Quirks and Quarks

'Mom Genes' explores the radical biological transformations of motherhood

Science writer Abigail Tucker says becoming a mother is arguably the most profound developmental shift adult humans go through after adolescence

'No doubt a degree of nature in there, but nurture is probably more important than anybody ever thought'

A father and a mother look at their newborn son during in a hospital in Paris, on November 17, 2020. (Martin Bureau/AFP via Getty Images)
Becoming a mother is a life-changing event in ways that really only become clear to new mothers when they go through it. It's not just about the additional responsibilities of having to care for a helpless newborn. There is a fundamental biological shift that gets wired into the brains and bodies of new mothers.
(Simon & Schuster)

It's an incredible transformation that science writer — and mother of four — Abigail Tucker, writes about in her new book called, Mom Genes: Inside the New Science of Our Ancient Maternal Instinct.

Tucker spoke with Quirks & Quarks host Bob McDonald about the science around becoming a mother. Here is part of their conversation.

The interview has been edited for length and clarity. 

At what point during a pregnancy does this transformation begin for women? 

I think it starts pretty early and intensifies as time passes in mid-pregnancy. And then by late pregnancy, is when the scientists who study humans are really most interested in watching the way that the maternal brain begins to change, and especially in terms of its response to infant cues, things like infant smiles, sounds of babies crying, things like that. So that's this really intense period of plasticity that occurs as the mom begins to change. 

You mentioned in your book that if someone was to wake you up at three a.m. screaming and covered in poo, you might not be too happy about that. But if a baby does hit mom and like, oh, OK, I'll take care of you. No problem. 

Exactly. So it's this idea that the hormones of pregnancy, childbirth and lactation are teaching your body, but they're also changing your mind and sort of chemically incentivizing you to care about this thing that you never cared about before. 

A 29-day-old male southern white rhinoceros nurses from its mother A-ju at an enclosure at the Leofoo Village Zoo in Hsinchu, Taiwan. Rhinoceros mothers are among nature's most protective mothers. (Sam Yeh/AFP via Getty Images)

Mothers do things a whole lot of different ways, but what unites us underneath the behaviour and what unites orcas, kangaroos, wallabies and all kinds of mammals is this desire to care. And that's this kindling that happens through the chemical exposures of pregnancy and childbirth that scientists are still trying to kind of unpack in the lab. It can also happen in adoptive mothers through similar parallel processes that scientists are also studying. 

At what point when you were having your first child, did you think that feeling of being a mother kicked in for you? 

It was when I first saw my daughter, who after a very difficult emergency C-section delivery, she had to go to the [neonatal intensive care unit.] I think it was when I first really got a good look at her that I suddenly felt this almost panicked push to a new self like, 'Oh my gosh, here's this diapered entity lying here. I must make sure that nothing terrible ever befalls this tiny stranger.' 

Soon after a baby is born — within a few hours to days — a mother can identify her baby by simply touching the back of the baby's hand. (Loic Venance/AFP via Getty Images)

I think that that sensory explosion that comes with meeting your own baby is something that scientists are still trying to understand. I explored it by going to a sheep barn and watching as these pregnant sheep were having their babies and trying to understand the nature of the sensory change that they go through. 

For them, it's a sense of smell-thing. There's an explosion of growth in their olfactory bulbs and they can memorize the smell of their new babies almost instantly. That's because they're herd animals and they have to be able to sort themselves out more quickly. 

Mother sheep can pick out their newborn lambs by scent. (Zuzuna Gogova/Getty Images)

But even humans, with experiments in a crowded maternity ward scientists have found that moms know to wake up only for the sound of their own baby's cries. 

There's even a study that showed that you can tell who your own baby is just by touching the backs of their hands — and this is just within being a mother of just a few hours to days. 

Parents, biological or not, can raise more doting caregivers the more they nurture their young. (Julie Charpentrat/AFP via Getty Images)

Now, the title of your book is called Mom Genes. How much of what we're calling the mothering instinct comes down to biology compared to what we learn? 

So we haven't really come up with a smoking gun for whether they're a good mom gene or bad mom gene. Where they have made a lot more progress, though, is this idea that what may be important is not the specific grab bag of genes that you're born with, but how those genes are turned on or turned off by the environment. 

When we're talking about biological moms, for example, in rats, the amount of licking and nurturing she gets from her own mom may actually somehow change the expression of her genes, silencing some and turning others on. And that may account for some of the variability in maternal behaviour that's so fascinating to scientists. 

But what's also really interesting is that it doesn't have to be your biological mother. If your caregiver was an adoptive mother, the baby changes in relationship to the care that she receives from that adoptive mother or that single father. 

Marcus Semien (right) #10 of the Toronto Blue Jays chats to his father Damien and son Joshua before the game against the Oakland Athletics on May 03, 2021 in Oakland, California. Men also get exposed to hormones that help them transition to fatherhood, but only if they’re present and involved after their babies are born. (Lachlan Cunningham/Getty Images)

In that way, by adopting a child and loving that child, you're not only being a mother, you're shaping a mother and maybe even whole generations of mothers by the way that you're loving that one kid, which I thought was so wonderful. 

You can listen to the interview with Abigail Tucker by clicking the link above.

Produced and written by Sonya Buyting