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Chimps Reveal Defining Element of Friendship

Do you trust all of your friends? If not, then those without your trust really aren’t your buds, new research on chimps suggests.

The defining element of friendship is trust, finds a new study on chimpanzee pals.

This means friendship based on trust evolved millions of years ago, and dates back to at least the last common ancestor of chimps and humans. The findings are reported in the journal Current Biology.

"Humans largely trust only their friends with crucial resources or important secrets," co-author Jan Engelmann of the Max Planck Institute for Evolutionary Anthropology said in a press release.

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Engelmann continued, "In our study, we investigated whether chimpanzees show a comparable pattern and extend trust selectively toward those individuals they are closely bonded with. Our findings suggest that they do indeed, and thus that current characteristics of human friendships have a long evolutionary history and extend to primate social bonds."

Prior research found that chimps have relationships that look a lot like friendships. For example, they will extend favors preferentially toward select individuals. To determine what those relationships were based on, Engelmann and co-author Esther Hermann observed the interactions of 15 chimpanzees living at Sweetwaters Chimpanzee Sanctuary in Kenya. The study took place over a 5-month period.

Based on friendly interactions among chimp pairs, including grooming and eating together, the researchers were able to identify each chimpanzee's closest "friend" as well as a "non-friend."

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Next, the chimps played a modified version of what is known as the human trust game. They played the game both with their friend and then again with their non-friend, repeating matches 12 times for each.

The setup consisted of a board positioned between the two players. A "no trust" rope as well as a "trust rope" connected to the board controlled what kind of food reward the players received. If a chimp pulled the no trust rope, he or she got immediate access to a not-so-great food item. If a chimp pulled the trust rope, the other player speedily received much more tempting treats that he or she could share with the rope puller.

Because of this win-win outcome with the trust rope, pulling it offered the best scenario for both players, but only if the first chimp trusted the other one enough to share the goodies.

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As predicted, the chimps showed greater trust when they were playing the game with a friend. The researchers explained that the "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."

Chimps might not hand out Valentine's Day cards in February, but they do have friends, the study confirms. Chimp besties are, as suspected, bonded in a comparable way that human buddies are.

"Human friendships do not represent an anomaly in the animal kingdom," Engelmann said. "Other animals, such as chimpanzees, form close and long-term emotional bonds with select individuals."

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Next the researchers hope to find out if chimps are more likely to offer help to their friends. Such studies not only reveal more about our fellow primates, but they also provide insight on human evolution.

Research on chimps show friendship is all about trust.

Chimps are smart, sassy and funny, especially when dressed up like little people. But did you know that they’re much more like us than we might realize? For one, they’re cold-blooded killers, carrying out brutal raids on other chimp groups to expand their territory. The attacks are most often done by patrolling packs of male chimps that are "quiet and move with stealth," according to the study’s lead author, John Mitani of the University of Michigan. And it works for them: they get land, extra food and resources, and even better access to females.

Chimps Engage in 'War' for Turf

Male chimpanzees have spines on their penises that likely increase stimulation during mating, according to a study in Nature. Human males once had them too, but they dropped this trait. Lucky for the ladies –- or unlucky, as the case may be -- because the penis spines, while improving stimulation, can also be pret-ty painful for females during intercourse.

Chimps Have Better Sex Than Humans

Chimps looove green monkey oranges and will go to great lengths to open the stubborn fruit. In fact, three chimpanzee groups opened the fruit in different ways, showing that chimps can innovate. The chimps, all living in Zambia, invented eight different ways to get inside the hard-shelled fruit: bang it against a tree or a rock; throw it; nibble a hole; go at it with your teeth; smack the fruits together; stomp on it; and peel it.

Chimps Invent 8 Ways to Open Hard Fruits

Tickle chimps and what do you think happens? That’s right, they giggle like children. Their laughter comes in the same sorts of situations as humans, sounds like a human and they laugh more than we do, since they can do it while inhaling AND exhaling. Other animals giggle too when tickled, including rats and puppies.

Apes Giggle Like Humans

When you’re working with someone on a project, you follow along with what they’re doing and offer them help when you sense they need it, right? Chimps do the same thing, sharing a tool or physically chipping in on team projects. And once they learn to help a friend out one time, they’ll do it up to 97 percent of the time.

Chimps Trade Tools To Help Out Pals

Videos of chimp colonies show our closest cousins treating each other in dying and death much like we do. In one video, two chimps kept a vigil over a dying community member, touching and grooming her. In another, a mother shoos flies away from her recently deceased infant. Mother chimps have also been seen carrying dead babies around for weeks after they pass, some until they’re mummified.

Chimps Face Death Like Humans Do