LEIPZIG, Germany, Jan. 14 (UPI) -- Trust is the foundation of a healthy human relationship, whether they be among friends, families or lovers, and research suggests the same holds trues for chimpanzees.
Researchers have long observed what appeared to be friendships among chimps. The apes can be seen spending time with and performing favors for specific individuals, but defining these relationships has proven difficult.
Because of the importance trust plays in defining human friendship, researchers in Germany proposed the concept as a way to define friendship among chimps. If scientists could show trust-reliant interactions among chimps, then they could say chimpanzees are capable of developing and maintaining friendships.
To see if chimp relationships were based on trust, researchers set up an experiments involving interactions between chimps categorized as friends and non-friends.
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The study participants played a trust game, which gave the chimps the option of pulling a "no-trust rope" or a "trust rope." The no-trust rope granted the first chimp access to a food item that he or she didn't much care for. The trust rope gave the second chimp access to a much more appealing snack. The second chimp could then choose to share the treat with the first.
The second option was clearly superior, but only if there was sufficient trust between the two chimps. The chimps played the game 24 times, half of them with a friend and half with a non-friend. Friends were more likely to pull the trust rope.
"Chimpanzees were significantly more likely to voluntarily place resources at the disposal of a partner, and thus to choose a risky but potentially high-payoff option, when they interacted with a friend as compared to a non-friend," researchers wrote in a new paper on the experiment, published this week in the journal Current Biology.
The findings suggest chimps are capable of human-like friendships.
"Human friendships do not represent an anomaly in the animal kingdom," lead study author Jan Engelmann, a researcher with the Max Planck Institute for Evolutionary Anthropology, said in a press relase.
"Other animals, such as chimpanzees, form close and long-term emotional bonds with select individuals," Engelmann said. "These animal friendships show important parallels with close relationships in humans. One shared characteristic is the tendency to selectively trust friends in costly situations."
