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Mom Genes:
Inside the New Science of Our Ancient Maternal Instinct 
By Abigail Tucker
Gallery Books, 336 pages, $28

On my study bookshelf stands a stretch of pastel-colored books: my library of “parenting” literature. Whole books could be written about the politics of such books, but of the genre in general we can say two things. First, while we pay lip service to the idea of “parenting” as a sex-neutral enterprise, my husband (who is a devoted and attentive father) has never read a parenting book. He is not unusual. “Parenting” books are written for mothers.

Second, while such books notionally discuss “parenting” (in reality, mothering), they rarely pay much attention to mothers. Instead, they focus on the child, offering advice on how eating this, buying that, or doing the other will help to optimize your offspring for today’s hyper-competitive world. 

This goes, too, for scientific research on motherhood. As the science journalist Abigail Tucker puts it at the start of Mom Genes, her new book exploring this neglected area, such research as exists into moms is to a great extent “really the disguised study of babies.” And what she uncovers in this highly readable summary of what science knows about moms—about the physiology of pregnancy, the nature of the parent-baby bond, and so on—has profound implications for contemporary dogmas on both sides of the aisle.

Such dogmas include, for instance, that moms and dads are the same apart from socialization, that “sex” really means “gender” and the latter is “assigned” at birth, and that parenthood is merely one lifestyle choice for an otherwise unaltered individual who could be of either sex. And, importantly, that having children is an “individual” choice that has no right to make calls upon wider societal structures.

As Tucker shows, moms and dads are not interchangeable. Pregnancy, it transpires, permanently transforms moms’ minds and bodies. “Baby brain” really is a thing: Moms’ higher cognitive functioning genuinely is impaired by the neurochemical changes induced by caring for a new infant. The more kids we have, the weaker our memory gets. And that’s just the start of the divide between mothers and fathers: Moms react more quickly to infant distress, handle crisis differently, and even show our own aggression patterns. 

True, fatherhood changes the brain, too—but to a lesser extent, and only once a dad has experienced caring for a baby. Mothers’ neurology starts to be transformed during pregnancy. Though Tucker shows that acculturation plays a role in this process, it is also a biological change, and similar changes are observable across numerous species. 

The stereotype of a special bond between mothers and babies also has a basis in science. Moms are intricately interconnected with our children, down to a cellular level: Our kids’ DNA remains in our bodies after birth, sometimes for years, a phenomenon known as “fetal microchimerism.” This is both a material fact and also a powerful metaphor for the physiological and emotional interdependence between a mom and baby. While in utero, our babies respond to our physiological arousal—elevated heart rate, changes in the volume of stress hormones, and so on. And the reverse is also true: In minute and subtle ways, pregnant mothers also respond involuntarily when their unborn babies are stimulated. This intricate, voiceless dialogue continues after birth as well: Moms and their babies co-create one another, in complex neurobiological feedback loops.

We also see in Mom Genes that far from being reducible to “gender,” a set of social roles “assigned at birth,” human sex dimorphism emerges at conception—and can even affect the likelihood of conception, while the unborn baby’s sex in turn affects the mother. Gestating and birthing boys is more immunologically taxing, and moms of boys produce more milk once their babies are born, too. This in turn influences the proportion of boys and girls conceived: When in conditions of stress, women’s bodies will conceive less readily overall, and then skew toward birthing girls. 

In the final section of the book, Tucker discusses the complex interaction between moms’ behavior and their wider environment. For just as moms shape and are shaped by our babies, in complex feedback loops, so too the experience of motherhood is formed through a kind of dialogue with the wider social order. 

Tucker shows how “optimum parenting” is not an absolute measure, as it sometimes appears in those “parenting” books on my shelf. Moms’ treatment of their babies is calibrated to a wider context: For instance, in a culture where material resources and empathy are scarce, a relatively harsh style of mothering may actually be more appropriate. 

In this context, it makes sense that Tucker avoids overly prescriptive statements on hot-button issues such as—for example—whether or not mothers should go out to work. But as Tucker demonstrates, mom science has profound implications for how we think about family life, not just in our own homes but also at the levels of policy and social norms.

She notes that evidence shows the happiest and most secure moms tend to be married; that moms who work more than 40 hours a week tend to be the least happy; and that the happiness of working moms depends considerably on working conditions. Supporting moms means not fruitless bickering over whether to work, but reflection on the conditions of doing so. For example, where we have predictable working patterns or can shape our own, working moms can reap many rewards without feeling conflicted. Conversely, a lack of agency or predictability, whether “swing shifts, seasonal work, and inflexible hours,” or pressure to return to a high-powered career weeks or even days post-partum, will make moms less happy. 

And Tucker shows how these conflicts are most acute where moms lack social infrastructure, building a powerful argument against the modern condition of social atomization. Moms do better with partners than when single, and thrive when their own mothers are around. We are happiest as moms when well-supported by a network of female friends, far more likely to get postpartum depression if lacking social support, and (as Tucker vividly illustrates with her own story) tend to struggle in the often lonely suburbs.

In a rare excursion into policy detail, Tucker contrasts America’s woefully minimal perinatal provision—which abruptly ends two months postpartum, when women are often most vulnerable—with those nations where dedicated healthcare professionals are available throughout a child’s early years. I live in Britain, where universal healthcare (with all its flaws) provides relatively comprehensive maternity services. Here, with few exceptions, moms are also entitled to six months of paid maternity leave and another six months unpaid on top. From this vantage point, Tucker’s plaintive call for perinatal care beyond the bare minimum, and entitlement even to a minimal twelve weeks at home with a new baby, is a sharp reminder that even a culture supposedly built on “mom and apple pie” may not practice what it preaches.

Mom Genes is far from a polemical book, and steps delicately across acres of political minefield. In terms of tone it is jolly to a degree I found slightly forced (I am British, after all). In terms of implications, though, it is seismic, and I suspect Tucker is aware of this. If anything, her restraint lends force to the cumulative power of her argument: that moms are, in truth, a special class of human, and that interdependence among babies, moms, and the wider world remains hopelessly under-valued and under-studied. Acknowledging this interdependence is not sexism. It is profoundly in the interests of women, and of the children we birth and raise. 

Mary Harrington is a columnist at UnHerd.

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