clock menu more-arrow no yes

Filed under:

The mom part of the brain

Every new mother, it seems, is many generations in the making

Illustration by Brian Cronin

When I experienced my first quickening — the goldfish flop of a daughter deep in my belly — I was about 16 weeks pregnant and on a trip with my mom and sister in rural Ireland, home of many of my mother’s ancestors.

We had just wandered the rocky ruins of a great-grandmother’s thatch-roofed seaside hut. I felt that first fetal tumble in my stomach afterward in a Galway pub, spooning up a bowl of piping-hot potato leek soup.

It’s a bit unnerving to think that what all those unnamed mothers did centuries ago — in a world of strained sunshine and wet gray stone — might have somehow trickled down to make the modern me. What lullabies did they sing between reviving the fire and boiling seaweed pudding for dinner? Could their actions help steer mine today, as I prance with my expensive stroller to grab falafel for lunch?

Every new mother, it seems, is many generations in the making. A female fetus already has her full complement of several million eggs when she’s in the womb, and thus I may have already gestated part of my own future granddaughters, just as my own maternal grandmother once carried part of me.

But the more I researched the science of motherhood, I came to learn that our collective story is still more mysterious, with intangible traits like maternal warmth also getting passed through bloodlines and across family trees — like a lit candle, or a whispered recipe, down from one woman to the next.


When I first started investigating the genetic influence on modern motherhood, I expected to be at once dazzled and depressed. That our genetic inheritance has power over us seems obvious: After all, maternal behavior is mediated by genes that have emerged and diverged over a million generations, with new variations constantly surfacing and getting spread or scrapped.

Part of me craved clear-cut answers about how this evolution shaped my own mothering, almost as if I were back at the sleepover parties of yore, quizzing the Magic Eight Ball. Even though there would be nothing I could do about the results, what mom doesn’t want to know who she is meant to be?

But to learn too much about the power of my own genes — whose blueprint is available from a simple cheek swab test — also seemed like a way to lose my already tenuous sense of maternal agency. If invisible genetic units with inscrutable names, like, say, OXTR rs53576, explain all the wide variety of maternal behavior, where does that leave our own individual efforts and dreams for our families? Could all of the hours spent reading how-to parenting books be revealed as wasted, our best efforts overwritten in advance by some twist of DNA?

A decade ago, science seemed ready to explain all kinds of human qualities and capabilities with a simple, “There’s a gene for that.” In 2008, geneticists claimed to have identified a faithfulness gene that supposedly predisposed men to be sexually loyal (or not). Others chased down the “wanderlust gene” that allegedly drove globetrotting impulses and human migration patterns. Perhaps most famous was the “warrior gene,” which allegedly triggered aggression and risk-taking.

Illustration by Brian Cronin

I assumed that a good mom gene — call it the I-Can-Tell-a-Mile-Off-That-You-Have-a-Fever-and-Also-Scrape-the-Last-Bits-of-Barf-Out-of-Your-Car-Seat-Crevices Gene — would be in this same vein. And scientists have indeed crafted dozens of studies seeking to isolate these telltale variants, which are often linked to how moms’ brains process neurochemicals like oxytocin, associated with childbirth and social bonding. They’ve sought them in barnyards, where livestock scientists apparently yearn to breed pig supermoms, and in our own living rooms, where researchers try to match sensitive human mothering behaviors with particular genetic variants parsed from our spit samples.

But in the course of writing my book about the maternal instinct — titled, yes, “Mom Genes” — I realized that a growing number of genetic researchers have moved past the idea of pinning a human behavior as complex as mothering on a few crucial strips of code. The more I talked to them, the more I discovered that the presence of any one subpar mom gene variant in the nuclei of my cells probably wasn’t going to scuttle my parenting.

“These genes may be involved,” says Andrew Smolen, a geneticist at University of Colorado Boulder’s lab, speaking about the gene candidates his own research has identified as plausible influencers for maternal impulses. “But it’s kind of hard to believe that a single gene is going to be responsible for such a complex behavior, even though it has consequences down the line. Our ability to look at specific genes involved in behavior is surprisingly not as robust as we once thought.”

“I see many things working together, interacting with so many other things,” says maternal behavior researcher Stephen Gammie of the University of Wisconsin-Madison. The transition into motherhood is not a one-note affair but a whole genetic symphony, “a score sheet with some things going up and others going down.”

Meanwhile, as the hope of swiftly pinpointing moms’ make-or-break genetic markers recedes, scientists are increasingly sure that at least some of the apparent heritability of mothering is actually a somewhat different biological phenomenon: not a genetic inheritance, but a chemical story inscribed atop the genes we carry — one that our personal choices help write.


The story itself is obvious to anyone who’s watched a family. In a sort of Russian nesting doll effect, moms and daughters especially (but also granddaughters and great-granddaughters) tend to repeat caregiving patterns, sometimes in obvious ways — like giving birth to their first babies at equivalent ages — but also in more subtle, textured mannerisms, like how they exude warmth or hostility toward their children.

The reality of these patterns hits me at random, eerie moments, like when I once realized that I was tightening my daughter’s ice skate laces with exactly my mom’s harried expression on my face, or looping the leather strap of my wristwatch through the handle of the pool bag just like how she used to. It happens especially when a kid is sick and I’m doling out earache medicine while speaking in her particular patient tone of voice, like a ventriloquist’s doll. I have such vivid flashbacks of my mom tenderly bathing seven-year-old me in a baking soda bath that sometimes I almost think it’s a shame that children don’t get chickenpox anymore.

Perhaps the weirdest epiphany came when my mother pointed out that I had decorated my first daughter’s nursery in primary colors, rich red and blue and yellow, instead of the default pastel pink. This scheme, she reminded me, was identical to the colors of my own childhood nursery — even though I have no conscious memory of that room.

In psychoanalytic circles, the notion of invisible third parties putting their oars into our parenting is literally called “ghosts in the nursery,” and your own mother is typically the most powerful spook. Figuring out just how and why we human mothers resemble our own moms is a very tall order indeed. And yet the fact remains that your feelings about your own mother are a major predictor of your relationship with your child. One team of scientists found that, in about 75% of cases, they could use a woman’s childhood-care recollections to forecast her relationship with her one-year-old.

Scientists have tried to understand repeating mothering patterns via longitudinal studies, arduous undertakings that follow families for 30 years or more, as subjects who started out as children under their own parents’ rule become parents themselves.

In the late 1980s, Rand Conger, now a University of California, Davis, professor emeritus, started studying Iowa farm families during a dire agricultural depression. He was initially interested in the crisis’ effect on the upbringings of several hundred seventh grade children, but ended up sticking around for a few extra decades until those seventh graders were moms and dads in their own right.

“We saw intergenerational continuities within the families,” he says. “Kids who were treated harshly by their own parents were more likely to become harsh parents.” Human lives are never foregone conclusions, but the recurring themes were hard to ignore.

Similar studies have since been carried out everywhere from England to Indonesia, in both highly educated populations and among the urban poor. In a New Zealand study, three-year-olds were followed until they had three-year-olds of their own. As adults, the original three-year-olds uncannily resembled their parents in their displays of warmth and sensitivity.

Obviously, some aspects of this repetitive mothering simply reflect shared mother-daughter genetics, even if the specific genes remain MIA. Presumably at least a few are the result of copycat behavior, a simple matter of learning and imitation.

But others are more mysterious, with nurture and nature intertwined.


Animal models offer evidence of this complexity. You can see that vervet monkeys, for instance, spend almost identical amounts of time with their babies as their mothers spent with them. And in rhesus monkeys, abusive mothering stretches back along matrilines for half a dozen generations or more.

In one watershed study from 2005, Dario Maestripieri, a scientist at Georgia’s Yerkes National Primate Research Center, recorded which infant female monkeys were abused — that is to say, dragged around, hit or stomped on by their moms. Then he watched as those baby girl monkeys grew up to slap around their own firstborns. Not surprisingly, more than half of the maltreated monkeys became abusive mothers. All the well-tended infants matured as competent mothers.

There was a catch, though. In the first phase of the experiment, Maestripieri had pulled a switcheroo. He’d swapped some of the day-old babies, so that the abusive monkey moms ended up taking charge of the offspring of outstanding monkey moms, and vice versa.

The monkeys grew up to match the behaviors of their adoptive mothers, not their biological mothers, from whom they’d inherited their genes. This suggests that the mothers’ abusive behavior is not passed down family bloodlines in any kind of straightforward genetic manner.

Similarly, in a McGill University lab in Canada some 15 years ago, Frances Champagne (whose fabulous name reminds us how parents can shape their children in ways that transcend genes) noticed that even though all the rat families she was studying were from the same genetic strain, living under identical laboratory conditions, the mothers behaved slightly differently, especially in how often they licked their babies (of which they had up to 20 at a time, poor things). The top 5% of moms licked and groomed their young with extra diligence, and the bottom 5% licked less than average.

“Why would these mothers behave differently?” Champagne asked herself. “Why would you get natural variation when there are no environmental cues that are changing?”

It turned out that the licking styles were passed down like the maternal habits of Maestripieri’s monkeys. When Champagne cross-fostered the rat pups, so that the high-licking moms raised the babies of low-licking moms, the babies of the below-average lickers grew up into prodigious tongue bathers — following in their adoptive moms’ footsteps, just as Maestripieri’s primates did.

Her collaborators even found they could tailor a baby rat’s maternal destiny by stroking it with a tiny paintbrush in lieu of its mom’s tongue, programming the future mom to be a diligent groomer.

But genetics may still play a role. Note that word: “programming.” Nobody imagines that the baby rats were consciously memorizing how to mother via practice and imitation, in the way that a human mother might learn how to change a diaper or pilot a stroller. Rather, the physicality of getting licked somehow shaped the infant females’ instincts and behavior beneath the skin, as if their maternal nature was some kind of drippy ice cream cone that could be contoured with the tongue.

“So then I focused on drilling down into what was behind that,” Champagne recalls. “I wanted to show that the care you receive leads to epigenetic changes in infancy, and that this could replicate.”

“Epigenetic” means “on top of the genes.” This newish field focuses on how and why and when certain bits of our (mostly) rigid genetic code get expressed or not. Every person has 37 trillion or so cells, far more cells than there are stars in the Milky Way. Each cell has the exact same DNA at its core. Yet some become liver cells, and others skin cells. And those that become a female’s brain cells will likewise function quite differently during her infancy versus after pregnancy.

The genes themselves are more or less set in stone in all of these cases. The changes are typically epigenetic ones, evoked by the female’s environment and life experiences, which somehow turn certain genes on and off. The experience of pregnancy, with its hormonal deluge, can kick off certain domino effects in the brain. But so might earlier and subtler experiences, like how the female was treated in her first days or weeks of life — in the rat’s case, via her experience of her own mother’s tongue. A process called “methylation,” for instance, silences particular genes by chemically coating them, so their recipes can’t be read.

In the less-licked rats, Champagne’s team discovered that certain DNA regions related to maternal chemistry seemed to shut down. With more of their stress-hormone receptor genes silenced, the underlicked rats were inefficient at processing stress in ways that seemed to make them less engaged, less lick-happy, when they became mothers in their turn.

The well-licked baby rats, meanwhile, were more likely to express their genes for certain estrogen receptors, which made them more sensitive to the key maternal hormone when they went on to have pups of their own. They were also more likely to express genes for oxytocin receptors, and to grow more oxytocin neurons in their brains. Which means, in turn, that when they had daughters of their own, the licking behavior was passed down — not through some be-all and end-all “licking gene,” and not through learned behavior, but through the complicated interaction between a soft rat tongue and the expression of her daughter’s genes.


Licking studies don’t apply directly to human mothers. Well, not usually, anyhow, although I can imagine how the “baby as lollipop” concept might tempt a particularly zealous back-to-nature mom group. But this would be, in the truest sense, a gross misinterpretation.

However, some promising parallel research suggests that touching or stroking human babies may be our equivalent of licking.

“Infants need to be touched,” explains Lane Strathearn of the University of Iowa. “If you don’t touch your teenagers, they will thank you for it. If you don’t touch your baby, that baby will die.” One striking study from the British Columbia Children’s Hospital asked parents to keep what’s been described as a “cuddle diary” of daily physical interactions with their newborns. DNA swabs taken years later, when the kids were four, showed that epigenetic differences arose between “high-contact” and “low-contact” kids, just as they did between the licked and unlicked rats.

These epigenetic changes may help explain not just patterns of observed maternal behavior through families, but some of the physical differences between our brains as well. One Baylor College-led study of 30 first-time mothers showed, via fMRI scans, that women who reported healthy childhood relationships with their own mothers had more powerful reactions in the reward-focused areas of their brains when shown pictures of their own kids. They also had more oxytocin in their systems when they frolicked with their seven-month-old infants.

Another study, from Yale University, showed that young mothers who had better childhood memories of their own moms had more gray matter in brain regions related to emotion processing, and had more pronounced responses to infant cries.

Women treated poorly by their own mothers, on the other hand, tend to pay less attention to baby faces even if they’ve gone on to have children of their own. They seem to be more upset by the sounds of babies’ cries. One British research group identified 18-month-old children who had insecure relationships with their mothers and then ran brain scans on the same kids more than 20 years later. Their adult brains looked different, with larger amygdalae — the part associated with fear and aggression.

Fascinatingly, the same types of findings seem to apply in foster families. Researchers wondered whether the best predictor of an infant’s relationship with a foster parent was the age at which the baby was taken into the family. Instead, it turns out to be the quality of the foster parent’s own childhood relationship with his or her own past caretakers. Even in the absence of blood relationships, family history repeats itself.


But for mothers, isn’t being ruled by our environments, particularly our barely remembered upbringings and our own parents’ inherited patterns, just as limiting as the tyranny of genes?

Not at all. Scientists increasingly see mothers as developing organisms, much like children are: Our brains are sponges for experiences, and we remain supersensitive to environmental cues. We continue to be shaped not just by our social pasts, but by the choices and surroundings we create here and now, and by the relationships we build for ourselves and for each other every day.

For instance, researchers who study patterns of intergenerational abuse have shown that the presence of a loving romantic partner in a new mother’s life can disrupt the vicious cycle, leading to healthier parenting behavior in the next generation. Moms who’ve selected a supportive partner tend to be more sensitive to their children’s cues and less stressed.

Close-knit support networks of family members and friends can also make a measurable difference in how our maternal brains and bodies function. Scientists are still discovering why exactly moms who feel “socially supported” thrive, but these women have lower rates of postpartum depression, maybe related to a modulated increase in a pregnancy chemical called placental corticotropin-releasing hormone. They also have fewer C-sections, more energy after birth and improved breastfeeding outcomes. They tend to deliver heftier babies who settle more easily into routines. Fascinatingly, emotionally supported women also seem to be slightly more likely to bear sons.

Meanwhile, isolated new mothers exposed to toxic social environments and other stressors often have opposite experiences, and are prone to depression and poor birth outcomes — which in turn only heighten their feelings of stress and loneliness. Studies in rats and monkeys show how chronic daily stress and isolation can alter the maternal brain’s typical development.

Scientists are figuring out how we might offer stronger emotional support to mothers who don’t have healthy networks of loved ones. Preliminary research involving before and after brain scans suggests that tools like talk therapy, which involve a close relationship with a therapist, can change mothers’ neural functioning. Governments are now experimenting with deploying low-cost baby nurses and other supportive presences that might act as a psychological balm for struggling moms and shore up their behavior in the long run.

And we mothers can also help ourselves. We can’t choose how we were raised, but we have more agency than rats or vervets when it comes time to mother in our own right. The simple desire to be a good parent might be enough to snap intergenerational chains. You can forge a new inheritance for your descendants — or for somebody else’s, because there are all kinds of ways for mothers to aid other mothers escaping a toxic cycle.

A homemade meal or a few kind words for a struggling pregnant stranger are more than niceties — they are a type of medicine. You can also make the decision to care for a baby who is not biologically your own, a deliberate form of love that can echo down generations. What our grandmothers and great-grandmothers did to shape us can be matched by what we do for our children and for each other — because every one of us has many mothers.

Abigail Tucker is The New York Times bestselling author of “The Lion in the Living Room.” This article is adapted from her latest book, “Mom Genes: Inside the New Science of Our Ancient Maternal Instinct,” from Simon and Schuster.

This story appears in the September issue of Deseret Magazine. Learn more about how to subscribe.