IT HAS become common currency--especially during the period of the last two decades, as mainstream ideas shifted to the right--to view human behavior as biologically innate. People make war because they're human--and therefore warlike--goes the claim.

These fashionable ideas, though continually offered as fact, have no foundation in any science. They are, in fact, ideological inventions that help bolster the status quo--alongside ideas like "the poor are poor because they don't try hard enough."

As the late left-wing biologist Stephen J. Gould wrote, "How satisfying it is to fob off the responsibility for war and violence upon our presumably carnivorous ancestors. How convenient to blame the poor and the hungry for their own condition--lest we be forced to blame our economic system or our government for an abject failure to secure a decent life for all people."

Search as they may, biologists will never find a war gene--because violence isn't innate to humans. For every example of "aggression" in human behavior, we can also find examples of peaceful cooperation and sharing.

And if human beings are naturally warlike, one wonders why it's necessary for governments to take young men going into the military and put them through a rigorous retraining to make them capable of systematically killing other humans.

The idea that humans have a natural propensity to war is hardly an explanation, any more than the idea that humans naturally try to enslave each other. It's easier to debunk the idea that slavery is natural--after all, slavery was abolished--but war is sadly still with us. But there was a time when defenders of the status quo argued that slavery was natural--and therefore eternal.

In short, war can't be understood by looking at the biological or psychological characteristics of individuals. It can only be understood in a social and historical context.

The British philosopher Thomas Hobbes believed that war was humanity's natural inclination. Only a state, granted a monopoly of armed force, could intervene and enforce peace and prevent the constant "war of all against all." This has become the "common sense" view of warfare and the state--and, as Gould points out, a convenient ideological justification for the violence of ruling classes around the world.

But states haven't always existed. In fact, for most of human history, humans lived in gathering and hunting societies where there were no judges, police or armies, no slaveowners or slaves. From what we know of these societies, there was little or no warfare in some--for example, among the Shoshone in the Western U.S., hunters and gatherers who lived in small, nomadic bands in the desert.

What's more, the character of war in pre-class and pre-state societies was vastly different from modern warfare. There were no professional groups of fighters--no special separation between the fighters and ordinary people. Humans were hunters or fighters, as conditions demanded.

These early societies consisted of small bands of people, spread out over large territories, foraging for food and sharing it among themselves--with groups of families occasionally coming together to form larger bands in order to engage in larger activities like a collective hunt. In such circumstances, there were both elements of cooperation and sharing--within bands and between loose collections of bands--and elements of competition for scarce resources.

But scarcity is a relative term. Gathering wild plants and hunting wild animals yields only enough for small populations spread out over large territory. Any sudden depletion of either supply could create conditions for inter-band warfare--or, alternatively, the application of new technologies to increase the supply of food.

But war wasn't as prevalent in pre-class societies for the simple reason that such societies didn't produce surpluses over and above their subsistence needs. One group couldn't seize the wealth of another, because it had no way to carry or preserve it. Nor could one person be enslaved by another--for the simple reason that no one could be forced to produce wealth above and beyond their own subsistence needs.

This explains why in earlier forms of warfare, captives were either killed or simply adopted by the winning side, and war itself often consisted of skirmishes producing light casualties.

Only with the rise of agriculture and the production of a surplus--which in turn produced the first ruling classes (the keepers of the surplus)--did warfare become a systematic practice, engaged in by specially armed subjects of the ruler in order to gain extra surplus and slaves. The rulers in turn created loyalty among their armed retainers by giving out the spoils of conquest--land, slaves and goods.

But the struggle for the surplus didn't just produce wars between rival kingdoms. Class society also gave rise, inevitably, to violent conflict between social classes over how the surplus was used. From slave and peasant rebellions to uprisings of workers against capitalism, the whole history of humanity, as Karl Marx and Frederick Engels put it, is one of class struggle, "now hidden, now open."

This is war of a very different kind--between oppressor and oppressed. "Force," wrote Engels, "plays yet another role in history, a revolutionary role…In the words of Marx, it is the midwife of very old society pregnant with a new one, it is the instrument with the aid of which social movement forces its way through and shatters the dead, fossilized political forms."

This system breeds violence