I started reading this book in the hospital the night our son was born, as we were all winding down from the birth experience. As the subtitle suggests, it's a wide-ranging work. In fact, it's so wide-ranging that it's extremely difficult to concisely identify a theme for this book. Hrdy's main field of study is evolution, and she is mainly concerned to understand just what "maternal instincts" might be, and how they've been shaped over millions of years by evolutionary pressures. Yet that simple inquiry masks a host of complex issues.
To be blunt, Hrdy does not believe that "mother love" is instinctual; rather, she sees the devotion for offspring that we normally associate with mothers as just one of many possible strategies for dealing with children in human societies. Note that "dealing with" does not always mean "raising"; one major chunk of the book deals with the truly appalling level of infanticide that the wet-nurse and foundling systems in western Europe camouflaged. Children with no mother have historically a very poor chance of survival -- but it may be a perfectly rational decision in evolutionary terms to kill an infant to maximize the chance of bringing at least some children to adulthood. At the other extreme are various foraging and hunting societies in which mothering is distributed among many "allomothers", often non-breeding females who see at least part of their own genetic material perpetuated as the tribe's children are raised cooperatively.
But, of course, things are always more complex when dealing with the human animal. Although mother love -- defined as built-in love for every offspring -- may not be instinctive, the ability to form bonds of maternal love with any infant probably is instinctive. Infants and mothers have co-evolved a system in which infants are designed to appeal to adults, and if the appeal is allowed to take hold, a series of biochemical changes (notably the rush of oxytocin and prolactin released by nursing in the maternal bloodstream) act to cement the bond in this particular case. Or so, at least, I read Hrdy's argument.
In distinguishing paternal and maternal instincts, Hrdy relies on one of the core notions of sociobiology: that although maternity is always certain, paternity is less so. Fathers are less primed by evolution to invest resources in a child than mothers are, simply because fathers are less sure to be nurturing their own genes in the process. Yet there are complex cultural dynamics layered on top of this. Hrdy points out the difficulty of woman in primitive (subsistence) societies even conceiving without outside help by noting that without a minimum level of body fat women won't even ovulate. Combined with the difficulty of finding food for two post-partum, this has brought about a common strategy of promiscuity in many subsistence societies; by having sex with multiple males, women seek to give many males a stake in any particular offspring.
This in turn brings infanticide back into the picture; several places Hrdy refers to her own early work studying lemurs, in which new males in a group may kill existing infants. Though seemingly this would hurt the survival of the species, Hrdy points out that it increases the chance of survival of the particular genes of the new male, who maximizes his chance of mating by abruptly cutting off the nursing of the female lemurs who thus go into heat more often. There are in fact some human societies in which this same pattern has been seen, and Hrdy marshals the anthropological evidence in that regard as well. Though she does not argue that humans behave just like other primates (or birds or fish or mammals), she does use animal studies to illuminate the human response and to suggest lines of inquiry.
If there's a single message to this work, it's that motherhood always involves tradeoffs. The extended childhood that people go through, the long period of helplessness, means that mothers (and allomothers) sacrifice part of their own individual chances of survival for genetic survival. This happened just as much, Hrdy argues, in foraging societies where gathering food meant leaving the child with allomothers as it does in the current industrial world where day care gives women a way to bring in a second income while still "raising" a child.
But this book is more a ball of yarn than a single thread. You can get the real scoop on that famous photo of the mother with the healthy breastfed male twin and the wasted bottlefed female twin (social prejudice against female infants and family control by the mother-in-law come into the story), learn about the nursing machinery of kangaroos (separate high-fat and low-fat nipples), or become familiar with the ruota (a rotating barrel used to insert infants into a foundling home), just to name a few side-trips. It's all exhaustively footnoted and written with style and grace.
All in all, reading this book has provoked a lot of thought about parenthood. Certainly it now seems to me that there's some hard-wiring somewhere to care about cooing infants; I would not have believed that I could find this small person more absorbing than a lava lamp without the actual proof. In keeping with Hrdy's own digressive style, I don't have any particular conclusions to relate -- but it's nice to have the confirmation, if I was ever in doubt, that parenthood is an exceedingly complex subject.