Like humans, chimps share to be social

IOWA STATE (US) — Humans aren’t the only ones who recognize the benefits of sharing. New research finds male chimps share plants and hunting tools with females, perhaps as a strategy for future mating.

A new study of chimps at the Fongoli research site in Senegal, has documented a frequency of sharing previously unreported for chimpanzees—not only do they transfer meat and wild plant foods, they also share tools, honey, and soil.

Most of the behavior was considered recovery or passive sharing, with females commonly taking food from males, with much of it taking place from dominant to subordinate recipients.

“They’re [the Fongoli chimps] not the only chimps that share, but in terms of the resources that we cover here, that is unique,” says Jill Pruetz, anthropology professor at Iowa State University.


“I guess all chimps share meat, but they don’t share plants or tools. Yet they do here, in addition to meat. It was intriguing when we first started seeing these events.”

For the study published online in Primates, the researchers witnessed 41 cases of Fongoli chimpanzees willingly transferring either wild plant foods or hunting tools to other chimpanzees. Male chimps transferred wild foods or tools to females 27 times.

While Christina Gomes and Christopher Boesch from the Max Planck Institute for Evolutionary Anthropology authored a 2009 study proposing that males and females exchange meat for sex—resulting in males increasing their mating success and females increasing their caloric intake to overcome the energy costs and potential injury from hunting—Pruetz contends that’s not all that’s going on in this instance.

“It’s a different set of relationships within the social group [at the Fongoli site], and I tend to think again that it ties back to the environment and the fact that the resources are distributed differently,” she says.

“They have a big home range—about 10 times bigger than Jane Goodall’s range in Gombe at 86 square kilometers—and that forces them to stay together. If they split up like chimps normally do, it could be days or weeks or months before they may see someone again—and  chimps are more social than that. So I think they stay together like monkeys and they move around their home range together.”

Some of the sharing behavior between males and females may be a product of the “food for sex” theory, Pruetz says. Both adult females in estrus [the period of maximum sexual receptivity of the female] and adolescent females cycling to estrus were more likely to receive food from adult male chimps.

The male chimps may be using food transfer as a future mating strategy with the adolescent females, particularly since there are a relatively small number of females in the Fongoli community.

“It may be used as a strategy [by the male chimps], anticipating a long-term gain on their behavior. We see that in baboons who have special friends.”

As the only habituated community of chimpanzees living in a savanna environment, the Fongoli provides detailed information on the effect of an open, dry and hot environment on social behavior and organization. Pruetz theorizes that it may also shed some light on how the earliest humans first came to share.

“There are aspects of human behavior, and I think that’s interesting because it’s not exactly the same, but it may give you an idea of how it [sharing among early humans] started,” Pruetz says.

“It’s at least one scenario and how it could have come about in our own lineage. To me, it just reinforces how important environment was.”

The research was funded in part by the Wenner-Gren Foundation for Anthropological Research and the National Geographic Society.

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