Men who worry that marriage will tame their wilder impulses may not be far wrong. Levels of the hormone testosterone, which is thought to contribute to aggressive and dominating behavior, are high when men are single, go down when they marry, and rise when they divorce.
Although some men have consistently higher levels of testosterone than others, hormone levels in all men respond to changes in status. In anticipation of a competition, for example, testosterone goes up; after it's settled, the testosterone of the winner rises further still, while that of the loser goes down. Researchers have found a similar process in marriage.
Allan Mazur, of Syracuse University, theorizes that single men have high levels of the hormone because they are in competition for women and other "resources," while married men have lower levels because they are less competitive and receive social support from their wives. The discord of divorce, however, may cause testosterone levels to rise again.
That can set a vicious cycle in motion: high testosterone levels create dominant behavior, which in turn creates more hormone-elevating challenges. Mazur's collaborator, Alan Booth, of Pennsylvania State University, says "some men, especially those with very caring early relationships with their parents, learn to use the energy and aggressiveness of high testosterone in productive ways."