Lee Gettler is hard to get on the phone, for the very ordinary reason that he’s busy caring for his two young children. Among mammals, though, that makes him extraordinary.

“Human fathers engage in really costly forms of care,” says Gettler, an anthropologist at the University of Notre Dame. In that way, humans stand out from almost all other mammals. Fathers, and parents in general, are Gettler’s field of study. He and others have found that the role of dads varies widely between cultures—and that some other animal dads may give helpful glimpses of our evolutionary past.

Many mysteries remain, though, about how human fathers evolved their peculiar, highly invested role, including the hormonal changes that accompany fatherhood (see sidebar below). A deeper understanding of where dads came from, and why fatherhood matters for both fathers and children, could benefit families of all kinds.