[1] The primary cause of war, as LeBlanc sees it, is ecological imbalance; humans compete for finite amounts of food when population outstrips supply or when the land becomes overgrazed and deforested.

But even they repeated the historical theme: "A few people occupy the...land, they exterminate many species, they heavily modify the landscape, and their numbers grow.

"Our closest ape relatives," he says, have always engaged in ferocious acts of warfare, chillingly reminiscent of human conflict (as Jane Goodall observed among chimpanzees in the jungles of Tanzania in the 1960s).

As humans evolved, violence was the norm; the myth of the "noble savage", is a distinctly modern invention (first advanced by Jean-Jacques Rousseau and his followers in the 18th century).

At burial locations of the ancient Aborigines of Australia-hunter-gatherers with no permanent settlements-we find "evidence of violent deaths and even massacres, and specialized weapons useful only for warfare."