02 September 2010

A Case Study Of Recent Human Evolution

Academic researcher and blogger John Hawks makes the point that a recent genome study shows significant evolutionary selection of particular genes (as opposed to population genetic differences arising from founder effects and population bottlenecks) in a human population in the last two thousand years:

Bray and colleagues report on genotyping of 471 people of Ashkenazi Jewish descent. This is one of the largest samples of a single human population, and is therefore very interesting for studies of population history and recent natural selection. . . . [P]ositive selection has now been demonstrated on six disease-causing alleles in the Ashkenazi population. Every one of these is a case of overdominance -- where the heterozygote carrying an allele has some selective advantage, while the homozygote carrying two copies has a disorder.

From here.

Sickle cell anemia is an example of overdominance selection in another population (Africa). One copy of the key allele is protective against malaria. Two produce sickle cell anemia.

A couple of other notable cases of recent human evolution that have been reported about in academic journals recently are the evolution of human populations in Tibet and the vicinity of adaptations to high altitude conditions, and the spread of lactose tolerance in adults among populations that have herd animals that can be milked.

John Hawks, generally, makes the point that rather than having stopped, human evolution has accelerated in the historic era. It doesn't happen has fast or in as stunning ways as it does in science fiction, but declining death rates from modern medicine have not rendered the multiple mechanisms of evolutionary selection (e.g. average generation length, number of descendants per generation, and non-reproduction of descendants who don't die prematurely) impotent. Premature death is only one mechanism by which natural selection acts.

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