Why are warriors capable of working together, although they like fighting with each other?

Men have a long history of fighting with one another for dominance, but why such duels did not leave tribal unity in tatters and warriors less capable of working together to fend off attacks from predators and hostile clans remains a mystery. One common theory is that men more readily make up after fierce physical conflicts than do women. And an experiment run recently at Harvard University suggests this may be true.

Artificial limbs are nothing new. An ersatz toe, made of wood and leather and found attached to the mummified body of an Egyptian noblewoman in Cairo, in 2000, is thought to be between 2, 500 and 3, 000 years old. Things have moved on since then. Modern prostheses sport things like articulated fingers that can be controlled by picking up impulses from their wearer’s remaining nerves.