Saturday, June 25, 2011

Population Growth Spurring Evolution?

The Daily Galaxy is reporting on some work by John Hawks at U of Wisconsin, Madison on the rate of evolutionary change in humans. They write:
A team led by University of Wisconsin-Madison anthropologist John Hawks estimated that positive selection just in the past 5,000 years alone -- dati back to the Stone Age -- has occurred at a rate roughly 100 times higher than any other period of human evolution. Many of the new genetic adjustments are occurring around changes in the human diet brought on by the advent of agriculture, and resistance to epidemic diseases that became major killers after the growth of human civilizations.

"In evolutionary terms, cultures that grow slowly are at a disadvantage, but the massive growth of human populations has led to far more genetic mutations," says Hawks. "And every mutation that is advantageous to people has a chance of being selected and driven toward fixation. What we are catching is an exceptional time."
The first caveat to this is that evolutionary biologists have discovered time and time again that small populations undergo evolution faster than larger ones because traits get expressed with a greater degree of frequency, hence the concept of founder effect. In larger populations, genetic load increases and the population bears more selectively disadvantageous traits.

The other caveat is that, as one goes back in time, genetic evidence gets scantier and scantier to the point where we really don't know exactly how fast evolution was happening in some populations, in part because we don't have all the fossil data. I think there is merit in what Hawks is trying to show but the above two concerns need to be addressed.

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