That's not the correct way to look at it. Those who won wars ended up more prosperous (up until very very recently) and where able to reproduce more.

Societal behaviour like war differs from individual behaviour like 'risky play'. War, as a societal behaviour, emerges from the individual behaviour of fighting others for resources in a world of scarcity. That was a beneficial behaviour in many situations, as it prevented starvation. It would take much longer than our time within complex society has allowed to weed this behaviour out of our DNA on account of emergent behaviour.

Have you read the whole article? He goes on to describe research on rats who are prevented from playing as pups and develops his argument from there.