Koski and co-author Jorg Massen of the University of Vienna found that chimpanzee buddies are remarkably similar to human friends. Both need emotionally rewarding, positive interactions with others, and these connections result in durable and mutually beneficial bonds. Chimp friendships, like human ones, can last for a very long time.
The researchers first investigated the personality similarity of friends among 38 captive chimpanzees. They determined that chimps were more likely to be friends if they possessed similar tendencies for sociability and boldness.
Sociability basically refers to how gregarious the individual is. In chimps, this is evident in grooming behaviors.
"So, highly sociable individuals hang out with others and groom them more often, while less sociable individuals are more aloof and do not groom much," Koski explained.
She and Massen presented chimps with a stuffed leopard and an artificial snake to test boldness.