Transcript:

Speaker 1: Could you please explain why we are all Africans?

Speaker 2: I'm a fairly recently retired professor, and I'm professorial enough to draw on this convenient whiteboard here. That is 6 million years ago. And that is the common ancestor of chimpanzees and bonobos and humans. That is about 7 million years ago, and that is the common ancestor of all those and gorillas. That's about 12 million years ago, and that's the common ancestor of all those and orangutans.

Orangutans, as you know, are Asian apes. Gorillas, humans, bonobos, and chimpanzees are African apes. Darwin conjectured long before there were any available fossils that the right place to look for human fossils was Africa. And he worked that out by pointing out that humans most resemble the other African apes, namely chimpanzees. Well, they didn't call them bonobos in those days, and gorillas.

The reason that we know approximately the date of the common ancestor is molecular evidence. Comparing the genes, comparing the proteins of these various animals, it's possible to calibrate the date at which a common ancestor happened. And we can date the common ancestor of humans and chimpanzees and bonobos at about 6 million years ago.

Unfortunately, there are no fossils down this line here. Possibly because they're forest-dwelling animals. Nowadays, unlike in Darwin's time, there are quite a lot of fossils down this line here, and they are all in Africa. We've got the genus Australopithecus, sort of about halfway down. Ardipithecus. There. And Homo habilis. There. Homo erectus about there. And then Homo sapiens, archaic Homo sapiens there, and then modern Homo sapiens there, lots and lots of little branches. Quite well documented in the fossil record here. All extinct, except the last one, Homo sapiens.

You may have heard the phrase "out of Africa." There were two out of Africas. Homo erectus, about a little over one and a half million years ago, left Africa and colonised Asia and Europe and arguably Indonesia as well. No, in fact, not arguably. Definitely Indonesia. That's the first out of Africa.

The second out of Africa is very recent, probably less than 100,000 years ago.

If you look molecularly, if you look at the molecules of modern human races, they are astonishingly uniform, and such variation as there is is mostly within Africa. So that suggests that the deepest divides of cousinship in our species are within Africa. The whole of the rest of the world is a very, very recent branch of the human species.

If you look at the amount of variation in the human species genetically, it's extremely low. We are a very, very uniform species compared to other species, even chimpanzees.

It's been said that if you take two chimpanzees from the same forest in Africa, they're likely to be more different from each other genetically than any two humans in the world. It's a bit surprising when you consider that we, to our eyes at least, look more different. But the genetics is very clear that we are an astonishingly uniform species.

We are all one species, one very uniform species. And we originate very recently in Africa. We are all Africans.

Thank you.