In his book Men in Groups, Lionel Tiger (damn, I wish I could have cool animals for my first and last names--Tiger Woods, eat your heart out) hypothesized that men who are attached to male groups will have greater reproductive success than isolated men. Even if a guy is not dominant, being a part of a group will enhance his attractiveness since he is perceived to have greater access to resources and protection.
Men who participated in the GSS were asked: 1) the number of close friends they have at work, and 2) the number of children they have (n = 136). The correlation between the two for guys who are old enough to have completed their families but are not yet retirement age (45-64) is .19. It is small but statistically significant. Men with more friends at work do tend to have more kids. (Work is not generally an all-male group, but it does tend to be dominated by men and is thus "male" in that sense).
UPDATE: I thought men with many friends at work might earn more due to connections which, in turn, would lead them to have more kids since they could better afford them, but the impact of friends on family size is not reduced when income is entered into an OLS regression model.