The most friendly of the great apes are also masters of diplomacy: they manage to cooperate peacefully with members of a group different from theirs, something very rare among primates like us. The finding comes from a study carried out with bonobos or pygmy chimpanzees (pan paniscus), which are the closest living relatives of humans, along with common chimpanzees.
Details about the peaceful and cooperative relationship between two groups of bonobos in the territory of the Democratic Republic of Congo (Central Africa) have just been published in the specialized journal Science. Liran Samuni, a researcher at the German Center for Primatology, and Martin Surbeck, from the Department of Human Evolutionary Biology at Harvard University, observed interactions between bonobos in the Congolese Kokolopori reserve for two years.
The combined population of the groups of apes monitored by primatologists is 31 adult individuals (11 animals in one group and 20 in the other), with a predominance of females (21 in total). Bonobos are an exception among primates in several aspects, starting with the social predominance of females, which, in general, leave males in subordinate positions.
The species also tends to resolve conflicts and tensions through sexual contact (which is frequent both between individuals of different sexes and those of the same sex) and is, in general, much less aggressive than its first cousins, the common chimpanzees. .
While contact between adults from different groups of chimpanzees almost always ends in severe aggression and even deaths, with attacks that resemble wars, it was already known that this type of carnage does not happen when different groups of bonobos meet. This suggested that cooperation between different bands could happen, as we see in human hunter-gatherer societies, for example.
Samuni and Surbeck verified that this happened, mapping at least three major categories of positive interaction between members of the two groups: 1) lice picking/hair cleaning (designated in English by the term “grooming”); 2) formation of coalitions (alliances that may involve “political” disputes for dominant positions, for example); and 3) food sharing, the rarest and most surprising.
“It is common for certain females and, more rarely, males to monopolize large fruits,” Surbeck explained to Sheet. “They can actively share pieces — with certain individuals that are nearby — or allow others to take a piece of the fruit directly or even from their mouth. It is common for other bonobos to ‘ask’ for a piece, even if it is by getting sitting right in front of the person holding the fruit.”
Furthermore, the detailed analysis of interactions, pair by pair (or by “dyads”, as scientists prefer), revealed that cooperation between monkeys from different groups is closely linked to what happens within the same group. What happens is that the most “diplomatic” individuals within their own band are also those who tend to have more positive interactions with bonobos in the neighboring group.
Apparently, this has nothing to do with kinship, because DNA analyzes revealed that only 6% of cooperation “dyads”, within or outside the same group, correspond to apes that are closely related to each other. One hypothesis that seems to make a little more sense is that of so-called reciprocal altruism, the famous “one hand washes the other”: monkeys would tend to cooperate with fellow species with a higher chance of returning the favor. As time passes and contacts continue between the groups, it seems that it becomes clear who is worth relating to in a way that is advantageous to both sides.
In addition to the understanding that these data bring about the social complexity of bonobos, the implications of the discovery for human evolution could also be significant. Cooperation between different groups, even in the case of human societies described as simpler, is a hallmark of our species that seemed to have no parallel in other primates. New data on bonobos indicates that this is not the case.
“You have to take into account the modest size of the groups and the fact that bonobos only interact with direct neighbors,” says Surbeck. “But overall, I think the scale of this cooperation could get broader with higher population densities and more mobility. It’s also important to mention that some of the large-scale cooperation we see in humans happens during hostile contacts. This would be unlikely to evolve in a system like that of bonobos.”