Chimpanzees also unite against the outside enemy

Faced with the threat of other groups, humans unite and increase their cooperative behavior, something that already Charles Darwin observed and judged as a capacity that we had developed thanks to evolutionary processes. Now, a group of researchers from the University of Tokyo has shown for the first time experimentally that this tendency is shared by chimpanzees, one of our closest evolutionary relatives.

In a job published this Wednesday in PLOS ONE magazine, The team of James Brooks details the result of a series of experiments with chimpanzees in captivity to check the reaction of these animals at a collective and individual level in the presence of other groups. “Despite the importance of understanding how humans can be cooperative with members of your own group and still carry out extreme assaults with members of other groupsSo far there have been few studies on whether this behavioral association occurs in non-human primates, ”says Brooks.

Work with chimpanzees in the wild has documented cohesive behaviors among group members when they encounter others for years, but to test these observations, Brooks’s team designed a series of experiments which consisted of simulate the presence of other primates in the environment using sounds and observe the response of individuals. During the tests, five groups of chimpanzees heard the vocalizations of unknown animals along with other control sounds, such as the squawking of crows.

Chimpanzees that detected the presence of others were more affectionate and less aggressive towards the group

The authors found that individuals who heard these sounds from animals outside their groups were shown more stressed and vigilant, but instead of transferring this tension to their colleagues, they showed more affective and less aggressive overall when caregivers made food scarce, compared to the control group.

In the researchers’ opinion, these results suggest that, as in humans, competition between groups favors cohesion. And they go further by stating that competition between groups during human evolution may have led to our ability to maintain relationships of cooperation and tolerance in large groups in the presence of a common enemy.

“It is the first experimental proof that humans share this propensity with chimpanzees”

“This is the first experimental proof that humans share this propensity with chimpanzees,” he says. Shinya Yamamoto, a partner in the study, “but it has yet to be proven if it is due to the strong evolutionary history of intergroup competition in both species or if it is a common trait shared with other great apes.” The next objective of the group is to carry out the same experiments on bonobos, whose behavior differs in some respects from that of chimpanzees and does not commit attacks on members of other groups.

A basic premise of evolution

“Social cohesion and cooperation were a basic premise in human evolution”, points out the naturalist, explorer and professor of Human Evolution Jordi Serrallonga, who has studied chimpanzees and other primates in the wild for years, and has seen them defend themselves in a group against predators such as the leopard. “Social cohesion in chimpanzees, now studied in this interesting paper, it is not strange that it is shared with humans and many other living beings where bringing a new creature into the world not only involves a high energy cost ”, he assures. “The union is not only strength, but it is a great adaptive strategy for the survival of the species ”.

A young chimpanzee in a sanctuary. Picture: Chimp Eden Sanctuary – Zeena (Flickr, CC)

For the doctor of biology and specialist in animal behavior Antonio Jose Osuna, the results of this work are very much in line with what has been observed in humans. “The triggers that lead us to strengthen ties within our groups tend to coincide with those that lead us to be more distrustful of external groups,” he explains to Vozpópuli. “We know that chimpanzees, when they attack other groups, they do it tactically. It is not reactive, impulsive, and irrational violence. The proactive violence of chimpanzees is carried out between groups where social ties are very important, as well as the size of the same, or the tactic used (usually ambushes). It is this species, both the attack and the defense require cohesion within the group, otherwise, it would be doomed ”.

In the case of humans, this aggression reaction appears to be modulated by the hormone oxytocin. “In our species, the administration of oxytocin leads us to favor cooperating within the group, but at the same time also to compete with those we consider external to our group,” explains Osuna. “It is expected that in chimpanzees, with whom we are closely related, there is a similar phenomenon,” he concludes.

Reference: Uniting against a common enemy: Perceived outgroup threat elicits ingroup cohesion in chimpanzees (PLOS ONE) doi: 10.1371/journal.pone.0246869

Source: Vozpópuli by

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