Friday, January 16, 2009
Hitchhiking by natural selection in humans
There is much reported evidence for positive selection at specific loci in the human genome. Additional papers based on comparisons between the genomes of humans and chimpanzees have also suggested that adaptive evolution may be quite common. At the same time, it has been surprisingly hard to find unambiguous evidence that either positive or negative (background) selection is affecting genome-wide patterns of variation at neutral sites. In a paper just published in PloS Genetics, we evaluate the prevalence of hitchhiking by positive or negative selection by using two genome-wide datasets of human polymorphism. We document that levels of neutral polymorphism are substantially lower in the regions of (i) higher density of genes and/or regulatory regions, (ii) higher protein or regulatory divergence, and (iii) lower recombination. These patterns are robust to a number of possible confounding factors. We suggest that effects of hitchhiking cannot be ignored in the study of the human genome and that the patterns are most consistent with pervasive, genomewide positive selection. See how Stanford Report describes this work. A recent paper by Vicker et al presents very similar results that confirm and extend these findings to suggest that our estimates were very conservative and the effects of positive selection on linked variation are even stronger.