You take the muscles, I'll take the ears

Natural History, April, 2004 by Aimee Cunningham

Geneticists are fond of pointing out that the DNA of people and chimpanzees is nearly 99 percent identical [see "Searching for Your Inner Chimp," by Car/Zimmer, December 2002/January 2003]. Explaining the manifest differences has become something of a cottage industry. What accounts for the elaborate verbal skills of humans, our technological proficiency, our ability to contemplate our own humanity?

Now Andrew G. Clark, a population geneticist at Cornell University in Ithaca, New York, and his colleagues have weighed in with a comparative study of more than 7,600 human and chimpanzee gene sequences that have a common origin but have been diverging as the two species have evolved. Any divergence could result from random mutation, but accelerated divergence suggests the operation of natural selection--the emergence and preservation of advantageous characteristics. Clark and his team aimed to identify the latter.

So what's been briskly diverging? To some extent, the genes that facilitate differing lifestyles. In chimpanzees, rapidly changing genes include the ones that encode embryonic muscle, bone, and connective tissue, as well as skeletal structure in adults. In people, notable modifications have taken place in the genes for smelling and hearing, for instance. Clark and his colleagues speculate that an increasingly fine-tuned sense of hearing has assisted humans in the comprehension of spoken language. ("Inferring nonneutral evolution from human-chimpanzee-mouse orthologous gene trios," Science 302:1960-63, December 12, 2003)