I thought this was a interesting study from Harvard.

Violent conflict may, under certain conditions, offer a biological benefit to those who take part in it, a Harvard study has found.

The study, authored by Luke Glowacki, found that... among members of an East African herding tribe, those who engaged in conflict -- in the >form of violent raids carried out on neighboring groups -- had more >wives, and thus more opportunities to increase their reproductive >success through having more children.

"The currency of evolution is reproductive success," Glowacki said. "By having more wives you can have more children. What we found was >that, over the course of their lives, those who took part in more raids had more children."

http://www.sciencedaily.com/releases/2014/12/141229164858.htm

In East Africa, it's violent raids that benefit the tribe. Of course, in the West, it seems to be career success and demonstrations of leadership and fitness.