On the one hand, this sounds like it supports the notion that stay-at-home dads are less “manly.”
On the other hand, in a earlier age, men had to do the hunting and heavy lifting, as well as producing the maximum number of babies (given the incredibly high infant mortality rate).
But time moves on, and the Big Balls types no longer have such an evolutionary advantage. Nowadays, families with fewer children — at least in the First World — have a survival advantage. And co-parenting also helps prepare the offspring for a world where success at social interaction is more important than throwing hands.