IT'S a question at the heart of what it is to be human: why do we go to war? The cost to human society is enormous, yet for all our intellectual development, we continue to wage war well into the 21st century.
Now a new theory is emerging that challenges the prevailing view that warfare is a product of human culture and thus a relatively recent phenomenon. For the first time, anthropologists, archaeologists, primatologists, psychologists and political scientists are approaching a consensus. Not only is war as ancient as humankind, they say, but it has played an integral role in our evolution.
The theory helps explain the evolution of familiar aspects of warlike behaviour such as gang warfare. And even suggests the cooperative skills we've had to develop to be effective warriors have turned into the modern ability to work towards a common goal.
These ideas emerged at a conference last month on the evolutionary origins of war at the University of Oregon in Eugene. "The picture that was painted was quite consistent," says Mark Van Vugt, an evolutionary psychologist at the University of Kent, UK. "Warfare has been with us for at least several tens, if not hundreds, of thousands of years." He thinks it was already there in the common ancestor we share with chimps. "It has been a significant selection pressure on the human species," he says. In fact several fossils of early humans have wounds consistent with warfare.
Studies suggest that warfare accounts for 10 per cent or more of all male deaths in present-day hunter-gatherers. "That's enough to get your attention," says Stephen LeBlanc, an archaeologist at Harvard University's Peabody Museum in Boston.
Primatologists have known for some time that organised, lethal violence is common between groups of chimpanzees, our closest relatives. Whether between chimps or hunter-gatherers, however, intergroup violence is nothing like modern pitched battles. Instead, it tends to take the form of brief raids using overwhelming force, so that the aggressors run little risk of injury. "It's not like the Somme," says Richard Wrangham, a primatologist at Harvard University. "You go off, you make a hit, you come back again." This opportunistic violence helps the aggressors weaken rival groups and thus expand their territorial holdings.
Such raids are possible because humans and chimps, unlike most social mammals, often wander away from the main group to forage singly or in smaller groups, says Wrangham. Bonobos - which are as closely related to humans as chimps are - have little or no intergroup violence because they tend to live in habitats where food is easier to come by, so that they need not stray from the group.
If group violence has been around for a long time in human society then we ought to have evolved psychological adaptations to a warlike lifestyle. Several participants presented the strongest evidence yet that males - whose larger and more muscular bodies make them better suited for fighting - have evolved a tendency towards aggression outside the group but cooperation within it. "There is something ineluctably male about coalitional aggression - men bonding with men to engage in aggression against other men," says Rose McDermott, a political scientist at Stanford University in California.