Gene Evolution and Human Adaptation

Abstract

Abstract Regions of the human genome that have been subject to past positive selection contain patterns of genetic variation that are markedly different in specific ways from regions that have not experienced positive selection. By uncovering these so‐called signatures of positive selection in the genome we can discover the unique ways in which humans have evolved. Genome‐wide scans have revealed signatures of positive selection on the human lineage since we diverged from chimpanzees, as well as signatures of positive selection specific to regional human populations. New research has found that much of human population adaptation may have occurred by positive selection causing modest increases in frequency of beneficial variants at multiple loci that all result in the shift of the expression of a feature (like height) in a particular direction. Key Concepts: Hundreds of genes have been found that bear signatures of positive selection on the human lineage with genes mainly falling into categories of chemoreception, immune defence, reproduction and fertilisation as well as apoptosis. Most studies of positive selection have focused their work on the protein‐coding portion of the genome, yet many sites of positive selection may fall in noncoding regions where new research is detecting many functional elements. There is much active research trying to identify the extent to which DNA substitutions in regulatory elements underlay our adaptations. Much needed in future research is experimental work that aims to pinpoint causal variants within genomes and the phenotypic effects of genomic regions showing signatures of positive selection. The traditional signature of selection, a ‘classic selective sweep’, appears to be rare in large resequencing datasets of diverse world populations leading researchers to begin searching for signatures of ‘soft selective sweeps’ where weak positive selection acts to subtly increase the frequency of DNA variants at multiple loci with all variants contributing to a shift in a phenotype's expression in the same direction.