Sunday, March 6, 2011

The Human Revolution

(Picture from here.)

For a long time anthropologists and archeologists have viewed human evolution as gotten some sort of kick start about 50k years ago. "Something happened" that gave rise to modern humans.

But some recent genetic work (see here) and anthropological work (see here) has called that into question.

A little history.

While human beings have a long history, hominins that are recognizably human don't really appear until between 200k and 400k years ago. The idea is that humans and Neanderthals had a common ancestor about 700k years ago. That common ancestor moved north into Europe and became Neanderthal. Our ancestors stayed home and evolved into human beings (likely, I think, down in South Africa) and rolled out of Africa about 200k-400k years ago. The first Homo sapiens fossils are dated to 100-200k years ago, implying the stock was already established earlier.

There's some debate about this-- notably involving some teeth discovered in Israel (see here)-- but mostly over whether the location of where the actual evolution of humans occurred. The migration of humans out of Africa is pretty well established.

Once they did migrate they acted pretty much the same until about 45k years ago marking the Upper Paleolithic. Then, all of a sudden, we came up with complex stone tool technology, bone tools, projectile weapons, etc. We had become, in effect, behaviorally modern humans. Earlier humans, the ones dated 100k-200k years ago, had none of these inventions and are lumped together as not behaviorally modern.

Hence, the "Human Revolution" idea.

John Shea of Stony Brook suggests things ain't quite so simple.

A Human Revolution implies a change in variability of behavior, an dramatic increase in the repertoire of what humans did. So he examined stone tools dating from 250k to 6k years in Eastern Africa. He found over that time no single behavioral revolution in that time. Changes in stone tools here and there could be explained in variability in the available materials or in the needs of a specific time and place. A Human Revolution was unnecessary to explain these changes.

Coincidentally, a different study has come from a team by Ryan Hernandez of UCSF. They examined the human genome looking for selective sweeps. A "selective sweep" is a genome change that is so beneficial that it spreads throughout the population very quickly. Along with the "Human Revolution", class sweeps were thought to have driven human evolution. Hernandez found only a few sweeps present in the genome and none that could drive human adaptability. Instead, he came to the conclusion that human adaptation has a complex genetic architecture and derived by subtle shifts in the genome and not any major changes.

So: we have no Human Revolution, behaviorally or genetic.

Shea goes so far to say that the is no such thing as a "modern human". We are the same animal now as we were 200k years ago.

But whether we are different genetically or cognitively is somewhat beside the point. We aredifferent from our ancestors in how we live and what we are capable of. While I think these scientists are correct in that the differences between our ancestors and ourselves may not be in the shape of our brain or our genes, there is no doubt we are culturally different. And that culture drives our ability to cooperate to astounding levels-- not even ants are capable of the our scale and level of cooperation. That had to come from somewhere.

Personally, I think it started when we started sequestering information. I suspect, like elephants, we've been capturing information since Lucy. But if you observe nomadic tribes that are without writing and presume they reflect our history before writing, there is a tremendous drive to retain knowledge across the group, across generations. Often in the form of story and song. Retention of information is a driving force in our species in the last several thousand years. It's no accident, I think, that control and destruction of information (think the Reformation, Nazis, Soviets and the Taliban) are among the levers of power.

Once we started retaining information-- broad, deep rivers of it-- we had the motivation to create writing. And once we had writing we had a mechanism in place to truly exploit the our phenomenal ability to cooperate.

If there was a "Human Revolution" it started with the valuing of information. Civilization started there.

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