For as long as she's been a sociobiologist, Sarah Blaffer Hrdy has been playfully dismantling traditional notions of motherhood and gender relations. In 1981's “The Woman That Never Evolved,” the newly minted Harvard Ph.D. blasted a hole in the dominant model of sexual selection, in which hypersexual males pull out all the stops to impress passive females. Despite the snickers of her male colleagues, Hrdy maintained that women are subject to sexual selection, too: Females apes, it turns out, frequently compete with each other for male attention, trick males into copulating with them, and engage in sexual activity for pure pleasure. Later, Hrdy's monumental “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.
Now a professor emeritus at the University of California at Davis, Hrdy is back with another book, “Mothers and Others,” and another big idea. She argues that human cooperation is rooted not in war making, as sociobiologists have believed, but in baby making and baby-sitting. Hrdy's conception of early human society is far different from the classic sociobiological view of a primeval nuclear family, with dad off hunting big game and mom tending the cave and the kids. Instead, Hrdy paints a picture of a cooperative breeding culture in which parenting duties were spread out across a network of friends and relatives. The effect on our development was profound.