In the wild, chimpanzees have been known to hunt together, particularly when conditions dictate that a solo hunter will not be successful. Yet this does not prove that our nearest living relatives understand cooperation the same way that we do: such group hunts may simply be the product of independent and simultaneous actions by many individuals with little comprehension of the need for coordinated action to ensure success. A new study, however, shows for the first time that chimpanzees understand when cooperation is needed and how to go about securing it effectively. And another study shows they might even be willing to cooperate without hope of reward.

Alicia Melis of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, and her colleagues presented chimpanzees at a sanctuary in Uganda with a cooperative challenge. To reach a food tray from behind bars, a chimpanzee had to pull on two ends of a rope threaded through metal loops on the tray. If the chimpanzee simply pulled on one end, the rope would slip the loop. If, however, the chimpanzee unlocked the door to an adjacent room, released a fellow chimp, and cooperated with it to pull on both ends of the rope at the same time, both would be rewarded with the food on the tray.

"Not only did they need to know when they needed help, they had to go out and get it," Melis says. "Then they had to wait until their partner came in and pull on the rope at the same time. The chimps really had to understand why they needed their partner."

When the rope ends were placed close enough together that a single chimp could accomplish the task, the subjects rarely enlisted aid. But when they required help--and were given a choice between potential collaborators--the chimps quickly learned to choose partners better at cooperation.

Although this provides one of the first glimpses of cooperative understanding outside humanity--and raises the possibility that such abilities might have been present in our common ancestor more than six million years ago--it does not mean that chimpanzees can communicate about a shared goal, like human children. However, in the second study, led by Felix Warneken, also at the Max Planck Institute, three young chimpanzees helped their human minder reach for objects even without any hope of reward--just like human children as young as 18 months old. "This is the first experiment showing altruistic helping toward goals in any nonhuman primate," Warneken notes. "It's been claimed chimpanzees act mainly for their own ends, but in our experiment, there was no reward and they still helped." Both papers appear in today's Science.