BFF's among primates date back to 6 million years ago, with friends that picked each other, literally.

Friendship as we know it today -- complete with BFF’s, trusted pals and more -- emerged in Africa 6 million years ago in the last common ancestor of chimpanzees and humans, a new Evolution & Human Behavior study suggests.

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This clever primate literally figured out that “I’ll scratch your back if you scratch mine” makes life a lot easier.

“We know that it must have been a group-living species with relatively developed cognitive skills,” co-author Sonja Koski of the University of Zurich told Discovery News. “For example, it knew how to make and use simple tools and it understood some aspects of what other individuals are thinking. It also learned most of its necessary survival skills and knowledge socially, giving rise to the possibility of cultural differences in behavior between populations.”

“The groups consisted of many males and females, and individuals formed cooperative friendships,” she added. “Our results suggest that the preference to form these friendships with individuals much like oneself was present in the ancestor of chimpanzees and humans.”

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.

Chimpanzee friends will seemingly do anything for each other, even picking their best bud's nose.Heather Paul, Flickr

“The bold individuals approached these ‘predators’ quickly and aggressively, while the shy individuals stayed back,” she said.

Earlier research found that humans also tend to select buddies who have similar levels of friendliness and assertiveness. Traits like neuroticism, which refers to the general tendency to respond with stress and anxiety to situations, do not lead to bonding, so a more neurotic human or chimp is not likely to connect with a similarly neurotic individual.

There could be a genetic component to friendship, given that primates appear to be born more or less social and bold, with those qualities reinforced -- or not -- via environment, upbringing and experiences.

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Anthropologist Joan Silk of the University of California at Los Angeles has also studied social interactions among primates. She said the new paper presents “very interesting results.”

“In our own work on baboons, we have found that certain pairs of females form social bonds that are characterized by high levels of friendly interactions and well-balanced grooming relationships; high ratios of friendly to aggressive interactions; and higher levels of support in agonistic conflicts,” Silk told Discovery News.

“Pairs that form the strongest relationships also have the most enduring relationships over time,” she continued, adding that baboons with the closest, longest-lasting friendly interactions display lowered stress levels.

Since all of this happens among baboons, a basic form of bonding might therefore go beyond the common ancestor of chimps and humans, possibly to as far back as 36 million years ago when the earliest socially living primates emerged.

The researchers are also quick to add that friendships are not unique to primates.

“Durable friendships have, for example, been described for elephants, horses and dolphins," Massen said, "and also in birds, like the common raven.”