I'm William Brangham, and this is "Horizons".

While most scientific research has focused on men, when it comes to parenthood, it's all about mothers.

But new research shows that fathers undergo profound changes as well in their hormones, behavior, and even their brains.

The surprising science of dad brain, coming up next.

♪ Narrator: Support for "Horizons" has been provided by Steve and Marilyn Kerman, and the Gordon and Betty Moore Foundation.

Additional support is provided by Friends of the News Hour.

♪ This program was made possible by contributions to your PBS station from viewers like you.

Thank you.

From the David M. Rubenstein Studio at WETA in Washington, here is William Brangham.

Welcome to "Horizons."

This weekend is when we celebrate Father's Day, and so we thought it would be a good time to take a look at what happens to men biologically and psychologically when we become fathers.

We're not talking about the act of conception here.

No, this is about the ways that men change when we enter the decades-long process of parenthood.

As some of the most recent research is demonstrating, including work done by our guest today, it is different for men than it is for women.

Darby Saxbe is a clinical psychologist and professor at the University of Southern California.

Her new book, her first, documents this emerging research.

It's called "Dad Brain, the New Science of Fatherhood "and How it Shapes Men's Lives."

Darby Saxbe, so nice to have you here.

Thank you for having me.

On one level, this seems a little bit odd to ask, because so much of scientific research has been male-focused over the decades, and this is a huge problem, but not when it comes to parenting.

That's mostly been about mothers and pregnancy and women.

Why so little research on men?

Yeah, it's an interesting question, right?

Because if you look at biomedical research writ large, men have dominated our understanding of the body and how it works.

Even our animal models tend to be male, and yet when it comes to parenting research, both in terms of science and in terms of culture, like if you go see the parenting books at the bookstore, it's a conversation that's all about and for women.

I think that's because we still really see mothers as the key parents and fathers frequently are treated as an extra appendage.

Brangham: Passenger over there.

Exactly.

And that makes sense.

The research should probably start with mothers because so much happens with pregnancy, which really transforms the whole body biologically with birth and with breastfeeding.

But there's so much more to learn about fathers, and some of that work is just starting to emerge.

Brangham: What do you think is lost when we don't have that understanding?

Saxbe: Yeah, then I think we don't know how to deploy fathers as full parents.

And we let mothers shoulder most of the work of caregiving, which I actually think and argue in the book runs counter to how we evolved, which is as alloparents who share care.

Alloparents, explain that term for people who don't know.

Yeah, so alloparent just means a caregiver who's not the biological mother.

And we really did evolve as humans to raise children in community and to share care cooperatively.

So another term for alloparents is cooperative breeders.

That's all the people that surround a child in a community or hunter-gathering community or suburban America.

Exactly.

So it's the grandparents, the extended family, aunts and uncles, community members, even paid helpers, frequently fathers.

And I think that the fact that we evolved this way reflects that raising a human infant is too much work for any one caregiver.

And so if you have a creature who needs round-the-clock care, you really want multiple caregivers on the scene.

And so that's one reason that when fathers are in the picture, we see much better outcomes for children and for mothers.

Brangham: Right.

You started this book writing, this is the first sentence, quote, "When I was 9 years old, "I watched my father "become a different parent in real time."

Can you just succinctly tell us that story?

Yeah.

So my parents got divorced when I was 9, and my mom moved out.

My parents ultimately negotiated joint custody, so we would do one week at my mom's house, one week at my dad's house.

But initially, my dad got sole custody.

And he was a kind of typical 1980s checked out caregiver.

And suddenly he's alone in the house with four feral children.

And he just had to kind of figure it out.

He had to do all the driving, he had to do all the cooking, all the laundry, all the meals.

So he ultimately, I think, rose to the occasion.

You know, there was a learning curve, but became a really stable and positive figure in my life.

And the book was kind of inspired by watching him go through that change and thinking about how transformative fatherhood can be for a man.

I mean, as you mentioned before, we as a society, even non-scientists, know how much a woman changes during pregnancy.

It's been researched.

We can see it with our own eyes.

We've lived it with our own wives.

But there is, as your book really does detail, a growing body of research about the way men change during this process.

Tick through some of those things that happen.

Yeah, definitely.

So, in my lab, we have looked specifically at the brain.

And we've also looked at the body's hormones.

So our longitudinal study scanned dads when their partners were pregnant with their first child.

So they were in mid-pregnancy.

And then we scanned them again at about six to 12 months postpartum.

And what we found was that the brain lost gray matter volume.

So it was shrinking, which when you say the parenting brain is shrinking, people usually get very worried.

That's actually seems to be an adaptive remodeling that makes the brain more streamlined so that it can work more efficiently.

And the patterns of volume loss look very similar to those that have been seen in new moms.

So dads are showing that kind of similar process of developing what we think are more efficient networks in parts of the brain that help mentalizing, thinking about other people's minds, social cognition.

Brangham: Interesting.

So, there's a little bit of closing, sort of, I don't know if this is too crude a term, but sort of scraping away some of the chaff so that you can focus on the task at hand.

Yeah, exactly.

So you also see the brain loses volume in early childhood as kids get ready for school.

And it loses volume in adolescence.

And so you have this kind of learning and consolidation that's happening.

And the brain is developing pathways that it can move along more quickly as it's starting to canalize that information.

And how about the hormonal changes?

Yeah.

So we see often dips in testosterone in new dads.

And that's not just from my lab.

There's a large body of work both in animal and in human fathers.

Frequently, testosterone decreases starting in pregnancy, rebounds after the first year or so postpartum.

And you see changes in hormones like prolactin, which we think of as a lactation hormone.

It's got... promotes lactation embedded in the word.

But we see that when prolactin levels are higher, dads are often more hands-on with children.

And we see also responsivity to child stimuli reflected in oxytocin, which is a hormone that we think of in terms of social affiliation.

Right.

Back to the point about testosterone, why would men see a drop in testosterone?

Because, I mean, as you know and you document, there's a whole cottage industry out there trying to convince men that having low testosterone is a sign of a failed male.

Yes.

There's a whole T-influencer industry.

And yet we find that there is this organic normative drop in testosterone around the transition to fatherhood.

And if you think about it, you really want high testosterone when you're trying to optimize your mating outcomes.

You want to reproduce as often as possible.

You want to sow your seed as widely as you can so that you can maximize the quantity of potential offspring that you can produce.

So that stereotypical testosterone, strong, aggressive, go out and get some mates, defeat my rivals.

Competition, status-seeking.

You want to rise in the hierarchy.

But after you have accomplished your task, mating is complete.

Now maybe you want to shift your reproductive strategy.

You want to invest in the children that you've produced.

So you might be moving towards a quantity-oriented, away from a quantity-oriented and towards a quality-oriented strategy.

You actually want to make sure that your offspring will survive and thrive.

And in really risky, unstable environments, you want to just focus on quantity exclusively.

The more children I produce, the more likely that some might reach adulthood.

But in more stable environments, like those that you see in much of the contemporary world, you actually just want to focus on parenting.

Because you want to make sure that if you're just having a couple of kids, you can devote your resources to them.

And in that context, you don't need to be out looking for brand new mates.

You want to be actually parenting the offspring that you have.

And testosterone doesn't help you accomplish that goal.

That's so interesting.

And it seems to happen organically.

Is it seeing your partner pregnant?

Is it the arrival of the child?

Is it you bonding with that child that corresponds with that dip?

Yeah, I think part of it is entrainment with your pregnant partner.

And so my lab has actually found testosterone levels are linked in men and women during pregnancy.

So cohabitating couples show correlated levels of testosterone.

But it might also have to do with infant exposure and with parenting experience.

And we do see testosterone drops in birds.

Testosterone spikes at the start of a breeding season.

It drops after mating's been accomplished and birds are provisioning their chicks.

So this isn't unique to humans.

It's something that seems to happen in a lot of different examples of bi-parental animals.

Brangham: That's so interesting.

One of the other things that I was really struck by in your book is that there's good research that men experience what we call postpartum depression, but depression after the arrival of their child in a way that we just don't think of.

We think of postpartum depression affecting almost always moms.

Yeah, that's exactly right.

And in fact, there's evidence that new dads report depressive symptoms at about twice the rate of the general population.

So, you know, there is this enhanced risk and prevalence in new dads.

And if you think about all of the factors that have been identified as causes of depression, you've got a perfect storm in early parenthood, right?

You have sleep deprivation, you have relationship conflict, identity challenges, changes to your social role, all of the things that might have you questioning, "Am I going to be able to do this?"

"Am I going to be good enough as a dad?"

A lot of men have postpartum or perinatal anxiety, so they worry about being a good caregiver, they worry about making money.

And so a lot of the same risk factors that women have in early parenthood, obviously men aren't delivering the infant, but they are sharing in many of those risk factors in addition to the neurobiological change.

And all of this is happening, as you so beautifully detail, when we're going through this cultural shift as to what fathers, I mean, you look at my father's generation versus my generation and how we parented seem like wildly different activities.

Yeah, that's exactly right.

So the Time Diary data really tells the story, that contemporary dads... Brangham: Time Diary.

So if you look at how are people actually spending their time at home, and they're writing that information down and telling researchers.

And we have a few really big studies, like the American Time Use Study, the ATUS data, which is kind of a gold standard, spanning many decades.

And if you look at the data that those researchers have collected from the 1960s to the present, you see that dads are actually tripling the amount of time, almost quadrupling in some studies the amount of time that they're devoting to hands-on daily childcare.

Brangham: In one generation?

Saxbe: In just a couple generations.

So from the men of the baby boomer generation to the millennials and the Gen Z dads, you basically have this revolution in hands-on fatherhood.

Brangham: Wow.

- Yeah.

So my dad was at the tip of the spear.

Brangham: [Laughs] Right.

Near the end of the book, you also detail how even much later in life, men who had children, there's a, I think it's a series of brain scan studies that show that the younger looking brains for the father, for the men who had children versus those who didn't.

Yeah.

So my pitch is that parenthood is like Botox for you.

So, you know, the book has some bad news, which is, you know, you're losing brain volume, you're dropping testosterone.

So I really wanted to end with some good news.

Brangham: Right.

That's good.

Yes, I think that's a cheerful note to end the book on.

But there is this really exciting body of research that's coming out from these big population level cohort imaging studies.

So the UK Biobank is a really big repository, tens of thousands of MRI scans from mostly midlife and older adults, people in their fifties and sixties.

And they found that the number of kids that both moms and dads had, the younger their brain looked, if you adjusted for, you know, how, how old would we estimate this brain to be using an AI algorithm?, and then we compare it to their actual chronological age, people are getting this kind of youth boost through having had more kids.

And it's, it's not a totally linear relationship.

So more kids means younger looking brain up to about two or three children, at which point it levels off.

So dads with six kids don't necessarily look all that different from dads with two kids, but it suggests that there really is some benefit to having had children.

And because it appears in both fathers as well as mothers, it doesn't just reflect pregnancy, birth and breastfeeding, right?

It's obviously connected to parenting experience and social integration.

And it also, I mean, all of this research seems to indicate that men are, you know, in a very profound way, biologically primed to be fathers, that it cuts against this idea, the fifties stereotype of the distant father, that this is, that we are biologically as invested.

Again, we're not birthing the child or breastfeeding the child, but our bodies are saying, this is something that's core to you.

Yeah, exactly.

And I really think our superpower as humans is our flexibility and our adaptability.

And so men come equipped with readiness to parent and to be sensitive and attuned caregivers.

They may not choose to exercise that ability, right?

So you do have fathers that are absent from parenthood.

But when men do acquire parenting practice, their brains and their bodies reflect that investment.

So it's like, if you think about, we all sort of have a dial inside us that can turn on the parenting brain.

Moms might give birth with their dial already turned up pretty high.

Dads have more volition, more ability, depending on culture and societal context, to turn that dial up or down.

But they can certainly turn it just as high as anyone who chooses to be a primary caregiver.

And yet there are, as you also detail, so many cultural impediments, the way we've organized our society, single family homes, living far away from our parents, two parents working, a car-centric culture, this masculine ideal that caregiving is feminine.

All of those things seem to fight against this.

Yes.

I think we've made it very difficult for people to parent without a lot of stress and investment.

We don't have those intergenerational networks of people that are ready to help us out.

And we've built neighborhoods that can feel very isolating.

And we don't have the kind of free-range childhoods that, even as a kid growing up in the 80s, I could roam around my neighborhood on my own until it was time to come home for dinner.

And I think one interesting irony of that is it actually puts more pressure on dads.

Because when you don't have the alloparental network that's very vast, you end up putting all the parenting on the nuclear family.

And so it's frequently shared by mom and dad.

Dads might be spending more time today than ever before because you don't have the grandparents, aunts and uncles and peers who are helping with raising kids.

Do you think... Your book is part of this movement.

Do you think this culture really is changing?

I mean, I just remember a story when my children were young in elementary school.

My wife was away.

I took them out to dinner at a pizza place.

We ran into some acquaintances.

And the mom made a bit of a fuss that dad was out with his three kids wrangling them at a restaurant, like it was a big deal.

My wife had done that a million times and no one would have said a word about it.

And yet, even in my own generation, it was still like, "Whoa, look at dad.

"He can take kids out to dinner."

Yeah, I talked to a dad for the book who said whenever he's out and about with his kids, people ask him if he needs help or they compliment him.

"You're doing such a good job."

When his wife is out and about, people are rolling their eyes if the kids are fussy.

So I think we still see fathers as champions to celebrate that they're involved at all.

But it's becoming more and more normative.

And I think if you look at countries where paternity leaves are more generous, you see a culture around fatherhood where men are expected to be very involved and present in their early months.

If you had control of policy, work policy, federal, state policy, your book details a lot of them.

What would you do to help encourage this evolution that you're celebrating in this book?

Yeah, I love that question because I would love to be in control of all of the policy, federal and state level.

But I think to me, the place to start is just through paternity leave, which we still don't have universally available.

We have FMLA, which is the Family Medical Leave Act, which is unpaid leave.

But many dads aren't eligible for it.

It excludes a lot of gig and shift workers.

So universal paid leave for both moms and dads, I think, is a great place to start and build policy.

And then I would layer on top of that, I like some of the programs you see, I wrote about in Norway, in Canada, in other countries, where there are nudge or incentive programs that are designed to earmark a certain amount of shared parental leave just for dad.

So if dad doesn't take it, the benefit goes away for the couple.

And so that sort of gives dad an extra reason to take leave.

And I think it reduces some stigma at work because even in the U.S., dads who have access to paid leave often don't take it.

Brangham: I know, I was struck by that detail that it's available... for those who it is available to.

A lot of them are just leaving it on the floor.

Yeah, exactly.

And I think, you know, understandably, they fear that they're going to have some negative consequences at work.

People might say, you know, "Oh, you're not the worker, "that you don't have the dedication "that we expected from you."

Brangham: Right.

"You just want to play with your kids instead."

But when it is normalized that all dads have this special chunk of leave that is just for them, then I think there ends up being a little more cultural, social pressure.

And dads feel more empowered to take that leave and I think can also connect with dads that are on the same leave.

And so you end up creating a little more community.

Brangham: And changing culture in a little way.

Exactly.

It helps to, you know, nudge dad's individual behavior, which also can change the culture.

In the last minute we have, what would you like people to take away from this research overall?

Yeah, I think one of the taglines for the book is great fathers are made, not born, which is to say we often assume we're just innately wired to parent and we're going to know what to do the second a baby shows up.

And we often assume especially that mothers will just have this instinct that is going to take over.

And I can say as a mom myself, I was totally clueless about what to do when my kids were born.

And my husband was equally clueless.

And so it's really through putting in the time and getting the practice that I think you become a skilled caregiver.

And I want fathers to feel like that role of sensitive and skilled parent is available for them too.

Darby Saxbe, the book is called "Dad Brain, "the New Science of Fatherhood and How it Shapes Men's Lives."

Really tremendous piece of work.

Thank you so much for being here.

Thanks for having me.

Before we go, we have been talking about how being an involved father can change men often for the better and how important that also is for children and moms and everyone else.

And there are lots of examples in the animal kingdom of other active fathers.

As Darby Saxbe details in her book, lots of frogs and fish and birds are extremely dedicated dads.

The vast majority of bird species, over 80 percent, have fathers who help construct nests or gather food or look after eggs.

Emperor penguins are some true stay-at-home dads, with males holding onto the eggs the females have laid, carefully guarding them for weeks while the moms are out hunting for food.

Seahorses are the only species on Earth where the male gets eggs from the female, puts them in a pouch on his stomach, fertilizes them, and carts them around until birth.

But amongst us mammals, there just are not that many examples of active fathers.

Male mammals care for their young in only about 5 to 10 percent of mammal species.

A lot of them are primates.

Male mountain gorillas not only lead and defend their family groups, they help teach their babies to socialize and help when they're weaning.

Some of the most involved dads among our primate relatives are the tiniest.

Pygmy marmoset papas help care for big families.

Mothers usually give birth to twins.

And the fathers are involved in many aspects of child rearing.

In her book, Darby Saxbe celebrates that humans are somewhat rare among mammals for having active fathers.

She documents how fatherhood is both innate and learned.

And she imagines how we could encourage this societal transition that fatherhood is undergoing.

She writes, "As long as care is solely feminized, "we will struggle to legitimize it "as the important work that it is.

"What if we valued men's contributions "to child rearing as a critical part "of the caregiving picture "and envisioned happy families as a public good "that enriches men's lives too?"

That's it for this episode of "Horizons."

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We'll see you next week.

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Additional support is provided by Friends of the News Hour.

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