It is generally believed that purely human phenomena, such as culture, traditions, and social norms, are necessary to make cooperation between different societies possible. At the same time, animals that lack such phenomena are typically considered social only in relation to their own group and hostile toward members of other groups. Of course, the importance of these phenomena should not be underestimated, but they may well be unnecessary for the emergence of cooperation between groups.
As demonstrated by research on pygmy chimpanzees, or bonobos—humans’ closest genetic relatives—they exhibit high levels of tolerance between members of different groups. They can travel, rest, and feed together. Resource exchange between groups is not uncommon among bonobos. Moreover, it has been noted that individuals who exhibited more pro-social behavior within their own group were also more pro-social toward members of other groups. At the same time, such cooperation does not arise under the influence of any culture or social norms. One could say that this is simply a natural state for bonobos.
It is also worth comparing bonobos with common chimpanzees. The latter are quite hostile to strangers; in their case, intergroup clashes can even end in lethal violence. Why does such a difference arise? If one compares the neurophysiology of common and pygmy chimpanzees, the latter are found to have twice the density of serotonergic neurons in the amygdala of the brain. Additionally, it is worth noting the relationship regarding aggression between serotonin, oxytocin (a hormone that promotes only intra-group pro-sociality, or so-called parochial altruism), and testosterone (a sex hormone). Common chimpanzees exhibit high testosterone reactivity, which reduces their tolerance and provokes a drive to fight for higher status. And as is known from studies, the function of the serotonergic system (which is more pronounced in bonobos) includes inhibiting the pro-aggressive influence of testosterone. Pro-sociality is also stimulated by oxytocin, and it should be noted that the serotonergic system can exert an influence on its release.
It should also not be forgotten that cooperative-communicative skills, which emerged in the early stages of human evolution, were key to the emergence of various forms of human cultural cognition, including language. Therefore, it is entirely possible to assume that pro-sociality and cooperation arise not simply because of culture. Rather, all these phenomena have common evolutionary roots. The basis for their emergence may well be the development of a violence inhibition mechanism and the strengthening of serotonergic function during evolution. Such adaptation is necessary for peaceful coexistence and the prevention of lethal violence, which in many circumstances is extremely detrimental to the entire population. Furthermore, the observation of such adaptation in an extremely strong form in bonobos indicates that “constant wars between neighboring groups are not necessarily a legacy of humanity and do not seem evolutionarily inevitable.”
