Force for change (Image: Beatriz Orduña/Flickr/Getty Images)

IT’S about 2 metres long, made of tough spruce wood and carved into a sharp point at one end. The widest part, and hence its centre of gravity, is in the front third, suggesting it was thrown like a javelin. At 400,000 years old, this is the world’s oldest spear. And, according to a provocative theory, on its carved length rests nothing less than the foundation of human civilisation as we know it, including democracy, class divisions and the modern nation state.

At the heart of this theory is a simple idea: the invention of weapons that could kill at a distance meant that power became uncoupled from physical strength. Even the puniest subordinate could now kill an alpha male, with the right weapon and a reasonable aim. Those who wanted power were forced to obtain it by other means – persuasion, cunning, charm – and so began the drive for the cognitive attributes that make us human. “In short, 400,000 years of evolution in the presence of lethal weapons gave rise to Homo sapiens,” says Herbert Gintis, an economist at the Santa Fe Institute in New Mexico who studies the evolution of social complexity and cooperation.

The puzzle of how humans became civilised has received new impetus from studies of the evolution of social organisation in other primates. These challenge the long-held view that political structure is a purely cultural phenomenon, suggesting that genes play a role too. If they do, the fact that we alone of all the apes have built highly complex societies becomes even more intriguing. Earlier this …