John van Wyhe is a British historian of science, with a focus on Charles Darwin and Alfred Russel Wallace, at the National University of Singapore. Here is the full text of his talk titled “How We Found Out Evolution is True” at TEDxNTU conference.
John van Wyhe – TEDx Talk TRANSCRIPT
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 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 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.