Chimpanzees show hints of higher human traits
New Scientist 2nd March 2006
Our closest relative the chimpanzee is capable of sophisticated cooperative behaviour and even rudimentary altruism, two new studies reveal. The discovery suggests that some of the underpinnings of human sociality may have been present millions of years ago. "At least some of [those behaviours] are already present in rudimentary forms in chimps – and maybe in the common ancestor of chimps and humans," says Alicia Melis of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany. "Humans are biologically prepared to develop these kinds of skills."
To study the cooperative ability of chimps, Melis and colleagues put individual chimps at a sanctuary in Uganda in a test cage with a heavy tray of food in plain sight but out of reach through the bars of the cage. A rope threaded through eyelets on the left and right sides of the tray allowed the animal to pull the food within reach – but only by pulling on both ends of the rope simultaneously. Otherwise, the rope merely snaked through the eyelets, leaving the tray in place. When they could retrieve the food themselves, the eight juvenile chimps tested almost always did so and ignored a second chimp locked in an adjoining cage. But when the tray was widened – and the two ends of the rope became too far apart for a single chimp to grab both ends simultaneously – all the animals quickly learned to unbar the door and let the second chimp in to help.
Then Melis repeated the experiment but gave each test chimp a choice of two potential helpers: a subordinate chimp who was well-practised at the cooperative task, and a dominant male who was not. The test chimps at first chose the dominant male, perhaps out of deference, but quickly learned to pick the better helper. Researchers have reported cooperative behaviour in chimpanzees before – in surrounding prey, for example – or in forming social alliances. However, Melis's experiments are the first to show clearly that chimps understand when they need help and can recognise and choose the best helper. The chimps in this experiment always had selfish motives for cooperating, but chimps will sometimes help others even when they gain no benefit from doing so, as a second study, by Felix Warneken and Michael Tomasello at the same institute reveals.
The researchers studied what three captive-raised young chimps would do when a familiar human caretaker dropped an object out of her reach. All three chimps were more likely to pick up the object and hand it to the caretaker when she reached for the object than when she merely looked at the object. This suggests that the chimps understood the human's goal and tried to help, says Warneken – even though they received no reward or praise. Human infants also helped in this way and performed other, more complex helping tasks. They would open a cabinet door, for example, to help an adult whose hands were full, while a chimp would not. "This suggests that a tiny bit of helping behaviour is already present in chimpanzees, but they're not as flexible as human infants are," says Warneken.
Such altruistic helping behaviour is common in humans, but had never been documented in other animals before. Researchers now need to understand how often, and under what conditions, it occurs, says Joan Silk, an evolutionary anthropologist at the University of California at Los Angeles, US. In earlier studies, Silk found that chimps are as likely to choose a food reward for themselves alone as for themselves and a companion.