Men tend to be more generous when they have women in their families. It goes beyond a wife making decisions about giving: Danish CEOs are likely to pay their employees less money after they have a baby boy, but not after having a baby girl. Fathers with daughters tend to vote more liberally than men with sons or no children. And how many sisters one grew up with makes a difference, too. Psychologist Paul Van Lange at the Free University in Amsterdam conducted an experiment in generosity. The participants had a choice in splitting money with someone they did not know:
(a) You get $25 and your partner gets $10.
(b) You get $20 and your partner gets $30.
The first option is the selfish one; you’re claiming most of the resources for yourself. The latter option is more generous as it involves sacrificing a small amount ($5) to increase your partner’s gains by a much larger amount ($20).
The players expressed consistent preferences in each of the nine rounds they played on Professor Van Lange’s watch. The data showed that players who made the more generous choices had more siblings. The givers averaged two siblings; the others averaged one and a half siblings. More siblings means more sharing, which seems to predispose people toward giving.
And once again, gender mattered. The givers were 40 percent more likely to have sisters than the people who made more self-serving, competitive choices. (There was no difference in the number of brothers; it was the number of sisters, not siblings, that predicted greater giving.) And Professor Van Lange’s team pointed to another study showing that the more sisters a father has, the more time he spends raising his own children. After growing up with sisters, men who have opportunities to give are more likely to do so.