Translator: Rik Delaet
Reviewer: Axel Saffran Hello. Today, I want to tell you a story
that's very interesting to me, which is that when Charles Darwin
published his Origin of Species in 1859, the world was, on average, a much more
religious world than it is today - the world has become much more secular. And, of course, his one book
didn't have that much evidence, but within 10 or 15 years, the scientific debate
over evolution was over. Darwin's book was victorious and the international
scientific community accepted that evolution was a fact, by the 1870s. Now the question is,
How could that have happened in a world that was so against evolution
and so religiously conservative whereas today, where the world is
relatively speaking much more secular, and we have billions of times
more evidence, many people seem to think
that evolution is controversial? These two things to me
don't seem to make sense, but I think the history of how evolution
came to be uncovered in the first place can clear this up. So, of course, centuries ago, people believed that the Earth
and the animals and plants in it had been created by a supernatural deity, rather as is depicted in this illustration
from Luther's Bible from the from 1530s. A century later, Archbishop Ussher from Ireland
tried to estimate the age of the Earth by counting the number of generations
of particular people named in the Bible. He came up with an age
of about 6,000 years for the age of the Earth. But, of course, there are
things in the Earth called fossils. Fossils have always been known. They are not new. Even the ancient Greeks and Romans
knew about fossils, and they explained them as the remains of the giants
and monsters from their mythology. So here's an image
of one of such of these monsters. In more recent centuries,
particularly in Europe, things like this were very common. This shell-like object, which we now know
is related to a type of oyster, was explained as the devil's toenails. And apparently the devil has some
pretty nasty problems with his toenails, but anyway - and needs a pedicure. But these were dropped in the millions
all over the world. This was a folkloric explanation -
similarly for these objects. These were believed to be lightning bolts
that had hit the ground. When lightning strikes the ground
it makes one of these. These were called snake stones for the obvious reason
that they look like a coiled up snake. There's just one problem
with that explanation, of course: none of these snakes have heads. But some local craftsmen
were able to fix that (Laughter) by carving some heads onto them. Here's another very common type.
These were called tongue stones. I'm not sure why. They don't
look much like a tongue to me. But anyway, it was tongue stones that first unlocked the secret
of what fossils actually are. And it was this man, a Danish Bishop named Steno,
who first established that the reason these tongue stones
looked just like the teeth of sharks is that they are the teeth of sharks, only that they are fossilized. And that got him to think
very seriously for the first time, How could an object -
part of a dead animal, like a tooth - become embedded in the middle of a rock? I mean, that shark's tooth
was once in the sea. Well, he discovered
various things about stratigraphy. That is that in places in the Earth
where the rocks are sedimentary, they began as mud or silt and settled in a horizontal fashion
on the bottom of the sea or a lake and that any hard objects
that fell in that mud would slowly be buried, and if more and more
sediment accumulates on top, eventually those layers become compacted, and they become shale or sandstones. But one of the important revelations
of this work, of course, is that that means that layers settle
sequentially on top of each other, which means that
the lower layers are older, and the upper layers are newer. And thus it was possible
to start to unlock the mysteries of the history of the Earth by examining the Earth itself. A hundred years later, the Scottish geologist Hutton
was able to use such studies. Like in this diagram here, he's describing something
called an "unconformity." The layers at the bottom
also originally accumulated horizontally, but somewhere in the depths of time, they have become tilted up vertically, then they had been raised up above the sea so that the top above them has eroded away from the erosion from being
on the surface of the land. Then, at some time after that, it had all gone down under the sea again, and new layers were deposited on top. He said that this sort of thing showed that the Earth must be practically,
from our perspective, eternal. It is unimaginably ancient. What about the fossils? Well, it's one thing to say that
a little oyster shell or a snake stone - well, if it really is
the remains of a living thing, they could still be in the ocean -
it's very deep - or maybe they live in a remote region
that we haven't discovered. But fossils like this,
you couldn't dismiss in the same way. This is the fossil of a mastodon, discovered around the beginning
of the 19th century. And the great French
comparative anatomist Cuvier is the person to establish
for the first time something that was
until then very objectionable. That is that living things can go extinct. Those shells, you could argue,
"Well, they might still be alive." But you couldn't argue that
about a gigantic elephant creature running around North America. Nobody, for centuries, had seen any
of these giant things running around. They were not hiding
behind a bush or a tree. They were extinct, and he also proved they were related
to the living species of elephants. This species, called
the Megatherium, big beast, was discovered in Brazil. Cuvier established once again, okay, this animal was the size of a car. But from its bones and teeth, he was able to prove
that it was related to a sloth, which lived uniquely in South America,
where this fossil was found. This also is just way too big
to be hiding somewhere. They were extinct. So extinction became
an accepted principle in science. Cuvier also conducted
very extensive examinations of the Paris Basin, with his colleague, and was able to prove that there had been many different eras
in the Earth's history, in this particular region. There had been different ecosystems
with different plants and animals which had been followed
by some sort of flood or disaster. Then there had been another age with different plants
and different animals. And that also had been wiped away. And yet another age. All of those species
were different in each era. And once they vanished,
they never appeared again. They went extinct. These images on the side there are some of his reconstructions
of what these animals looked like. They were mammals, but they weren't like any mammals
that were alive today. They were unknown types. Then these were found. Gigantic ocean-living creatures. At first they were thought to be fish, but their bones and teeth demonstrated
that they were in fact reptiles. The one on the top they called
an ichthyosaur, fish lizard. They didn't have very - They gave all the best names
away at the beginning. Big Animal, right? Could have used that later, too bad. And the lower one was a plesiosaur. These were also obviously extinct. No fisherman had dragged up any of these. They also were found in deposits
with these bizarre objects. They were scattered in millions in the same rock layers
as the ichthyosaurs. And indeed, with close examination they were even found inside
the fossilized bodies of the ichthyosaurs. And soon they figured out what they were. These are nothing less than fossil poo. Or fossil feces, if you prefer. This is ichthyosaur poo. And what it showed was
that ichthyosaurs were carnivores. By slicing open these coprolites,
as they are called, they contained fish scales and the crunched up bones
of smaller ichthyosaurs. Which led some people to claim
they must have been carnivores - not carnivores ... cannibals, yes. So this allowed people to start
to reconstruct a very realistic idea of what this ancient world looked like. And this is the first depiction
of the ancient Earth. You've all seen something
like Jurassic Park, etc. Yes, yes. Very fancy computer modeling. This is the first one, the first image of an ancient Earth, and there they are: ichthyosaurs, etc. - munching each other and presumably
producing lots of coprolites. (Laughter) And shortly after that,
the dinosaurs were discovered. The so-called extinct family,
with which we are most familiar, of giant creatures. Well, all of this
was put together by the 1830s to a picture that was something like this. The world was unbelievably ancient, and the fossils that had appeared in it had appeared in a sequential
story of progress. That is to say that in the earliest rocks
were the most primitive creatures - shells, mussels. Later they were fish. After that, the reptiles appeared,
and after that, the mammals appeared. This was universally accepted
by all these men of science, long before Darwin
or evolution were on the scene. Because this was not evolution for them. This was simply the history of the Earth,
and these were all religious men, as you can see from
the Reverend William Buckland, whose book we're looking at. This is a close-up of the same diagram just to show you that nowhere
in this history of the Earth were any human remains ever found. All of human history is composed of that tiny little white layer
of scum at the top. So there was no doubt at all that these ancient worlds existed
before the appearance of human beings. And so this is the way these pre-darwinians
depicted the history of life on Earth. It was a story of
progressive change over time. Presumably they thought
it was a series of new creations, one era after another. This is another one. You see that most ancient Earth
is at the bottom, and you come up
towards the age of mammals. Then of course there are the animals that were being found alive
in the world today. The diversity of living things
was mind-boggling. It was far beyond what had
been expected centuries before. And so this became
a very fashionable subject to study and try to figure out what was
going on with all of these living things. And they began to categorize
them in ways like this, which to our modern eyes looks like
an evolutionary tree, but this is not. This is simply a diagram arranging different kinds
of mollusks according to groups. It's a bit like say, mammals. You have dogs, cats, mice. Those are all different groups, but they're underneath
one group: the mammals. And then, of course,
we meet Charles Darwin. Recent graduate
of the University of Cambridge, he had the opportunity
to travel around the world on a government ship,
the Beagle, as a naturalist. He made some amazing discoveries, including his own fossil animals. This one, the glyptodon, on the top,
was an extinct giant mammal - also almost as big as a car - found in South America. And it struck him immediately
that this mammal - not a dinosaur - this mammal with bony armor plating
on its back was strikingly similar to the only other mammal in the world
with bony armor on its back, the armadillo, which lives in the same place. Similarly, he discovered this one,
called the Macrauchenia patachonica, "the big neck of Patagonia," which he was told -
it later turned out to be incorrect - that it was a giant extinct llama. And the same thing was true for Australia. They found giant extinct kangaroos,
"killer kangaroos." Their fossils were found in caves. Again, the same kind of creature
from the ancient past as in the present. Of course most famously, Darwin went to the Galapagos Islands,
and he saw some pretty little birds. What was interesting is that he noticed there seemed to be different
types of birds on different islands. Why should that be? Darwin as a geologist knew that these islands had erupted
as volcanoes out of the ocean. They were sterile and naked and dead. Species had colonized them. As an expert of South America, he knew these birds were obviously
South American - sort of - birds, but they were different species. It was obvious in those days
that a local variety could emerge. You could take, say,
cattle and horses from Europe, take them to America, after a hundred years or so,
they were a bit different. That wasn't evolution; that was just
the formation of a local variety. They were sure there was a sort of limit
beyond which things couldn't change. What about those in the Galapagos? There they are, 600 miles away
from South America - they obviously came from South America - but did each species independently
arrive at its own island and no other? Of course not. It's much more likely that they
arrived somehow to the Galapagos and then diverged. And Darwin figured they must have evolved. When he got home, he took a little bit of time off
from theorizing to get married, and the consummate naturalist that he was, these are his notes
on whether or not to get married. (Laughter) Pros and cons: marry - not marry. I don't have time to read them to you, but I will just point out
that on the on the positive side here - a constant companion,
a friend in old age, one to feel interest in one, an object to be beloved
and played with. Well, but then he writes above that line: "Better than a dog, anyhow." (Laughter) Okay, he was not a romantic,
he was a scientist. (Laughter) Around the same time,
he drew this notebook sketch, which was the first time that
a real evolutionary family tree was drawn to represent how living things
can descend from common ancestors and diverge into many family groups. So this is the same diagram with the dogs. I've photoshopped the dogs
onto Darwin's diagram. To explain, from the common
ancestor of the dog groups, you have all of these possible descendants
with lots of them that have gone extinct. So, how to explain
that some groups are very similar, but others are rather different? It's from differential relatedness. Similarly with his idea of natural
selection - his most famous idea. But I won't go into that so much because it actually had very little to do
with the acceptance of his idea, which was that all individuals vary, some survive and some die. But other evidence was equally powerful
for Darwin's theory, such as embryology. Embryos. The embryos of animals
do not start out as little tiny adults, that just get bigger and are born. Embryos go through a weird set
of stages and shapes, which all resemble each other despite them being
completely different adult organisms. So in this diagram: a turtle,
a chicken, a dog and a human. Their embryos all look
remarkably similar at the same stage. Why? Because they are related
by common ancestors. Similarly with homologies, the same structures in the bones
of all of these different animals. There was no other explanation,
and there still isn't, whether they share common ancestry. Why should the wing of a bat
or the paddle of a whale have the same identical bone structure. Then there are vestigial organs. Why should the manatee
have fingernails on its flippers or whales that are born with no teeth when their embryos
have teeth in their jaws or birds that are flightless
that have wings? Well, this young man,
Alfred Russel Wallace, came along, had identical theories to Darwin's and prompted him into print
after 20 years of working on it. He published the
Origin of Species in 1859. Shortly after that,
even more evidence arrived. A new fossil: the Archaeopteryx, still one of the most famous
fossils in the world, halfway between
the dinosaurs and the birds because it has a dinosaur's skeleton,
but it has feathers. And this is the shocking point: you've always been told
that the dinosaurs are extinct. That is not true. One family of the dinosaurs
never went extinct. They are called birds. So, the next time you have chicken,
remember you are eating dinosaur. (Laughter) So, Darwin's theory is often called
"The survival of the fittest," as a sort of shorthand. It's not a very good shorthand. I think probably a better shorthand is
"It's often survival of the luckiest." Thank you very much. (Applause)
