Drawing heavily from sociobiological theory and evolutionary psychology, Hrdy argues that (1) the mother at some deep level calculates the benefit/loss ratio that's involved in parental investment, and (2) the infant/child employs various evolutionary strategies to ensure maternal investment in its survival and well-being. There are no guarantees in this business. The mothering "instinct" is not unconditional and the infant's and child's sense of security is not assured. Hrdy strips the parent-child relationship of much of its romance, and she argues that this is why there's been extensive abuse, abandonment (foundling homes), and infanticide (post-birth version of late-stage abortion, used before abortion became a safer practice). Hrdy, in short, challenges the reader to look at parenting from the perspective of evolutionary theory that makes "love" conditional, calculating and colder.
There are, however, a couple of issues with her presentation. Hrdy does not describe how her perspective is consistent with her endorsement of kin selection which is a central tenant of sociobiological theory. Much of Hrdy's book is about "allomothers," a community of support that behaves "as if kin." That seems to contradict kin selection theory that has our other-regarding tendencies limited to kin relations. We know of course that non-kin allomothers (her term) extend their love, care, concern and interest to babies even when non-related. Why is that the case if they are not kin? For that matter, why did the gooslings follow Lorenz even though he was obviously not kin? Hrdy skims over these as if they are not issues. "All early caregivers become the emotional equivalents of kin," she writes, without explaining how this matches up or doesn't match up with kin selection theory. In addition to her numerous "as if kin" references, she writes about the importance of being part of a "community," but then adds without a blink that such a community is "a group of kin" without accounting for the fact that most communities today are not at all kin related. Could it be that kin selection cannot explain other-regarding, altruistic tendencies beyond the parent-child relationship? Could it be that other-giving tendencies are based on the individual's need to be part of a group for survival purposes and that genetic tendencies push the individual to the group and vice versa? Could it be that infants and children need to bond (imprint) with a caregiver, and for caregivers to do the same for dependent infants and children because that's how the group and individuals within the group were able to survive?
Another potential issue with Hrdy's presentation is the implicit assumption of her "parental investment theory" that maternal instinct expression depends on environmental circumstances. Hrdy says there's no pure genotype because genotypes always get expressed within a context. In other words, the environment modifies the genotype and this always results in a phenotypic expression. Within that framework, Hrdy states that, "I assume that mothers in the past were emotionally similar to me. But they made their decisions under different, vastly more arduous, circumstances." No doubt, there is a considerable truth here, but it does raise a question: Is it fair to say that mothers everywhere have the same "emotional make up"? How does that match up with the genetic variation within species that is the guts of Darwinian theory? How does it match up with Hrdy's various references to different, innate temperaments? Hrdy talks about differences in phenotypic expression among identical twins, but there are ample studies about how genotypic expression is remarkably the same among identical twins regardless of the environment. Could it be that some women (and men for that matter) have more of a nurturing, maternal instinct than others because of basic innate differences that are more or less independent of the environment?
As a final comment, Hrdy refers to the Harlow studies (infant deprivation of love objects) without condemnation or, at least, acknowledgement of the problematic aspects of that scientific type of approach from a maternal or paternal point of view.