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Home » Transcript of Dr. Darby Saxbe Interview on Diary Of A CEO Podcast

Transcript of Dr. Darby Saxbe Interview on Diary Of A CEO Podcast

EDITOR’S NOTE: In this episode of The Diary of a CEO, host Steven Bartlett interviews psychologist and neuroscience researcher Dr. Darby Saxbe about the profound ways fatherhood reshapes a man’s brain, hormones, and body. Drawing on her pioneering studies, she explains why testosterone drops, why the “dad bod” may signal a more attentive parent, and how these biological shifts influence bonding, relationships, and even mental health. The conversation offers surprising, science-backed insights into what it really means to become a dad. Read the full transcript of this interview below:

The Shrinking Father Brain

STEVEN BARTLETT: (00:01:33 – 00:02:52) Dr. Darby Saxbe, you’ve discovered something 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.

And I’ve got the report here in front of me, but I have a model brain over there. Could you explain to me what exactly it is that you discovered?

DR. DARBY SAXBE: (00:02:52 – 00:04:19) Yes. So we found that in fathers, and this is similar to what’s been observed in mothers, the brain is actually losing grey matter volume. So it is shrinking. So 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. And that’s a part of the brain that helps us understand other people’s feelings and intentions. Those areas are kind of concentrated around the midline of the cortex, which is kind of what we’re seeing here.

And then you also see volume reduction in the visual areas, which is 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. And 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. We also see changes in moms to what’s called the subcortex, which is this part of the brain that kind of controls our gut feelings and our sense of reward and is really strongly linked with our hormones. So moms are kind of changing all across the brain. Dads are mostly changing in this top layer, the cortex, which kind of controls our higher-order thinking, reasoning, and executive functioning.

And that tells us something about fatherhood, which is that fathers choose to engage in parenting. It’s a sort of cognitively mediated investment that dads are making.

STEVEN BARTLETT: (00:04:19 – 00:04:20) What does that mean?

DR. DARBY SAXBE: (00:04:20 – 00:05:06) So if you think about a mom who’s been through 9 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 that it takes to sustain a pregnancy, it’s thousands. And so there’s a very high floor for maternal investment, and moms are undergoing plasticity all across the brain that reflects that.

In dads, there’s a tremendous amount of cross-cultural variability. So there are cultures in which dads participate in childcare 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.

STEVEN BARTLETT: (00:05:06 – 00:05:08) You don’t pick babies up in the first year in some cultures?

DR. DARBY SAXBE: (00:05:08 – 00:05:11) You don’t pick babies up because it’s considered unmanly.

STEVEN BARTLETT: (00:05:11 – 00:05:12) Okay.

DR. DARBY SAXBE: (00:05:12 – 00:06:08) 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.

And so this sort of top layer of brain changes reflects that. You know, dads are modulating their investment depending on what they’re learning from the environment. And the word that biologists use for this is facultative. So a facultative adaptation is an adaptation that is optional but extremely useful.

You could think about an animal that walks on 4 legs suddenly having something really important to grab, and switching to walk on 2 legs so that it can use its hands. Hands are really useful for that animal. Fathers are really useful for humanity.

STEVEN BARTLETT: (00:06:09 – 00:06:10) But are you saying they’re optional?

DR. DARBY SAXBE: (00:06:10 – 00:06:30) But they vary depending on situation. And 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.

STEVEN BARTLETT: (00:06:30 – 00:06:33) And a woman’s brain shrinks as well, but it shrinks a little bit more.

DR. DARBY SAXBE: (00:06:34 – 00:07:00) Yes, it covers more of the brain, and it also shows a larger across-the-board volume reduction. And I should explain volume reduction. We often think about deficit, mommy brain, you’re forgetting things. Volume reduction is not a bad thing. What it means is that the brain is actually working more efficiently because it’s building better connected pathways and better channels for communicating information.

STEVEN BARTLETT: (00:07:00 – 00:07:03) Is it accurate to say that the brain is focusing?

DR. DARBY SAXBE: (00:07:04 – 00:07:28) Yes, exactly. So it’s reshaping in a way that enables more efficient communication. It’s learning, it’s consolidating. So it’s kind of like if you think about the director’s cut of a movie that has lots of interesting extra scenes and characters, and then you watch it in the theater and it’s like this lean, mean, 2-hour cut, right? Like, many of us prefer the theatrical release because it’s easier to follow.

STEVEN BARTLETT: (00:07:30 – 00:07:37) And by getting rid of certain parts of the brain, that means more energy can be used in the other parts of the brain.