Testosterone Expert: The Truth About DAD BOD & Why Women Find Fathers More Attractive!

You've discovered something about the brain that I think is quite surprising.

We found that in fathers the brain actually shrinks—I'll explain why. There are also studies finding that both men and women who report having more children show markers of a younger-looking brain age. And typically, men undergoing this show about a 25% drop in testosterone.

Studies of single women have found that when shown a series of body types, the "dad bod" is the most popular.

So if I go out and get a dad bod, you're telling me the science says I'll be more attractive?

Yeah, go for it.

"See what my fiancé says." The other thing worth talking about is—have you done any studies on that?

"Yes. That is one of the most robust findings in parenthood research, and my lab found actually that—"

"Wow. So, I've always been really interested in families, and becoming a parent is one of the biggest transformations you can experience, but I'm concerned about the declining birth rate. I think we've managed to market it as an undesirable choice."

"According to the CDC and Pew Research data, the US total fertility rate just hit an all-time recorded low."

"Yeah. The transition to parenthood can be really challenging. You are sacrificing yourself, it can be very isolating, you're losing your sleep. But in becoming a parent, you benefit from this sense of connection and purpose. You will rediscover your priorities in a way that will ultimately bring a lot of value."

"So if all goes well, next year I will be a dad, and I'd like you to give me some advice on becoming a father based on all the research you have."

"Great fathers are made, not born. There's a lot you can do."

"I'm going to write it down."

"Love it. So first—"

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Dr. Darby Saxby, you've discovered something about the brain that I think is quite surprising to a lot of men and women as it relates to what happens to a man's brain when they become a father. I have the report here in front of me, but I have a model brain over there. Could you explain what exactly it is that you discovered?

Yes. We found that in fathers—and this is similar to what's been observed in mothers—the brain is actually losing gray matter volume. So it is shrinking. If I had stronger hands, I could probably squish this brain and make it look tinier.

But the parts of the brain that are shrinking the most are in what we call the mentalizing network. That's a part of the brain that helps us understand other people's feelings and intentions. Those areas are concentrated around the midline of the cortex, which is what we're seeing here. You also see volume reduction in the visual areas at the back of the brain, which is really important for understanding, when you look at an infant's face, what kinds of emotions it's trying to tell you. So we see changes to those parts of the brain in new dads. In moms, we see changes to these same parts of the brain, but also changes in what's called the subcortex—the part of the brain that controls our gut feelings and our sense of reward, and is strongly linked with our hormones. So moms are changing all across the brain, while dads are mostly changing in the top layer, the cortex, which controls our higher-order thinking, reasoning, and executive functioning.

That tells us something about fatherhood: fathers choose to engage in parenting. It's a sort of cognitively mediated investment that dads are making.

What does that mean?

If you think about a mom who's been through nine months of pregnancy, she is flooded with hormones when her baby is born and she has a really high investment in the baby's survival. Just thinking about the number of calories it takes to sustain a pregnancy—it's thousands. So there's a very high floor for maternal investment, and moms undergo plasticity all across the brain that reflects that.

In dads, there's a tremendous amount of cross-cultural variability. There are cultures in which dads participate in child care and are very hands-on with babies from the moment of birth. There are cultures in which there are prohibitions against men picking babies up.

You don't pick babies up in the first year, in some cultures.

You don't pick babies up because it's considered unmanly. So there's a tremendous amount of variability, and dads calibrate their investment according to what the culture says and what the context looks like. If mom becomes unavailable, dad is often needed to step in and provide more of the care. This top layer of brain changes reflects that: dads are modulating their investment depending on what they're learning from the environment.

The word biologists use for this is "facultative." A facultative adaptation is an adaptation that is optional but extremely useful. Think about an animal that walks on four legs suddenly having something really important to grab and switching to walk on two legs so it can use its hands. Hands are really useful for that animal. Fathers are really useful for humanity.

But are you saying they're optional?

They vary depending on the situation. I don't want to say that fathers aren't important—they're incredibly important. There are dads who are primary caregivers and even sole caregivers of children. But dads vary, and they vary depending on what is needed for children to thrive in their specific local context.

A woman's brain shrinks as well, but it shrinks a little bit more — the changes cover more of the brain and show a larger across-the-board volume reduction. I should explain what volume reduction means. We often think of it as a deficit, like "mommy brain" where you're forgetting things, but volume reduction is not a bad thing. It means the brain is working more efficiently, because it's building better-connected pathways and better channels for communicating information.

Is it accurate to say the brain is focusing? Yes, exactly. It's reshaping in a way that enables more efficient communication — it's learning and consolidating. It's like the difference between a director's cut of a movie with lots of extra scenes and characters, and the lean two-hour theatrical release. Many of us prefer the theatrical release because it's easier to follow.

So by getting rid of certain parts of the brain, more energy can be used in the other parts? Exactly — so we're better able to focus on what matters. And when we become parents, what matters is our children and the inputs they're giving us.

The way you described the part of the brain that men lose when they become fathers made it seem like they're losing empathy. No — they're actually improving in their empathy, because they're becoming more efficient processors of social information. The fact that the biggest changes appear in what we call the mentalizing social cognition networks tells us those networks are really important for dads when they become parents, and they're getting a lot of practice putting those networks to use.

I thought you said that section of the brain shrank. Yes — because the brain is becoming more efficient. It's losing the extra pathways and building a superhighway for that specific social information.

That sounds counterintuitive; I imagined my brain would grow when I get better at something. You would think so, but in this case the brain actually shrinks. It feels like a puzzle to wrap your head around, but it reflects that the brain is working better.

Is there a relationship between how hands-on the father is and the amount of shrinkage? Yes, and my lab found that relationship. When dads told us before birth that they felt more bonded to their unborn baby, when they wanted to take more time off work, and when they reported three months after birth that they enjoyed their babies more, felt more connected to them, and were spending more time caring for them, they had more profound brain shrinkage. All of this supports the contention that the shrinkage is adaptive and enables men's adjustment to parenthood.

Are there other biological changes when someone becomes a father? Yes—men's hormones change too. Men who are hands-on as fathers typically show about a 25% drop in testosterone, and some of the best studies of this have been done longitudinally in the Philippines.

Before longitudinal studies existed, people argued that maybe lower-testosterone men were simply choosing to become fathers. Looking across time lets us tease that out and see whether fatherhood itself changes testosterone. Across decades, testosterone is typically pretty high before pregnancy happens—and it's adaptive to have it high. Testosterone has been studied a lot in birds, rodents, and other mammals: you want high testosterone at the start of breeding season, when it's time to maximize your chances of producing offspring—to compete, build status, and fight off rivals, high testosterone is your friend. But once you've accomplished your reproductive goal and caused a pregnancy, and you want your offspring to survive, you want to be investing in and nurturing that new baby.

That's exactly what they saw in the men in the Philippines: as they spent more time taking care of their kids, they showed a sharper drop in testosterone. You typically then see some rebound as the baby gets older. And this isn't unique to humans—we see it all over the animal kingdom.

So during a pregnancy, some chemical tells my body to make less testosterone, even though the baby isn't here yet? It might just be your proximity to your pregnant partner. Our lab found that expectant dads and expectant moms had correlated levels of testosterone during pregnancy, and the stronger that relationship was, the more the dad showed a drop in testosterone after birth. But I want to caveat, because I—

A lot of men are really concerned about the idea that testosterone might drop, and we have a strong narrative right now that testosterone equals successful masculinity.

But masculinity is not about a particular hormone. It is about a body that is responsive to our goals and that sets us up to meet the demands of our environment. Having a biology that fluctuates across the lifespan as our reproductive strategy shifts is really adaptive—we want to be flexible, and that doesn't always mean maxed-out testosterone. High levels of testosterone actually decrease sperm count and are bad for the immune system.

Is lower testosterone a threat to performance and ambition?

Some men worry that dropping testosterone might make them worse in the gym or less ambitious and less able to pursue their goals. There is definitely a link between testosterone and men's muscle mass, motivation, and drives, but these are not one-to-one relationships. The human hormone literature is messy, and many of these are weak correlations—testosterone doesn't necessarily equal success at work, for example. And high testosterone can get in men's way in multiple ways.

My lab did a study where we found that men who had relatively higher testosterone after their baby's birth had partners who were more dissatisfied in the relationship and reported more intimate partner aggression, and the dads themselves reported more parenting stress. So it's a bit of a mixed bag with high testosterone.

The sweet spot: mid-range, flexible levels

What you want is to hit a sweet spot. You don't want testosterone levels that totally crash—my lab has also found that when testosterone is really low after a birth, men have higher postpartum depression symptoms. But you don't necessarily want sky-high levels either, because that can cause problems in your intimate relationship and make it hard to switch into nurturing and parenting mode. The men who seemed most successful in our study were men with mid-range testosterone levels that could be flexible and adapt to different life changes.

Hands-on fatherhood and testosterone

The interviewer asked whether the more time you spend hands-on as a father, the lower your testosterone goes. Yes—longitudinal work in the Philippines found that when men spent more time changing babies, doing hands-on care, and sharing a sleeping surface with babies, they had more of a testosterone drop. Hormones are responsive to the context and to what we're doing. But testosterone does rebound after birth, so it's not necessarily the case that it will bottom out and stay low forever.

Is there an ideal "dose" of fatherhood?

Asked whether fathers should aim for an ideal amount of hands-on time to keep testosterone in the mid-range, the researcher said she doesn't know that we know for sure if there's a dose of parenting involvement that lends itself to an ideal amount of testosterone. It's hard to optimize your way out of these natural changes.

She doesn't want to discourage dads from being hands-on with their kids because they're worried they'll pay some kind of physiological tax. Instead, protect your sleep, which we know is linked with overall health, and make sure you get time to exercise, socialize, and participate in activities that bring you joy. Those are ways to mitigate risk that she thinks will be more successful than trying to hit a particular hormone level.

My brother is a year older than me and has three young kids under the age of seven. They were actually just here—they just left. I noticed a remarkable difference in him when his wife Julia got pregnant.

What did you notice?

Just a total shift in what he wanted out of life. Growing up, I remember seeing him on the computer figuring out which job would pay the most money. He was very, very smart—he still is—and he oriented his career toward the job that would make the most money. He was successful: he went to LSE, got the job. Then shortly after graduating university, he met someone and they got pregnant unexpectedly.

I watched my brother go from someone really striving for material goals to someone who suddenly placed the material goal immediately after the question: how do I retire and spend the maximum amount of my time with my kids? His kids are number one above anything else, and I admire that a lot about him. The most remarkable thing, as someone who hasn't gone through that transition because I don't have kids yet, is just watching how profound the change was in his stated goals and ambitions.

I'm so glad you said that, because that's something I heard from so many of the fathers I interviewed for the book: you experience this profound shift in your values and priorities. If you survey parents and ask what the most meaningful priorities in your life are, men are just as likely as women to say "my kids." Fathers increasingly recognize that the parenting role is really central to their self-concept.

We're in a culture where it can be hard for men to find a sense of meaning, purpose, and connection to other people. Being a parent can give you that sense of meaning and purpose. That's an important framing around the fact that your testosterone level might change or your brain might shrink—things that maybe sound a little scary and negative, but they're in the service of this larger goal, which is building a more meaningful life.

A message to men and also to women, to moms and to dads: anything that's worth doing is hard. Being a parent is really hard. You are sacrificing yourself, losing your sleep, getting extra wrinkles—ask me how I know. But you are benefiting from this sense of connection and purpose that it sounds like your brother has been totally transformed by.

In a lot of ways we're selling young men the message that you should be optimizing your bank account and your body fat percentage and hustling as much as possible. That can be a hollow message, because what we keep learning again and again from the longevity studies is that the quality of men's relationships is the best predictor of their well-being in old age. Men with healthy marriages, men who have positive relationships with their kids—those are the men who age well, not necessarily the men who've maxed out on riches or the perfect body fat score.

It's really remarkable, because when you look forward to becoming a parent, you mostly hear about the sacrifices: you won't sleep as much as you used to, and you'll face the anxieties of loving something more than yourself. But the profound psychological, biological, and hormonal shift is something you kind of just have to believe in. People describe it almost as if it were a religion — you have to have faith that the profound upside will be worth the very obvious costs you see parents paying.

I think that's exactly right, because the downsides are highly visible. We've all been on a plane with a crying kid and seen the frantic parent trying to calm them down, or watched a tantrum in the grocery store. That stuff is right in your face. The upsides, though, are sort of invisible: the joy of seeing your child's face as they discover something new, or getting to snuggle late at night and feeling a sense of closeness you've never had — a love bigger than yourself.

It's important to speak about the benefits as well as the downsides, because we humans crave connection and care, and becoming a parent is an opportunity to provide care on a scale that's hard to find in other ways.

I also want to hear about how the mother's brain changes through pregnancy and beyond. My brother's wife Julia was here too, and she's remarkably different now that she's had these three beautiful children. Last night I asked her — which is probably the worst thing you could say to a mother of three young kids who's already anxious that someday they'll fly the nest — what will take the place of these three kids in her life when they grow up and leave home? Would she want to go back to the corporate world she was in before, or do something else? How has it reordered her sense of meaning? But tell me: how does the mother's brain change?

The mother's brain changes really profoundly. Moms lose about 2 to 12% of their brain volume from before pregnancy to after birth. In our studies, dads lose about 1%. It's a similar pattern in similar parts of the brain, but the magnitude is different, and there's more variability in the —

How did you conduct these studies? We recruited a group of first-time parents—all couples recruited during pregnancy. Our only rule was that they had to be cohabiting and planning to continue cohabiting after the birth, because we wanted to capture the dads' experience of being in proximity to their babies.

We brought them into the lab and asked them every question we could think of. We sampled their blood, saliva, and hair. We had them fight with each other on camera, and we scanned the men's brains. Then, about six months after the baby was born, we brought them back: blood, saliva, and hair samples again, plus a breast milk sample and a sample of baby poop. We had them fight again and scanned the dads' brains again.

We did this to see how couples communicate with each other, whether that changes across the transition to parenthood, and which communication styles predict better couple-level adaptation to becoming parents.

How did you get them to fight? We gave them a list of topics that couples commonly argue about and asked each partner to independently mark which were hot-button issues for them. We then picked issues both people endorsed and told them to talk about it without holding back, for 15 minutes, while we watched. They weren't punching each other, but the conversations were often contentious because they were discussing issues that were frequent objects of conflict.

What did you discover? Couples who fought more negatively with each other subsequently reported more difficult birth experiences. This is interesting because birth is a time when moms need a lot of support, and the partner is often the primary person in the room providing it. So a toxic, difficult relationship can really color the mother's experience of the birth.

The interviewer asked whether the worse birth outcomes came simply from having a partner they fought with in the room, or whether something actually happened during the birth itself.

The researcher explained that they didn't record couples' conversations during the birth, but they did obtain the charts from the hospital or birth center after delivery and examined complications and how medically complex the birth was. They found that when couples fought more negatively and less positively during pregnancy — around six months in — then a few months later, at delivery, they had more medically complex births and also appraised the births as more stressful. The conclusion is that the couple relationship actually matters when we think about birth.

How dads entered the birthing room

There has been a huge sea change in how we deliver babies. Men were never in the birthing room; babies were typically delivered with the assistance of a female midwife and female relatives. It wasn't until birth moved into hospitals in the late 19th century that a male physician presided over the birth. And it really wasn't until the 60s and 70s that dads started advocating for their inclusion in the birth room, saying they didn't want to miss it and wanted to be present.

Because dads historically haven't been part of the birth experience, we haven't necessarily thought about the couple relationship as a place to intervene. If we want birth to go smoothly, we should be thinking about dad's mental health and the couple's relationship functioning, because those things might affect mom's psychological experience of the birth.

"So you're saying don't fight during pregnancy." The answer: not exactly — or just find more effective ways to fight. Figure out ways to calm each other down and validate each other, rather than amping each other up and spiraling into real negativity.

Fighting isn't the problem — how you fight is

The interviewer pushed on a point of nuance, concerned that expectant parents listening might be looking at each other thinking they had a fight last week with the birth coming up in a couple of months.

The researcher reassured them: there's nothing wrong with fighting. In fact, airing out your concerns and grievances is good. What the study looked at specifically were negative conflict behaviors — things like criticizing, showing contempt, and stonewalling, meaning refusing to listen or see the other person's perspective.

One of her grad students is now studying what "magic ingredient" helps couples shift from being negative to positive with each other during the same conflict tasks. The ingredient he's finding is validation: conveying to your partner, "I understand what you're saying. I see where you're coming from. I'm right here with you. I get it." Those behaviors make a huge difference because they take much of the tension and frustration out of the conversation. As soon as you feel really heard by your partner, the wind goes out of your sails for being furious.

I sometimes worry that a lot of people are waiting for perfection before they step into the next season of parenthood. Maybe I'm guilty of this myself to some degree. My fiancée and I talk about this sometimes — it doesn't feel like there's ever going to be a perfect time to have kids. When you look at the nature of our lives, with our crazy schedules, there really is no time right now. But when I reflect, everything I do now, including this podcast — at the time I recorded the first episode, there was no time, but I made the time.

I sometimes worry that as young people, we're in a culture waiting for more perfection than is actually coming, whether in a romantic partner or our circumstances. Of course, there's a fundamental basis of security everybody needs to bring a life into the world, and often people don't have that. But I'm wondering what your thoughts are.

I had this conversation with my grad school adviser. I said I'd love to have kids — what do you recommend? When is the right time? She laughed and said there is no right time. You just have to do it and make it work, because once the baby shows up, you'll figure it out. That was tremendously good advice, and it led me to start having kids within the next few years after that conversation.

I decided, okay, I'm just going to go for it and make it work. It was hard, but we did in fact figure it out. When you optimize everything and feel you need the perfect conditions — owning a house, a certain number of bedrooms, a certain level of stability — yes, all those things are terrific. But historically, people had kids young and often found that having kids gave them a strong impetus to get those things together.

We used to think of having kids as a cornerstone of a life — a foundation you lay before building your career and everything else. Now we think of it as a capstone, a crowning achievement: you've got everything perfectly set, and now it's time to have kids. The problem with that is, first, our biology doesn't always agree — we can lose our best window in which to have kids.

I also think having kids isn't just an individual responsibility; it's a collective, societal one. We are an alloparenting species — cooperative breeders who raise our kids in community. That's how we evolved; look at hunter-gatherers, that's how they raised their kids. We are not designed to do this in isolation. A healthy society provides things that reduce stress for parents: generous maternity and paternity leave, job protections, child care. I'm a big believer in strong policies that make it easier to have kids, because in the absence of those policies, you feel it's your job to get everything completely lined up — and that time might never come, especially not in a tempestuous economy.

We're seeing some of the symptoms of exactly what you described. A landmark 2024 study published in the Lancet projects that by the year 2100, 97% of all countries and territories will have fertility rates too low to sustain their populations. The global fertility rate has plummeted from an average of five children per woman in 1950 to just 2.2 today. According to CDC and Pew Research data, the US total fertility rate just hit an all-time recorded low of 1.6 — far below the replacement rate of 2.1 children per couple required to keep the population stable without immigration. CDC data shows total US birth rates dropped yet again by 1% in 2025, falling to roughly 3.6 million babies, continuing a nearly two-decade slide since the Great Recession. And because fertility rates are crashing in high-income nations while remaining comparatively high in specific low-income regions, a massive demographic shift is predicted: by 2100, one in every two children born on the planet will be born in sub-Saharan Africa.

It's quite shocking to hear. Growing up, everyone was talking about there being too many people on the planet.

Right — there was this narrative of the population bomb, a really popular theory in the '60s that we had too many children and needed to adopt contraception to prevent too many from being born. We all took that too literally and maybe overcorrected, because now we have this population drop. It's concerning because what you don't want is a society with an inverse age curve — many more old people than young people. Then you don't have enough caregivers for the older people, not enough people to sustain the economy, no innovators, no one building your future. You've depopulated that, and you have a very aging population, which can create a lot of instability.

So we need to think about how to make parenting easier and more desirable for young people, because we've managed to market it as an undesirable choice.

Making parenting easier and more desirable

How do we do that?

Part of it is the conversation we're having right now — talking about the meaning, the purpose, and the benefits you can get from your relationships with others. We need a cultural reframe around care to raise its value. One of the reasons I'm interested in fatherhood is that seeing men as talented caregivers unlocks this appreciation for the importance of care. The shift your brother underwent — from transactional, "how can I make the most money," to "my kids matter, how can I spend the most time with them" — is a really valuable shift in purpose that, at scale, would make societies healthier and more empathetic.

There are a few things worth saying from my perspective. First, not everybody can have kids, for reasons beyond their control. Second, not everybody wants — or should want — to have kids, depending on their circumstances. And third, in my personal circumstances, when I think about what I want from my life — this is about me — I do feel tremendously, positively jealous of his life. It's a strange thing, because he has a couple more gray hairs than me even though he's only a year older, so everything in life is a trade-off. But the deep sense of meaning and purpose that even I experience when those kids are around — they were at my house for the last couple of weeks — everything seems incomparable in terms of meaning to these beautiful children.

They're just endlessly curious and fascinating, and there's very little you can get from scrolling on a screen that is as fulfilling as watching a baby learn something.

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Is it true that parents have different brains in terms of protection? Yes — an emerging body of research suggests that being a parent is neuroprotective in late life. The UK Biobank, the biggest repository of brain scans from people in their 50s and 60s, finds that both men and women who report having had more kids show markers of a younger-looking brain age. When a machine learning algorithm adjusts for chronological age and estimates brain age from the scans, you look relatively younger if you report having had more kids. The greatest benefit seems to come at two or three kids; after that it levels off — you don't get much extra benefit from six kids compared to two. The suggestion is that the practice this gives your social brain and empathetic brain benefits brain plasticity and functioning later in life.

That's surprising, because you'd assume parents of lots of kids are stressed and sleeping less, which should be bad for the brain. It helps to think about the short-term cost versus the long-term benefit. Plenty of studies find that moment to moment, parents of young kids say they're less happy, more tired, more stressed, with more going on — plus the brain and hormone changes we've discussed. But looking at later life, people report more fulfillment. You're doing something taxing, not very fun, and potentially isolating, yet you reap a long-term benefit from the power of those relationships, the sense of connection, social integration, and the practice of trying to understand others — which is like a glue for creating good relationships.

What exactly about being a parent protects the brain? One theory: with three kids around, I was playing all kinds of games — hide-and-seek for seven hours — and constantly picking them up, even the eight-year-old who complains when she's not picked up. It's a real workout. It's both a cognitive and a physical workout. Is it that I'm building brain reserve because they're challenging me, having tantrums, wanting to play, engaging me all the time?

I think of it as sudoku for your social cognition. It's like crossword puzzles, except instead of practicing putting words together, you're practicing understanding people's minds and intentions, communicating, responding, and being sensitive to them. All of that is a workout — and a full-body one, because kids are really embodied. There's interesting research that dads especially play in physically demanding, vigorous ways.

My other theory around why having children would be neuroprotective for the brain was around oxytocin. I say that because I sat with Robert Waldinger, who runs the long Harvard study on human happiness, and the conclusion is that one of the single biggest predictors of longevity is whether you have strong relationships. Another scientist told me that oxytocin, the bonding chemical, is neuroprotective. So I imagine having three children means a lot of oxytocin, which means some neuroprotection.

We are social animals. We are designed to bond with each other—we pair bond, we bond with our kids—and that's really healthy. I love the Waldinger studies and cite them in the book: if you really want to think about what creates longevity and well-being late in life, look at your relationships. He shows that really well with this 80-year study he's been doing.

There are all these brain changes and hormone changes designed to help us build those bonds, and a lot of what goes on in early parenthood is that we are reorganizing to become more sensitive, more attentive caregivers. It's not that some people are just destined to be great parents and others aren't. As we put in the experience, get the practice, and put in the reps, we're building the brain and body that make us really great, sensitive caregivers. And I think that can transfer over to our other relationships, too. If you've learned how to calm a kid down from a tantrum, you're probably going to be a very effective manager at work. If you've had to negotiate with three kids who all want to be picked up at different times, you're probably going to be a better problem solver in your couple relationship. Those are skills you're building that can cross domains.

I was just looking at some of the research on this, and it shows that oxytocin actively downregulates harmful pro-inflammatory cytokines in the brain. It acts on the brain's immune cells, making toxic inflammatory responses lower. Studies on aging mice demonstrated that long-term oxytocin treatment concurrently enhanced the brain's plasticity, which directly improved learning and made them better with memory as they aged. And in terms of Alzheimer's: in animal models of the disease, oxytocin has been shown to reduce the toxicity of amyloid beta plaques—the toxic protein clumps that are the hallmark of Alzheimer's disease—which is fascinating. And that's the chemical produced from bonding.

Yeah, that's a pair bonding chemical. It's an affiliative neuropeptide, so it helps us shore up our social bonds.

Touch is really important, isn't it?

Yeah. My lab actually found that when dads engage in more physical touch—specifically a type called proprioceptive touch, which is exactly what you were just describing, like picking babies up, moving them around, playing with them in space, the vigorous touch we often associate with fathers—they subsequently had higher oxytocin levels when we did a blood draw in our lab. That's been found in some other labs as well.

The interviewer brought up Erica Komisar, who has appeared on his show before. One of her claims, which has been somewhat controversial, is that placing children under the age of three in daycare causes profound separation trauma and elevates cortisol to dangerous levels, making her quite opposed to daycare.

The guest politely disagrees. Both of her own kids went to daycare and thrived there, and she believes in "alloparenting" — the idea that we collectively raise children, since we are designed to help each other out and share care. The model of a single parent with a single child, isolated in a suburban home, is a very unusual one in the context of human history. In her view, the claim that we can't participate in shared care, or that kids can't do well in group care settings, is somewhat exaggerated.

That said, she thinks timing genuinely matters. Ideally, children enter group care when they can benefit from social interaction, which usually comes a bit later in toddlerhood — around 18 months and beyond. Very young babies often do better with a single caregiver, giving them a more stable attachment figure to bond with. But babies can form really strong attachments with their dads or another caregiver; it doesn't have to be the mother who is present for every moment of an infant's life. That expectation isn't sustainable for parents, and parenting stress is really bad for kids.

This connects back to the earlier birth rate discussion: we need to think about parenting in sustainable ways that allow us to get help. And if we truly don't want children in a lot of early child care, we need to support that with universal paid parental leave — which most parents in the United States don't have. As a result, many mothers face a reality that doesn't match what some parenting gurus tell them is the only way to raise their kids, and that creates a lot of distress.

This creates a lot of anxiety. When it comes to the early years of a child's life—year one, year two, year three—is there any difference in the roles each parent plays?

There's a little bit of difference, and it depends on the parenting styles and the child's situation. In my book, I talked with Richard Reeves, who has done a lot of great work on masculinity and manhood. He thinks dads should be able to take paternity leave up to their kid's 18th birthday, because dads often find that their best relationship with their kid happens later in childhood, even in adolescence—he talked about taking his kids on trips and teaching his sons how to drive. So dads can come in at different points along a kid's development and provide a lot of value.

In early infancy, if mom is breastfeeding, it's important for the baby to get regular access to milk. Moms can pump and dads can do feedings, but it's often a source of challenge for couples when a baby is first born: dads feel like mom has a really big biological head start. She had the pregnancy, she's been able to build a bond with the child, and breastfeeding is like a magical formula she can use to soothe the baby. A lot of dads struggle to find their place in the first year or two of parenthood—wondering, "What am I supposed to do?" It takes a while for dads to come online as parents.

Dads need some space and opportunity to figure things out, and this often creates a dynamic where mom becomes the default parent in the early years while dads are waiting for their instructions.

You've spoken to both fathers and mothers for the book. What's the central point of contention you discover?

It's funny—I was just at a friend's book club meeting with a mix of moms and dads, and the concept they all got into was maternal gatekeeping and male malingering, a double-edged dynamic. Maternal gatekeeping is a somewhat controversial term, but it refers to any time a mom consciously or unconsciously puts up a roadblock to dad fully participating in parenting. It can be as simple as the baby being fussy and crying, and mom saying, "Hand him to me—I know what to do." Over time, that can spiral into a pattern where mom becomes the authority figure and dad is seen as the bumbling, hapless appendage. Dads ultimately feel like their contributions aren't valued, or that mom doesn't really want them to have independent time—maybe because mom doesn't trust dad. That's an area where communication and building trust before the birth really matter.

The flip side of maternal gatekeeping is what's called weaponized incompetence, or husbandly malingering: a dad who's a totally competent project manager at work, handling spreadsheets and whole workflows, suddenly doesn't know what to put in the diaper bag. At the book club, one mom told a story from when their baby was a couple of days old: there was a giant diaper blowout, she had gone out for a 10-minute walk, and her husband called asking what to do.

"I've been a parent for exactly two days—that's exactly as long as you. I have no idea. You've got to figure it out." "But the poop's on the wall." "I'm sorry. You can use the wipes."

That same husband, she told me later, was in charge of packing lunches, and at some point asked, "Do you give the kids anything but chicken nuggets?" She said, "Well, there's fruit—you can cut up some avocado, throw stuff in." That's when dads act like they have no idea and it's mom's job to solve the problem.

A lot of moms are frustrated watching that dynamic happen. At the same time, I've talked to many dads who said, "I would love to have done more, but my wife insisted on organizing everything, scheduling everything, telling me what to do. I never felt like I got an opportunity to fully step up." This is an area where couples really need to iron things out even before the baby comes: who's going to do what, and how to balance it so both partners get some ownership, some opportunity, and can trust each other.

Interviewer: Parents often report that after pregnancy there's a change in their relationship and intimacy. Have you done any studies on that?

Yes, and it's one of the most robust findings in transition-to-parenthood research: couple relationship satisfaction often drops around the birth of a new baby. It's not surprising — you take two people who are having fun together, sleep-deprive them, give them a lot of extra responsibility, and add a baby who's crying and demanding they get out of bed multiple times a night. You often get a lot of conflict over who's going to do what and who's more connected to the baby. Forewarned is forearmed: if couples know this is a risky time for their relationship, they can do more to shore up their communication before the baby is born.

Interviewer: Have you quantified how different the relationship is on the other side of giving birth?

We've given lots of different couple relationship questionnaires, measured them, and looked at that dip — there is in fact a statistically significant drop in relationship quality.

Interviewer: And sex life.

And sex life, yes. Of course — you've got an extra person in your bed, or near it, a lot of the time. And if the baby was delivered vaginally, there's a lot that's sore and may need stitches, and even more so after a C-section.

Interviewer: Does it eventually go back to pre-birth levels of relationship satisfaction?

There's a lot of variability in couples' relationship trajectories. Some couples' relationship quality continues to dip, and often the relationship dissolves. Others report a better-quality relationship after parenting together — a richer one. I feel that with my husband: I appreciate him so much because I've seen him negotiate with terrorists in the form of our young children. How well couples fare diverges depending on how well they can muscle through those early years.

The interviewer noted that hearing men experience postpartum depression after the birth of their child is unconventional, since we typically think of it in the context of what the woman is experiencing.

Technically, postpartum depression just means depression that occurs after the birth of a baby—that's what "postpartum" means. The term doesn't necessarily refer to the person who delivered the baby; it just refers to the time period after birth. There's some evidence that new dads' prevalence rate for depression is about twice that of the general population: non-fathering men have about half the risk of depression as new dads, so there's a big uptick in depression risk. That doesn't mean every new dad is depressed, and new dads have lower depression rates than new moms, just to be clear. But it's also not a competition or a zero-sum game.

There can understandably be a lot of consternation from moms who feel that they fought for the term "postpartum depression" to be widely recognized by the medical community, and now that they've succeeded, men are trying to take it over. I'm sympathetic to that argument, and many moms have suggested calling it "perinatal depression" instead. That's totally fine—perinatal just means around the birth of a baby, and that's legitimate too.

But consider the risk factors for depression, in moms or dads, in the period following a baby's birth: it's multi-determined. It's hormone changes, sleep changes, identity changes, relationship changes and conflict, changes to how you show up at work and to your extended family. It can reawaken unresolved childhood traumas about how you yourself were parented. All of these things come to the fore while you're preoccupied by what can be very isolating and repetitive care for a young baby, creating a perfect storm of mental health risk.

The interviewer asked whether cortisol changes in couples offer a biological divorce predictor—whether the way a couple's cortisol syncs up or clashes in the first year of parenting could reveal a failing marriage before the partners realize it themselves.

The researcher confirmed she has studied cortisol interconnection in her lab—how cortisol levels between partners become correlated over time. She found that couples with strongly linked cortisol levels reported lower marital satisfaction. That seems counterintuitive, since similar hormones might seem like a good thing, but she believes the explanation is that you don't want to be contagious to another person's stress. When one partner is highly stressed, it helps to have a partner who can modulate and calm that stress rather than amplify it.

She noted that other labs have found the opposite in the transition to parenthood: more cortisol synchrony can actually be beneficial from the prenatal to postpartum period, though outside of childbirth her lab's finding held.

The interviewer shared a personal example: he believes his relationship with his fiancée Melanie works because she is more emotionally variable while he acts as a "prefrontal cortex sounding board" who brings her back down. Her emotional variance is useful because she acts like a threat detector—if the relationship is drifting, she notices fast, whereas he takes longer to develop empathy for those shifts. The trade-off is that she may be more prone to worry, and she has expressed gratitude for his ability to restore calm. He has come to see that as his role, and thinks the relationship works precisely because they are two different types of people. He added that, as an investor in the company Whoop, he has looked at their stress measures on the devices—imperfect, but indicative—and his stress response is very stable while hers is much more unstable, suggesting opposites attract in this regard.

The researcher agreed it's an interesting dynamic: paired with someone super stable, life might feel boring; paired with someone really volatile, life might feel too chaotic. We are often drawn to people who complement something about ourselves and are different enough to expand our worldview. She cited a couples therapist's theory that the very differences that draw us together can ultimately polarize us when things go awry. One possible future is that she is always the emotional one and you are always the calm one, the pattern becomes entrenched, and it pulls you apart. The alternative is meeting in the middle—you become more emotionally attuned and she becomes calmer and more stable. That joining around the differences is the ideal.

The interviewer said that is definitely what has happened in his relationship, and the researcher concluded that it's a good sign.

The guest and host agreed it was a good sign for the relationship, and the host joked it was time to have a kid. The guest said they were trying and had frozen their embryos, which he described as a really interesting process.

He explained that he had assumed in his early 30s he could simply decide when to have a child and have sex during the ovulation window, but it turned out to be trickier than he expected.

The guest noted there is a chapter in her book about paternity uncertainty. One thing that is unique and interesting about humans is that we conceal our ovulation. This makes us different from many other animals, where a fertile female changes color, dances in a certain way, or smells different—obvious cues that let males know exactly what window to jump in on. Because humans conceal ovulation, it is always a little murky.

Asked why we do that, she offered several explanations. For one thing, it encourages pair bonding: a man cannot just show up on the one day it's time to cause a pregnancy and then take off. He needs many repeated opportunities, so if he actually wants to cause pregnancy, he is much better off sticking with one woman and investing in that relationship than going out every night looking for a different lady. We form stable monogamous relationships because that is adaptive for spreading our genetic material.

It also reduces aggression. One theory holds that it reduces rivalry between women: if you knew one of the ladies in your group was fertile and had it out for her, you would want to attack her during her fertile period, so concealing ovulation reduces that rivalry and aggression.

Finally, it makes everybody a little more invested in babies, because no man knows exactly who caused which pregnancies. As a result, everyone has a bit of an altruistic stake in the future of our children.

A listener asks whether there's research on what increases the probability of conceiving a child — mentioning that he often thinks about reducing stress for his partner, keeping her safe, and making her feel secure.

The guest responds that those are good instincts. There is research on reducing stress: we know that stress makes it harder to conceive. Of course, the last thing you want to tell someone struggling to conceive is "reduce stress," because that's so invalidating — they're already stressed about how hard it is to conceive, and telling somebody to be less stressed is frequently not that helpful.

But the intuition is right that you probably want to make the environment calmer and safer. You can also optimize nutrition — there's a lot you can do — but there's also a lot that isn't up to you, and sometimes more intervention is needed.

Asked what advice he would have for new fathers, the speaker said this is one of the themes of his book: great fathers are made, not born. You might feel you lack the qualities to become an amazing dad, but what really matters is your time, your investment, the practice you get, and how much you care. That will shape you—it will build a brain and a body that make you a tuned-in parent.

Give yourself grace. The transition to parenthood can be really challenging, but you can become an expert in your own child, and there is a reward in that: you will find enrichment and meaning, and you will rediscover your priorities in a way that ultimately brings a lot of value.

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Of all the studies we've done—probably too many— one of the most formative looked at couples' plans for dividing up baby care. We gave them a questionnaire we called "who does what," listing 10 common baby care tasks like changing diapers and feeding a bottle. Each partner used a slider to indicate how much mom would do and how much dad would do. Then we brought the couples back to the lab about six months after birth and had them complete the same scale.

The interesting finding was that couples weren't great predictors of how much dad would actually do. Every single couple expected dad to do more before birth than he actually did afterward. There are many reasons for that—it doesn't mean anyone is a villain. Maybe mom got more time off work, or she was breastfeeding and so was with the baby more. But we found that when dads were doing more, they reported being happier in their couple relationship.

We also examined how moms and dads talked about dividing baby care, measuring how often they said the pronoun "we" compared to "I." Using "we" means you're talking about you and your partner. The more "we-ness" dads showed, the happier they were in their relationship after birth. So their investment and willingness to chip in—even if they didn't fully realize their plans—was still linked with their satisfaction, and that was controlling for how they felt about their partner before birth.

It's a little counterintuitive, because you might think that sitting back and relaxing while your partner does more is the winning strategy. But it was actually the dads who did more who told us they were happier.

The guest, expecting to become a father next year, asks for actionable advice on becoming a dad—what to do before, during, and after the birth—based on the research.

Use the window before birth

First, take advantage of the time before the baby arrives to work on communication with your partner. Talk about how you want to divide up baby care. Many people say, "We'll just wing it once the baby comes," but that can be a recipe for frustration: moms feel like they're doing everything, and dads feel shut out from care. Have those conversations sooner, and make sure both people are clear on how responsibilities will be split.

Also discuss the bigger value questions: What will we do about our extended families? What religion do we want to raise our kids in? What do we think about education? If you haven't had those conversations about values, have them now, because it will ward off conflict that would otherwise crop up later.

Build your social support network

Second, also before birth, build up your social support network. For many men, their primary confidant and intimate relationship is their partner. After the baby comes, mom is preoccupied, and dads are left asking, "What about me?" Depression research shows that a strong social support network is one of the best buffers. So ask yourself: which friendships can I count on, and who can help me? Think about how your mom can help, how a friend can help—maybe your brother has his own kids and is too busy to take yours, but he can help in some other way. Plug the people in your life into your social support needs.

The guest agrees it's a huge problem, and many parents struggle with loneliness and isolation. Building your support network doesn't just mean existing friendships and family—sometimes you end up far away from those people. It also means building community with other expectant parents and with your neighbors; we thrive when we build community. One nice thing about becoming a parent is that there are many mechanisms for doing that, though far more for moms than for dads. When she became a mom, she could go to a breastfeeding support group, a baby-wearing group, or walk in the park with the Silver Lake Moms' Club. Dads have fewer of these organic community structures, so take advantage of the ones that exist—she recently spoke with the founders of the Daddy Stroller Social Club, which has chapters all over the country where dads meet up for stroller walks with their kids, an amazing way for dads to connect. Build that as much as you can.

After the baby comes: protect your sleep

Summing up: build your friendships, work on your couple relationship, and think about how you want to balance things out when the baby comes. First of all, protect your sleep—and that's really hard.

Everyone tells you to sleep when the baby sleeps, and your sleep is going to be totally scrambled. But if you have healthy routines and good sleep hygiene even before birth, you'll fare better after birth.

I can hear parents screaming through the cameras: easier said than done. I'm not trying to gaslight anyone, but a good foundation of healthy sleep hygiene helps. That means the obvious things: no devices right before bed, dim the lights, make sure your room is the right temperature — dial in your sleeping environment, because sleep is the first thing to go and the hardest thing to lose.

There's a bit of a paradox here: when we're stressed or sleep deprived, we often reach for dopamogenic things — foods that are maybe a little higher in, you know, not the good stuff. It's a total vicious cycle.

Think about becoming a parent like preparing to run a marathon — not to the point of becoming totally neurotic about it, but focus on being healthy and doing things that prepare your body for the big shakeup you're about to undergo.

Once the baby comes, take any opportunity to bond. A lot of men think they'll avoid as many diapers as possible. Changing diapers seems gross, but it's also a chance to make eye contact with your baby and really get to know them in a different way. Jump into those baby care opportunities, find your own style, and remember: the more windows you have to bond, the better you'll feel that you know your baby, and the more confident you'll be.

Finally, give yourself grace. Know that this is hard, know that it's temporary, and know that you're sacrificing in the short term for a lot of long-term benefit.

One thing that might be missing from this list is making an effort to hold my relationship together with my fiancée.

That's also important—and it's part of what you want to do before the baby is born: shoring up communication and having those hard conversations.

Date night is probably going to be the first thing out the window, and yes, it does go out the window. But one nice thing about newborns is that they'll sleep pretty much anywhere. When our babies were little, my husband and I would just put the baby in a car seat and go eat at a nice restaurant. It was the last time we got to do that for a few years, because once they start walking around, they're much less portable. So take advantage of the early baby stage to travel and make sure you still get out.

That advice was all for me—for Steven. Would there be any different advice if my fiancée were sitting here and you were advising her?

I'd say the "give yourself grace" advice would go double. Know that Steven is going through a lot, and know that she's going through a lot too. Her whole sense of self is going to be in upheaval. There's a thing called matrescence, and also patrescence—the idea that becoming a parent changes your priorities and your sense of who you are. She's going to go through a lot of transformation, as will you, so hanging in with each other during that period is really fundamental.

Sometimes couples grow apart, or dads are jealous that the baby is getting all the attention and feel left out, while moms are frustrated that dad isn't doing more to help. All of those things can lead to conflict. You can know in advance that those will be hot spots for conflict and try to talk your way through them, even ahead of the birth.

Asked what topic they hadn't covered yet, Derby brought up the "dadbod" — something people frequently joke about, picturing Homer Simpson. But studies of both animals and humans have found that males tend to gain weight when they become fathers.

Is it just cortisol and lack of sleep? It's a mix of all the hormones — prolactin, which hasn't been discussed much, is rising — plus sleep deprivation, changes in physical activity, and changes in diet due to stress and food choices. She jokes in her book that she and her husband basically ate peanut butter pretzels from Trader Joe's every day while their kids were babies. A lot is happening at once — a perfect storm. And yet even animal models show weight changes around the transition to fatherhood.

She points to the tamarind monkeys: one study fed expectant tamarin fathers a standardized diet and compared them to males whose partners weren't expecting. The expectant dads gained more weight even though they ate the same diet, showing body changes occurring even before birth.

Why would that be? It's probably adaptive — increasing body size to be more imposing and better ward off attacks from rivals, plus extra fat as a buffer against scarcity. It looks less adaptive in a modern context with an obesogenic environment, where you can start to see more cardiometabolic risk.

But one thing the book discusses is that women actually like a dadbod. Studies of single women have found that when shown a series of body types, the dadbod — a lightly marbled male torso — is the most popular. She recalls the British singer Ali Mirrors (as heard), who did a big tone-up at the gym and posted selfies with something like a 12-pack, and women online said they liked the before picture. There's something to the reproductive signal of a dadbod: when shown torsos of different male body types, women say the dadbod man is more likely to be a hands-on father, more attentive and more caring — traits that are really attractive to women.

"So if I go out and get a dad bod, the science says I'm going to be more attractive?" "Yeah, go for it. Worth a shot." "See what my fiancée says."

How much of your work has been influenced by this?

Oh, this is my dad. So much of my work. My parents got divorced when I was nine, and my dad became a solo parent to me and my brothers. My parents ultimately worked out a joint custody schedule—one week with my dad, one week with my mom, switching off every week as I was growing up.

He became a really great dad, though he had a major learning curve. He wasn't a hands-on dad; he was like an 80s dad who showed up for the big stuff. But when he was alone with the four of us, he suddenly had to be the guy making our meals, helping us with our homework, and driving us to sports practice. He really rose to the occasion, and I'm still really close with him.

How do you think that's influenced your overarching mission and your focus on dads and parenting?

I've always been really interested in families. They say psychologists are always trying to fix the thing that went wrong in their lives, so as someone interested in couples and families, I probably want to reverse my own parents' divorce. But seeing my dad be a great caregiver and then realizing how much parenting research is solely focused on moms made me see there's a real gap in the literature. Men play a really important role in parenting and deserve a lot of recognition and respect for that.

It's interesting—I'd never heard before that there are really any changes that take place in a man's brain when he becomes a father.

I think it's not something that gets talked about a lot, which is why I wanted to write about it. But we are dynamic—we're plastic, we humans adapt—and becoming a parent is one of the biggest transformations you can experience.

Asked whether she had researched the impact of divorce on children, she said she hadn't done much — which she found ironic, since she is herself a child of divorce. There is some research on the topic, and it definitely shows evidence that divorce can create challenges for kids.

Asked whether humans are supposed to be monogamous, the speaker describes humans as "sort of monogamous with benefits." The evidence comes from body size differences between the sexes. Male humans are a little bigger than females, but not twice as big.

Male gorillas, by contrast, are far bigger than females—a huge size differential that reflects a harem-dominance model. Fully monogamous animals are exactly the same size: male and female prairie voles are almost identical, which indicates real pair bonding.

Humans fall somewhere in between. Different societies use different models: polygyny, one man with many women, and polyandry, which is rarer—one woman with many men, found in only a few societies. Monogamy is actually the most common arrangement across many cultures and societies, likely because it brings benefits: concealed ovulation helps motivate men to invest in a single partner, and it is generally good for children.

"What are you concerned about?"

"I mean, our future as a planet."

"Which part of our future as a planet?"

"I'm definitely concerned about what we've been talking about—the declining birth rate. I'm concerned not just because it portends problems in our future societies, but because of what it signals about young people's hopefulness for the future. When you look at the world and say, 'I don't want to reproduce. I don't want to bring children into this world,' to me that suggests a nihilism and a darkness that concerns me. Marriage rates are dropping, and young men and young women seem to be on different paths. Part of that is that we're in these algorithmic echo chambers where the content we're absorbing is really different, so you see increasing political polarization not just in the US but in other countries too—more adversarial interaction, and I don't think that's good. Going back to the idea that a healthy late life is about building strong relationships, which is a good predictor of longevity, I want us to live in a world where we see ourselves as being on the same team."

"Are you hopeful?"

"Yeah, I'm super hopeful. I'm a very optimistic person. I have teenagers, and I'm hopeful for them. I think they're going to take over, and hopefully they'll be wiser than my generation has been. That's them with my husband, from a few years ago."

"Your boy's a bit older now, right?"

"Yeah, he's 14 now."

Dr. Darby Saxby, PhD.

The podcast has a closing tradition: the last guest leaves a question for the next guest, without knowing who will answer it. The question left for Dr. Darby Saxby was: people are increasingly distrustful and lonely — if you could flip a switch and make one systemic change to turn the tide, what would it be?

Her answer: build a better policy environment around parenting. She is a strong advocate for parental leave, to protect time and space to bond — a change that would benefit many parents in the US who have no access to leave.

The State of Parental Leave in the US

Asked about the current policy, she explained that the US is a huge outlier compared to the rest of the world: there is no universal paid leave policy for parents at the federal level. Some policies exist at the state level, and every state differs slightly, but what is most often available is unpaid disability leave provided by the state — and not every parent qualifies. Shift workers, gig workers, and many retail employees probably have no access to paid leave. As a result, many new mothers in the US are back at work within a couple of weeks of giving birth, which she called totally bonkers when you consider what it takes to build a healthy society.

The baseline federal protection is the Family Medical Leave Act, which guarantees up to 12 weeks of unpaid leave, during which the employer must maintain group health insurance — but it pays nothing.

What is surprising, she noted, is that no law has been passed in this direction, because it is not a partisan dispute. It is one of the best-polling issues: bipartisan, with both Republicans and Democrats saying they support leave — something like 80% of Americans are in favor — yet the political will to make it happen has not been found.

Closing Reflections

The host thanked her for the book, saying it shines a light on issues mystified by pop culture and shows, through storytelling, animal analogies and rigorous science, that men matter in raising children — and that it starts a conversation about the upsides of parenting. She agreed that those upsides are less obvious than the pain of being a parent, and that rebalancing that equation makes it more likely we raise a healthy generation of kids.

The host added that he pauses because friends close to him either don't want children or can't have them, so the stigma can cut both ways — but as someone who wants kids, her work helps him prepare for what he hopes will be the most fulfilling journey of his life. He held up both the UK and US editions of her book and said he would link it below, noting that she does the first-party research herself and is at the forefront of what we know about the "dad brain," couples' interactions, and where they can go wrong.

The episode closed with the host pointing viewers to a recommended next video, chosen by YouTube's algorithm based on each viewer's behavior.