Study: Our generosity likely originated with apes

How generous is an ape? The answer could tell us a lot about ourselves.

People in every culture can be generous, whether they are lending a cellphone to a co-worker or sharing an antelope haunch with a hungry family.

“One of the things that stands out about humans is how helpful we are,” said Christopher Krupenye, a primate behavior researcher at the University of St. Andrews in Scotland.

This generosity might have been crucial to the survival of our early ancestors who lived in small bands of hunter-gatherers.

“When our own attempts to find food are unsuccessful, we rely on others to share food with us — otherwise we starve,” said Jan Engelmann, a researcher at Göttingen University in Germany.

To understand the origin of this impulse — known as prosociality — a number of researchers have turned to our closest living relatives. A new study involving bonobo apes suggests that the roots of human generosity run deep, but only came into full flower over the course of the evolution of our species.

Roughly 7 million years ago, our lineage split from the ancestors of chimpanzees and their cousin species, bonobos. Chimpanzees and bonobos share a common ancestor that lived about 2 million years ago.

These two closely related species of apes look almost identical to the untrained eye. But they have evolved some intriguing differences in their behavior, including how generous they are with food and tools.

Recently, Krupenye and his colleagues tested the generosity of bonobos that live in the Lola Ya Bonobo sanctuary in the Democratic Republic of Congo.

The researchers designed an experiment that could provide strong evidence that bonobos would give things to one another simply out of generosity.

“Would they do it if there was no benefit to them?” asked Brian Hare, a primatologist at Duke University who helped run the study.

For their experiment, the researchers took advantage of the fact that the Lola Ya Bonobo apes have learned to crack open palm nuts with rocks. Without a rock, they have to gnaw on the nuts for a long time to get them out of their shell.

The scientists put one bonobo in a cage with five nuts. In an adjacent cage, a second bonobo — a stranger to the first one — had two rocks, but no nuts. The cages were connected by a window.

In 18 percent of the trials, the bonobos with the nuts handed one through the window to their neighbor, a rate that showed their willingness to give food to others.

But the bonobos in the other cage almost always refused to pass one of their rocks through the window.

In another experiment, Krupenye experienced their lack of generosity firsthand.

Each bonobo would sit in a cage, with a mesh wall hanging in front of the door to the hallway. A colleague would slip a stick into the cage near a bonobo and leave.

Then Krupenye would come to the doorway and beg for the stick. He would reach out his arm, plaintively calling the bonobo’s name.

The bonobos almost never handed Krupenye the stick. In fact, sometimes they seemed to tease him with it.

Felix Warneken, a University of Michigan psychologist who was not involved in the study, said what makes it surprising is that chimpanzees in the same situations tend to do the opposite.

“Chimps are really reluctant to give food away,” Warneken said.

On the other hand, when it comes to tools, chimpanzees are generous. They will give stones to other chimpanzees.

It is possible that the separate evolutionary paths of bonobos and chimpanzees have shaped their generosity. Chimpanzees live in habitats where food is often scarce and they have to compete for food.

Bonobos, by contrast, live in forests where food is far more abundant. Adapting to this ecosystem, they seem to recognize the value of food to others, and do not feel an urge to hoard it for themselves.

“We’re really good at realizing when other individuals could benefit from something,” said Hare.