Book excerpt: The Shortest History of War by Gwynne Dyer | Why humans fight wars

The chimpanzee clashes were even more distant from civilised warfare than the ‘wars’ of human hunter-gatherers. Chimpanzees rarely use weapons (the occasional tree-branch, perhaps), and it is not easy for one chimpanzee to kill another with his bare hands. There are never pitched battles between chimpanzee bands; all the killing is done by ambush, in which a number of chimpanzees from one band encounter an isolated individual from a rival band.

It began as a border patrol. At one point... they spotted Goliath [an elderly chimp], apparently hiding only 25 metres away. The raiders rushed madly down the slope to their target. While Goliath screamed and the troop hooted and displayed, he was held and beaten and kicked and lifted and dropped and bitten and jumped on... They kept up the attack for 18 minutes, then turned for home... Bleeding freely from his head, gashed on his back, Goliath tried to sit up but fell back shivering. He too was never seen again. - Richard Wrangham and Dale Peterson, Demonic Males: Apes and the Origins of Human Violence

Was it really war? Well, these attacks did not happen every time a patrol caught a lone member from a rival band. They would listen for the calls that other members of the rival group made to keep in touch as they moved through the forest, and only attacked if there were no members of that band nearby who might come to the aid of the intended victim. Otherwise, they would quietly withdraw and leave it for another day. But it was deadly serious stuff. Despite their extreme caution and the fact that the killing was always done one chimp at a time, there were instances when all the males of one troop were finally eliminated. Thereupon the males of the rival band would move in, appropriate the surviving females, and kill the existing babies to make room for their own.

Some of these chimpanzee bands have been observed for 50 years now, and across all the bands studied, this endemic warfare ultimately caused the deaths of about 30 percent of the adult males and 5 percent of the females. The territories controlled by the chimpanzee bands were far smaller than those of Yanomamo villages – only three or four miles between one band and the next – but the chimps spent'almost all their time in the central third of their territory. The rest of the territory was equally rich in resources, and yet treated as a ‘no-man’sland’ and only visited in large groups due to the danger of ambush and death at the hands of a neighbouring troop.

Murngin hunter-gatherers in Arnhem Land, Yanomamo horticulturalists in Amazonia, chimpanzees in Gombe: a bell was tolling for our illusions in the way these statistics lined up. They signalled a style of warfare whose casualties were proportionally far greater than anything experienced by modern civilisations, and that was very ancient indeed. Archaeologists were alerted to start looking for evidence of warfare in the fossil record of humans and closely related species. It wasn’t long before they found it.

They found Homo erectus fossils from 750,000 years ago bearing signs of violence inflicted by human-style weapons, like depression fractures in skulls (perhaps made by clubs) and cutmarks on bones that suggest de-fleshing and cannibalism. Such killings generally require complex purification rituals afterwards, and ritual cannibalism is often part of them. They also found Neanderthal fossils dating back to between 40,000 and 100,000 years ago with injuries inflicted by spears, a stone blade lodged between the ribs, even mass graves.

Going forward to just a few thousand years before the rise of the first civilisations, they found scenes of mass slaughter that could only have been associated with war, like the 27 people massacred at Nataruk, west of Lake Turkana in Kenya, about 10,000 years ago. They were men, women and children, mostly clubbed or stabbed to death (although six were probably killed by arrows) and their bodies were not buried but left to rot. The media treated it as a revelation; however, no doubt it was just another incident among tens or hundreds of thousands of similar ones in the long pre-history of human and hominid warfare. So what are we to make of all this?

Two Conditions

Do we bear the mark of Cain? Are we simply doomed to wage ever greater wars until we finally destroy ourselves? Not necessarily. But we do meet the two conditions needed to account for the war-like behaviour of any species towards other members of its own kind: is the species predatory, and does it live in groups of variable size?

We and our ancestors have been hunters for millions of years, and we can therefore easily kill other human beings. Indeed, we have been able to kill even the largest animals for at least a couple of hundred thousand years, so we definitely tick the ‘predator’ box. (Chimpanzees, who regularly hunt, catch and eat monkeys and other small game, are the only other primate species to tick that box – and also the only other primate species that fights wars.)

On the face of it, ‘living in groups of variable size’ is a more puzzling requirement, but it works like this. Solitary predators rarely engage in serious fights with other members of the same species, because there’s about a 50 percent chance of death in such an encounter, and it’s just not worth it in evolutionary terms. In any case, warfare is by definition a group activity. But if those groups are all of similar size, and their members stick together, the likelihood of a head-on battle is equally low: they would be more or less evenly matched, there would be lots of deaths, and any victory would be Pyrrhic.

By contrast, groups of variable size, which must sometimes split up into smaller groups or single individuals to forage, present opportunities for ambushes in which the odds will be very much in favour of the attackers. Attritional warfare is thus possible between such groups, and although the attacks are mostly opportunistic, they may result in the extermination of all the males in one of the groups. Lions behave like this, and wolves, and hyenas too, and of course chimps and humans – all predators that live in groups of variable size. But what benefit are the winning groups actually getting out of this? What evolutionary advantage does it confer?

The world was never empty, and food has always been limited. Whether the environment is desert, jungle, seashore or savannah, both the predator- and the prey-species will tend to breed up to the carrying capacity of the environment – and a bit beyond it. Human hunter-gatherers often practised infanticide as a form of birth control, but the decision to expose the infant seems generally to have been taken by over-burdened parents, not imposed as a matter of band policy. It probably didn’t slow population growth very much.

If your band is living up around the maximum carrying capacity of the local environment, even a brief interruption in food supply (e.g. changes in the weather pattern or in animal migration routes) will create an instant crisis, since most of the foods people eat cannot be stored. In a matter of weeks or months everybody is hungry all the time, and since human beings are gifted with foresight, they know what lies ahead for most of the group if this goes on. But if your band has been systematically culling the adult male population of the neighbouring band by serial ambushes for a long time, it may now have the option of going for broke, exterminating the rest of the neighbouring band’s males, and taking over their food resources to get you through the crisis.

Evolution is not driven by rational calculation, and the chronic warfare that fills our pre-history was not consciously designed as a device for ensuring the survival of our own genetic line. But to explain it, you only have to assume that there was always some degree of competition for resources between neighbouring bands, even in good times, and that in bad times some groups might be driven to violence. Whether for cultural or genetic reasons, some bands will be at least marginally more aggressive than
others. Those are the bands that are likeliest to survive when the resources get scarce, and to pass on both their culture and their genes to the next generation. Put these factors on a low heat and stir occasionally for a few hundred generations, and you get the plight of the Yanomamo people.

[Yanomamo] villages are situated in the forest among neighbouring villages they do not, and cannot, fully trust. Most of the Yanomamo people regard their perpetual intervillage warfare as dangerous and ultimately reprehensible, and if there were a magic way to end it perfectly and certainly, undoubtedly they would choose that magic. But they know there is no such thing. They know that their neighbours are, or can soon turn into, the bad guys: treacherous and committed enemies. In the absence of full trust, Yanomamo villages deal with one another through trading, inter-marriage, the formal creation of imperfect political treaties – and by inspiring terror through an implacable readiness for revenge.

- Wrangham and Peterson, op. cit., 65

Just change the names around, and this would serve as an explanation of the relationship between the great powers in the period before the outbreak of the First World War in 1914. And just as the trigger for the First World War – the assassination of an Austrian archduke in a Balkan town – seemed a trivial cause for such a huge event, so the explanations the Yanomamo gave for their wars seem pathetic and even ridiculous. In fact, they usually blamed them on conflicts over women. But many people always suspected that there was something deeper going on too.

Excerpted from  The Shortest History of War by Gwynne Dyer, with permission from Pan Macmillan India.