The New York Times,
March 3, 2006Link
One of the hallmarks of being human is cooperation. No other primate exhibits the same kind of helpfulness to others. Humans have made even violence a highly cooperative effort, and scientists have wondered how far back in evolution this trait goes.
New studies on chimpanzees suggest that this part of human nature may have already existed millions of years ago, perhaps before the human and ape lineages divided.
Scientists had observed chimpanzees in the wild apparently cooperating in the past. ''They work together to chase monkeys, and they're quite effective when they chase them together,'' said Brian Hare of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany.
But skeptics argued that these observations might be illusions. ''Maybe they just run at the monkey because they all want it,'' Dr. Hare said. ''It just happens that because they're all doing it at the same time, it helps them catch the monkey. You really need an experiment to get at what they are doing.''
Dr. Hare and his colleagues in Leipzig set up a series of experiments to do just that. They published their results in the current issue of Science.
In one series of experiments, Dr. Hare, Alicia P. Melis and Michael Tomasello placed an adult chimpanzee in a cage, outside of which was a plank with food on it. It was possible to get the food by pulling on two ropes. In some trials, the ropes were too far apart for one chimpanzee to get the food on its own. The chimpanzee could get help by opening the door of an adjoining cage where another chimpanzee was waiting.
The scientists found that the chimpanzees were much more likely to open the door if the ropes were too far apart for them to get the food themselves. ''They know when they need help,'' Dr. Hare said.
The chimpanzees even kept track of who did a good job. When the scientists gave the chimpanzees a choice between two partners, they almost always chose the better rope-puller.
''So what we see in the wild may be really sophisticated,'' Dr. Hare said.
Chimpanzees not only cooperate, but are also willing to help even when they are not getting a direct reward.
In another series of experiments, Dr. Tomasello and Felix Warneken compared the altruism of 18-month-old children with that of juvenile chimpanzees. Chimpanzees were not as helpful as the children in complicated tasks. But in simple tasks -- picking up a dropped sponge, for example -- they readily came to the aid of humans.
''All in all, this bolsters the view of chimpanzees as highly cooperative creatures,'' said Dr. Frans de Waal, a primatologist at Emory University who was not involved in the research.
Chimpanzees are the closest living relatives to humans, sharing a common ancestor that lived roughly six million years ago. If their nature is as cooperative as these studies suggest, then scientists say they may have inherited this ability from that common ancestor.
As for how human ancestors evolved more sophisticated cooperation, Dr. Hare suggests that one major adaptation must have been the ability to avoid being exploited. Psychological tests have shown that humans tend to cooperate with people who have cooperated with them in the past. They also avoid offering help to those who have not helped them.
''You can't be helpful if you don't have a way to avoid being cheated,'' Dr. Hare said.
Copyright 2006 The New York Times Company