"Women Are Furious About This Research." - Darby Saxbe

2026-07-27 - 94 min - source - Read full transcript

Chris Williamson (host)Darby Saxbe

Key insights

New fathers lose about 1% of gray matter volume across the transition to fatherhood, concentrated mostly in the cortex.

Saxbe's decade-plus lab work scanning men mid-pregnancy and again after birth found a smaller, more variable brain change than in mothers, who lose about 2.5% of gray matter volume across both cortex and subcortex (including reward- and hormone-linked regions like the amygdala and ventral striatum).

dad-brain-neuroscience

The size of a father's brain change tracks his caregiving investment, not just the fact of becoming a dad.

Dads who felt more bonded with their baby before birth took more time off, spent more day-to-day time with the child, and reported more pleasure in caregiving showed the largest brain changes, suggesting the biology follows behavior rather than causing it outright.

dad-brain-neuroscience

Dad brain is a facultative adaptation: the biological capacity for caregiving is present in all fathers but only activates with hands-on involvement.

Saxbe contrasts the Aka of the Congo, where fathers spend most of the day within arm's reach of infants, with the Kipsigis, who prohibit fathers from touching babies in their first year; both patterns are adaptive to each society's resource-gathering structure, showing culture - not fixed biology - sets how much a father's caregiving dial gets turned up.

fatherhood-culture-and-history

US fathers' daily parenting time has roughly tripled or quadrupled since the 1950s-60s, with the pandemic as a clear inflection point.

Millennial dads spend more time with kids than any prior US generation, and early evidence suggests Gen Z dads are exceeding even that. Saxbe attributes part of the sustained shift to pandemic-era remote work exposing more fathers to day-to-day caregiving they'd previously missed while commuting.

fatherhood-culture-and-history

Testosterone drops in men only when they actually engage in caregiving, not from becoming a father in name.

Saxbe's data show the testosterone decline seen around a baby's birth is tied to hands-on involvement; without caregiving, the drop doesn't happen. She frames this as evidence the hormone shift is adaptive, shifting a father's reproductive strategy from mate-seeking toward nurturing and reducing aggression toward infants.

testosterone-and-caregiving

Fathers of daughters show a bigger testosterone drop but also less caregiving time, more parenting stress, and worse bonding than fathers of sons.

From a new, unpublished analysis by Saxbe's lab, drawn from their longitudinal sample: men having daughters showed steeper testosterone declines yet spent less time in direct infant care and reported worse bonding, which Saxbe frames as evidence fathers of girls may need more explicit coaching to become effective caregivers.

testosterone-and-caregiving

About 10% of new dads experience perinatal depressive symptoms, versus 19-21% of new moms, roughly tracking each sex's general-population baseline rate.

Saxbe argues this makes the elevated risk in new fathers unsurprising rather than novel: women have roughly double the general population's rate of anxiety and depression, so postpartum rates for both parents largely mirror pre-existing group-level risk, layered on top of shared stressors like sleep loss, identity change, and relationship strain.

postpartum-depression-in-dads

A father's mental health and a mother's postpartum mental health are linked, and paid paternity leave measurably improves maternal outcomes.

Saxbe cites a Swedish paternity-leave policy expansion study showing lower rates of anti-anxiety prescriptions among new mothers after the reform, and her own lab's work finding that dads' access to paid leave reduces mothers' postpartum depressive-symptom trajectories, arguing family mental health functions as one interconnected system rather than a zero-sum resource.

postpartum-depression-in-dads

Household division of labor produces an asymmetric, near zero-sum stress pattern between partners.

From Saxbe's dissertation research tracking dual-income couples for a week: moms' evening cortisol recovery improved when dads did more housework, while dads' cortisol improved when they got more leisure time and their partner got less, illustrating a structural tension in how couples currently divide labor and rest.

masculinity-and-care

Becoming a parent appears neuroprotective in late life, likely through social connection rather than pregnancy or birth mechanisms.

UK Biobank data on middle-aged and older adults found that people with more children, up to about three, have brains a machine-learning age-estimation model codes as younger. Because the effect shows up in fathers as well as mothers, Saxbe argues it isn't driven by pregnancy hormones or birth itself but by increased social integration from caregiving and connection to others.

dad-brain-neuroscience

Saxbe reframes masculinity around adaptability and caregiving rather than maintaining high testosterone.

She argues that being a good, hands-on father is one of the most masculine acts a man can perform, since it means guiding, protecting, and teaching the next generation; positive masculinity, in her framing, is about flexibly showing up for what a situation requires rather than defending a fixed hormonal or behavioral baseline.

masculinity-and-care

Books referenced

Dad Brain: The New Science of Fatherhood and How It Shapes Men's Lives - Darby Saxbe, PhD - Saxbe's new book on how fatherhood changes men's brains, hormones, and behavior; the source for most of the study references discussed.

Media referenced

Bob Odenkirk on what being a dad meant to him - other - Clip played mid-episode where Odenkirk describes fatherhood as giving him a sense of daily purpose, used to discuss meaning and identity in parenting.
The Times TikTok clip on paternal postnatal depression - other - Video of a dad describing his own postnatal depression, followed by dismissive comments; used to discuss gatekeeping around who 'owns' the postpartum label.
BBC toddler gender-swap experiment - other - Study where toddlers were dressed and named as the opposite gender to see how adult volunteers played with them differently, cited as evidence that socialization shapes gendered play from a very young age.
UK Biobank cognitive aging study - paper - Large repository of scan data from middle-aged and older adults, used to show that having up to about three kids correlates with a machine-learning-estimated younger brain age.

Companies

Homeboy Industries - LA gang-intervention organization where a formerly incarcerated father Saxbe interviewed now works and runs a project fatherhood program.
Function - Podcast sponsor; at-home lab testing service including hormone panels.
Element (LMNT) - Podcast sponsor; electrolyte drink mix.
Shopify - Podcast sponsor; e-commerce platform.
Momentous - Podcast sponsor; Fiber Plus supplement.

Techniques and frameworks

Facultative adaptation - Saxbe's framing for dad brain: a biological capacity for caregiving that switches on only when triggered by hands-on parenting, unlike moms' more fixed biological priming.
Challenge hypothesis - Evolutionary model, first described in birds, where testosterone rises during mate competition and drops once mating and caregiving begin; used to explain why testosterone falls in engaged fathers.
Westermarck effect - Incest-avoidance mechanism where close, sustained childhood proximity between roughly ages 1-10 produces later sexual aversion; discussed as a parallel to how caregiving time (not biology) builds parent-child bonding.
Couvade syndrome - Sympathetic pregnancy symptoms (nausea, weight gain, labor-like pains) reported by some expectant fathers; Saxbe found no hormone link to these symptoms in her own sample and considers the evidence weak.
Evolutionary mismatch hypothesis - Saxbe's explanation for postpartum depression: humans evolved as cooperative breeders with communal caregiving support, and modern isolated nuclear-family parenting creates conditions depression risk didn't evolve to handle.

Summary

Darby Saxbe, a USC psychologist who has scanned new fathers' brains for over a decade, joins Chris Williamson to lay out the emerging science of "dad brain" and argue that the backlash to some of her research misreads what it actually says. Her core finding: new fathers lose about 1% of gray matter volume across the transition to parenthood, concentrated in the cortex, a smaller and more variable version of the roughly 2.5% loss seen in new mothers across a wider set of brain regions. Crucially, the size of a father's brain change tracks how much hands-on caregiving he actually does, not the fact of becoming a dad on paper. Saxbe frames this as a "facultative adaptation": all fathers carry the biological capacity for caregiving, but whether it switches on depends on culture and context, illustrated by her contrast between the Aka of the Congo, where fathers stay within arm's reach of infants, and the Kipsigis, who forbid fathers from touching babies in their first year.

The conversation traces how this biology plays out historically and today. US fathers' daily parenting time has roughly tripled or quadrupled since the 1950s-60s, with the pandemic marking a clear inflection point that stuck, and Saxbe and Williamson discuss testosterone's role in the shift: it drops in men specifically when they engage in caregiving (not from fatherhood alone), part of an evolutionary "challenge hypothesis" pattern where the hormone rises for mate competition and falls once nurturing begins. A newer, unpublished finding from Saxbe's lab complicates the picture: fathers of daughters show a steeper testosterone drop but also spend less time caregiving and report worse bonding than fathers of sons, suggesting daughters' fathers may need more explicit support to become fully engaged.

The episode's most pointed section addresses the title's premise directly: why some women are angry about research on paternal postpartum depression. Saxbe reports that roughly 10% of new fathers experience perinatal depressive symptoms versus 19-21% of new mothers, a gap that largely mirrors each sex's baseline population rate of depression rather than revealing anything uniquely maternal about the postpartum period. She pushes back on the idea that recognizing paternal mental health "steals" attention from mothers, citing her own and Swedish research showing that when fathers get more support (paid leave, involvement), mothers' postpartum mental health measurably improves. Williamson and Saxbe argue that treating family mental health as zero-sum is self-defeating if the shared goal is a well-supported mother and child, and Williamson gets visibly animated pushing back on the online gatekeeping he's observed around the term "postpartum."

Later sections cover the asymmetric stress dynamics of household labor (moms' cortisol recovers when dads do more housework; dads' cortisol recovers when they get more leisure, at their partner's expense), the "daughter effect" on paternal hormones and involvement, and Saxbe's late-life finding that having children up to about three appears neuroprotective, likely via social connection rather than pregnancy biology, since the effect appears in fathers too. The two close on reframing masculinity: rather than defending a fixed high-testosterone baseline, Saxbe argues real masculine strength is the adaptability to show up for a vulnerable dependent, and that "potential parent guilt," the common fear among expectant fathers that they feel nothing and will be bad dads, is a near-universal, temporary experience rather than a sign of unfitness for the role.

Notable Quotes

"I think it's really valuable for moms who benefit from having a partner there to provide support, again, because we don't have these close intergenerational ties that maybe were normative a couple generations ago." - Darby Saxbe

"Are you most concerned about owning this area of cognitive real estate like it's some sort of cultural appropriation by men? Or do you care about the outcome of the kid and of the mom?" - Chris Williamson

"The best predictor actually of mom's mental health is the support that she gets from her partner. So if dad is not well, dad is not showing up, mom's mental health suffers either way." - Darby Saxbe

"I would argue that being a good dad is one of the most manly things you can do. You're literally rearing the next generation." - Darby Saxbe

"Pregnancy doesn't just make a baby, it also makes a mother... but pregnancy doesn't make a father in the same way." - Chris Williamson