A Question for Anthropologists

This year's special issue of Scientific American is "Beyond the Limits of Science." One of the articles is about human evolution. The title is Super Humanity in the print issue but the online title is Aspiration Makes Us Human.

The author is Robert M. Sapolsky, a professor of biology and neurology at Stanford University in California (USA). Stanford is a pretty good school so he probably knows his stuff.

Here's how Sapolsky starts off ...

Sit down with an anthropologist to talk about the nature of humans, and you are likely to hear this chestnut: “Well, you have to remember that 99 percent of human history was spent on the open savanna in small hunter-gatherer bands.” It's a classic cliché of science, and it's true. Indeed, those millions of ancestral years produced many of our hallmark traits—upright walking and big brains, for instance.

This doesn't make sense.

Let's assume that our ancestors left Africa only 50,000 years ago. If that represents 1% of our evolutionary history then it means that our species and it's immediate direct ancestors lived on the African open savannah for 4,950,000 years.

Could that possibly be true even if you only count the main line of descent? What is the evidence that supports these claims? How much of the early history of Homo sapiens was influenced by adaptation to open savannah? Does anyone have a scientific answer to this question?

Setting aside the "main line," we now have good evidence that modern Homo sapiens acquired alleles from Neanderthals, Denisovans, and, perhaps more ancient Homo erectus. All three spent substantial time evolving in places that looked nothing like the open savannah in Africa. The proportion of the "invading" alleles may be only 10% or less but that's still significant.

Do we know for sure that all of the important features of modern humans came from alleles that were fixed by adaptation on the savannah? What if some of the more important behavioral alleles came from Neanderthals and became fixed because they were so much fitter than the savannah alleles?

Take the alleles that make women like to shop, for example. Maybe they arose in the Denisovans because they have access to better trade routes in central China? Maybe the women on the savannah preferred to store their cash in elephant tusks?

The evolutionary psychologists have developed awesome explanations for human behavior based on their detailed understanding of the social structure of hunter-gatherer groups living on the savannah for millions of years. What if our genetic ancestors lived elsewhere? The bad news is that all those just-so stories will be wrong. The good news is that they can publish a completely different set of stories and get twice as many publications.

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