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.

Chronic-fatigue syndrome, or CFS, which afflicts over 1 million people in America and 250,000 in Britain, is certainly chronic and surely fatiguing. CFS’s symptoms — debilitating exhaustion often accompanied by pain, muscle weakness, sleep problems, "brain fog" and depression — overlap with those of other conditions.