In the forests of Uganda's Kibale National Park, male chimpanzees on the make know what they want in a sexual partner—wrinkled skin, ragged ears, irregular bald patches, broken teeth, and elongated nipples. For these guys, nothing beats the sex appeal of an old female chimp.
If that preference makes no sense to the average human male who's entranced by young, smooth-skinned women, it's because the mating game has evolved in different directions in chimps and in people, say anthropologist Martin N. Muller of Boston University and his colleagues.
People usually form long-term sexual partnerships. Men thus tend to look for women's physical signs of youth, which signal childbearing potential for years to