MBE Advance Access published online on August 21, 2008
Molecular Biology and Evolution, doi:10.1093/molbev/msn184
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Letter |
Positive selection in ASPM is correlated with cerebral cortex evolution across primates but not with whole brain size
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* Department of Psychology National University of Singapore, Singapore
Department of Biological Sciences, National University of Singapore, Singapore
To whom correspondence should be addressed: Department of Biological Sciences, National University of Singapore, S2 #02-01, 14 Science Drive 4, Singapore 117543. Tel: +65 6516 2968. Fax: +65 6779 2486. Email: farhan.ali{at}alumni.nus.edu.sg
Received for publication June 27, 2008. Accepted for publication July 24, 2008.
The rapid increase of brain size is a key event in human evolution. ASPM (abnormal spindle-like microcephaly associated) is discussed as a major candidate gene for explaining the exceptionally large brain in humans but ASPM’s role remains controversial. Here we use codon-specific models and a comparative approach to test this candidate gene that was initially identified in Homo-chimp comparisons. We demonstrate that accelerated evolution of ASPM (
= 4.7) at 16 amino acid sites occurred in nine primate lineages with major changes in relative cerebral cortex size. However, ASPM’s evolution is not correlated with major changes in relative whole brain or cerebellum sizes. Our results suggest that a single candidate gene such as ASPM can influence a specific component of the brain across large clades through changes in a few amino acid sites. We furthermore illustrate the power of using continuous phenotypic variability across primates to rigorously test candidate genes that have been implicated in the evolution of key human traits.
Key Words: ASPM • cerebral cortex evolution • positive selection • primates • PAML • maximum likelihood