Sharing comes naturally to apes

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Conversely, chimps are notorious for hogging food, by force if necessary. While chimps will share as youngsters, they grow out of it as adults.

In several experiments to measure food-sharing and social inhibition among chimps and bonobos living in African sanctuaries, Duke and Harvard University researchers say these behavioural differences may be rooted in developmental patterns.

When compared with chimps, bonobos seem to be living in "a sort of Peter Pan world," said Brian Hare, assistant professor of evolutionary anthropology at Duke, who participated in both studies. "They never grow up, and they share."

Hare and his mentor, Richard Wrangham, professor of anthropology at Harvard, think this kinder, gentler ape's behaviour has been shaped by the relative abundance of their environment.

Living south of the Congo River, where food is more plentiful, bonobos don't compete with gorillas for food as chimps have to, and they don't have to compete much with one another either.

In essence, they don't have to grow up, Hare said, and cognitive tests that the team performed on the captive animals seem to bear that out. Bonobos shared like juveniles even after they reached adulthood.

"It seems like some of these adult differences might actually derive from developmental differences," said Harvard graduate student Victoria Wobber, who is the lead author on one of the papers. "Evolution has been acting on the development of their cognition."

To measure sharing behaviour, paired animals at the Tchimpounga Sanctuary in the Republic of the Congo were put into an enclosure with some food.

Younger chimps were found to be quite similar to young bonobos in their willingness to share food, but the chimps become less willing to share when they're older.

In a second set of sharing experiments, Hare and a colleague at the Lola ya Bonobo sanctuary near Kinshasa, Democratic Republic of Congo gave bonobos an opportunity to have all of a food pile to themselves while a fellow bonobo watched helplessly from behind a gate.

Instead, the subjects universally preferred to open the gate and let their friends share. Their friends weren't even begging or carrying on.

"A chimp would never voluntarily do that," Hare said. "Chimps will do things to help one another, but the one thing they will not do is share food."

In chimp society, where hogging the food pile is a privilege of rank, younger animals have to learn which adults can be begged from and which cannot, Wobber said.

These findings were published in the latest edition of Current Biology.