Most species differ from their closest relative by thousands if not millions of differences in their DNA sequences. For example humans differ from chimpanzees by at least 30 million single letter changes. What proportion of those differences have helped each species adapt to their respective environments, and what proportion are neutral changes, changes which have little or no effect, that have been fixed by genetic drift? This is one of the central questions of molecular evolutionary biology and one that I became interested in when I was an undergraduate, under the tutelage of Bryan Clark (www.nottingham.ac.uk/biology/people/bryan.clarke). Twenty years on and we are now beginning to answer this question.

Our work has involved the development of new methods to estimate the rate of adaptive evolution (Bierne and Eyre-Walker 2004; Eyre-Walker and Keightley 2009; Smith and Eyre-Walker 2002) and the application of those methods to a broad range of species including Drosophilids (Bierne and Eyre-Walker 2004; Eyre-Walker and Keightley 2009; Smith and Eyre-Walker 2002), primates (including humans)(Eyre-Walker and Keightley 2009), enteric bacteria (Charlesworth and Eyre-Walker 2006), rodents (Halligan, et al. 2010 )and many species of plants (Gossmann, et al. 2010). Estimates of the proportion of amino acid substitutions range from close to zero in some plants, to 10% in humans to 50% in Drosophilids, rodents and bacteria. It is suspected that part of the difference between species might be due to variation in population size, something we have recently confirmed (Gossmann, et al. 2012). However, it is likely that this only explain a small fraction of the variation.

Bierne N, Eyre-Walker A 2004. Genomic rate of adaptive amino acid substitution in Drosophila. Mol. Biol. Evol. 21: 1350-1360.

Charlesworth J, Eyre-Walker A 2006. The rate of adaptive evolution in enteric bacteria. Mol. Biol. Evol. 23: 1348-1356.

Eyre-Walker A, Keightley PD 2009. Estimating the rate of adaptive molecular evolution in the presence of slightly deleterious mutations and population size change. Mol Biol Evol 26: 2097-2108.

Gossmann T, Song B-H, Windsor AJ, Mitchell-Olds T, Dixon CJ, Kapralov MV, Fialtov DA, Eyre-Walker A 2010. Genome wide analyses reveal little evidence of adaptive evolution in many plant species. Mol. Biol. Evol. in press.

Gossmann TI, Keightley PD, Eyre-Walker A 2012. The effect of variation in the effective population size on the rate of adaptive molecular evolution in eukaryotes. Genome biology and evolution 4: 658-667. doi: 10.1093/gbe/evs027

Halligan DL, Oliver F, Eyre-Walker A, Harr B, Keightley PD 2010. Evidence for pervasive adaptive protein evolution in wild mice. PLoS Genet 6: e1000825. doi: 10.1371/journal.pgen.1000825

Smith NGC, Eyre-Walker A 2002. Adaptive protein evolution in Drosophila. Nature 415: 1022-1024.