Friday, July 02, 2010

How quickly can humans evolve?

Even fifteen years ago cognitive science courses taught that the human mind was frozen in the Paleolithic Pleistocene. Humans didn’t evolve any more

Now we wonder how fast can humans evolve ...

Scientists Cite Fastest Case of Human Evolution – Nicholas Wade -

…. Comparing the genomes of Tibetans and Han Chinese, the majority ethnic group in China, the biologists found that at least 30 genes had undergone evolutionary change in the Tibetans as they adapted to life on the high plateau. Tibetans and Han Chinese split apart as recently as 3,000 years ago, say the biologists, a group at the Beijing Genomics Institute led by Xin Yi and Jian Wang. The report appears in Friday’s issue of Science.

If confirmed, this would be the most recent known example of human evolutionary change. Until now, the most recent such change was the spread of lactose tolerance — the ability to digest milk in adulthood — among northern Europeans about 7,500 years ago. But archaeologists say that the Tibetan plateau was inhabited much earlier than 3,000 years ago and that the geneticists’ date is incorrect.

When lowlanders try to live at high altitudes, their blood thickens as the body tries to counteract the low oxygen levels by churning out more red blood cells. This overproduction of red blood cells leads to chronic mountain sickness and to lesser fertility — Han Chinese living in Tibet have three times the infant mortality of Tibetans…

This is vicious selection; in pre-technological times the infant mortality gap was probably even greater.

Which reminds me of something I wrote two months ago

… Even after the development of agriculture and writing we see thousand year intervals of relative stasis in China, Egypt and Mesopotamia. How could this be when our fundamental technologies change in decades. Are the minds of modern Egyptians radically different from the minds of only 6,000 years ago? Why? Why do we see this graph at this time in human history?

What did humans do in Georgian caves for 30,000 years? Thirty thousand years of waving and sewing and nothing changes?! They could not have had the same brains we have. They seem more … Neandertal…

Six thousand years is twice the time it took humans to adapt to the Tibetan plateaus. So that’s plenty of time for brains to change.

Except brains are qualitatively different from red cells. Brains are a platform for minds. Left handed people flip hemispheric specializations, and yet seem to think very much like right handed people.

Think about that. Mutations that flip cardiac orientation are 100% lethal. Flipping hemispheres though – the mind adapts. People born with half a brain can function in human society. Five percent of the population have big ugly looking mutations in brain development systems – yet they seem fine.

The human mind can run similarly on a diverse infrastructure. The software analogy is irresistible. A browser running on an iPhone can look and act a lot like one running on a Win 7 box – but the two systems are very different.

This gives a lot more leeway to evolution. It means that the ‘variation controls’ on the genetic programs for neural development can be “set” (by evolution) to “high variation” – and we can still turn out functioning humans minds. It means that brains may be evolving very quickly – over the course of a thousands of years.

It will be interesting to compare the DNA of Homo sapiens 2000 BCE with Homo sapiens 2010 ACE.

See also

Update 7/20/2010: John Hawks reviews the evidence for active selection. I think when he talks about "demographics" he might be talking about how the unification of dispersed human populations causes new phenotypes to emerge -- but he's tip-toeing around something and is being cryptic.

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