process of
that happening around us. Here is a patch of the sky
visible only from the Southern Hemisphere. Actually it looks at, for those
of you familiar with this, a small dwarf neighbor
galaxy of ours called the Large
Magellanic Cloud. In 1987, that patch of sky
suddenly looked like this. A star that had reached
the end of its normal life exploded in a massive
explosion, ejecting the chemical elements it had
synthesized in its interior. During these explosions,
for about a few weeks after the explosion takes
place, a single star can outshine an entire galaxy. This shows the same region, that
same star, about a dozen years later in the late– I think
this is around 1999 that this was taken. There’s a ring of
material– this is sort of a clump in the
middle– rings of material illuminated by the radiation
and the shock wave that is streaming out into space. And by studying
these, we can study how this process of
returning of the material to the interstellar matter to
make new stars takes place. The Chandra X-ray Observatory
is particularly well suited for studies like this
because as the material flies out, it gets heated to very high
temperatures, about typically 10 to 100 million degrees
when it radiates X-rays, and those X-rays can be detected
by our Chandra telescope. This shows such a remnant
now, a similar ring, but now this is of a star that
exploded some 350 years ago. It was sighted around 1650
by the astronomer Flamsteed. And the colors, we can
analyze the X-ray signal to actually do a chemical
analysis of the material that’s been ejected. And this is almost
entirely– this is about 20 times the amount
of material that’s in the sun and is almost entirely
silicon, sulfur, and iron and other such elements that
were not present in the Big Bang but were synthesized
inside the star. And those of you
with sharp vision can see a little
knot in the center. That is, we think, is either
a neutron star or a black hole that was left at the core
when the star exploded and is another
interesting object. But there’s no
time, unfortunately, to tell you about that. This sequence of stellar
birth and stellar death and regeneration and returning
of the chemical elements to make new stars takes
place in a neighborhood, and the neighborhood
is the galaxy. Our own galaxy, the Milky
Way, is a spiral-shaped system not unlike this one. This is our neighbor,
the Andromeda Nebula, its spiral-shaped system of
stars flattened containing about 100 billion stars. I notice that another similarity
between studying the cosmos and studying the genes is
that we like big numbers. There are about 100 billion
stars and maybe 100,000 light-years across. Now, let me remind you
a light-year is actually an astronomer’s
unit of distance. It’s the distance
that you would travel if you travel at the speed
of light for a whole year, and that’s about
5 trillion miles. This is another one. These galaxies are
the sites in which stellar birth and death takes
place and planetary systems form. And you can see
here, for example, this bright spot in
this spiral galaxy is expanded here in
the Hubble picture to show a nebula not too
different from the Eagle Nebula, the one with the columns
that I showed you earlier. The universe, we now know, is
teeming with such galaxies. A very long observation with
the Hubble Space Telescope of a patch of sky, where
previous observations showed that there was hardly
anything there so that you wouldn’t be bothered
by anything so bright that you could see it
with a normal telescope, Hubble stared at this patch of
sky for something like a week and took a very,
very long exposure. What it uncovered is
a remarkable diversity of galaxies. Each one of these things
is like a Milky Way with 100 billion stars. We found that
there are something like 100 billion
galaxies probably in the part of the universe that
we can receive signals from, the visible universe, and a rich
variety of shapes and colors. The other thing about looking
at very distant galaxies is because of the
finite speed of light, when you look at
a distant galaxy you’re seeing the light that
was emitted a very long time ago because it’s had to travel
so long to get to us. So for example, in this picture
there are three galaxies shown. This one, the light was
emitted a billion years ago, so we’re seeing what galaxies
looked like a billion years before. I remind you that
the interesting scale is the age of the universe
is about 13 billion years. This one was about 4 and
1/2 billion years ago, about the time the Earth
and solar system formed. That’s when the light
left that galaxy and arrived at the
Hubble Space Telescope sometime a couple of years ago. And then this little
funny thing is a galaxy that’s just forming. It doesn’t even look like
a normal, simple galaxy. And the light was emitted
over 10 billion years ago. So this is a record,
it’s a historical record of a different sort than
the one that Eric mentioned, but just as useful in astronomy
for understanding how galaxies form and looking backward into
the early part of the evolution of the universe. Now, galaxies themselves
are not randomly scattered throughout the
universe, but they tend to congregate,
kind of like people. They are often bound together
in groups and sometimes even great clusters of galaxies
that contain hundreds to even thousands of galaxies
and fill regions of space that are several million
light-years across. These are the largest
gravitationally-bound systems in the universe. Now, again, to contrast this
picture in visible light that shows the galaxies
with X-ray astronomy. It was discovered
that in addition to the individual
galaxies, the entire space between those
galaxies– remember we’re talking about 100
million light-years across now here– is filled with
a very diffuse gas that glows in X-ray radiation. The interesting thing
is that this discovery showed that there is actually
three or four times more matter in the hot gas than there
is in all the stars and all the galaxies. But the other thing that came
out was even more surprising, and it was a confirmation
of suppositions from earlier work in optical astronomy. And that is that there
must be something more there than the
galaxies and the gas, that, in fact, the total
amount of matter required to hold this entire assemblage
together and keep it from flying apart into
space requires something like 10 times more matter. Now, this matter is
something still of a puzzle, but we’re sort of
zeroing in on it. It’s often called dark matter,
just because it’s dark. We can’t see it. But we know it’s there because
otherwise the gravity simply wouldn’t be so strong. And so it’s most
plausible right now to attribute this to some
kind of exotic particle. It cannot be normal matter. We know it can’t be
neutrons, protons, electrons. It cannot be the same sort of
stuff we see around us or that we see even in stars. It has to be
something different. And the most likely place
that astronomers look is to our colleagues
in particle physics to eventually discover some
new exotic particle that will explain this. In the meantime, though, its
evidence is very, very clear. Here is another
cluster of galaxies, and you see these funny, blue,
wispy things on the outside. Pretty much all the other
sort of yellowish things are galaxies. And you can see this is
actually quite a dense cluster, so there’s a lot of them there. It’s a lot of matter. These blue things are actually
more distant galaxies, much more distant
than the cluster. And the reason that
they look distorted and that you can see them at
all, since they’re so much more distant, is that the
gravity of this cluster, primarily the dark
matter in that cluster, bends the light,
acting literally like a gravitational
lens, or one could call it a cosmic telescope, and
magnifying the background galaxies. So we have ample evidence
that the dark matter exists. There’s really, at this
point, I think, no question that that is the case. Something that’s a
little more controversial but is now becoming more
and more widely accepted is that the universe also
contains another thing that we don’t understand very
much of at all called dark energy. This dark energy actually
acts like a repulsive force in the expansion
of the universe. And it may be that
our universe is just about to enter a new
accelerating phase of expansion thanks to its presence. That is something
which is very new and still the subject
of very active study. Well, let’s move to
an even larger scale. This picture doesn’t do justice
to what I’m going to describe. It is a map of galaxies
in a region of space that’s probably about 100
million light-years across. And there are entire clusters
of galaxies sort of lost in this thing. These are not
gravitationally-bound structures. Rather they’re a dynamic
motion of galaxies and clusters of galaxies that are not, again,
spread uniformly over the sky, as one might think, but tend to
congregate in these filaments and structures separated
by large regions where there’s very
little going on. And the size of this region
on the sky, as I said, is several tens of
millions of light-years. This entire dance of
galaxies and clusters slowly in the universe is
the formation of structure. It’s the thing that’s happening
thanks to the Big Bang. Material along in
certain regions was dense enough to condense
to make stars and galaxies. In other places, that
simply didn’t happen and nothing formed. Even about this very
early and largest scale we’re getting some
new information. And the information is coming
by studying these galaxies and clusters themselves,
but also going back even further to look at what we can
get from the Big Bang itself. When the universe was
about 200,000 years old, after the Big Bang,
which, as I remind you, was 13 billion years
ago, so just very shortly after the explosion on
a cosmic time scale, matter became neutral. And all the radiation that then
had been generated– before that it was a sea of
radiation and matter– at that point, the radiation
simply streamed out into space. We are still detecting
that now, and it’s the so-called cosmic microwave
background radiation. It’s in the microwave
region of the spectrum. It was actually first
detected by accident by a couple of Bell
Telephone engineers in New Jersey in the early ’60s. And the measurement
of that radiation has actually been a
goldmine of information about the earliest
moments in the universe. 200,000 years, that’s
as early as we can get after the Big Bang so far. What we find is
really remarkable. Consider this paradox. You and I and planet
Earth and this plant are lumps of matter
that are some 30 orders of magnitude denser
than the mean density of the universe around us. That’s 10 to the power of 30. Yet in its infancy, by
looking at this radiation we can see that the
universe was an exquisitely uniform and homogeneous
broth of matter and energy with no differentiations
of bubbles or lumps that were bigger
than 10 parts per million. It is the tiny
ripples, which now have been measured from
several space experiments and now most recently from
high-altitude balloons, these tiny ripples–
this is a map of the sky and this radiation
but at a very tiny level. The ripples are of the
order of 1/1,000 of 1%, ripples on top of a
uniform radiation. These ripples from the
early edge of the Big Bang, so to speak, are
the seeds from which all galaxies, all stars,
all planets, and all genomes eventually emerged. The ripples appear in
addition to confirming a lot of the theories. And this slide is
a very poor attempt that I think came out
of National Geographic to depict the entire
span of the universe. This is the Big Bang. Doesn’t look too
impressive, does it? And what we’re
talking about is how we went from some very smooth
aftermath of the Big Bang to suddenly make galaxies. As the cartoon shows, I
think, with the two physicists standing at the blackboard
with their equations. And then there’s
a line that says, and then a miracle happens. Well, we don’t think
it’s a miracle. [LAUGHTER] But we do think
that, in fact, it is something which is
calculable and which we are trying to
get a handle on, that these tiny seeds that
occurred here, 1/1000 of 1%, eventually made the
galaxies and the stars. Now, there’s something
even more remarkable, which I’ll only be able
to mention in passing. But if you want to ask
questions about it later, I’ll do my best. And that is that these
observations now are also confirming the fact that in
the very earliest moments of the Big Bang, there was
an extraordinary period of rapid expansion. The inventor and pioneer
of this is right here at MIT, Alan Guth,
and it’s called the inflationary
universe theory. And it is a theory which has
to be Alan Greenspan’s worst nightmare because– [LAUGHTER] –in a tiny instant of time,
10 to the minus 35 seconds after the initial event
that caused the Big Bang, the universe expanded by
some 30 orders of magnitude and then continued on
with its, by comparison, relatively gentle expansion that
we still see going on today. What’s even more remarkable
about the inflationary universe theory is that it says that this
entire process could have been started by a tiny seed,
and that, in fact, all of the matter and
energy of the universe could be created out
of that tiny seed. And that is what
about Alan Guth often calls the ultimate free lunch. [LAUGHTER] Well, speaking of
lunch, I’ve whisked you out to the edge of
the universe and back to the beginning of time. But I guess it’s time to
come back to the home planet and have coffee. Gauguin’s wonderful painting
and some of the remarks that Chuck Vest made
speak to the age-old quest to understand our origins. We certainly aren’t anywhere
near to having answers to all the questions. But one of the
things that’s been most fun for me is to
see, simultaneously from the level of the genome
through to understanding the inflation that occurred
at 10 to the minus 35 seconds after the Big Bang, we’ve
made extraordinary progress in the last few decades. And we are just
poised on the verge of making a whole lot more. So thank you very much
for the opportunity to tell you about this. [APPLAUSE] VEST: Thank you, Claude. This really is indeed
the essence of MIT. We are going to take a
15-minute break right now. And this is a plaintive
plea, let’s please try to hold it to 15 minutes. When you come back, you will
all receive an index card on which you can write down
questions for the Q&A session that will follow the talks. There will be a student on
hand who will collect cards during the remainder
of the program if you simply and quietly
catch their attention. I also need to
mention, unfortunately, that Eric Lander has a
commitment in Washington and was unable to
stay for the Q&A. Going to Washington
on a Saturday for a scientist is what is
known as doing God’s work. So we wish him
well in any event. So see you in a few
moments, 15 minutes. Let me begin by reminding
you to write down your questions on the cards
that have been handed out and give them to one
of the students who will be collecting them
during this second part of the session. Now, it gives me great
pleasure to introduce the two speakers for this session. First will be Maria Zuber. Maria is the E.A.
Griswold Professor of Geophysics and
Planetary Science at MIT and is a senior
research scientist in the Laboratory for
Terrestrial Physics at the NASA Goddard Space Flight Center. Maria’s research focuses on
understanding the structure and evolution of solid
planets through her modeling of altimetry, gravity,
and tectonics data obtained by spacecraft. Her work has her
looking simultaneously at a range of celestial bodies,
including Mercury, Mars, Earth, the moon, and several
asteroids, including one, I might add, of her own
discoveries, Asteroid 6635 Zuber. Be sure to run home
to your telescopes and look up 6635 Zuber. Following Maria, our final
speaker for the morning will be Charles R. Marshall. As I mentioned
earlier, Charles is professor of geology and
biology at Harvard University and curator of the invertebrate
paleontology at Harvard’s Museum of Comparative Zoology. He is also an adjunct
professor in earth atmospheric and planetary
sciences here at MIT. When he was growing
up in Australia, Professor Marshall was
fascinated by the vanishing world of volcanoes,
ferns, and dinosaurs that had once thrived on
the site of the family’s well-tended lawn. That boyhood
interest has led him to a career marked by
path-breaking research on the relationship between
inheritance, environment, and catastrophe in directing
the path of evolution. We will hear first
from Professor Zuber. [APPLAUSE] ZUBER: Great. Thank you. It’s a great honor to
be with you here today. You know, what I tell
my students in class is, if you play your cards right
and you do all your homework and you study hard, when
you grow up you won’t have to work for a living. You’ll get to explore space. And I hope that I’ll be
able to convince you of that by some of the things
that I’ll show you here. Let’s see. Let’s just move on here. OK. Well, I’m going to
sort of pick up where Claude Canizares left off. And Claude showed you
this diagram moving out, and I’m going to use this
diagram here of the Eagle Nebula and move in. And what we’re going
to look at today is how one actually forms
planetary bodies out of the wispy hydrogen
and helium material that makes up the tenuous
interstellar medium. And this diagram that
you see right here– I guess for scale this is
about 1 light-year, or 8 trillion kilometers across. I should say that when
you do things for NASA and you put press releases out
with NASA, whenever we would put out press releases–
I work on altimetry, and so we would show
the heights of things. And they would always
make us change kilometers to feet and miles– [LAUGHTER] –because they said people
don’t understand kilometers. So after the Mars Climate
Orbiter was lost last fall due to– [LAUGHTER] –a units error– [LAUGHTER] –a decree came out. Now we use metric,
so I don’t have to change any of
my figures anymore. [LAUGHTER] [APPLAUSE] OK. Well, the challenge
here is that, even though this material
looks rather dense and you can’t see through
it, the actual density of atoms within this area
is actually quite low. OK? It ranges from
thousands of atoms to maybe hundreds of thousands
of atoms per cubic centimeter, and that’s actually
a very low density. And so then the
challenge comes into, how do you actually make this
condense into a solar system? OK. Well, people had thought about
the idea of collapsing disks for some time. And if you have a cloud
of hydrogen and helium gas out in the interstellar medium,
for a long time people said, well, it would just
begin to collapse. OK? But why would it? OK? Well, then the thought
came that perhaps there are spiral density
waves in galaxies, and these spiral density
waves consist of places where you have a higher than
average density of stars. And as these spiral density
waves would pass through, they would interact with
these interstellar clouds and perhaps make them collapse. And that, in fact,
is an idea that is still held up today as
a possibility for making clouds collapse. OK? Another idea is that
you can actually have a supernova explosion. OK? This is a diagram that Claude
showed of Supernova 1987A in the Large Magellanic Cloud. And here is a star– this
is not actually a supernova. This explosion actually
occurred about 150 years ago, and this star in
the constellation of Corina for a while became
the brightest star in the sky. But the star actually
recovered from it, but it has met a rather
violent end of life. And it’s still expanding. It’s a very tenuous body today. But it is thought that
the shock waves that are associated with a supernova
explosion or something just like this could, in fact,
provide the compression that would be required to
take a very tenuous cloud and make it into a collapsing
cloud, which is what we need in order form solar systems. And in fact, one of the ideas
is that our solar system formed or initiated its
collapse because of the fact that there was a
supernova nearby. OK? Now, there is, in fact,
evidence for this. OK. This is a meteorite. This is a meteorite
called Allende. It is probably the most
important meteorite ever discovered. It was found in the
early 1960s just as we were getting
high-precision geochemical instrumentation online
to study moon rocks because we were
going to the moon. And so this meteorite
turns out to be a very primitive
representation of the material that we think coalesced
to form the solar system. Now, inside the
Allende meteorite, you see these
materials here that are called CAIs, or
Calcium-Aluminum Inclusions, and they have an
unusual isotopic ratio. There is an isotope of
aluminum called aluminum-26. Now, the regular
isotope of aluminum that makes airplanes and
soda cans is aluminum-27. But aluminum-26 decays
into magnesium-26 with a half-life
of 730,000 years. OK? And aluminum-26 is
made in supernovae. OK? And you find in these
inclusions an enhancement of this isotope
here, which indicates we find an amount of
this material in here that is consistent
with the fact that this was produced within
early time of when our solar system formed. So there is, in fact,
evidence that there was a supernova nearby. Now, there’s more
evidence than that. OK? What you see right here–
many of you in the audience are wearing one of these. This is a diamond. This is the spectrum
of a diamond. And in fact, you observe
diamonds in the interstellar medium. And when we go and
we take samples using high-altitude
aircraft of cosmic dust, you, in fact, find micron-sized
diamonds within this dust. OK? And the only way to make
diamonds, OK, out in space is with very, very
high pressures, and these are associated
with shock waves that come from supernovae. So it is, in fact, believed that
there was a supernova nearby when our solar system
formed, but that is a very unsatisfying thought. OK? And the reason for that is
because it means supernovae are rare events, and
what that would mean is the formation of our own
solar system is a rare event. OK? It’s a much more
desirable outcome to make solar system formation
a common process that occurs without special circumstances. But as you will see,
many of the things in the evolution of the Earth
and the evolution of planets are associated with catastrophe. OK? And for a long time,
catastrophe is something that we avoided in
geological sciences because we looked at
stratigraphy and watched things, one layer lay
down on top of another, and occurring over a
very long period of time. But in fact, we are learning
that catastrophe is a hallmark of planetary evolution. OK. So we begin the collapse
of these clouds. And then, as they
collapse in order to conserve angular momentum,
these clouds begin to rotate. And as they begin
to rotate, there are collisions that occur, which
causes individual particles to lose energy. And the consequence of that
is that these disks spin, and they tend to flatten
out and look like a pancake. And then we begin
to form something that looks like a solar system. Now, what you see here is a
Hubble Space Telescope image in a star in the
constellation of Pictor. And here is another view of
it, which has been filtered. And what you see here
is that we have a disk, and here is our own
solar system for scale. The full length of this disk is
about maybe 25 solar systems. So it’s bigger than
our solar system here. This is the closest best
example of a nearby disk of perhaps planet formation
occurring right now. And one of the interesting
things about this disk is if you look at this bottom
diagram, the disk is warped. OK? Now, you can do calculations. If you had a stellar encounter,
if you had another star passing by that would cause a
gravitational perturbation that would cause a disk
to warp, the disk would spread itself
out and thin out then in a very rapid period of time. And in fact– and
that’s pretty unlikely. It’s possible,
but it’s unlikely. And so what we think
is going on here is that this disk is
actually being perturbed out of a flat state by the
presence of a planet. OK? And so here is more
indirect evidence that planets are indeed
forming out of these disks. OK. I want to talk a little
bit about composition now. Our own solar system, if
we look at the constituents in our solar system, we find
that, in general, the planets are very much like the sun in
terms of their composition. So we can measure the
composition of the sun and of other stars by
looking at spectral bands. And what we find is
that the sun is mostly composed of hydrogen and helium
but also some heavier elements. And these, of course,
heavier elements were produced, many of
them, in supernovae. Now, what becomes
interesting is as we get away from the central
star, there will be a gradation in
composition that is associated with
the temperature distribution in the disk. OK. Now, when you just have
an interstellar cloud, it turns out that
the temperature within an interstellar
cloud is fairly homogeneous. OK? But what we are going
to see evidence here is that as these
clouds evolve, you begin to accrete
dust particles, OK, and the disk goes from being
largely transparent and wispy to being dusty and opaque. And when parts of the
disk become opaque, they can’t release
energy as effectively as when they’re
thin and tenuous. And as a consequence of that,
those areas hold heat better. And the outcome of
that is that you form large gradients
in temperature, we believe, within
these nebulae. So if we start here
out at the sun then, here are all the planets, and
this one does include Pluto. We have here Mercury,
Venus, Earth, and Mars. These are the
terrestrial planets, and these planets tend
to be rich in iron. They have iron cores. Silicate– so they
are mainly rock. They do have water
associated with them. They do have some volatiles. Then we get out to
the outer planets. And in the Jupiter
system, Jupiter is where water ice
becomes stable. And then we get out to the
Saturnian system and beyond, and in addition to
water being stable we also start to get
methane and ammonia. But one of things that
we try to understand is what the distribution
of primordial elements is. What is the stuff from which
our solar system initially accreted? OK? Well, this comes from sort of
icy snowball features, which occur in space, and here’s an
example of one right out here. OK? Out in the vicinity
of Pluto and beyond, we have an area that is
called the Kuiper Belt, which essentially has protocomets,
comets that have not yet been gravitationally perturbed out. What happens with
the Kuiper Belt, these icy bodies
get perturbed out of them due to encounters with
Neptune or something like that. And they come in, they go
into orbit about the sun, then they become comets. OK? And this is a space
telescope– they’re dark because they have
organics mixed with the ice, and this is actually what
one of them looks like. They are very
difficult to detect, but we are detecting
more and more of them. And we hope to detect many more
with the Magellan Telescope in which MIT is involved. And then they get
perturbed out, and they come in and form comets,
which are very volatile-rich. And we’re now in the situation
where we can begin to sample, actually, what this
material is made of. This is a mission called
Stardust here, which has been– it was launched in
1999, I believe. And it’s going out, and it’s
going to fly essentially through a comet tail. It’s going to fly within 50
kilometers of the central coma, of the nucleus of a comet. And one of the interesting
things about this spacecraft is it’s got this tennis
racquet sort of thing that has this material
called aerogel in it. Now, a comet is
volatile-rich, and if you want to sample what
the original stuff that made the solar system is like,
you don’t want to melt it. OK? And so you want to try
to encounter the comet at a low enough velocity that
when you capture the particles, you don’t change them,
melt them, vaporize them. So this material actually
has a density that is– well, it’s 99.8% air. OK? And the structure, the
web-like structure, is actually at the
nanometer scale. And some space
shuttle flights have shown that you can take
interstellar particles, and they come in here, and
they get stuck in there. And this is actually
going to come back to Earth in about 2006, I
think, and we’ll actually have samples on the ground
of particles from a comet. And this, we think, is going to
provide us with the best idea yet of the primordial
composition of what the solar system is made of. OK. So we have this
disk of material. We know a little bit
about what it’s made of. And then out of this, we want
to try to build a solar system. We want to try to build planets. OK? Now, the process of sort of
making a sun once collapse begins is understood somewhat. And the process
of making planets, once they get to be about
100 kilometers or so big up, that’s also somewhat
known because then gravity takes over. Once something’s
100 kilometers big, it attracts other particles. But going from the gas
stage and condensing dust and then getting dust to accrete
into particles that get up to sizes of 100
kilometers is really something that’s
not well understood. This is actually a painting
here by a planetary scientist named William Hartmann, who
is also a gifted artist. And this is his impression of
what the early solar nebula might have looked like. OK? So we have an early
protosun, which has condensed far enough that
the pressures in the center are large enough for
hydrogen to fuse. And then we have
dust condensing, and it is condensing
into particles. And one of the things
we don’t understand is essentially how you get
these things to stick together. OK? Mechanisms have been
discussed, such as sintering, vacuum welding,
electrostatic attraction. And these are very difficult
to simulate in the laboratory. In order to go a little
bit farther about this, though, we need to understand
something about the life cycle of the central star. OK? This is a picture of our sun
from the Soho spacecraft. And this is a diagram that
we use a lot in astrophysics called a
Hertzsprung-Russell diagram, and it is a measure
of luminosity as a function of
temperature for stars. OK? And it turns out that most
of the stars in the sky plot up in this nice
luminosity-temperature diagram like this, and this is
called the main sequence. And this corresponds
to the period of time where most stars exist
in their evolution. This is a period
of time when a star is undergoing stable
hydrogen burning in its core. But when you’re
forming a protosun, it needs to come on
to this main sequence. And before it comes on
to this main sequence, it undergoes a stage
in its evolution called the T Tauri stage. OK? And the T Tauri stage, if
you’ve raised teenagers, then you’ll understand
what the T Tauri stage is because it’s the
period of stellar adolescence. OK? These stars are not
yet stable adults, and they undergo huge
variations in brightness. [LAUGHTER] They throw off mass. They have variable
magnetic fields. And here are some examples of
stars undergoing the T Tauri stage. This is in the constellation
of Serpens, a protosun throwing off
material right here. One of the classic– here’s
one with the interstellar disk right here having an outflowing
jet going out of the top. And what is
interesting about this is that because the star
is behaving so violently, it is actually
throwing material out, and it’s clearing out the
interior part of the nebula. OK? So it’s blowing out all
of the gas and the dust. So you have this thick, opaque
nebula that I showed you in the last diagram. And essentially, the T
Tauri stage of the sun starts to clear things out. OK? So this actually contributes to
the planet formation process. Now, just to show you that the
process of planet formation is a rather violent sort of
place, this is the Trapezium. This is in the belt of Orion,
Messier object number 42. It’s about 1,500
light-years away, and it’s a very near area
of active star formation. And what you find
within this– this is a Hubble Space
Telescope image– are bodies that
look like this, that look essentially tear-shaped. And we think that these
are sort of protodisks. But what is happening here
is that these bright stars, they’re just nascently
forming, they’re throwing out huge amounts
of ultraviolet light. And if anybody here
is a fluid dynamicist, these are essentially
teardrop forms that are affecting
the shape of these, and they’re actually
breaking them apart. OK? Now, we have models that
say that these forces that are associated with
these young stars operate on time scales of
a million years or less. OK? Now, the time it takes
to accrete planets, we’re not positive. But we have computer
models that tell us that it’s somewhere in the
million to tens of millions of years range, which is very
rapid when we consider the time scale over which our
solar system has existed. But it is a longer period
of time than the time scale over which these
forces work that try to tear these planets apart. OK? And so whether or not you
can form a solar system is a balance on how
intense these forces are and the time scales
over which they’re working. OK. Now, other theoretical
models, and this is one by Doug Lin over here
and Pawel Artymowicz over here, show that when you
begin forming planets and you do Monte Carlo
simulations of planet formation, you tend to always
form something like a Jupiter first. OK? And you form it out about
where our Jupiter is, about 5 astronomical
units from the sun, or five times the distance
of Earth from the sun. And to begin, we begin
accreting dust and rock out of the solar nebula. And this grows, somehow,
up to about 100 kilometers. And then it can attract
material and actually can pull in gravitationally
material from around it. And so this process here of
planet formation, giant planet formation, draws in material
from the accretion disc. And actually, gravitational
perturbing forces, because this thing
is spinning, actually produces something that looks
like spiral density waves that we’ve seen for galaxies. So we have a commonality
in these processes. Now, with the giant planets, we
begin accreting rock and dust, and if we’re out as far
as Jupiter, ice as well. But initially, the solar
nebula there is very dense. And these planets out
here become massive enough that they can even suck
in the gas around them before the T Tauri
phase gets them away. And so in the outer part of
the solar system where there is an abundance of
gas, we can actually grow planets that have
rocky cores, mostly hydrogen interiors. But what’s interesting
is that when you get to very high
pressures, the pressures are so high that the electrons get
stripped off the hydrogen atom, and they form a [? sea. ?]
So they essentially act like transition metals, and
we call this metallic hydrogen. The pressures also get
so high that helium begins to rain out and fall. And so you actually
get something that’s called helium rain inside
of these giant planets forming. OK. I was making this slide,
and my eight-year-old came up and said, is
that the three bears? And I said, yeah. And he says, well, we
did that in kindergarten. [LAUGHTER] And I said, well, some of the
most important lessons that you learn in life are
learned in kindergarten. And that is the case right here. OK? So there’s Goldilocks and
here’s the three bears with their porridge. If you remember Goldilocks,
this one was too cold. This one was too hot. This one was just right. And this actually
ties in perfectly with an understanding of
what the role of collisions is in planet formation. OK. If you think about it, if
the velocities of which these particles are undergoing
are too slow, what happens is that all these particles
in the solar nebula will just fall into
concentric orbits, and they will never accrete. They’ll never collide,
and they’ll never be able to build planets. OK? And if these collisions
are too fast, what happens is that these things
bang into each other, and they just break
each other apart. And then you can’t build a
planet out of that either. OK. So the collisions
have to be just right. OK? And so this diagram from
the three bears just nicely and colloquially, I think,
expresses the sentiment that was produced by the
theoretician Safronov, who actually went through
and formally determined what the range of
collision velocities had to be to actually
grow things as opposed to breaking things apart. OK? However, the
process of impact is one of the most important
processes in planet building. OK? This is an image of
the moon actually from the Cassini
spacecraft, which just recently flew by Jupiter. And what you can see here is
that the surface is pockmarked with many, many impacts. These dark ones here are
flooded by volcanism. But these smaller ones
here– the surface essentially is saturated. And if we look at the number
of craters per square area over the age of the moon– the
moon is 4.6 billion years old– what you find is that
early, early on, this body was sweeping up all the junk
that was left after the planets accreted. And that all this material, in a
relatively short period of time by cosmic standards, impacted
the planets and, in fact, probably greatly
influenced their evolution. So one of the
things that we want to try to understand in planet
formation very, very well is, what is the
role of collision in planetary evolution? And I’m going to give
you some evidence here that we don’t really
understand this process very well. This is the Asteroid 433 Eros,
which is a near-Earth asteroid. And it’s the asteroid that the
Near Earth Asteroid Rendezvous spacecraft orbited for a year
and then landed on for a year. And this is, by the
way, an experiment– my experiment from MIT
was on this spacecraft. And this is a diagram
of that asteroid. And one of the
things that we found is that this asteroid,
which is a piece of junk left over from the accretion
of the solar system, we expected to find craters
all over the place on it. It turns out this
asteroid has on it more boulders than it does
craters, OK, house-sized boulders. We’ve measured
the size of these. Here’s a good example of one. There are millions of
millions of boulders. If you go to the moon,
you don’t see this. OK? Until this past,
I guess last fall, we had no real
realization process that something in the
collision process of asteroids produces boulders and
doesn’t produce craters. And so our understanding
of what this process acts like on low-gravity bodies,
we need to essentially go back to ground zero. This is essentially a “hall of
fame” diagram of the biggest impact craters on planetary
bodies in our solar system that we have measured relative
to the size of the body. OK? Right here, let me start
with this satellite. Mimas is one of the
satellites of Saturn. And this large crater, Herschel,
was imaged by the Voyager 2 spacecraft when it flew by the
Saturn system in about 1980. At the time of
this fly-by, it was believed that Herschel,
relative to the size of Mimas, which is about 250
kilometers across, was about the biggest crater you
could make on a planetary body without breaking it
apart, that if you had a bigger impact than that,
it would break it into pieces. OK. However, we began to look. This is an Asteroid
253 Matilda, which was flown by by the
NEAR spacecraft in 1999. This is an image of the
brightest asteroid, Vesta. This is a space
telescope image that was taken by Professor
Rick Binzel here of MIT. And here you can see the
whole bottom of the asteroid has been lopped
off by an impact. One of the
characteristics of impacts is that when they
get very big, you get a central peak in
the middle because you get the shock wave propagating
through the planetary body. And then it generates another
wave, which unloads it, and everything comes flying
back out and excavates it. OK? Here is a divot that takes up
about half the asteroid Eros that was observed
by my instrument on the NEAR spacecraft. And here is a crater
that we observed on the backside of the moon. Actually, this was detected
in the 19– this hole, this is called the
South Pole-Aitken Basin. And it’s about seven
kilometers deep, and we didn’t know about it. It was actually observed
by the Soviet Zond spacecraft in the 1960s. And no one believed that you
could have a big hole that big on the back of the moon
without breaking it up, so the data was dismissed. And here it is now mapped by
the Clementine spacecraft. And indeed it does
exist, and you can see what its size is
compared to the United States. And down here, which
is my favorite, is the Hellas Basin on Mars. Hellas is 2,200 kilometers wide,
and it’s 9 kilometers deep. It is the biggest
impact crater that we know of in the solar system. And in fact, the energy
that was generated that was associated
with its formation, if you converted that
to the amount of energy that we use in
the United States, it would give us energy
in the United States for a trillion years. OK? But if there’s anybody from
the Bush administration who’s considering
this as an option, there are definite
negative consequences of– [LAUGHTER– –of going this route. So the thing that
you can see here then is that we now
understand, just from data taken in the last several years,
that one can produce impacts that are quite large compared
to the size of planetary bodies. And in fact, that these impacts,
huge impacts, catastrophes, not only have happened,
but that they were actually the rule rather than the
exception during the process of accretion. OK. Now, in order to
try to understand the process of planet
formation better, one of the things that
we try to understand is the bulk chemical
composition of a planet. OK. If we look at the Earth– this
is a very simple-minded diagram to show the relative size
of the core of the Earth compared to the
size of the Earth, and the core is about half
the radius of the Earth. OK? Now, if you go to Mercury,
we don’t know too much about what the inside of
Mercury’s like, but we know the mass and we know the size. And so if the core is made
of iron, which we believe, then the radius of
the core is about 75% of the radius of the planet. OK. Now, so we have a question here. Did Mercury form because it was
closer to the sun with much, much more iron than
the Earth formed? Or did something happen to
remove the crust of Mercury? And we’ll talk about this. It is possible that an impact
could have stripped off much of the crust of Mercury. This is a spacecraft
called Messenger, and this will be
launched in 2004. And this spacecraft is actually
going to go and orbit Mercury. And we have been to
Venus a number of times. We send multiple spacecraft to
Mars every two years whenever we have a launch opportunity. But we have only sent one
spacecraft to Mercury, and that was Mariner
10 in the 1970s. And we didn’t even
get into orbit. We just flew by
the planet twice. And in fact, we don’t have
images of half of Mercury. OK? We only have seen
half of Mercury. And the reason why
that’s the case is that it is very, very
difficult to go to Mercury. OK? Because in order to get
into orbit around a planet, essentially what happens
is the spacecraft has to throw on the brakes
and slow down and allow the gravitational
attraction of the planet to pull it into orbit. But if you think
about what it’s like if you launch a spacecraft from
Earth and you go into Mercury, it’s like throwing a
penny in a wishing well. And what happens is that
the spacecraft speeds up. OK? So you need to take a
lot of fuel with you, and so you’re essentially
taking a fuel tank to Mercury. And the mission that
we’re sending here, it essentially has to do
three fly-bys of Venus and two fly-bys of Mercury
just to slow it down. So it’s going to take it
five years to get there. And it is, of course,
close to the sun, so the radiation is
intense, and the temperature is extremely hot. It is hot enough to melt lead. So those of us who are
involved in this mission say, we’re going to hell,
and we couldn’t be happier. [LAUGHTER] But it’s great because
it’s a technical challenge. And in fact, the way
you get around it is this is a heat
shield that is kept between the planet
and the spacecraft, and that keeps it nice and cool. But actually what kills you is
that the infrared radiation is reflected off of Mercury
towards the spacecraft because those are where
the instruments look. So these ideas of how
much iron Mercury has, they can be addressed, but it’s
quite a challenge to do so. So this is why I said that
it is perhaps possible that Mercury lost some of
its crust to an impact. This is how we think the
moon formed right here. OK. This is a calculation that
was done by Jay Melosh out at the University
of Arizona. But we think there is a
fair amount of agreement in the community that this is
a viable possibility for how the Earth’s moon formed. It is thought that a body the
size of Mars with an iron core hit the Earth. OK? What happens is that it
hits the Earth at an angle. And what you see
here is the core of the planet wrapping
around the core of the Earth, and you throw all
this stuff out. And it turns out the
moon has no iron, and that was always
a puzzle to people. But it turns out that
the iron core of the moon is actually part of
the core of Earth now. And this is not fiction. We think this happened, or
something like this happened. And so the idea of huge
collisions affecting planetary evolution,
I think, has a lot of credence associated with it. OK. I’d like to spend a couple
of minutes here just talking about what’s typical, what’s
an average solar system. We used to think we knew what
an average solar system was until we began finding
other solar systems. OK? Claude hinted at
this a little bit. But we now can
detect the presence of Jupiter– well,
Saturn-size and larger objects around other stars. And essentially this
is the way we do it. We take a star, and if the star
has a planet coming around it, the planet– there will be a
mutual gravitational attraction here, and it will cause the
star to wobble in its orbit. Now, the kind of wobbles
that are detected using this so-called
radial velocity method are essentially equivalent
to the size of a quarter over 10,000 kilometers. So these are extremely
tiny wobbles that we are detecting to see giant planets. OK? And so we have seen
other solar systems, and we expected them
to be like this. OK? So here’s our
solar system again. And then we have
the nine planets, and they are mostly
in a plane that cuts the sun’s equator, with
the exception of Pluto, which is a little bit unusual, and
Mercury, which is slightly out of the plane. But for the most part, we have
giant planets forming out here, where all of the
numerical simulations told us they should form. And we have terrestrial
planets in close to the sun, which
are smaller and have gas associated with them. But what you find is that
you get Jupiter-sized objects in these other solar
systems, and they’re all inside– most of them are
inside the orbit of Mercury. OK? And they can’t form
there because there’s no gas there because the
T Tauri sun blows it out. And so what we think
might be happening is that these planets
form out by Jupiter, and they migrate in. But if they migrate
in, then what happens is they might take out
terrestrial planets. OK? And so that comes to the idea of
habitability, and how can there or are there out there
habitable planets? And so we then look
at the possibility that we have
habitable zones here, and we define habitable
zones as places where you can get liquid
water forming on planets. And we can’t detect these
planets, but there are plans. These are 10 years down the
road that can actually– we’ll be able to look at
atmospheres of planets to look for carbon
dioxide and to look for non-equilibrium
gases, like ozone and like water,
that would perhaps indicate the presence of life. And I just want to close
by saying that, of course, there are plans now to be
able to look for these planets and to be able to look
for non-equilibrium gases and atmospheres. But we think,
perhaps, that looking for places where there
are water are good places to look for life. If indeed we have things
like oceans beneath Europa that, in fact, have life
associated with them, we wouldn’t have
the faintest idea how to detect these
beyond our solar system. And in fact, we’re
not quite at the point where we can detect them
within our own solar system. But the stakes are high, and
the possibilities are there. And all we need to
do is keep at it. And I think that there’s
a lot of hope for progress on these in the future. So thank you for your attention. [APPLAUSE] MARSHALL: Well, let me first
say it’s a pleasure to be here. MIT’s one of my
favorite institutions. What I’m going to
try and do today is– let me get rid
of these lights. I can’t see anything. What I’m going to try to do
is three things this morning. First of all, I’m
a paleontologist, and I’m going to
try and give you a feeling for the slippery
nature of evolutionary theory. Having done that, what
I’m going to do then is try to give you a
sense of how, working with an incomplete
fossil record, we are developing methods
to introduce levels of rigor into the sort of
statements that we can make about the history of
life given that fossil record. And third, I’m going to return
to the beginning of today’s session, which is give
you a glimpse of the way that the genomics
revolutions are beginning to change our view of
the evolution of life on the planet. And so if I could
have the first slide. Oh, I guess I control that. That’s easy. So here’s a picture
of Charles Darwin, who wrote a very long book
called the Origin of Species. He called the book an abstract. And in fact, in the
abstract of the abstract, there’s a paragraph, and
the paragraph is here. And this, in a nutshell, is
Darwin’s theory of evolution. And he simply states,
“As many more individuals of each species are born
than can possibly survive; and as, consequently, there
is a frequently recurring struggle for
existence, it follows that any being,
if it vary however slightly in any manner
profitable to itself, under the complex and sometimes
varying conditions of life, will have a better
chance of surviving, and thus be naturally selected. From the strong
principle of inheritance, any selected variety
will tend to propagate its new and modified form.” That is the theory of evolution. And the question is, how
can something so simple be so difficult to
understand in practice? Rewriting it, I’ve cast it
this way, Darwin’s syllogism. He simply states– and
it’s a thought experiment– if there’s a struggle
for existence, and if the phenotype
is variable, and if existence depends,
at least in part, on the phenotype, and if at
least some of those attributes are heritable, then you expect
a transformation of species with time, that is, descent–
misspelled– with modification. And so most of the abstract
that Darwin talked about was trying to provide
empirical evidence for each of these statements. I think it’s key to
remember that the driving force of evolution itself
is not natural selection, but the fecundity of nature, the
propensity to over-production. And of course, that’s
the proximal cause. The distal cause, of
course, is solar energy, which is ultimately what’s
driving the Earth’s system. The significance of
Darwin is that it’s the first evolutionary
theory that clearly separated the existence of variation
from the direction of evolutionary change,
and it’s that uncoupling that adds to the
complexity of understanding evolutionary phenomena. And so I want to try to give you
a sense of those complexities and how they operate. Here is Darwin’s famous example
of the long neck of a giraffe. Being already the longest
animal in its environment, if, in the case of
occasional drought, longer-necked animals
can reach food that other animals
can’t, you might expect them to differentially survive. So it’s relatively
easy to understand how, by the process of natural
selection and variation, you might get an increased
length of giraffe necks. This gives you a beguiling
sense of how easy it should be to construct
an evolutionary explanation. But when you think about,
say, the complexity of the human hand
or the human mind, you might ask, how can we
understand that in these terms? And so what I’m going
to do now is run you through a very quick
computer simulation to show you how complexity gives
rise to morphological form. This is a little diagram
here in the corner here of a fossil plant
called Cooksonia. It’s the first plant to,
metaphorically, crawl up onto land. It’s very, very simple. It’s known from the Silurian
Period in the fossil record. And here, what Karl
Niklas did at Cornell is simply develop
a computer model of variation within the plant. And what he did is say it
can generate new branches. It can have different angles
between those branches, and those branches
can swivel around. And using the morph space
generated by those principles, he asked the
question, what plants do I expect to get under
different selective pressures? So here I have a plant selection
for only reproductive success. I want as many branches as high
as possible and many branches for lots of seeds
and high as possible for the dispersion
of those seeds. And then finish up
with one optimum, and it doesn’t look
much like a tree. He then selected for
mechanical stability. Branches will break off
if they’re horizontal, but long branch are
fine if vertical. So here we have long
vertical branches and short horizontal branches. Three optimal solutions, none
of them look much like trees. Light interception. Here I want to have many
branches out as horizontally as far as possible
to collect light. And here again, three optimal
solutions, and some of these begin to look like trees. But you note there’s
a conflict with some of the other constraints. And so what then
Karl did was simply run the simulation again
now but using all three selective criteria. And what you find is you
get multiple solutions, and a lot of these start looking
at an awful lot like trees. And so just like
spin glasses where an atom squeezed between two
atoms with different spins has trouble recognizing whether
it should be up or down, so, in morphological
evolution, we represent complex compromises
in the very many complex forms and needs that we
have as organisms. And so one of the
reasons why it’s so hard to look at an
organism and understand what the selective pressures
are is because of the hidden ways in which
these selective constraints interact. Notice, also, that
the mathematical idea that there should be one master
species and it should win is sort of undermined by this
sort of computer simulation, which indicates, in
fact, that diversity is in part a product of these
different solutions equally good to conflicting needs. So evolutionary theory is also
structured somewhat differently than physical theory. And we’ve all seen this before. And the whole point of Newton’s
law of universal gravitation is that the law operates
at any time, at any place. Evolutionary theory is
built very differently. It’s about consequences. Here’s a very simple example. It turns out in the
Triassic period, about 220 million years ago,
the first turtles evolved. They have shells. They could not
retract their necks. And then what we find
happens later in evolution in the Jurassic period, the
evolution of two distinct forms of neck retraction. Of course, having a shell
both gives you the need to retract your
neck– you’re slow– and the place to
track your neck to. And so what happens now
in the Northern Hemisphere is you have turtles that
retract your neck vertically into the shell. And now only in the
Southern Hemisphere there are turtles that wrap
their neck around the side. With the extinction of the
non-neck-retracting turtles, you now lose the capacity
to evolve a third, and a fourth, and a fifth
form neck retraction. They’re already committed to
one or another way of doing it. And so the point is in
evolutionary theory, and it’s why it makes it
so difficult to understand the future as well
as the past, is that evolution is historically
contingent, that is, windows of opportunity
both open and close. So you get this succession
of opening opportunities and closing and open and close. So it’s deeply
hierarchical in structure. In fact, the
contingency has reached new levels of contingency. This is a famous
diagram that’s showing the extinction of the
dinosaurs 65 million years ago, with the survival of mammals
to give rise to people like us some 65 million years later. What is interesting is the
earliest mammals, including the origin of fur, occur
with the earliest dinosaurs 225 million years ago. So you have coexistence
of mammals and dinosaurs throughout this
entire interval here. And to give you a sense of how
long this period of time is, it is more correct to show
humans with Tyrannosaurus Rex than it is to show Tyrannosaurus
Rex with Stegosaurus. The error in the first
instance is 65 million years. The error in the second
is about 80 million years. So the dominance of
dinosaurs is long. The question is, how
do they become extinct? And there have always been
two classes of hypothesis. The first is that they
should have seen it coming. [LAUGHTER] That is, that biological
interaction, natural selection in the narrow sense,
was operating, and these take many forms. It got too cold. There’s that little mammal there
scurrying through the snow. Or perhaps it got too hot. And there it is hiding
underneath the palm tree there. Of course, there’s a second
class of explanation. That’s the catastrophic. And here we have our
fried-looking mammals there surviving. And these explanations
range from perhaps passing supernovae stars to my
second favorite explanation, and the reason why I
go to the supermarket– [LAUGHTER] We’ll ignore the error in time. It is, after all, the
[INAUDIBLE] news report. And then my favorite
explanation of all– [LAUGHTER] And of course, this is the
favored explanation now. And part of the reason
is because geologists over the last couple
of decades have been finding debris
deposits from the ejecta blanket of the impact, which
happened right here in Mexico. And so there’s, obviously, an
extreme case of contingency, where a meteorite
impact, of which we just saw in the previous
talk as well, wiped out the dinosaurs,
in large part, we think, due to their large
body size, giving opportunity for evolution of mammals to gain
ecological ascendancy, which means increased body size,
which means ultimately something like Homo sapiens. So phase one finished. Phase two, how do we
handle the incompleteness of the fossil record,
particularly ancestors, in biodiversity? So some people get
upset with the notion that humans might have
evolved from chimpanzees. And so similarly,
some chimpanzees might be upset at the notion
that they evolved from humans. [LAUGHTER] And of course, the point is
that neither of them is true. That is, that there was a last
common ancestor of chimpanzees and humans, and we’ve each had
our own independent histories. Now, it turns out
that the attempt to understand these
ancestral forms has changed very radically
in the last few years. And I’m going to
start the story with, in fact, the only fossil
that was described and named before it was found. And this is the famous fossil. It’s called
Pithecanthropus alalus. It’s also known as
Java Man, and it is now known as Homo erectus. Darwin produced
Origin of Species. Hegel in Germany
picked up the idea and convinced the
Dutchman Dubois that there should be an
ancestor of chimp and human, and he took his whole
family off to Java to look for that ancestor. Pithecanthropus– ape man,
alalus– cannot speak. Thought to be unique to humans. And so after many
years of frustration, he found Java Man
here, a skull cap. Who knows whether it
could speak or not. So he decided to duck the
issue of whether it could. So he called it
Pithecanthropus erectus. And he called it erectus
because the angle here at the head of the
femur, going down towards the toes in
this direction here, indicate that the legs were
held underneath the body, and therefore it walked
erect, unlike a chimpanzee. And so this is the first
fossil of Homo erectus. And so if we take
Pithecanthropus erectus, Homo erectus, and put it in
our revolutionary tree– here’s human, here’s chimp– we
can insert it right here, indicating that bipedality
arose before a large brain did. Now, building these
trees can be problematic. Here’s a diagram of a skull
of Australopithecus boisei and robustus, with these
strong sagittal crests on the top of the heads for
attachment of massive jaw musculature. If we insert this into the
tree, we get a problem. Here’s Australopithecus
boisei here. We gain bipedality. We gain the sagittal crest. And now we have a problem. We have to lose it again before
we get to Homo erectus and Homo sapiens. And so it seems perhaps a
little more efficient to suggest that this species belonged to
a completely different lineage of hominid-like. And so we swing it out into a
different evolutionary lineage, so. So it turns out what happens
now in modern paleontology, we don’t really look
for ancestors anymore. All we do is try
to place fossils in one of these
branching diagrams. And so two simple examples. This is Archaeopteryx, probably
the most famous fossil known. It is clearly a bird. It has a full set of feathers. But it is strange for a bird. It as a long tail. The pelvis is unfused. It has teeth in its jaws. It’s got claws sitting at
the end of its fingers. Creationists like to
debate whether it’s really a bird or really a dinosaur. And from our point of
view, we don’t mind. Because what one does is
build a diagram like this. Here’s dinosaurs. Here’s modern birds. We place Archaeopteryx
in this position here, and what it indicates is
that feathers originated prior to the fusion of
fingers, loss of teeth, the development of a large
sternum and a short tail. And so these fossils,
then, help us to order evolutionary
innovations, and that’s our key goal
now as paleontologists. We can ask the question,
well, given that we don’t even look for ancestors,
how likely are they to be in the fossil record? The top diagram is
an evolutionary tree starting with one species
and finishing up with 100. And what we’ve done here is grab
just 3% of the fossil species. And you can see that if you just
grab three species out of all the ones that are
sitting in there, you don’t statistically
expect to see any direct ancestor-descendant
relationships. You’ll get a couple of
indirect ancestor-descendant relationships, and
for the most part, you pick up cousins or second
cousins or triple cousins. And so, in fact,
statistically, ancestors are not expected in
the fossil record. And in fact, those 3% I picked
for a very specific reason. It looks like that’s
the proportion of all primate species
that ever existed that we have found in the fossil
record, which isn’t very many. And so this can be
done mathematically, where you can simply plot the
relationship as the proportion of the species preserved,
the probability of having a direct or an
indirect ancestor. And so paleontology
has reached sort of having a new level of
analysis in the last few years with these sorts of studies. And so now finally returning
to Mr. Homo sapiens here at the top and all
these various fossil forms, a lot of the relationships
are highly controversial. The material is
very, very scrappy. But what I’m going
to argue now is by building these cladograms,
these evolutionary trees, it’s possible to make very
strong inferences with very, very little information. And here I’m going to show by
just looking at two relatively complete fossils, we
can get a nice sequence of the events that led from
the last common ancestor of us and chimps to humans. The first one is the famous
Lucy, known from Africa, with its in-turned pelvis, with
the head of the femur there. And so this leads us to
believe that Lucy was bipedal, and we have spectacular
evidence of this. As most of you are
probably aware, these spectacular
fossil footprints that occur in an ash flow
dated 3.6 million years ago in Africa, as well as a
protohorse and its foal walking over the same ash bed. And the second fossil is
the famous Nariokotome Boy at about 1.6 million
years, also found in Africa, a relatively
complete skeleton shown here. And with just these
two fossils, just two, one can draw a diagram from
chimpanzee to human starting from the last common
ancestor and show that bipedality and
a low, broad pelvis evolves first, followed by a
barrel chest and long legs, followed by, in us, chin, large
brain, and probably language. So the fossil record
and its incompleteness is not so much of a concern. I think in the interest of
time, what I’ll simply do is describe verbally
another issue that we’re involved in is trying to
understand how biodiversity has changed through time. And I guess it’s
worth one diagram. This is a diagram showing the
number of, effectively, species from the Cambrian Explosion 500
million years ago running up to the recent. And what is special
about this diagram is it suggests that
we, living today, are in a privileged world. That is, a world
where there are more species alive today than
there ever have been. But there’s been
something very disturbing, is while this is an
accurate description of the fossil record as it
is, the question is, is it an accurate description of
the history of life as it was? And what you find is that if
you drew a graph, a simplified graph, of species
diversity through time, and you also plot a graph
of the geologic map area available to find fossils
in for each of those times, the correlation is
extraordinarily high. More rock, more fossils. So what we’ve been
doing, actually, following the lead from
the genomics people, is trying to unify our
discipline of paleontology by digitizing and computerizing
our entire fossil record into some unified database so
that all the data can speak to each other
rather than existing as isolated paleontologists. And we’ve collected in the
order of 100 million specimens worth of fossil data. And here’s the same diagram
showing the species increase up to the recent. We’ve collected data from
just these two time slices. And what we find is that this
great diversification that occurs under most ways of
measuring diversity just isn’t happening. It’s staying very,
very flat here. And it is possible that
there were more species 400 million years ago than
there are alive today. And this is ongoing research,
but it shows the importance of taking a statistical
approach to the fossil record rather than taking it literally. That ends phase two. Phase three, the molecular
genetic revolutions. I argued earlier that evolution
is a two-step process. There’s variation
followed by selection. That’s a nutshell
of Darwin’s theory of evolution, the
disjunction between the two. Variation is interesting. It’s said to be
random in the sense that variants
thrown up by nature do not anticipate the
needs of the organism. It does not mean
anything could happen. And quoting from
Darwin, says, “We are profoundly
ignorant of the cause of each slight variation.” And that is still
largely the case today. So in fact, I like to recast
Darwin’s theory of evolution in this way, to
say that evolution can be viewed as the filtering
of development by ecology. Development from egg
to adult, of course, is where variation
is mediated by. So developmental
biology is core. And ecology, of course,
is the arena within which natural selection operates. And I mean ecology in the
broadest possible sense– interaction with other
species, interaction with the physical environment. And what is interesting
is evolution departments have lots of ecology and
virtually no development these days. And so the genomics
revolutions are beginning to give us an insight
as to where these variants come from. And I want to give you a hint
of what some of those things look like. To show it’s extreme
importance, here’s a diagram of a
puppy with a snout here, back of the skull
viewed from above, and an adult dog, so the eyes
are sitting in here, back of the skull, snout,
and a kitten and a cat. And what is interesting
in this instance is that, as you all
know, puppies start off being very cute
with short snouts, and as they grow their snouts
get proportionally longer. But kittens tend to look
like juvenile versions of the adults. And if you had no
scale bar, it’s hard to know whether you have
a kitten or an adult cat. If you wanted to evolve a
really long-snouted dog, all you could do is take
this process and extend it a little bit further. And so, in fact, if
you think about it, large dogs tend to have long
snouts, like greyhounds, et cetera, and short
dogs tend to have short snouts, pugs, et cetera. So the variation exists
within the development to give you a wide
range of breeds of dogs. In cats, if you wanted to
evolve a long-snouted cat, you’re in trouble. [LAUGHTER] You don’t have the variation
available to select upon. So the way the
development operates has a major bearing on the
evolvability of a species. And there are relatively few
breeds of cats, for example, compared to the number
of species of dogs. But I still haven’t
begun to explain where that variation comes
from, and I’m not going to here. So the issue then is, where do
all these body plans come from? The Cambrian Explosion,
evolutions’s Big Bang. And we’re now
beginning to get hints of the sort of
genetic mechanisms that might be responsible for
these very, very different body plans. And so you can ask questions
like, the eyes of trilobites, are they independent
inventions, or are they actually essentially the
same as the eyes of dinosaurs and of us? So this is the
last complex slide. Here I have a fly
embryo, front to back. And some of the
discoveries that have been made over the
last decade or so are beginning to give us an
understanding of how embryos are actually constructed. So there are a series of genes
called the Hox genes that run along the chromosome. And it turns out
that these basically lay down the Cartesian
coordinates within which the embryo develops. They define front to back and
divide it up into a series of regions, which then
differentiate differently producing wings or legs
or antenna, et cetera. It turns out that you have
four sets of these genes and so does the mouse. And most animals have at least
one complete set of them. So it turns out the
front-to-back genetic mechanism in a fly and a
human is the same. And so even if you take
something like a sea urchin, or a fly, or a human,
you’ve got the problem of comparing apples and oranges
at the morphological level. At the genetic level, you
have a common language. And as soon as you
have a common language, you can start to
formulate hypotheses of mechanism and process. What I’m going to do is
look at this one gene here, Ultrabithorax, to give you
a sense of what these genes do, and it’s pretty spectacular. This is part of the fly. The head sits here. This is the thorax. This is the abdomen. Three thoracic segments– 1, 2
sporting its very large wing, and a third thoracic
segment sporting a structure called a haltere. It’s a little sphere
on a stick that it rotates at really high speed
that provides stability while a fly flies. Maybe think of a dragonfly. They don’t fly
very well, and it’s because they have four
wings rather than two. You knock out the Ultrabithorax
gene, and if you’re lucky this is what you get. Four wings instead of two. Now, what’s happened
here is very sneaky. What’s happened is we have
a second thoracic segment producing wings, and we’ve
converted the identity of the third thoracic
segment into the identity of the second thoracic
segment and, therefore, getting wings again. So I’ve not evolved the
haltere into a wing. I’ve simply changed the
identity of the segment so there’s now two
thoracic segments 2. But this hierarchical structure
of genetic information suggests that major
morphological changes may be much easier than
was previously thought. And so, accordingly then,
here is a fossil mayfly nymph from Permian rocks of Oklahoma,
about 250 million years old. And here you can
see it has wings down the full
length of the body. In fact, they’re paddles. It lives in the water. And it looks like it may
be a relatively simple task to simply turn
off the expression of those genes in these
abdominal segments here. Hypothesis, we don’t know. Get’s even more
spectacular than that. It turns out there’s a gene
in Drosophila called eyeless. If you knock out
the gene, no eyes. It turns out you
can inject it back into developing embryos
of Drosophila fruit fly. Here’s the major
eye, and here are the secondary eyes formed here. They’ve got the lenses. They’ve got the
little hair follicles. They’re not hooked to the brain. So it turns out
there’s one master switch that tells the rest of
the eye genes to switch on. And here’s more
examples of it showing that even the pigments there. This was antenna, now
making eyes instead. This is a developing wing
with an eye growing on it. So a highly modular
form of development. Now, what’s interesting
is you have in yourselves a gene called that is
the same as eyeless. And it seems to be involved
in eye development in humans and in mouse. So if you take the mouse
PAX6 and put it into the fly, does the fly recognize it? It’s a little bit like
saying if I take a Mac disk and put it in a PC,
is it going to work? And the answer is it does. This is an eye in Drosophila,
but the switching mechanism is from the mouse,
not from the fly. And so the commonality of
genetic architecture– this is just the beginning
glimpse of it, fairly old papers now–
is absolutely spectacular. In terms of understanding
the rates at which evolution can occur, genetics is
also extremely important. Can, for example, species
originate very rapidly in geologic time, or do they
have to occur fairly gradually? And here’s just a fairly
simple thought experiment. Humans that have
three chromosomes 21 are down syndrome. And on chromosome 21,
there’s a gene called ETS2. And on mouse, that gene
is on chromosome 16. And if you take a
copy of that mouse and re-inject it back into
mouse so the mouse has three copies of that one gene
rather than its normal two copies, this is what you get. Normal mouse
embryos, and here you get the mutant mouse
with one extra copy of the gene with a domed
head and the shortened face and malformations in
the neck, et cetera. Notice it’s the same gene. It’s just got
three copies of it. So it’s not a new gene. It’s not a new protein. The genetic differences
are trivial, and yet you can get major
morphological changes. So the ability to perform
experiments like this is also radically
[INAUDIBLE] our understanding of morphogenesis. And finally, I want to talk
about just these two genes here in Drosophila in some of their
relatives, the lobsters, et cetera. This is a funny diagram. I apologize for that. These are crustaceans. The first three segments
here are the head. And so this here is– Artemia
here is the brine shrimp– sea monkeys that you get on
the back of cartoons. This is the lobster here. And it turns out that if
these two genes are expressed, you get walking appendages. But if they’re not expressed,
you get feeding appendages. So it looks like
the transformation of one type of
appendage to another can be simply controlled by
when and where these genes are expressed. And so the take-home
message is that it doesn’t look like new genes
make new species, as we heard in our
first talk today, but it looks like it’s when and
where the same common genes are expressed that’s responsible
for the differences between us and a fly and a jellyfish. And so what’s going to be
really critical, once we have the sequence of not
just the human genome, but all the other genomes,
is understanding how those genes talk to each other. What is the wiring
within the genetic code? And that, I think, is going
to be the great challenge of the future. And so with that, I
think I will close. Thank you. [APPLAUSE] VEST: We are going
to move directly into what will be a
somewhat abbreviated and highly-informal
question and answer session. I have a whole host
of questions here. No way we will get
through all of them, but we’ll try to
hit some highlights. The first question is for me. It says, if 6635 Zuber
is name for Maria, is [? 2 ?] Vest a name
for you or your wife? [LAUGHTER] And the answer’s no. Second question is
also for me, but it’s about Charles Marshall. It says, is being a
professor at Harvard a necessary and
sufficient condition to be an adjunct
faculty member at MIT? [LAUGHTER] MARSHALL: And the answer is? VEST: And the answer is also no. Now here’s a serious question. Interestingly, about a
third of the questions were all, if not identical, all
along exactly the same theme. And I’m going to at least
initially direct them to Claude, although any of
you may wish to dive in here. They all have to
do with Big Bang. They’re all some variant on what
existed before the Big Bang. Claude will have
the answer to that. [LAUGHTER] What is the size of the object
that exploded in the Big Bang? And let’s see, there
was– another one here. Could the seed that
perpetuated the Big Bang be a reoccurring event with
other such seeds scattered throughout the vast
expanse of space? And then, finally, there
were a few questions that picked up those
same themes from more of a religious
perspective and ask if anybody had any
comments, for example, on intelligent design theory. So Claude, if
you’ll handle those. [LAUGHTER] CANIZARES: I just remembered
a very important engagement. I have to go visit
Stephen Jay Gould. It’s hard to know
where to begin. it’s actually
interesting that now, with the level of sophistication
that the theory of the Big Bang has achieved, thanks
in many ways to Alan Guth and the inflation
theory, there are actually some
cosmologists who are daring to try
to think about what may have happened beforehand. Is this a recurring event? There are papers published that
talk about multiple big bangs, so to speak, and this one
may be just one of many. I think it’s fair to
say– and of course I’m an observational scientist,
an experimentalist more than a theoretician, so
maybe it’s harder for me to wrap my head
around those things. I think it’s wonderful
that people are starting to think about those. There is, at the present time,
I can say no observational way to discriminate any of
those, and so it’s still in a highly speculative state. But after all, a lot of
the things that we now have very good
experimental evidence for were once in the same kind
of highly-speculative state. So it’s very good
that we can do it. But I think that will
be a very long time before we have
any way of testing one hypothesis against another. VEST: Thank you. Charles, giraffe necks
are easy, it says. What about elephant trunks as
an example of a complex feature with no selective
advantage until surpassing a certain threshold? Can you comment on how one
might think about such issues? MARSHALL: Yeah. It’s a good question. It runs to the question of
intermediates and the need to have some degree of
functional continuity as you evolve
intermediate forms. There are other
species out there such as tapirs that actually
have somewhat long noses that are floppy. And so the question is
obviously they’re not using that for sort
of moving objects, but it may be, in fact, still
be able to sniff things out better. So my suspicion is the
primary function, then, of an elephant’s
trunk prior to its use as a fifth arm, so
to speak, is actually used for smell in that
sense and the fact that it can be waggled around. It’s a “Just So” story,
but that would be the one that I would come up with. But it does raise an
interesting issue, which is if you look at the
number of genes that are responsible for the
difference between modern wheat and its last common ancestor
in the natural environment, it turns out there
look like there are about five genes involved. And so it’s beginning to
look like what happens is rather than having to
accumulate a very large number of small mutations to
get from here to there, that the gap sizes are sort
of exponentially distributed. There are a few very large
jumps and a whole bunch of little ones. And so, in some cases,
it may be possible to get jumps in morphological
space genetically rather than having to
actually traverse them minute step by minute step. And this is a new
theory that’s coming out in the last two or three years. So the genetics revolution’s
got a long way to go yet, but I think we’re on
the brink of them. VEST: Thank you. There were several questions
around another somewhat more modest theme, which I
will address to Maria. Claude, you may want
to jump in as well. But there are several
questions asking about the current status
of the SETI project and what is being learned. ZUBER: OK. I will take it. SETI is run, I
think, a little bit like a mom-and-pop operation. It’s being done at
radio frequencies and also up the street at
Harvard at optical frequencies. And it will soon
be coming online. CANIZARES: –SETI stands for. ZUBER: Oh, SETI. CANIZARES: Search for– ZUBER: Search for Extra– VEST: Search for
Extraterrestrial Intelligence. ZUBER: Seach– that’s right. Search for Extraterrestrial
Intelligence. And what that is is an attempt
to detect signals of life from planets beyond
our solar system. And I guess the short answer
to what has been found so far is that there have
been no detections that can unambiguously
be called positive. OK? But the bottom line
is that within, say, 50 light-years of our
sun, there are thought to be perhaps as many as
100,000 places to look, and so we have barely
scratched the surface of what is out there. In addition to
looking, you need to be looking at the right time. You need to be looking when
somebody is transmitting to us. And so what is needed are more
observations, and right now a lot of that’s being
privately funded. And it’s not a large operation,
but it’s very efficiently run at the scale that
it’s operating at. VEST: Thank you. Claude, I gave you a
tough one to start with. So let me give you a little
more, a little easier one here. Is the Chandra
Telescope performing up to its expectations? I know you love to
answer that question. CANIZARES: Absolutely. It’s really been extraordinary. As a few of you
may know, it took us 20 years of effort, some
of it actually political and a lot of it technical,
to get to the point where we could launch
Chandra two years ago. I think Eric Lander
mentioned in his talk about how science is
really now, and biology, moving towards a place that
actually Maria and I know very well, where you
only make progress when you bring together the
best engineers, the best scientists, the best operations
experts, mathematicians and computer scientists
and so forth. And that’s been the great fun
of Chandra is getting the team effort together and
having it work so well is the great satisfaction,
I have to say. VEST: Charles, here’s your
equivalent softball, I hope. Who is the author of the
tree simulation paper, and is it available? MARSHALL: It’s Karl
Niklas, N-I-K-L-A-S. It was Proceedings of the
National Academy of Sciences. I can’t remember the year. He’s also published a book,
University of Chicago Press, which fills out the evolution
of plants in that way. So yes, both are available. VEST: Thank you. There is also a related
publication question that came in several
guises asking, would the various
PowerPoint presentations be made available on the web? And let me give a tentative
answer of yes to that. think we can put it up through
the Alumni Association. So we will try to meet
that demand, which was raised by several people. Here’s a question. How do you determine
the age of galaxies? CANIZARES: With some difficulty. [LAUGHTER] In many cases, one can determine
the age using something that Maria was talking about. She talked about how stars form
and then go through their lives most of the time– well, after
they get through adolescence– through their adult lives. They change subtly
during that time. And we have a very good
way of understanding how their observed
properties will change. So when you look
at the, just as you could do for a population
of humans, when you look at the– you take the average
of their characteristics, you can get a reasonably good
idea of how old the stars are in those galaxies. Then there’s some
cases where we think galaxies, two
different galaxies, will come together and merge,
and we can see that happening. Now, that, of course,
confuses things quite a bit. But at least that
first is one good way of getting a sense of the age
of galaxies, of a given galaxy. VEST: This one addressed
to Maria Zuber. What do you think
happened on Mars to have caused it to
lose its atmosphere? And do you think the same
thing could happen on Earth? ZUBER: Hm, good question. CANIZARES: And if so, when? [LAUGHTER] ZUBER: OK. Well, the easiest way to lose
an atmosphere on a planet is to take it off
with an impact, if you want to get
rid of a lot of it. And that could well
have happened on Mars. The other way that you can
get rid of an atmosphere is the solar wind
particles can interact with molecules in the
atmosphere and dissociate them. So if you have water
in the atmosphere, it can break it into
hydrogen and oxygen, which are then lighter and
can then go off into space. However, when we
look at evidence of the surface of Mars, it shows
vast evidence for liquid water having been present
on the surface. We also now have good evidence
that the magnetic field on Mars shot off very, very early. But kind of no
matter what you do in terms of looking
at models then where you would dissociate
molecules by the solar wind, whether you could have
thermal escape mechanisms, there’s nothing you can
do to get rid of as much of the water in the
atmosphere as we believe there was once on the surface. And so barring
the kind of impact that you saw right
there, which would have lost a lot
of the atmosphere, we don’t know the
answer for that. And that’s one of,
essentially, the golden rings of Mars exploration is
to try to figure out where the atmosphere went. And could it happen on Earth? Who knows? Maybe. VEST: Mark that down. It was said here– maybe. Charles, and I apologize I can
only read part of the writing here, but I think
have the thrust of it. Why are plants round? I assume in
cross-section as opposed to other kinds of shapes. While the name is
Rudyard Kipling. [LAUGHTER] It’s almost certainly
just a structure of mechanical
engineering and the fact that plants aren’t moving and
that the stresses that they’re receiving from the
environment are sort of from all possible directions. And so [INAUDIBLE] so you need
a cause of symmetry breaking. And if you’re an animal
that’s– a plant in this case, that’s sitting in one place
with winds going in different directions, then there’s going
to be no mechanism of symmetry breaking in that sense. So I suspect it’s a fairly
simple answer like that. CANIZARES: Sounds plausible. MARSHALL: Yeah,
sounds plausible. Right. VEST: Here’s, again, a question
that came in multiple forms. Claude, you might start. Maria and others may
want to chime in. Can we yet tell
if there’s a limit or a boundary to the universe? And then once you’ve
answered that succinctly– [LAUGHTER] –the corollary question,
does the universe have an edge or boundary, if
so, what’s on the other side? [LAUGHTER] MARSHALL: Congratulations. CANIZARES: This is a question I
actually get asked frequently, and I’ve yet to come up
with a succinct answer. But I’ll try again. First of all, there is an
effective observational boundary, which I think
is easy to understand. And that is the fact that light
travels at a very finite speed. I mean, it’s a large speed,
but it’s still finite, and nothing can travel faster. And that means that there is a
limit to the universe that we can see and we can know or that
could in any way could have sensed– could have communicated
with us, even metaphorically, in terms of transfer
of information or transfer of material. And that is the
distance that light can travel in the age of universe. Anything beyond
that is something that we can have
no connection to. Now, the other part of
the answer– and in a way, I could stop there,
and that would probably be the easiest thing to do. But the other part of the
answer is that, unfortunately, the expansion of the
universe is not quite the same as the expansion
of, say, I don’t know, a souffle in your oven. Because in the case
of the universe, we’re talking, by
definition, about everything. That is the universe. And so the universe is
not just the material, but it’s also the spacetime,
the four-dimensional spacetime in which the events of
the universe unfold. And so when we’re talking about
the expansion of the universe, we’re actually talking
about a stretching and an expansion of that
multi-dimensional spacetime. And that is something
which, in fact, can occur without
having a boundary and without having any
other side to it, anything beyond its edge. And if people want to
pursue that discussion, you’ll find me out in the lobby
after the session is over. [LAUGHTER] VEST: Well, these
are difficult. Here’s one that was addressed
to Dr. Gould mistakenly. Did you choose to
be on The Simpsons? You don’t have to answer that. MARSHALL: I think I
could answer that one. The answer is yes,
since it’s his voice. Unless he speaks in his sleep
and is taped unknowingly. VEST: One of my tasks is to
keep us pretty much on schedule because we have to do
some moving around, and we want to be fair to
the wonderful opportunities in the afternoon. And so I’m going to
ask one question here of each of our speakers, which
may be the wrap-up question. It was indeed addressed
to all speakers. And the question is, what do
you think the most important one or two questions to be
answered in your fields are? And would you like to
start with that, Maria? You actually mentioned one
just a minute ago, I think. ZUBER: OK, Well, certainly
the question of life is one. But yeah, I think
just the commonality of the origin of the planets. I mean, there’s the question
of, did life develop? And when I get asked
about that, I usually give the answer, no matter what
the answer is, it’s remarkable. Because if you look at
the conditions for life being water and an energy source
and some lower-level elements, you get that in a lot of places. So taking that
point of view, you ought to find life everywhere. But if you take– the answer
to the question turns out to be it only occurred here,
then that’s telling you something remarkable too. And so I think in
the work that we do in our field, what we try to
do is a basic characterization of what’s there, and is it
unusual or is it common? And it’s a very difficult
question to answer, but I think that
pervades quite a bit of what we do for that reason. VEST: Thank you. Very thoughtful. Claude? CANIZARES: Well, I guess
I also touched in my talk on what I think is probably one
of the outstanding questions. But one thing I wanted
to say is that we talked a lot of progress being made. And of course,
progress in science is often as much in
being able to formulate the new questions as it is
in answering the old ones. And we have answered
a lot about the age and the structure and
content of the universe, but we’ve also
raised some new ones. And the new ones that
fascinate me and that I think will keep us busy for a while
deal with those components of the universe, the contents
of the universe, that we’re just discovering are there and
that we don’t understand. And the ones I mentioned
are the dark energy– the two major ones that
exist– the dark energy and the dark matter. Right now there are what I
think Eric Lander referred to as the clever– inventing words. They’re not very big
words, but inventing words to hide our ignorance. And we need to
uncover those if we’re going to really make progress. VEST: Thank you. Charles? MARSHALL: So yeah, I guess one
of the fundamental questions in all science is how
things come to be, and particularly, using
a language of science, is what are the mechanisms
by which things come to be? And in some respects,
initially the world was just there by God. It was a machine
to be understood by us in a philosophical sense
with Plato and Aristotle. With Kepler, et cetera,
we see a characterization of the machine. But it isn’t until
we get to Laplace that he starts to
talk about, well, how do you actually
form solar systems? The next great revolution
that, once we’ve talked about how do we
form stellar bodies, how do we form the Earth? James Hutton and Lyell–
where do rocks come from, the fact that there are
processes responsible for that. I think the third great
revolution was Darwin– where do species come from? And now I think the
fourth and the fifth that are happening together,
the fourth most important in my field, but I think
a fifth is, where does morphological form come from? Just taken for
granted by Darwin, and that’s the realm of genomics
and developmental biology. And then I think
just behind that from a mechanistic basis
is, where does mind and consciousness come from? Neurobiology. And so I think those
last two questions are the great, rich ones that I
think we’re on the verge of and institutions like this
are right in the middle of. Origin of morphological form and
consciousness, thought, mind. VEST: Well, thank you very much. The last two cards I was
handed were answers rather than questions. But they are answers
to another one of the great questions
of the universe, which is, how do we get to lunch? [LAUGHTER] And lunch is going to be in
the Johnson Athletic Center. And most of you think
that’s a very short walk, but that’s because you’re
not aware of the construction fencing that is on the campus. So there will be people
to guide those of you. Most of us, I suspect, we’re
going to walk over to Johnson. Just go out the
front door as always. There will be people
to point the way. But we also will
run the shuttle bus for any of you who prefer
to have a ride over, and my understanding
is it will board over in front of McCormick Hall. So either way. But please join me in thanking
all three of our panelists this morning. [APPLAUSE]

, , , , , ,

Post navigation

Leave a Reply

Your email address will not be published. Required fields are marked *