You can never have too many mothers

"Mother Nature," published in 1999, thoroughly refuted the idea that there is any such thing as maternal instinct: Mothers in nature often abort fetuses, favor healthy babies while nudging runts away, and even commit infanticide so that they can try to breed again under better circumstances.

She argues that human cooperation is rooted not in war making, as sociobiologists have believed, but in baby making and baby-sitting.

Unlike ape mothers, who were fiercely protective of their little ones and rarely shared them with anyone, early human mothers needed help raising their uniquely high-maintenance babies. They found it in the form of what Hrdy calls "allomothers," substitute caretakers of either sex who took over for a mother while she went to work scrounging up nuts and berries to feed her family.

those complex, community-wide nurseries spurred us to develop empathy, cooperation and what psychologists call "theory of mind