Rapid evolution of male reproductive genes in the descent of man

A diverse body of morphological and genetic evidence has suggested that traits pertaining to male reproduction may have evolved much more rapidly than other types of character(1-3). Recently, DNA sequence comparisons have also shown a very high level of divergence in male reproductive proteins between closely related Drosophila species(4-6), among marine invertebrates(7,8) and between mouse and rat(9). Here we show that rapid evolution of male reproductive genes is observable in primates and is quite notable in the lineages to human and chimpanzee. Nevertheless, rapid evolution by itself is not necessarily an indication of positive darwinian selection; relaxation of negative selection is often equally compatible with the DNA sequence data. By taking three statistical approaches, we show that positive darwinian selection is often the driving force behind this rapid evolution. These results open up opportunities to test the hypothesis that sexual selection plays some role in the molecular evolution of higher primates.