*More genes underwent positive selection in chimpanzee evolution than in human evolution* * Margaret A. Bakewell, Peng Shi, and Jianzhi Zhang * Observations of numerous dramatic and presumably adaptive phenotypic^ modifications during human evolution prompt the common belief^ that more genes have undergone positive Darwinian selection^ in the human lineage than in the chimpanzee lineage since their^ evolutionary divergence 6--7 million years ago. Here, we^ test this hypothesis by analyzing nearly 14,000 genes of humans^ and chimps. To ensure an accurate and unbiased comparison, we^ select a proper outgroup, avoid sequencing errors, and verify^ statistical methods. Our results show that the number of positively^ selected genes is substantially smaller in humans than in chimps,^ despite a generally higher nonsynonymous substitution rate in^ humans. These observations are explainable by the reduced efficacy^ of natural selection in humans because of their smaller long-term^ effective population size but refute the anthropocentric view^ that a grand enhancement in Darwinian selection underlies human^ origins. Although human and chimp positively selected genes^ have different molecular functions and participate in different^ biological processes, the differences do not ostensibly correspond^ to the widely assumed adaptations of these species, suggesting^ how little is currently known about which traits have been under^ positive selection. Our analysis of the identified positively^ selected genes lends support to the association between human^ Mendelian diseases and past adaptations but provides no evidence^ for either the chromosomal speciation hypothesis or the widespread^ brain-gene acceleration hypothesis of human origins. PNAS | *May 1, 2007* | vol. 104 | no. 18 | *7489-7494* http://www.pnas.org/cgi/content/abstract/104/18/7489?etoc -- ========================================================= Cindy Martens VIB DEPARTMENT OF PLANT SYSTEMS BIOLOGY, UGent Bioinformatics and Evolutionary Genomics Technologiepark 927 B-9052 Gent Belgium Tel: +32 (0)9 331 38 22 Fax: +32 (0)9 331 38 09 E-mail: cindy.martens@psb.ugent.be Website: http://www.psb.ugent.be/bioinformatics =========================================================