parallel evolution
Tennessen JA & Akey JM 2011 Parallel adaptive divergence among geographically diverse human populations. PLoS Genet 7:e1002127.
- most putative examples of adaptive divergence between human populations lack the full signature of a classic hard sweep
- classic sweeps may have played a negligible role in the evolutionary changes that have occurred since the most recent common human ancestor
- divergent loci may indicate more complex and subtle modes of selection
- it is often difficult to demonstrate with statistical confidence that they are not merely the tail end of a stochastic neutral distribution
- if selection acts independently on the same loci in different geographical locations, data from multiple populations can be leveraged to provide strong evidence for non-neutral evolution
- demonstration of parallel evolution among populations provides strong support for the hypothesis that repeated selection of the same alleles in distinct environments is an important mechanism of local adaptation
- the goal is to test whether the same SNPs show high divergence in phylogenetically independent contrasts
- to this end, we calculate pairwise FST for all SNPs between all pairs of groups
- for each pair of groups, we identify divergent SNPs that exceed the 95th percentile of FST values
- our results are consistent with fluctuations in the allele frequencies of standing variation, as in soft sweeps
- although alleles have rarely actually swept to fixation
