Polygamy, lost boys, in other cultures?

On TV show "Law and Order" last night they had a case involving Polygamy and the "lost boys" problem that it creates where to maintain an abundance of available females the males must be expelled. In the USA where it is an extremely small subculture of religious cults that practice this the boys simply leave the church and go into the general culture. My question is in ancient or tribal cultures where the whole culture is polygamous what happens to the surplus boys? or is there a different dynamic at work to where there are not excess boys competing for mates?