16 April 2007
It is time to stop thinking we are the pinnacle of evolutionary success -- chimpanzees are the more highly evolved species, according to new research.
Evolutionary geneticist Jianzhi Zhang and colleagues at the University of Michigan in Ann Arbor, US, compared DNA sequences for 13,888 genes shared by human, chimp and rhesus macaques.
For each DNA letter at which the human or chimp genes differ from our shared ancestral form -- inferred from the corresponding gene in macaques -- researchers noted whether the change led to an altered protein. Genes that have been transformed by natural selection show an unusually high proportion of mutations leading to altered proteins.
Zhang's 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.
This contradicts what most evolutionary biologists had assumed. "We tend to see the differences between us and our common ancestor more easily than the differences between chimps and the common ancestor," observes Zhang.
The result makes sense, he says, because until relatively 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 that the macaque genome has been sequenced, biologists will be able to learn more about the differences between the apes.
Journal reference: Proceedings of the National Academy of Sciences (DOI: 10.1073/pnas.0701705104)