EDWARD WILSON, the inventor of the field of sociobiology, once wrote that “war is embedded in our very nature”. This is a belief commonly held not just by sociobiologists but also by anthropologists and other students of human behaviour. They base it not only on the propensity of modern man to go to war with his neighbours (and, indeed, with people halfway around the world, given the chance) but also on observations of the way those who still live a pre-agricultural “hunter-gatherer” life behave.

Add this to field studies of the sometimes violent behaviour of mankind’s closest living relative, the chimpanzee, and the idea that making war is somehow in humanity’s genes has seemed quite plausible. It has even been advanced as an explanation for the extreme levels of self- sacrificial altruism people sometimes display. (If a neighbouring tribe is coming to wipe yours out completely, then giving up your own life to save your fellows might actually make evolutionary sense.)

But a paper in this week’s Science, by Douglas Fry and Patrik Soderberg of Abo Akademi University, in Finland, questions all this. Dr Fry and Mr Soderberg have reviewed what is known about modern hunter-gatherers. They suggest that although such people are far from peaceful they are also far from warlike. Most who die violent deaths in their societies do so at the hands of fellow tribesmen, not “foreigners”. Murderers, this research suggests, humans may often be. But they are not the died-in-the-wool warriors of anthropological legend.

Dr Fry and Mr Soderberg came to this conclusion by scrutinising 21 hunter- gatherer societies from all over the world. They looked at ethnographic studies of these groups, published over the past 100 years or so. Inter alia, these studies recorded homicides and their circumstances.

The two researchers classified such deaths into interpersonal events (what modern policing would dub “domestics”), interfamilial feuds, group-sanctioned executions and intergroup events. Only the latter could be described as war.

One of the 21 groups was extremely warlike. More than half of recorded killings perpetrated by the Tiwi, an Australian people, were acts of war—and nearly half of all homicides from all causes in all 21 groups involved the Tiwi. This group was such an outlier that Dr Fry and Mr Soderberg did their analysis twice: once with and once without the Tiwi.

Nomad’s land

Excluding the Tiwi, deaths in war were only 15% of the total. Including them, the figure was 34%. But even that is still a minority. These numbers do not suggest hunter-gatherers are going out looking for trouble with their neighbours.

This finding seems different from that arrived at in 2009 by Samuel Bowles of the Santa Fe Institute, in New Mexico. Dr Bowles looked at eight modern hunter-gatherer groups, including the Tiwi, and at archaeological evidence concerning 15 ancient ones. He concluded that death in warfare is so common in hunter-gatherer societies that it was an important evolutionary pressure on early Homo sapiens, and might easily account for the emergence of self-sacrificial altruism.

Dr Bowles’s analysis did not, however, separate the Tiwi from the rest, so was influenced by this outlier. Treating outliers with caution is reasonable. An analysis of modern warfare that looked at the 1940s would come to a different conclusion from one that looked at the 1950s, 1960s, 1970s, 1980s or 1990s. Nor could the archaeological studies clearly indicate which violent deaths were caused by war. As Dr Bowles himself says, “one cannot always distinguish between deaths due to intergroup violence and that occurring within groups”.

Dr Bowles was not the first to conclude that war was common during human evolution. Early in the 20th century, studies of the Yanomami, who live in the Amazon rainforest, suggested as much. But that idea was overthrown when, decades later, a researcher called Brian Ferguson re-examined all documented cases of Yanomami warfare. These, he found, were overwhelmingly in areas penetrated by settlers rather than in places where the Yanomami dwelt undisturbed.

Something similar happened to chimpanzee researchers. The first big field study of these animals was done by Jane Goodall. Her chimps, which live in Tanzania, are often aggressive, sometimes engage in cannibalism, and even steal and kill others’ infants. And they do engage in something that looks like warfare. When a large group of chimps split, for instance, vicious intertribal conflict followed. All this suggests an evolutionary origin for some of the darker aspects of human nature.

A second study, though, conducted in Congo-Brazzaville by David Morgan and Crickette Sanz of Washington University, in St Louis, came to contrary conclusions. It found chimps to be peaceful creatures. For a while, that confused primatologists.

The difference between the two populations turns out to be density. The Tanzanian chimps are crowded together as deforestation around their reserve reduces the amount of habitat available. Those in Congo do not, at least yet, suffer in this way.

Chimps, then, do offer a useful lesson on the origin of warfare—just not the one that was originally believed. Groups of chimpanzees, like groups of people, will fight each other if need be, but will otherwise leave each other alone.

Whether modern, industrial man is less or more warlike than his hunter-gatherer ancestors is impossible to determine. The machine gun is so much more lethal than the bow and arrow that comparisons are meaningless. One thing that is true, though, is that murder rates have fallen over the centuries, as policing has spread and the routine carrying of weapons has diminished. Modern society may not have done anything about war. But peace is a lot more peaceful.