From The New York Times Science:
As with any other species, human populations are shaped by the usual forces of natural selection, like famine, disease or climate. A new force is now coming into focus. It is one with a surprising implication — that for the last 20,000 years or so, people have inadvertently been shaping their own evolution. The force is human culture, broadly defined as any learned behavior, including technology.
Where might we look for evidence in support of this hypothesis?
People adapt genetically to sustained cultural changes, like new diets. And this interaction works more quickly than other selective forces, “leading some practitioners to argue that gene-culture co-evolution could be the dominant mode of human evolution,” Kevin N. Laland and colleagues wrote in the February issue of Nature Reviews Genetics.
Such as?
Lactose tolerance is now well recognized as a case in which a cultural practice — drinking raw milk — has caused an evolutionary change in the human genome.
Amylase is an enzyme in the saliva that breaks down starch. People who live in agrarian societies eat more starch and have extra copies of the amylase gene compared with people who live in societies that depend on hunting or fishing.
A third group of selected genes affects brain function.
How might we differentiate between genetic mutations from natural selection and those from cultural practices?
In the last few years, biologists have been able to scan the whole human genome for the signatures of genes undergoing selection. Such a signature is formed when one version of a gene becomes more common than other versions because its owners are leaving more surviving offspring. From the evidence of the scans, up to 10 percent of the genome — some 2,000 genes — shows signs of being under selective pressure.
Can we base predictions on this information and test the hypothesis? Well, not so much, because our ability to compare changes to a baseline is very limited, which means we must rely more on statistical and other mathematical models rather than hard data. But the evidence clearly suggests that our genome is affected by established cultural practices.
Mathematical models of gene-culture interaction suggest that this form of natural selection can be particularly rapid. Culture has become a force of natural selection, and if it should prove to be a major one, then human evolution may be accelerating as people adapt to pressures of their own creation.
tildeb
Questionable Motives 
The evolution of lactose tolerance is a splendid example of gene-culture coevolution. The authors give others. One that I didn’t know about was the correlation between yam cultivation in Africa and the frequency of the sickle-cell hemoglobin allele, which in heterozygous form confers some protection against deadly malaria. Apparently those populations that cultivate yams, which involves cutting down forest, have a higher frequency of this allele than those who don’t eat yams. This difference is ascribed to one of the byproducts of yam culture: the creation of pools of water that serve as breeding sites for mosquitoes.
Jerry Coyne, from whose article I snatched this excerpt, also has an excellent article on this subject over at Why Evolution Is True. Read his piece here.
Comment by tildeb — March 3, 2010 @ 3:09 pm |