IT鈥橲 time to stop thinking we鈥檙e the pinnacle of evolutionary success, folks. The fact is, chimpanzees are the more highly evolved species.
Evolutionary geneticist Jianzhi Zhang and his colleagues at the University of Michigan, Ann Arbor, compared DNA sequences for 13,888 human, chimp and rhesus macaque genes. For each DNA letter at which the human or chimp genes differ from the ancestral form 鈥� represented by the corresponding gene in macaques 鈥� they noted whether the change led to an altered protein. Genes that have been transformed by natural selection show an unusually high proportion of these mutations.
Zhang鈥檚 team found that 233 chimp genes, compared with only 154 human ones, have been changed by selection since chimps and humans split from their common ancestor about 6 million years ago (Proceedings of the National Academy of Sciences, DOI: 10.1073/pnas.0701705104).
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This contradicts what most evolutionary biologists had assumed. 鈥淲e tend to see the differences between us and our common ancestor more easily than the differences between chimps and the common ancestor,鈥� observes Zhang.
The result makes sense, he says, because until recently the human population has been smaller than that of chimps, leaving us more vulnerable to random fluctuations in gene frequencies. This prevents natural selection from having as strong an effect overall. Now the macaque genome has been sequenced (see 鈥淢onkey genome springs surprise for human origins鈥�), biologists will be able to learn more about the differences between the apes.
