How motherhood changes us

A new book explores the science of the elusive maternal instinct, and the ways having children transforms the brain.

Welcome to Is My Kid the Asshole?, a newsletter from science and parenting journalist Melinda Wenner Moyer, which you can read more about here. If you like it, please subscribe and/or share this post with someone else who would too.

Hello everyone! We were in Washington state last week, visiting grandparents, cousins, aunts and uncles. It was wonderful to see (and hug!!) them after so terribly long, and we miss them already. Now we’re back home in New York, trying to get un-jet-lagged and waiting rather anxiously for school to start up on Thursday. For those of you wondering about plane travel right now: Our flights were uneventful, and everyone was pretty good about wearing masks the entire time, including in the airport. (Our son wore these medical masks, and our daughter wore these LL95s — we gave them several options for comfort.)

Today, I’m excited to be running a Q&A with science journalist Abigail Tucker, author of the wonderful book Mom Genes: Inside the New Science of Our Ancient Maternal Instinct, which came out in April. It’s a fascinating exploration of the science of motherhood and what happens to our brains and bodies when we have children.

But before I delve into the Q&A, though, a quick request: Would you be willing to fill out this short, anonymous survey? I’d like to know a bit more about you and what you like most about my newsletter. I would also love your thoughts on what type of content you might like me to add. Thank you! OK, onto my conversation with Tucker.

What inspired you to write Mom Genes?

In the months and years after birth, moms often struggle with these feelings that we have never quite snapped back to normal. Physically, our new selves are very much on display, which is why people tend to focus on pregnancy pounds and “mom bods” and stuff like that. But mom brains are even more interesting, and certainly more central to the story of our species. These more mysterious and hidden interior alternations were at the heart of more private conversations that I had with close friends in the early years of motherhood, as we questioned who we had become, and where we hoped to go next in life. And it’s not just a hunch: there’s a growing amount of hard evidence, like the spike in women’s mental health disorders around the time of first birth, suggesting that the maternal mind is very much in flux, with sweeping implications for both personal happiness and public health.

So I started visiting labs where scientists study the maternal transformation in research animals like rats and mice, and also in human beings. I was pregnant with my fourth child by the time I started reporting, so I had the chance to participate in some human experiments myself, where scientists spied on my brain as I did things like look at baby pictures, or listen to meditation tapes. Gradually it became clear to me that the brain is the most important organ of childbirth, even though it may not be the first body part that comes to mind when you waddle through those labor and delivery ward doors.

One thing that I found fascinating from your book is that, for people and many animals, the transition to motherhood is quite profound — the changes that happen in a short amount of time are extraordinary. Can you talk a bit about how moms change, and what these changes tell us about motherhood?

The most obvious changes are behavioral, especially when you boil them down in a simpler sort of maternal critter, like a lab rat. Before rats become mothers, they despise squeaky, stinky rat babies. They will hilariously run away from them and even (somewhat less hilariously) attack and eat them. What these virgin female rats like is food: they are especially partial to Charleston chew bars and other super-sweet candies.

But then in the day or so before they give birth for the first time, these female rats do a 180. They start choosing pups over snacks, and will hit a bar hundreds of times to get more and more pups delivered into their cages.

Scientists are getting closer to understanding what’s behind moms’ abrupt and striking shift in motive.

Some of it is anatomical change. Using before and after brains scans, scientists can see how the volume of women’ brains shifts over the course of pregnancy, and how these alterations seem to be permanent. This degree of physical metamorphosis  means that motherhood is like a stage of adult development — a phase of radical growth and plasticity akin to adolescence.

Compared to non-parents, mothers also draw on unique brain anatomy to process infant cues and other signals, and are overall more sensitive to those signals.

I guess it should be no surprise that since your mom brain looks and acts different, so do you — maybe you’re not pushing a bar to send more and more babies down your chute, but suddenly you find the smell of diapers to be not so disgusting, for instance.

Can you talk about the differences between dads and moms in terms of their behavior towards and responses to their children?

Men, like all humans, have a kind of maternal seed inside their brains that, with enough exposure to babies, can flourish. In particular, studies of two-dad households suggest that when men are the primary caregivers, their brains come to react more like moms’ brains, and that very dedicated dads can go toe-to-toe with moms when interpreting infant cues. Dads also experience measurable physical changes, like drops in testosterone.

But overall the brain changes are more dramatic and much more consistent in mothers, who get a chemical jumpstart of gestational hormones as well as a ten months-long advance preview of their child. For instance, there’s a fascinating lab at Johns Hopkins that studies how particular fetuses may be shaping and conditioning their mothers from within, via all those karate chops and somersaults that we only feel.

Some other avenues of influence are unique to moms. For instance, I visited a New York lab to learn about microchimerism — when fetal cells cross over the placenta to permanently embed in their mothers’ bodies, including in their brain tissue. Lactation also appears to change the brain, linked to growth in certain neural zones, at least in rat moms.

You write about how moms are generally calmer in the face of adversity and tragedy than non-moms are, but that they are also more aggressive when in danger. These two reactions almost sound contradictory. Can you unpack these observations a bit and explain why moms might respond in these ways, from an evolutionary standpoint?

Speaking of how lactation alters the brain: it catalyzes one of mothers’ trademark behaviors, maternal aggression (also called lactational aggression.) New mothers have dampened stress systems which allow them to stay calm and focused on their babies, perhaps to facilitate nursing. Some scientists think that this normal and adaptive dampening is the root of pathologies like postpartum depression. Late-term pregnant women and very new moms are thus less stressed out by events like earthquakes and other natural disasters. In the lab they exude lower levels of stress hormones if you put them on a treadmill and they are not as freaked out by things like pictures of scary dogs.

But it’s not just moms are unafraid to face threats — they are also good at detecting them. Chill human moms are unusually good at noticing potentially dangerous elements like the faces of strange men. These two factors — dampened stress plus environmental hyper-awareness — yield those famously aggressive maternal moves, like when mom walruses charge Russian naval vessels, and mom squirrels take on rattlesnakes many times their length. These attack moms are hormonally emboldened and buffered from the stress, which makes them ready to rumble.

As good as they are in a crisis, though, moms are actually also unusually vulnerable to other types of threats. It the nature of the stress switches from acute — an out-of-the-blue earthquake, a hissing rattlesnake — to chronic, then moms are not so insulated. Subject to enough stress over prolonged periods, moms’ brains may not develop in the expected ways. For example, in experiments in which mother rats were separated from their pups and placed in clear plastic tubes on a regular basis — a harmless but highly stressful event for them — their maternal brains did not grow in the usual patterns. Perhaps this is why when conditions sour in the wild and mothers are exposed to chronic stresses like hunger, mothers frequently abandon the litters they otherwise would have died to defend.

For humans, chronic stresses like war and poverty and childhood abuse can have powerful effects on mothers. We’ll rise to any occasion, but moms don’t do as well when those unpleasant occasions become the stuff of daily life.

You explain that a mother's age shapes her maternal capabilities — older moms are in some ways "better" than younger moms. How and why does age benefit moms?

Well: first, a caveat. I got pregnant for the first time at 29 and I was 39 this last time, but I haven’t noticed any kind of personal renaissance in my parenting, alas!

Yet maternal age really is one of the better-studied predictors of maternal competency. It’s not so much that a 34 year old trumps a 29 year old, but rather that adolescent mothers and perhaps mothers in their early 20s may be at risk for certain behaviors, like neglect and infanticide, and are more prone to mental health problems. I was a bit surprised by this because I had always assumed that “in olden times” human females had born kids at very young ages — but that may not be as true as I thought, since it’s the calorie-rich conditions of modernity that may be pushing back the age of menarche and leading to more teen moms. I also assumed that age at first birth would be almost impossible to disentangle from factors like wealth and class — but apparently when researchers study populations where mothers are all from equivalent social and economic backgrounds, the older moms are still on average more sensitive to their babies’ cues, and less likely to spank, etc. Young is not necessarily a euphemism for poor.

Two explanations stuck out for me. One relates to this idea of motherhood as a stage of adult development. If you are an adolescent mother and your brain is still growing and changing as teenagers’ do, then maybe there are consequences for layering the mental upheaval of motherhood on top. This is an especially interesting ideas now that we know that adolescence lasts into a woman’s mid-20s.

One other explanation for why old moms bring their A-game is this idea from evolutionary biology, that with each year that passes we “senescent” mothers, as scientists sometimes call us oldsters, have fewer chances left to have more babies and to spread our genes. Thus it behooves us to invest more in these late babies that we have in our arms today. Younger moms, on the other hand, might play their cards with future reproductive prospects in view and use different strategies to invest their bodily and mental resources, spreading themselves more theory. This is just a theory that scientists debate when they study various populations of decrepit mammalian mothers. In part, I think I just get a kick out of the name: “the terminal investment hypothesis.” Whenever I spoil my one-year-old, a voice in the back of my head says: stop terminally investing!  

What is one big takeaway that you hope parents reading your book will have?

At the start of my research I was intrigued by these studies of what I nicknamed “mom genes” — simple snippets of genetic code that typically have to do with how our brains process the chemicals of pregnancy, childbirth and lactation. The scientists were testing to see whether women born with certain versions of these moms genes were likely to display more desirable maternal behaviors. This idea isn’t actually as crazy as it seems. For decades livestock scientists have been attempting to breed animal supermoms, for instance, because aspects of maternal behavior do seem to run in families, and “super sows” who don’t say, roll over and crush their piglets, could be barnyard money-makers. To tell you the truth, I was dreading getting the DNA test to show which of these  oxytocin and dopamine-oriented genetic variants I had been blessed or cursed with.

But the more I spoke with scientists, the more I learned that the genetic side of motherhood is too complex to be pinned down to a simple set of “good mom” / ”bad mom” genes. Obviously our genetic inheritance matters, but so do many, many other things: Human moms are born of our environments, shaped by everything from our culture, to how we were nurtured as children (by our biological moms or any other caregiver), to our financial resources and our social relationships today, to the amount of plastic and other toxins in our bodies, to whether we gave birth to a boy or a girl.

And we’re born from our own choices, too — because as humans, we have the ability to build a better environment for mothers who are themselves in a sense being born again. We tend to think of mothers as being all-powerful and somewhat monolithic, the hands that rock the cradle. But mothers’ worlds are also rocked by many forces, and it behooves us a culture to understand and harness these. I think we’ve seen this a little bit during the pandemic. Moms ourselves were surprised by how vulnerable we were to this years’ long period of stress and isolation and financial hardship. That’s because mammalian mothers are designed to read and respond to our environment, and the environment of the last year and a half hasn’t been a great one. These women need extra social and financial support from the government, and also from each of us as individuals.

The mental changes of motherhood are real and measurable. But that doesn’t mean that we can sit back and count on the “maternal instinct” to carry moms through, come what may. Mothers are both more magnificent and more fragile than I ever imagined.  

Thanks again for reading my newsletter, and if you didn’t do it already, please fill out my short survey!

Also, some book news: Katie Couric just recommended HOW TO RAISE KIDS WHO AREN’T ASSHOLES in her newsletter this morning, in part because the inimitable Zibby Owens recommended it as one of the 11 books every parent should read this fall. Also, on Monday, September 13th at 8pm Eastern, I’ll be doing a virtual event hosted by the Strand Bookstore with Zibby and Christina Hillsberg, the author of the excellent new book License to Parent. Register now so you don’t miss it!