Male primates care about status, since dominance offers a host of benefits, from better food to more children. But researchers have long believed that female chimpanzees don't go in for such status-seeking because rank doesn't matter to them very much. A study in tomorrow's issue of Science reveals, however, it's not just a male trait. Female chimps with higher status, it turns out, also enjoy privileges of rank, including producing more offspring than their underlings.
Male chimps often engage in fights and dramatic displays to establish and maintain their positions in a community's rigid hierarchy. Since rivalries between female chimps are much more rare--they spend most of their time independently foraging for food with their youngest offspring--researchers had assumed that rank wasn't important to them.
But over the years, primatologist Jane Goodall, of the Jane Goodall Institute in Ridgefield, Connecticut, and behavioral ecologist Anne Pusey, a colleague from the University of Minnesota (UM), St. Paul, had noticed some advantages for higher ranking females. Now they have looked more carefully at the evidence from 35 years of chimp observations at Gombe National Park in Tanzania--enough data to establish the relative rank of a number of adult females in the group and document their complete reproductive lives. They found that higher ranking females not only produced more offspring, but a greater fraction of them survived and sexually matured at earlier ages.
The reason for this reproductive success is that higher status females probably get better access to food, either by controlling the areas with the best food supplies, or by intimidating lower-ranking females into granting them priority, says team member Jennifer Williams, a behavioral ecologist at UM. Females seem to have "a lot of control of what goes on within their group," she says. Pascal Gagneux, a population biologist at the University of California, San Diego agrees, saying the work will encourage others to take "a much more careful look at what each of the sexes is doing."