by Helen Currie Foster
Okay—Mom Genes is such a great title, it couldn’t not be used. But Abigail Tucker’s new book of that title doesn’t focus just on moms. Tucker, a New York Times best-selling science writer, dives deep into the burgeoning science examining parental behavior—genetic? hormonal? learned?
And you writers may find it a rich source for potential plots.
Moms will recognize Tucker’s description of the weird sensation of being kidnapped, of feeling like victims of an Invasion of the Body Snatchers. Not feeling quite yourself? In the first of a series of jaw-dropping recent research findings, Tucker reports, “Our children colonize our lungs, spleens, kidneys, thyroids, skin”—and brains. Far from being that familiar image of the one-way street, with mother’s blood, nutrients and even cells flowing into the fetus, the fetus also sends its own fetal cells into the mother. It’s “fetal microchimerism.” No wonder a burgeoning mom feels…she’s changed.
Tucker doesn’t dodge painful issues of maternal and paternal favoritism. “Some 80 percent of us allegedly … prefer one of our children to the others, and more than half of parents demonstrate so-called differential treatment toward various progeny.” The most striking predictor? “Moms appear to dote on their cutest kids.” Apparently “the components of infant attractiveness…are rigid and globally constant,” including big eyes, large forehead, small chin, and chubby cheeks. Tucker says this preference extends to nearly all baby mammals.
But dads apparently outperform moms on “child facial resemblance determination” – i.e., dads are more skilled at noticing whether a child looks like them. Indeed, one Senegal study found “kids grow up bigger and are better fed if they look and in fact smell more like their dads.” A different kind of favoritism…favoring the child which dad feels sure is his.
Jane Austen knew this. You remember that Mr. and Mrs. Bennet, the parents in Pride and Prejudice, have different favorites? Mrs. Bennet favors beautiful Jane; Mr. Bennet favors sensible Lizzy (Elizabeth). Mrs. Bennet scolds her husband: “Lizzy is not a bit better than the others; and I am sure she is not half so handsome as Jane, nor half so good-humoured as Lydia. But you are always giving her the preference.”
Humans share mothering tendencies across species. Will you recognize yourself if I mention “left-handed cradling bias”? In a “near-universal” mothering behavior, “Something like 80 percent of right-handed women and, remarkably, almost as many left-handed women hold their babies automatically on the left.” Check out many paintings of the Madonna, suggests Tucker. This “lefty” preference extends to other mammals. Why? It may allow the infant to “view the more expressive left side of the maternal face.”
Tucker points out it’s not all about genes. Life experience also affects maternal behavior. She describes studies of new monkey mothers showing that, of those roughly treated by their mothers, “more than half of the maltreated monkeys became abusive mothers. All the well-tended infants matured as competent mothers.” But when the scientists swapped some babies, so the abusive monkey moms took charge of the offspring of outstanding monkey moms, “the monkeys grew up to match the behaviors of their adoptive mothers, not their biological mothers.”
Here’s another potential genetic component. Canadian scientist Frances Champagne wondered why mother lab rats from the same genetic strain, living under identical conditions, engaged in different “licking/grooming” of their babies. When Champagne swapped the rat babies, so high-licking moms raised the babies of low-licking moms, the babies of below-average lickers followed in their adoptive mom’s footsteps. Then other scientists found they could program a baby rat’s future licking behavior by stroking it with a tiny paintbrush. “The physicality of getting licked somehow shaped the females’ instincts and behavior.” According to Champagne, “I wanted to show that the care you receive leads to epigenetic changes in infancy, and that this could replicate.” Epigenetics focuses on whether and how bits of genetic code may be “expressed.” Champagne found well-licked baby rats “were more likely to express their genes for certain estrogen receptors…” which made them more likely to express genes for oxytocin receptors and to grow more oxytocin neurons in their brains.
Fascinating research discusses how different bits of our genes “express” themselves, particularly in response to hormones. For instance, various sorts of stress can result in hormonal effects on gene expression: “Physiological changes that affect mRNA stability occur during development, nutritional stress, hypoxia, inflammation, cancer, and aging.”
The notion that our genes are static? Maybe not!
So…parental behavior factors include genes plus life experience with hormones kicking into action to affect gene expression.
Back to favoritism! Harry Potter? Reluctant adoptive parent Mrs. Dursley can’t abide her own sister’s son. The internet is full of books and studies on why parents have favorites and how favorites impact families, including impact on sibling rivalry.
Being a favorite can be dangerous, as Joseph learned. “Now Israel loved Joseph more than any other of his children…But when his brothers saw that their father loved him more than all his brothers, they hated him….” (Genesis 37.)
And I haven’t touched on what Tucker calls the “murderous tendencies of mothers,” citing Sarah Blaffer Hrdy’s theories on infanticide in Mother Nature.
Tucker’s final chapters look at the impact of our own stressful society on parents. “Social-support deficits and perinatal depression are intimately linked.” Tucker reports that compared to Dutch mothers, American mothers appeared comparatively quite miserable, with high levels of unhappiness and worry, because they don’t get enough support in their health care or workplace. To transform this problem “would involve taking on some of the most grinding and deadlocked political issues of our day: not only income inequality, but also health care, education, and other topics that have consistently stumped our government,” including racism (citing pregnant Black women’s higher blood pressure and elevated risks of prenatal diabetes, preterm delivery and death).
Tucker visited Erin Kinnally, a scientist at the UC Davis California National Primate Research Center. “Kinnally rattles off the factors that can shape primate moms…age, number of births, genetics, her own mother’s rearing history, the baby’s sex and other characteristics, access to food and shelter and sundry other environmental factors.” But the most potent force is “social chemistry.” The low-ranking macaque moms at the primate center “have weaker immune system and other distinct traits…the lowest ranking moms had four times the amount of stress hormones in their blood.” “Low-ranking [macaque] moms grasp that they have to be vigilant at all times. Fascinating studies have shown that these moms are much more likely to try to shush their infants’ cries when higher-ranked animals are around, for fear that the fussing will draw unwanted attention and attacks.”
Hormonal impact? Stress can mean a baby gets more cortisol in breast milk. In monkeys, “these high-cortisol babies grow unusually quickly, ‘prioritizing’ growth instead of social exploration…”
Tucker, like Bill Bryson in The Body, respects her readers enough to include a serious index. Hers is excellent: for her assertions in each chapter, she includes detailed links to the research studies involved.
We’re all from families; we’re all affected by our genes and our experiences, by how we were parented (and, indeed, how those who parented us were parented, and so on back up the long chain of humanity). Mom Genes confirms what writers already suspect: plots abound!
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Helen Currie Foster lives north of Dripping Springs, Texas, supervised by three burros. She writes the Alice MacDonald Greer Mystery series. Ghost Daughter, Book 7 of the series, was published June 15, 2021. Helen’s active with Austin Shakespeare and Sisters in Crime – Heart of Texas chapter. Find out more at www.helencurriefoster.com.
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