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
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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
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