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selective sweeps and human evolution

When natural selection favors a beneficial mutation, neighboring genes within the same chromosome are also selected. This is called linkage drag and to calculate the speed at which the selected mutation is fixed in the population. In the case a mutation that involves a significant survival advantage, the dramatic and rapid fixing it in the population may reduce the variability of the nucleotides close, not giving time to the accumulation of variations on them. In this case we will have produced what is known as a "selective sweep."

In humans there is evidence of selective sweeps in several chromosomes, as in the case of pigmentation of the skin, hair, teeth morphology or the ability to digest lactose. Some researchers have proposed that selective sweeps have been very common in the evolution of Homo sapiens . However, a recent study published in Science on February 18 and has been carried out by a team of geneticists from the Universities of Chicago, Oxford and Jerusalem, is to support the opposite view: it is very selective sweeps may be an exception and not the norm in human evolution.

By computer analysis of 179 genomes belonging to individuals from Europe, Asia and Africa, the study shows that selective sweeps have been rather rare in human evolution. The researchers found that, unlike as expected by recurrent selective sweep model, the regions surrounding specific mutations of the human being did not show lower variability than those in regions close to synonymous substitutions. These data indicate, the team that selective sweeps have been the predominant model of human adaptation in the last 250,000 years, although not ruling that may be more important in other species.

One of the reasons why the selective sweeps are not important in the human species may consist of widely dispersed that the species has had in its history throughout the world. In this scenario, a beneficial mutation would a long way before them to propagate.

We are obliged to resort to more elaborate models to explain the genetic mechanisms of adaptation in the human lineage, said Molly Przeworski, one of the geneticists at the University of Chicago.

Source: ScienceNews

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