Matt Ridley: The deep divergence in African genomes

News is dominated by sudden things — bombs, fires, election results — and so gradual news sometimes get left out. The past month has seen three discoveries in Africa that radically change our understanding of a crucial phase in human evolution. For those interested in the common history of all humanity, this should really be among the biggest news of the year.

The first of these discoveries is genetic. Swedish and South African scientists have made the origin of us — modern human beings — an even more mind-bogglingly gradual phenomenon than we used to think. Here is what they found. A skeleton of a boy who died 2,000 years ago at a place called Ballito Bay has yielded a good sample of preserved DNA. He was a Khoe-San, that is to say an indigenous native of southern Africa of the kind once called “bushmen”, who still live in the Kalahari desert.

But unlike all today’s Khoe-San he had no DNA from black Africans or white Europeans in him. Neither had yet arrived in southern Africa. So comparing the Ballito boy’s DNA to all modern people’s DNA made it possible to calculate when we last shared a common ancestor with him.

The date was a big surprise: more than 260,000 years ago. That is to say, 2,600 centuries, ten times as long ago as the extinction of the Neanderthals in Europe, and halfway back to the split between human beings and the ancestors of Neanderthals. Surprisingly, the Ballito Boy’s people appear to have had little or no genetic contact with other African people as recently as 2,000 years ago, but they have had considerable gene mixing since.

So, until they experienced recent hybridisation, the Khoe-San people of southern Africa had been more distantly related to the rest of us than we had thought by a long way. Yet they are still recognisably human. There is no way anybody would describe them as “sub-human”, intellectually, linguistically, adaptively. They are just people.

This throws all our ideas about the “human revolution” into the air. Until a few years ago, anthropologists were talking of a “great leap forward” in human evolution around 50,000 to 100,000 years ago when tools suddenly became much more sophisticated, and were speculating about this being the moment that language or consciousness crystallised. It has been clear for a while that this was too Eurocentric; African tool kits had begun to change much earlier in a mysterious technology known as the Middle Stone Age.

Another discovery also announced this month seems to confirm that early human beings living in Morocco around 300,000 years ago were showing anatomical “modernisation” much earlier than we thought. So one possibility is that people throughout Africa were changing in parallel, rather than one small tribe becoming “modern human beings” and taking over the continent and later the world, as had been the assumption. Put the two discoveries together and you can conclude that as far apart as South Africa and Morocco, people experienced both growing culture and more modern anatomy.

It is certainly possible that culture was the horse and genetics the cart, not vice versa. That is to say, once human beings reached a certain level of culture, they created selection pressure to change their genes to make things like the development of language and imagination easier. So it could happen in parallel in different lineages. This phenomenon is known as “gene-culture co-evolution” or “niche construction”.

In passing, these findings reinforce my view that genetic differences in intelligence among human races today really do not matter. Human civilisation is a collaborative achievement, not a product of individual intelligence or innate capacity. It came about because we networked our brains, not because we improved them. We had very primitive lives for a quarter of a million years despite having modern IQs. There may be a lesson here for artificial intelligence.

However, the story may not be quite so simple. Other genetic evidence suggests that the initial effective population size of the modern humans in Africa was small, which is not compatible with a large population occupying most of a continent. “Ghost genes” in modern Africans testify to hybrids with now-extinct kinds of African hominid — similar to what happened between Africans and Neanderthals (as well as Asian hominids called Denisovans) when the former spilt out of Africa and into Eurasia at around the same time. As the anthropologist John Hawks of the University of Wisconsin tells me, these “ghost” populations had to have been living somewhere.

Hawks and his colleagues have made another startling discovery. The fossils of a far more distantly related species of hominid called Homo naledi, which retained a small brain and a chimp-like jaw, have been discovered recently in a South African cave. But instead of being millions of years old, such fossils have now been dated — in yet another announcement this spring — at (you guessed it) between 236,000 and 335,000 years old.

So as we push back the date of modern human beings, we pull forward the date of the extinction of other kinds of hominid. When already culturally advanced, we shared the African savannah with a small-brained ape-man that was much more closely related to us than chimpanzees are, but was a quite different species.

So who made the Middle Stone Age tools, which are found all over the continent but vary from region to region? Almost certainly several different archaic lineages contributed, as well as the particular species or race that was on the way to turning into modern human beings. Perhaps even Homo naledi made some of them.

The truth probably lies somewhere between two extremes, one of which has distinct species of early human living all over Africa, interbreeding not very much and with only one on the way to modernity; the other has frequent hybridisation between populations in different parts of the continent, both genetically and culturally.

Either way, something was stirring in Africa that would lead eventually to iPhones and nuclear weapons, Beethoven and the Beatles. And it was stirring much earlier than we had thought, almost a third of a million years ago. It is hard to get your mind around just how gradual the emergence of modern human beings was. We are talking of 10,000 generations. Now that’s long term.

Matt Ridley, a member of the British House of Lords, is an acclaimed author who blogs at www.rationaloptimist.com. This article was first published in The Times.