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Book Summary: The Book of Humans: A Brief History of Culture, Sex, War and the Evolution of Us

Author: Adam Rutherford

Substory: Violent Chimps

The death of others to help secure the survival of an organism’s genes into the future is inherent to evolution. Fighting, feeding, reproduction, competition and parasitism are all primary drivers of evolutionary change. Although we see the adoption of tools for threats or actual violence, what we do not see in nature is strategic, premeditated, prolonged, armed conflict between groups of animals, which fits the definition of war.

With one notable exception: chimpanzees. While the bonobos embrace enthusiastic sexual contact to relieve tensions and conflict (examined in detail later), their closest cousins the chimpanzees are much more systematically violent. We’ve known that for decades, but escalation in our understanding of the degree of violence that is embedded in chimp society began just after the summer of love had waned. Appropriately enough, the contrast between the two species in the genus Pan has been encapsulated in the hippy counterculture phrase ‘make love not war’, bonobos being the lovers, and chimps the warriors. It was Jane Goodall who first noted the scale of chimpanzee conflict, in the Gombe Stream National Park in Tanzania. In the early 1970s, factions in a previously united society were being seen, with a north–south rift. No one knows why this schism occurred, but it did coincide with the death of an alpha male Goodall called Leakey, who was replaced by Humphrey. Some chimps began following Humphrey, but others from the south apparently perceived him as weak, exemplified by the switching of allegiance to two brothers called Hugh and Charlie. What followed were strategic raids by each side into the other’s territory, targeted killings or severe beatings of male enemies and an escalation of violence into running battles. Humphrey’s legion was eventually victorious, and after four years of persistent conflict, the rebels were all eliminated.

The Ngogo chimpanzees live in the Kibale National Park in Uganda. Over a decade, researchers have watched them and seen more concerted and systematic violence and apparent battle strategy. Every few weeks, young males would congregate at the edge of their territory, and in a silent single file would patrol their boundaries. During eighteen such excursions they were seen infiltrating neighbouring territory and beating a male from another troop to death, tearing him limb from limb and pouncing victorious on his dismembered corpse. After ten years of these vicious skirmishes, the Ngogo chimps had fully annexed the territories that they had been raiding.

In the Mahale Mountains in western Tanzania, one group of chimps is known to have similarly encroached upon and then annexed a neighbouring troop, after which all the adult males simply vanished. Like a mafia hit, no assaults were actually witnessed or bodies ever found. But it is assumed that they were killed in territorial attacks.2

The data is sparse, but we have multiple incidences of sustained lethal aggression with what scientists sometimes call ‘coalition violence’ (to avoid a description that invokes the very human behaviour of war). There has been the suggestion that it is humans who have forced this level of warlike behaviour upon the chimpanzees. By perpetually encroaching upon their territories, razing forests to the ground, by introducing diseases, by hunting them, we have driven conflict for resources in chimp troops, and killing is an incidental by-product of the escalated violence that ensues as a result. In the case of the Gombe chimps, humans had over the years handed out bananas to encourage them into areas where they could be observed.

The idea that our behaviour has influenced theirs is a testable hypothesis, and in 2014 it was subjected to that scientific benchmark. If human activity were a driver of increased levels of aggression and violence, we would expect to see more of it where humans are close by. It was a hell of a study: eighteen chimp sites, analysing every recorded act of violence and killing over a combined total of 426 years of research. They found strong links between violence and competition for territory or resources, and population density (particularly of males), and little link to proximity to human activity. In Tanzania and Uganda, both spells of coalition violence (presumed in the former case) resulted in major territorial gains. From an evolutionary point of view, this means more fruiting trees, which means an abundance of food, which means a healthier population and more baby chimps.

Therefore, lethal aggression in chimps, including coalition violence, is best understood as an adaptive strategy. In time and genes, we are close to chimps and bonobos, and the temptation to suggest an evolutionary relationship between us all to explicate on complex behaviours is ever-present. Did the predisposition towards violence exist in a common ancestor of these three groups of apes, and only bonobos have grown out of it? Or is it the other way around – was sexual conflict resolution the norm, and only bonobos have retained it? Though these are valid questions to ask, there is little data either way, and comparisons must be made with scientific caution. Let us not forget that during the six million years in which our lineage diverged away from the other great apes, they were evolving too; in the case of chimps, evolving towards utilising violence to maximise their own survival. Their propensity for violence is a behaviour that needs to be understood on its own terms, not merely as a model for understanding ourselves. We have had enough wars for the behaviour of chimps to be of limited relevance to our own.

This tour through some of the less admirable characteristics of humans and other animals shows that violence, extreme and lethal in some cases, is part of the struggle for life, and it is universal. Survival is at the expense of others who do not share your genes. We often talk of arms races in evolutionary theory, as the prey will evolve to beat the assets of the predator, and the predator will evolve in turn. This eternal conflict exists within species between the sexes, and between species at every scale. Here’s a cute macroscopic example: moths are prey by the dozen for echolocating bats. Arizonan tiger moths have evolved a cunning twofold ruse to avoid being eaten: they secrete an obnoxious chemical which the bats don’t like, but they also emit a high-pitched sonar click that the bats can detect. Once the bat has eaten one, and associated it with the warning sound, they avoid those moths in the future. At the microscopic level, your entire immune system is nothing but offensive and defensive strategies to battle the relentless attacks by organisms that wish to continue their existence at the expense of yours. After all, natural causes of death in humans far outstrip our own determined attempts to wipe ourselves out. It is the smallest things in the living world that have had the biggest negative impact on the lives of humans: plague, Spanish flu, tuberculosis, HIV/AIDS, smallpox, and malaria – probably the single most lethal agent in our history.

Nevertheless, we have had a pretty good stab at destroying each other. What is beyond doubt is that with our brains, ingenuity and skills, we have made the act of killing more and more efficient, both interpersonally and now globally. Maybe the days of mutually assured destruction by nuclear weapons are behind us, and it doesn’t take any evolutionary theorist to recognise that that is a good thing for our genes and for our species. Our reasons for going to war are difficult to justify by evolutionary theory, and this is reinforced by the fact that only chimpanzees seem to emulate a scale of conflict that could be described as anything like warfare. Most cultures agree that killing other people is forbidden, and it is even enshrined in the Abrahamic commandments, though it seems this is interpreted as more of a guideline than a rule, given the enthusiasm with which the disciples of Christ and Muhammad have engaged with the snuffing out of other people’s light.