All wild chimpanzees eat fruits and nuts, but research in this week’s Proceedings of the National Academy of Sciences now confirms that adult male chimps regularly eat meat. These findings may suggest that differences in what food the sexes gather and eat may not be a recent development in the human lineage, but go much further back.
Chimpanzees usually dine on plants in the wild, as well as termites if they can get them. They are also known to eat vertebrate flesh—one group is known to hunt other primates with spears, and some are even known to engage in cannibalism. However, it remained uncertain how much of a role meat actually plays in their diet, since following chimps throughout entire hunting seasons is a challenging prospect at best.
One of the most capable groups of hunters among these apes are the chimpanzees of the Taï National Park in Côte d’Ivoire, who cooperatively kill prey such as colobus monkeys and divide up the spoils with fellow hunters, rather than family. To see just how much of an impact consuming this flesh had on these chimps, anthropologist Geraldine Fahy and her colleagues at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, analyzed the hair and skeletons of chimpanzees they followed in the park over 20 years.
Animals accumulate the isotope nitrogen-15 in their bodies, and animals that eat animals—that is, carnivores—build up more nitrogen-15 than herbivores. On average, the nitrogen-15 levels of adult male chimps were about 10 percent higher than those of adult females. Moreover, adult male chimps that field research had revealed were gifted hunters could possess nitrogen-15 levels about 13 percent higher than less successful ones.
The researchers stress adult and juvenile male and female chimps in the park all still got most of their protein from fruits and nuts. Still, these findings reveal that flesh is important for some adult males there, and more than an uncommon luxury item.
As humanity’s closest living relatives, chimpanzees are often studied to learn more about human evolution. Until now, there was apparently little difference in diet between male and female chimps, leading to an assumption that the role of man as hunter and woman as gatherer in humans occurred following the split from the last common ancestor of humans and chimpanzees about 5 million years ago, Fahy said. Although these findings might suggest otherwise, given controversies over the origins of such differences, “our suggestion that our data implies that sex differences may have persisted throughout human evolution may be contentious to some,” Fahy notes.
Future research into sexual differences in chimpanzee diet “would greatly benefit from similar studies at other sites where hunting and meat-eating are observed,” Fahy said. “Once we have a large, clear data set from multiple chimpanzee populations, we will get a clearer idea of how unique the Taï chimpanzees are.”