How long has humanity been at war with itself?

The famous American astronomer Carl Sagan once said, “You have to know the past to understand the present.” But can we ever know the history of human origins well enough to understand why humans wage large-scale acts of appalling cruelty on other members of our own species?

Last month, the Geneva Academy was monitoring no fewer than 110 armed conflicts globally. While not all of these reach mainstream media, each is equally horrific in terms of the physical violence and mental cruelty we inflict on one another.

Chimpanzees, our closest living relatives, are known to partake in violent intra-specific skirmishes, typically to preserve privileged access to resources in response to breaches in territorial boundaries. But only humans engage so extensively in large-scale warfare.

Do massive acts of intra- or interpopulational violence conform with Darwinian precepts of natural selection, or is this something we do as a competitive response to the stresses of living in such large populations? Looking back in time can help us find answers to such questions.

Evidence preserved in the archeological record can tell us about when and under what conditions the preludes to warlike behavior emerged in the past. Scientific reasoning can then transform this information into viable hypotheses that we can use to understand ourselves in today’s world.

As archeologists continue to unearth new fossil evidence at an increasing rate, so too are they piecing together the human story as one of complex interactions played out by (a growing number of) different species of the genus Homo that lived during the tens of thousands of years preceding the emergence – and eventual global dominance – of our own species: Homo sapiens.

In fact, scientists