Compared to other mammals, human offspring are slow-maturing and outrageously costly to rear, yet men's motivation to care for children is highly variable. Some fathers will do anything to remain nearby and care for their children while others (even men certain of their paternity) act as if they don't know they have children. Most fall someplace in between, prompting evolutionists to ask how Darwinian natural selection could have favored production of such costly children without concurrent selection pressures on fathers to provide what progeny need to survive? Resolving this paradox of “facultative fathering” requires us to consider the deep history of the human family, and in doing so to rethink the tremendous potential for nurture that resides in human males.