"It was only reinforced when the invention of the placenta and the mammary gland gave male mammals a gigantic prize to compete for: nine months and several year

"It was only reinforced when the invention of the placenta and the mammary gland gave male mammals a gigantic prize to compete for: nine months and several years of somebody else's bodily efforts." There are plenty of species, humans included, where male parental investment, over the life of the child, is comparable with that of the female. The average human child receives significant investments of time and effort from his or her father, not only in the form of playing catch and going on trips, but also because that father will spend a good portion of his working week earning resources to be used for the child's benefit. And weigh that with the fact that, until recently, it was even impossible for the man to know for sure that the child was his.