Jan. 6 - Like humans, chimpanzees choose their friends on the basis of shared personality traits, according to a study by European scientists. Their findings suggest that the 'similarity effect' commonly shown in humans, was inherited from a common ancestor six million years ago. Jim Drury has more.
It's long been known that chimps and humans have much in common. Now a pair of biologists say those similarities include friendship preferences - they say chimps, like humans choose friends with similar personalities to themselves. Jorg Massen, from Vienna University, co-authored a behavioural study into 38 chimps at two zoos. In one experiment a stuffed leopard was placed in a chimps' enclosure. While other chimps stood back on their own, Massen observed two close female companions trying to teach the predator a lesson. SOUNDBITE (English) JORG MASSEN, CO-AUTHOR OF CHIMP STUDY, SAYING: "What you see here is one of the individuals, she's called Raimee, coming up with a stick and very interestingly just a bit later also coming with a stick is Tushi. They're both showing the same behaviour, so they are fetching sticks and they're fetching these sticks, and not without any reason but actually to throw at the predator." UPSOT: STICK HITTING CAMERA The findings are consistent with what psychologists call the 'similarity effect' in humans. Massen says it suggests that choosing friends with similar personality traits dates back six million years to our last common ancestor. One exception says Massen, is neurotic chimps, who struggle to find friends, even among those of a similar disposition. The phenomenon also shows how members of families differ, just like their human cousins. SOUNDBITE (English) JORG MASSEN, CO-AUTHOR OF CHIMP STUDY, SAYING: "We found that, although they do spend a lot of time together, those individuals that were actually related weren't necessarily similar in personality. So from that we inferred that these individuals choose their friends to be similar in personality, but they cannot choose their family." Massen and co-author Sonja Koski, from the University of Zurich, say the trait is likely to be adaptive. They think that co-operation in difficult tasks is optimised when a pair share behavioural tendencies and emotional states...primates apeing one another for their mutual benefit.