Employers reward fatherhood by paying higher wages to men with children. But if fathers take time away from work for their children, whether for childbirth or pediatrician appointments, employers penalize them.

That seeming contradiction is at the heart of the debate over paternity leave, which I wrote about last weekend. For the first time, social scientists are discovering that men who take leave and other time off work for child care pay a price, in the form of lower hourly pay or demotions, just as working mothers do.

Researchers say it is because men who take time off fail to meet expectations of the roles they should play. Fathers get paid more because they are expected to work harder than ever to support their families. But if they start spending time with their families away from work instead, they lose the fatherhood bonus.