Still Evolving After All These Years

Maybe there is yet hope for humanity: According to an analysis of 2.8 million variations in the human genome, we are still evolving.

People the world over differ by about one in a million of the nucleotides that make up our DNA, but what’s interesting is evidence that those differences are not random but, instead, the work of natural selection, report Lluís Quintana-Murci and colleagues of the Institut Pasteur in Paris, in the online edition of the journal Nature Genetics. That basic assertion is not surprising; the extent of the effect of natural selection's effects on our genes, in the recent past, is.

Geneticists have known for decades that traits such as resistance to malaria, and the ability to digest lactose in adulthood, confer a survival advantage and therefore have been under selective pressure—that is, individuals with mutations allowing them to be lactose tolerant had an edge over those who lacked the mutation, at least in certain environments (in this example, an environment where cows are raised for milk). In the case of malaria resistance, a mutation in the gene called CR1 is present in 85 percent of Africans, but absent in populations from other continents; this gene modulates the severity of malarial attacks, suggesting it has been positively selected for in Africans.

The Pasteur scientists find that genes showing the strongest signs of positive selection are involved in skin pigmentation and hair development, immune response to pathogens, the repair of DNA, sensory functions such as smell, insulin regulation in ways that affect obesity and diabetes, and metabolic pathways for, among other things, alcohol. (Yes, some people really can hold their liquor better, thanks to DNA.)

For example, the gene named EDAR regulates the density of hair follicles and the development of sweat glands and teeth; changes in the EDAR gene made hair denser in cold climates, and altered the regulation of body temperature so as to allow people to conquer the frozen north. And in the case of diabetes, the gene called ENPP1 harbors a mutation that has been shown to protect against obesity and type II diabetes; the mutation is present in about 90 percent of non-Africans but virtually absent in Africans.

In addition to showing that humans are still subject to the laws of evolution in terms of their physiology, the research challenges the claim that our minds are still stuck in the Stone Age. Evolutionary psychology argues that behavioral traits that stood our Paleolithic ancestors in good stead—male promiscuity, female coyness, stepfathers’ inclination to murder their stepchildren and other admirable qualities—still have our behavior in 2008 on a short leash. Many scholars have questioned that assertion, which even some diehard proponents are now wondering about. The new genetic research makes the very premise of Stone Age genes for anachronistic traits suspect.

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