Female chimpanzees are well known for their wanton ways, mating, as they do, with multiple males in the community. But in recent years primatologists have painted an even lustier picture of the female chimp love life, asserting on the basis of genetic data that females routinely sneak away from home for trysts with males from other social groups. Now new findings may restore their reputation for more moderate promiscuity. According to a report published yesterday in the Proceedings of the National Academy of Sciences, the most extensive genetic study to date indicates that, in fact, female chimps rarely mate with males from outside communities.
Extracting DNA from feces, bones, teeth and hair, Christophe Boesch and colleagues from the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, conducted paternity tests for 41 chimps belonging to three communities in the Ivory Coast's Ta National Park. In contrast to the earlier study, which inferred 50 percent extragroup paternity, the new study found only a single offspring whose father most likely hailed from a different community. In explanation, the authors suggest that the error rate in the previous study was too high to produce accurate assignments of paternity. "The community is the primary but not exclusive unit for reproduction in wild chimpanzees," they conclude, "and females do not typically reproduce with outside males."
The team also reports that the males in a given social group are not more closely related than the females are. Earlier work had suggested that relatedness among community males is comparable to that of half-siblings, hence the high degree of cooperation seen in male intragroup interactions. Taking the new data into consideration, the researchers propose that rather than having a primarily male-bonded social structure, the chimpanzee group is bonded through relationships between males and females.