Is it natural for humans to make war? Is organised violence between rival political groups an inevitable outcome of the human condition? Some scholars believe the answer is yes, but new research suggests not.
A study of tribal societies that live by hunting and foraging has found that war is an alien concept and not, as some academics have suggested, an innate feature of so-called "primitive people".
The findings have reopened a bitter academic dispute over whether war is a relatively recent phenomenon invented by "civilised" societies over the past few thousand years, or a much older part of human nature.
In other words, is war an ancient and chronic condition that helped to shape humanity over many hundreds of thousands of years?
The idea is that war is the result of an ancient evolutionary predisposition that humans may have inherited in their genetic make-up, as long ago as 7 million years, when we last shared a common ancestor with chimpanzees - who also wage a kind of war between themselves.
However, two anthropologists believe this is a myth and have now produced evidence to show it.
Douglas Fry and Patrik Soderberg of Abo Akademi University in Vasa, Finland, studied 148 violently lethal incidents documented by anthropologists working among 21 mobile bands of hunter-gatherer societies, which some scholars have suggested as a template for studying how humans lived for more than 99.9 per cent of human history, before the invention of agriculture about 10,000 years ago.
They found that only a tiny minority of violent deaths come close to being defined as acts of war. Most of the violence was perpetrated by one individual against another and usually involved personal grudges involving women or stealing.
About 85 per cent of the deaths involved killers and victims who belonged to the same social group, and about two thirds of all the violent deaths could be attributed to family feuds, disputes over wives, accidents or "legal" executions, the researchers found.
"When we looked at all the violent events, about 55 per cent of them involved one person killing another. That's not war," Fry said.
"When we looked at group conflicts, the typical pattern was feuds between families and revenge killings, which is not war either. It has been tempting to use these mobile foraging societies as rough analogies of the past and to ask how old warfare is and whether it is part of human nature. Our study shows that war is obviously not very common."
Only a tiny minority of cases involved more organised killing between rival bands of people, which could fall into the definition of warlike behaviour.
Most of these involved only one of the 21 groups included in the study - the Tiwi people of Australia who seemed to be particularly prone to violent incidents, Fry said.
Rather than finding war ubiquitous, the two researchers found little evidence that hunter-gatherer societies were in a constant state of violent conflict with rival groups.
In short, they found that some of the most "primitive" peoples on Earth were actually quite peaceful compared to modern, developed nations.
"These findings imply that warfare was probably not very common before the advent of agriculture, when most, if not all, humans lived as nomadic foragers," Kirk Endicott, an anthropologist at Dartmouth College, told the journal Science, where the study is published.
The findings question the conclusions of well-respected academics such as Harvard's Steven Pinker and University of California's Jared Diamond, both of whom have published best-selling books on the topic of warlike aggression and tribal societies.
In Diamond's The World Until Yesterday, for instance, war is defined as recurrent violence between groups belonging to rival political units that is sanctioned by those units.
Under this definition, many tribal societies, left to their own devices, would be in a state of chronic war, Diamond said. He cites the case of the Dani people living in the Baliem Valley of the New Guinea Highlands who in 1961 engaged in a series of violent conflicts that led to many deaths. Although the Dani are agriculturalists, Diamond uses them as examples of how early humans societies may have interacted with one another.
Meanwhile, Pinker in his book The Better Angels of Our Nature argues that humans are innately violent and have only become less so in recent years because of cultural influences that have kept this aggressive nature in check.
Both Pinker and Diamond have been criticised by some anthropologists for simplifying and exaggerating the research they use to support their conclusions. Even worse, some argue that they used discredited work of anthropologists such as Napoleon Chagnon who has claimed that the Yanomami people of the Amazon are in a state of chronic warfare with one another.
"Chagnon's work is frequently used by writers such as Jared Diamond and Steven Pinker who want to portray tribal peoples as 'brutal savages', far more violent than 'us'. But none of them acknowledge that his central findings about Yanomami violence have long been discredited," said Stephen Corry, director of Survival International.
"This latest research is the latest nail in the coffin for Pinker's 'Brutal Savage' thesis. Pinker selects highly questionable data, and leaves out anything which contradicts his argument," Corry said.
"Although he and his supporters, such as Jared Diamond, present those of us who question them as 'anti-science', in fact their own work is simply a social and political argument with a pseudo-scientific wrapper," he said.
In response, Diamond said that many scholars agree with his conclusions that tribal societies are on average more violent than state societies.
"This conclusion might at first seem surprising, but tribal warfare tends to be chronic, while even nations with the highest war-related death tolls in the 20th century - Russia, Germany and Poland - were mostly at peace and only intermittently at war," Diamond said.
"Corry's passionate and error-laden condemnation of my book is clearly driven by something other than the facts. It's Corry's romanticised view of traditional societies that is really dangerous," he said.