42 Supported by research
Studies find that both men and women who report having had more children show markers of a younger-looking brain age.
"there are studies that find that both men and women who report having had more kids have markers of a younger looking brain age." (said at 0:00:01)
Large-scale observational neuroimaging studies using the UK Biobank have examined the relationship between parenthood (parity) and MRI-derived brain-predicted age. These studies specifically report that having had more children (or having offspring vs. being childless) is significantly associated with a lower/younger brain age in both women and men, although effect sizes and regional neuroanatomical patterns differ somewhat between sexes. Because these findings are derived from large cross-sectional cohort analyses rather than longitudinal randomized designs, causality cannot be definitively established.
According to CDC and Pew Research data, the total fertility rate in the United States reached an all-time recorded low.
"According to the CDC and Pew Research data, the US total fertility rate just hit an all-time recorded low." (said at 0:01:01)
Analyses of vital statistics data from the Centers for Disease Control and Prevention's National Center for Health Statistics (NCHS) confirm that the US fertility rate declined continuously following the 2007–2008 recession, dropping below previous historical benchmarks (such as the 1976 trough) to reach record/historic lows in recent years.
Fathers lose gray matter volume in their brains, with the largest reductions occurring in the mentalizing network and visual cortical areas.
"So 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... 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" (said at 0:02:33)
The speaker accurately summarizes findings from longitudinal neuroimaging research on first-time fathers (conducted across two cohorts in Spain and the United States). The prospective structural MRI study demonstrated that men transitioning into fatherhood experience significant longitudinal reductions in cortical gray matter volume, particularly concentrated in the default mode network (closely overlapping with the mentalizing/social cognition network in the cortical midline) and the visual cortex, while subcortical structures were preserved.
Mothers show structural brain volume changes across both the cortex and subcortex, whereas fathers change predominantly in the cortex.
"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" (said at 0:03:03)
Longitudinal neuroimaging research comparing the transition to parenthood in mothers and fathers supports the claim. In mothers, pregnancy and the postpartum period induce widespread structural volume and plasticity changes across both cortical regions and subcortical structures (which are heavily modulated by pregnancy hormones). In contrast, prospective structural MRI studies in first-time fathers show gray matter reductions that are largely restricted to cortical networks (such as the default mode and visual networks) with relative preservation of subcortical volume.
Mothers lose approximately 2.5% of their brain volume from pre-pregnancy to postpartum, while fathers lose approximately 1% of their brain volume.
"Moms are losing about 2 and 1/2% of their brain volume from before pregnancy to after birth. Dads in our studies, we found they lose about 1% of their brain volume." (said at 0:21:29)
Prospective longitudinal neuroimaging studies tracking parents before and after the birth of their first child confirm that mothers and fathers experience substantial structural brain remodeling, specifically cortical gray matter volume reductions. Landmark studies in first-time mothers (e.g., Hoekzema et al., 2017) demonstrated pronounced gray matter reductions (typically averaging around 2-3% across cortical/social cognition regions) from preconception to postpartum. Subsequent prospective neuroimaging research in first-time fathers across international cohorts (Martínez-García et al., 2023) demonstrated that fathers also undergo experience-induced cortical gray matter volume reductions averaging approximately 1%, concentrated in visual and default mode networks.
Fathers who reported higher prenatal and postnatal bonding, desired more parental leave, and spent more time caregiving exhibited greater brain shrinkage.
"So when dads told us before birth that they felt more bonded to their unborn baby, when they wanted to take more time off after work, and when they told us 3 months after birth that they enjoyed their babies more, they felt more connected and bonded to them, and they were spending more time taking care of their babies, they had more profound brain shrinkage." (said at 0:09:00)
The speaker accurately summarizes the findings of their prospective neuroimaging study on first-time fathers (Saxbe and colleagues, 2024; PMID 38615244). In this longitudinal cohort of 38 first-time fathers scanned prenatally and at 6 months postpartum, greater cortical gray matter volume reductions ('brain shrinkage') were significantly associated with stronger prenatal and postnatal infant bonding, plans to take more parental leave (time off work), lower parenting stress, and more time spent caregiving with their infant. Because this is a single observational prospective neuroimaging cohort with a modest sample size (n = 38), the overall GRADE certainty is low.
Hands-on fathers typically show approximately a 25% drop in testosterone levels.
"typically men when they're hands-on as fathers show about a 25% drop in testosterone and some of the best studies of this have been done longitudinally in the Philippines." (said at 0:09:46)
A landmark longitudinal cohort study of 624 men in Cebu, Philippines (Gettler et al., 2011) demonstrated that men transitioning into partnered fatherhood experienced a median decline of 26% in waking testosterone and 34% in evening testosterone over a 4.5-year follow-up period. Furthermore, fathers who were hands-on (reporting 3 or more hours of daily childcare) had significantly lower testosterone levels than uninvolved fathers. The claim accurately reflects the specific longitudinal findings and magnitude from this research.
In longitudinal research in the Philippines, fathers who spent more time providing hands-on care and co-sleeping with infants showed steeper drops in testosterone.
"the longitudinal work in the Philippines found that when men spent more time changing babies, doing hands-on care, sharing a sleeping surface with babies, they had more of a testosterone drop." (said at 0:14:18)
Longitudinal cohort data from the Cebu Longitudinal Health and Nutrition Survey in the Philippines led by Lee Gettler and colleagues directly support this claim. In a 2011 longitudinal analysis (PNAS), transition to fatherhood was associated with significant declines in testosterone, and fathers reporting three or more hours of daily direct childcare had significantly lower testosterone than uninvolved fathers. A subsequent 2012 study in the same cohort (PLOS ONE) found that fathers who shared a sleeping surface with their children experienced significantly greater longitudinal declines in evening testosterone over the 4.5-year follow-up compared to fathers who slept solitarily.
Expectant mothers and expectant fathers have correlated testosterone levels during pregnancy, and a stronger correlation predicts a greater drop in the father's testosterone postpartum.
"Our lab found expectant dads and expectant moms had correlated levels of testosterone during pregnancy. And the more strong that relationship was, the more dad showed a drop in testosterone after birth." (said at 0:11:21)
A prospective longitudinal study by Saxbe's research group evaluated 97 couples expecting their first child during pregnancy and at 7 months postpartum. The researchers found significant within-couple testosterone synchrony during pregnancy, and this prenatal testosterone synchrony predicted a larger decline in paternal testosterone from pregnancy to the postpartum period.
Fathers with higher testosterone postpartum have partners who report greater relationship dissatisfaction and more intimate partner aggression, and report higher parenting stress themselves.
"my lab did a study where we found that men who had relatively higher testosterone after their baby's birth had uh partners who were more dissatisfied in the relationship and reported more intimate partner aggression. So the dads themselves reported more parenting stress." (said at 0:13:02)
The speaker accurately summarizes the findings of a 2017 longitudinal study from their laboratory (Saxbe et al., Hormones and Behavior, n = 149 couples). In that study, higher paternal salivary testosterone measured postpartum (at 9 months) significantly predicted greater maternal relationship dissatisfaction, greater mother-reported intimate partner aggression at 15 months postpartum, and greater self-reported fathering/parenting stress at 15 months postpartum.
Men who have very low testosterone levels after the birth of a child experience higher levels of postpartum depression symptoms.
"My lab has also found that when testosterone is really low after a birth, men have higher postpartum depression symptoms." (said at 0:13:30)
A 2017 longitudinal study led by Darby Saxbe's laboratory (PMID: 28757312) evaluated 149 couples and found that fathers with lower aggregate salivary testosterone reported significantly more depressive symptoms at 2 and 9 months postpartum, as well as a curvilinear association where low (and high) testosterone at 9 months predicted higher depressive symptoms at 15 months postpartum. While some subsequent studies in other cohorts have found mixed or null associations, the speaker accurately reported the specific findings from their laboratory.
Longevity studies show that the quality of men's relationships is the best predictor of their well-being in old age.
"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." (said at 0:18:50)
Longitudinal longevity studies, most prominently the Harvard Study of Adult Development (which followed cohorts of men across their adult lifespans for over 70–80 years), consistently demonstrate that social connection, emotional support networks, and relationship quality are among the most powerful predictors of late-life psychological well-being, cognitive health, and reduced depression in older age. The evidence comes from prospective observational cohorts, warranting low GRADE certainty.
Couples who engaged in more negative and less positive conflict during pregnancy had more medically complex births and appraised the births as more stressful.
"And we found that when couples fought more negatively and less positively during pregnancy... when it's time to deliver the infant, they had more medically complex births. And they also appraised the births as more stressful." (said at 0:24:32)
The speaker accurately describes the findings of their 2020 prospective observational study (Saxbe et al., PMID 32162942). In 47 first-time expectant couples, observationally coded negative conflict behavior during pregnancy predicted higher cumulative medical birth risk scores (derived from medical charts) and higher mother-reported birth stress, whereas positive conflict behavior was associated with lower cumulative birth risk scores and lower father-reported birth stress. As an observational study with a relatively small sample size (n=47 couples), certainty is low.
Male physicians began presiding over births when delivery moved to hospitals in the late 19th century, and fathers began advocating for inclusion in the birthing room in the 1960s and 1970s.
"It really wasn't until birth moved into hospitals in, you know, the late 19th century, suddenly you had a male physician who's presiding over the birth. And then really it wasn't until the '60s and '70s that dads started to advocate for their inclusion in the birth room." (said at 0:25:15)
Historical scholarship on American and British childbirth confirms both assertions. Prior to hospital-based childbirth, birth was traditionally a female-centered domestic event; the medicalization and shift to hospital deliveries in the late 19th and early 20th centuries established physician-led (predominantly male) hospital obstetrics. As hospital delivery became standard in the mid-20th century, fathers were initially excluded from delivery rooms and relegated to hospital waiting rooms. During the 1960s and 1970s, propelled by the natural childbirth movement and parental advocacy, fathers actively challenged exclusionary hospital policies to gain entry and support their partners in birthing rooms.
- supports: Judith Walzer Leavitt, Make Room for Daddy: The Journey from Waiting Room to Birthing Room (Social History of Medicine 2010)
"Make Room for Daddy provides a compelling historical account of medicalised childbirth in the United States with particular attention to the contributions of fathers-to-be between the years of 1935 and 1985. In this monograph, Judith Walzer Leavitt traces how expectant fathers, with the assistance of their birthing partners, challenged exclusionary hospital policies to create a space for themselves." (abstract, passage verified)
openalexfull study (doi) - supports: Hiding in the Pub to Cutting the Cord? Men’s Presence at Childbirth in Britainc.1940s–2000… (Social History of Medicine 2016) · cited 11x in the literature
"Since the 1940s, men's presence at childbirth has changed from being out of the question to not only very common but often presented as highly valuable. This article examines this shift, charting how many men were present at their children's births over recent decades, considering how medical practitioners influenced men's participation, and analysing what meanings parents gave to this experience." (abstract, passage verified)
openalexfull study (doi)
Validation is the key communication behavior that enables couples to de-escalate from negative to positive during contentious conflict discussions.
"he's looking at like what is kind of like a magic ingredient that helps couples shift from being negative with each other to being positive with each other during these conflict tasks. He's like literally looking at the same task and he's finding the ingredient is validation." (said at 0:26:46)
Observational research examining dyadic conflict interactions using behavioral coding (such as the Specific Affect Coding System) demonstrates that partner validation (communicating understanding, acknowledgment, and interest) facilitates the transition from negative affect states into neutral or positive affect states during conflict discussions.
A 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.
"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." (said at 0:31:07)
A major 2024 demographic study by the GBD 2021 Fertility Collaborators published in The Lancet evaluated fertility trends across 204 countries and territories with projections to 2100. The study projected that by 2100, 198 of 204 countries and territories (97.1%, or 97%) will have total fertility rates below replacement level (typically ~2.1 livebirths per female), meaning their fertility rates will be insufficient to sustain population sizes over time without immigration.
The global fertility rate has dropped from an average of five children per woman in 1950 to 2.2 children per woman today.
"The global fertility rate has plummeted from an average of five children per woman in 1950 to just 2.2 today." (said at 0:31:18)
Global demographic analyses, including comprehensive data from the Global Burden of Disease (GBD) studies and the United Nations Population Division, confirm that the global total fertility rate (TFR) was approximately 4.8 to 5.0 children per woman in 1950 and has declined continuously over the past seven decades to approximately 2.2 to 2.3 children per woman in recent years.
- supports: Global age-sex-specific fertility, mortality, healthy life expectancy (HALE), and populati… (The Lancet 2020) · cited 2043x in the literature
"The Global Burden of Diseases, Injuries, and Risk Factors Study (GBD) 2019 produced updated and comprehensive demographic assessments of the key indicators of fertility, mortality, migration, and population for 204 countries and territories and selected subnational locations from 1950 to 2019." (abstract, background, passage verified)
openalexfull study (doi) - supports: Global fertility in 204 countries and territories, 1950–2021, with forecasts to 2100: a co… (The Lancet 2024) · cited 610x in the literature
"The Global Burden of Diseases, Injuries, and Risk Factors Study (GBD) 2021 produced up-to-date and comprehensive demographic assessments of key fertility indicators at global, regional, and national levels from 1950 to 2021 and forecast fertility metrics to 2100" (abstract, background, passage verified)
openalexfull study (doi)
According to the CDC and Pew Research, the US total fertility rate reached an all-time recorded low of 1.6.
"According to the CDC and Pew Research data, the US total fertility rate just hit an all-time recorded low of 1.6." (said at 0:31:26)
According to the CDC's National Center for Health Statistics (NCHS) and demographic analyses (including reporting by Pew Research), the total fertility rate (TFR) in the United States dropped to record lows of approximately 1.6 births per woman (e.g., ~1.64 in 2020 and ~1.62 in 2023), falling well below the replacement rate of 2.1 births per woman.
The replacement fertility rate required to keep a population stable without immigration is 2.1 children per couple.
"This is far below the replacement rate of 2.1 children per couple, I guess... Required to keep the population stable without immigration." (said at 0:31:33)
In standard demography, replacement-level fertility is defined as the total fertility rate at which a population exactly replaces itself from one generation to the next without net migration. In populations with low infant and child mortality, this benchmark is conventionally set at approximately 2.1 children per woman (or per couple). The 0.1 above 2.0 accounts for the natural human sex ratio at birth (around 105 boys per 100 girls) and the small fraction of female children who do not survive to reproductive age.
Projections indicate that by 2100, one in every two children born globally will be born in sub-Saharan Africa.
"And by 2100, one in every two children born on the planet will be born in sub-Saharan Africa." (said at 0:31:58)
A major demographic forecasting analysis for the Global Burden of Disease Study 2021 published in The Lancet (GBD 2021 Fertility and Forecasting Collaborators, 2024) projected that by 2100, over half of all global livebirths (approximately 54%, or more than one in every two children born worldwide) will occur in sub-Saharan Africa due to shifting global fertility rates and demographic divergence.
UK Biobank brain scan analyses show that men and women with more children exhibit markers of a younger brain age in their 50s and 60s, with the effect leveling off after two or three children.
"the UK Biobank is the biggest repository of brain scans from people in their 50s and 60s, and they find that both men and women who report having had more kids have markers of a younger looking brain age. So if you do a machine learning algorithm that adjusts for your chronological age and then, you know, takes what the scans look like and uses that to estimate what they think your brain age is, you look relatively younger when you report having had more kids. It seems like the greatest benefit is at two or three kids. After that it kind of levels off." (said at 0:38:20)
Analyses of brain MRI data from the UK Biobank (such as Ning et al., 2020 and de Lange et al., 2024) used machine-learning-derived brain age algorithms and found that having children is associated with a younger structural brain age relative to chronological age in both men and women. Specifically, subjects with two to three offspring showed the largest reductions in brain age compared to childless individuals. Because these findings come from cross-sectional observational neuroimaging data, the GRADE certainty is rated low due to the potential for residual confounding.
Moment-to-moment studies show that parents of young children report being less happy, more tired, and more stressed.
"there are plenty of studies that have found that moment to moment, parents of young kids say that they're less happy. They're more tired, they're more stressed, they have more going on." (said at 0:39:26)
Moment-to-moment and daily diary methodologies, such as the Day Reconstruction Method (DRM) and Experience Sampling Methods (ESM), consistently demonstrate that caring for young children is associated with elevated momentary stress, fatigue, and lower net positive affect compared to many leisure and social activities. In landmark DRM research by Kahneman and colleagues assessing daily life experiences among working women/mothers, childcare episodes ranked relatively low in positive affect (comparable to household chores and commuting) and higher in daily fatigue and time pressure, directly supporting the speaker's claim.
Research indicates that oxytocin downregulates pro-inflammatory cytokines in the brain and acts on brain immune cells to lower inflammatory responses.
"research 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." (said at 0:43:52)
Preclinical in vitro and animal studies show that oxytocin acts on microglia (the brain's resident immune cells) and suppresses the production and release of pro-inflammatory cytokines, including TNF-α, IL-6, and IL-1β, thereby reducing neuroinflammatory responses. Because the direct evidence is established primarily in cellular and animal models, certainty is graded as very low.
- supports: Oxytocin Suppresses Inflammatory Responses Induced by Lipopolysaccharide through Inhibitio… (Cells 2019) · cited 77x in the literature
"Furthermore, our analysis revealed that oxytocin (OT), a nonapeptide synthesized in the hypothalamus, suppressed the production of these proinflammatory cytokines by inhibiting activation of the eIF-2α-ATF4 pathway." (abstract, results, passage verified)
pubmedfull study (doi) - supports: Oxytocin alleviates cognitive and memory impairments by decreasing hippocampal microglial … (Brain, behavior, and immunity 2023) · cited 63x in the literature
"Moreover, during the early stages of sepsis, hippocampal microglia are activated, while OXT application reduces microglial phagocytosis and the release of inflammatory cytokines, thereby exerting a neuroprotective effect." (abstract, results, passage verified)
pubmedfull study (doi)
Studies in aging mice showed that long-term oxytocin treatment enhanced brain plasticity and improved learning and memory.
"And 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." (said at 0:44:02)
The claim accurately describes preclinical findings in aged mice. A study evaluating chronic (13-week) oxytocin administration in 12-month-old mice demonstrated enhanced spatial learning and recognition memory, alongside increased hippocampal neurogenesis and markers of synaptic plasticity (GluR1 and NMDAR2B). Because the evidence is based exclusively on animal research, certainty is rated as very low.
In animal models of Alzheimer's disease, oxytocin has been shown to reduce the toxicity of amyloid-beta plaques.
"And in terms of Alzheimer's, in animal models of Alzheimer's, oxytocin has been shown to reduce the toxicity of amyloid-beta plaques, the toxic protein clumps that are the hallmark of Alzheimer's disease" (said at 0:44:18)
Preclinical studies in animal and cellular models of Alzheimer's disease demonstrate that oxytocin mitigates amyloid-beta (Aβ)-induced neurotoxicity, reduces apoptosis, promotes microglial clearance of Aβ, and reverses synaptic and behavioral impairments. Because this evidence is limited to animal and in vitro experimental models, the certainty of evidence for clinical human outcomes remains very low.
Fathers who engage in more vigorous physical or proprioceptive touch with their babies subsequently exhibit higher oxytocin levels in blood tests.
"My lab found actually that when dads engage in more physical touch that there's a type of touch that's called proprioceptive touch, which is exactly what you were just describing: like picking babies up, moving them around, playing with them like in space. It's that sort of like vigorous touch that we often associate with fathers. When dads did more of that, they subsequently had higher oxytocin levels when we did a blood draw in our lab" (said at 0:44:57)
Published findings from laboratory studies directly support the claim. In a study evaluating 45 fathers and their 6-month-old infants, micro-coded playful proprioceptive touch during a laboratory free-play session was significantly associated with higher post-interaction paternal blood plasma oxytocin levels (measured using both extracted and unextracted immunoassays). Prior longitudinal observational research similarly found that paternal plasma oxytocin levels correlated with stimulatory parenting, including proprioceptive contact. The evidence is rated as low certainty due to the observational and correlational design and modest sample size.
- supports: Oxytocin and the development of parenting in humans. (Biological psychiatry 2010) · cited 470x in the literature
"Maternal OT was related to the amount of affectionate parenting behaviors, including "motherese" vocalizations, the expression of positive affect, and affectionate touch, whereas paternal OT correlated with the degree of stimulatory parenting behaviors, including proprioceptive contact, tactile stimulation, and object presentation." (abstract, results, passage verified)
pubmedfull study (doi) - supports: Physical touch during father-infant interactions is associated with paternal oxytocin leve… (Infant behavior & development 2021) · cited 41x in the literature
"Among 45 fathers and their six-month-old infants, we micro-coded paternal physical touch at 1/10 s intervals during a laboratory-based free-play interaction. Paternal oxytocin was measured via blood plasma and was processed both with and without the extraction step prior to immunoassay so that results from the two methods could be compared. Unextracted and extracted oxytocin were moderately correlated within our sample. Fathers who engaged in more playful proprioceptive touch showed higher levels of both unextracted and extracted oxytocin." (abstract, methods and results, passage verified)
pubmedfull study (doi)
Transition-to-parenthood research consistently finds a statistically significant drop in couple relationship satisfaction and sexual intimacy following the birth of a baby.
"And that is one of the most robust findings in transition to parenthood research is that there is a drop in couple relationship satisfaction often around the birth of a new baby... we've looked at that dip and we've seen that there is in fact a statistically significant drop in relationship quality and sex life." (said at 0:52:36)
Transition-to-parenthood literature consistently documents statistically significant declines in relationship quality/marital satisfaction and sexual satisfaction/intimacy following the birth of a child. A 2022 meta-analysis of 49 studies (PMID: 35936242) demonstrated a medium decrease in marital satisfaction between pregnancy and 12 months postpartum, with continued declines into the second year for both mothers and fathers. Multiple longitudinal dyadic studies further confirm parallel declines in couples' sexual satisfaction, frequency, and relationship functioning across the transition to parenthood.
New fathers experience depression at approximately twice the rate of the general non-fathering male population.
"And there's some evidence that dads' prevalence rate for depression, so in new dads, it's about twice that of the general population. So if you look at non-fathering men, they have about half the risk of depression as new dads." (said at 0:55:09)
A landmark meta-analysis by Paulson and Bazemore (JAMA 2010, PMID 20483973) synthesizing 43 studies with 28,004 participants estimated the overall rate of paternal prenatal and postpartum depression at 10.4% (95% CI, 8.5%-12.7%), with rates peaking at 25.6% during the 3- to 6-month postpartum period. The authors note that this overall rate of ~10.4% is approximately double the 12-month prevalence of major depressive disorder typically observed in the general male population (which is around 4-5%).
CDC data shows that total US births dropped by 1% to roughly 3.6 million babies, continuing a nearly two-decade decline since the Great Recession.
"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 downfall slide since the Great Recession." (said at 0:31:40)
CDC National Center for Health Statistics (NCHS) vital statistics reports confirm that annual US births declined to approximately 3.60 million (3,596,017 registered births in 2023, following provisional and final tabulations showing a continued 1% to 2% annual decrease and declining fertility rates). This trend continues the broader, nearly two-decade downward trajectory in US births and fertility rates that began after the peak around the 2007–2008 Great Recession.
Research shows that fathers specifically engage in more physically demanding, vigorous play with their children.
"And there's actually interesting research that dads especially play in these physically demanding kind of vigorous ways with" (said at 0:41:10)
A systematic review and meta-analysis of 40 studies (PMID: 42200809) comparing maternal and paternal interaction styles found that fathers engage in significantly higher levels of activation parenting and physical/rough-and-tumble play compared to mothers (Hedges' g = 0.27, p < 0.001), with the largest mother-father differences observed specifically in studies assessing rough-and-tumble and physically demanding play.
New fathers have lower rates of depression than new mothers.
"And new dads have lower depression rates than new moms, just to be clear." (said at 0:56:25)
Large systematic reviews and meta-analyses consistently find that while paternal postpartum depression is common (affecting approximately 8% to 10% of new fathers), its prevalence is lower than that observed in new mothers (where estimates generally range from 13% to 19% on screening instruments, or roughly 1.5 to 2 times higher than fathers).
- supports: Prevalence of paternal depression in pregnancy and the postpartum: An updated meta-analysi… (Journal of affective disorders 2016) · cited 587x in the literature
"The meta-estimate for paternal depression was 8.4% (95% confidence interval [CI], 7.2-9.6%) with significant heterogeneity observed among prevalence rates." (abstract, results, passage verified)
pubmedfull study (doi) - supports: Prevalence of prenatal and postpartum depression in fathers: A comprehensive meta-analysis… (Journal of affective disorders 2020) · cited 252x in the literature
"The prevalence of postpartum depression was 8.75% within a whole year, 8.98% within one-month, 7.82% between one- and three months, 9.23% between three months and six months and 8.40% between six months to twelve months after child-birth." (abstract, results, passage verified)
pubmedfull study (doi) - supports: Nutritional factors and cross-national postpartum depression prevalence: an updated meta-a… (Frontiers in psychiatry 2023) · cited 35x in the literature
"412 studies of 792,055 women from 46 countries were identified. The global pooled prevalence of PPD was 19.18% (95% confidence interval: 18.02 to 20.34%), ranging from 3% in Singapore to 44% in South Africa." (abstract, results, passage verified)
pubmedfull study (doi)
Studies examining the transition to parenthood from prenatal to postpartum have found that greater cortisol synchrony between partners can be beneficial.
"There are some other labs that have found that especially in a transition to parenthood context, more synchrony in cortisol can actually be a good thing if you're looking from prenatal to postpartum." (said at 0:58:20)
The claim is supported. Published research and systematic reviews investigating physiological and hormonal synchrony across the transition to parenthood (prenatal through postpartum) have documented cortisol and other endocrine synchrony between partners, showing that this coordination is associated with positive outcomes, including facilitation of the romantic bond and adaptive parenting behaviors.
Unlike many other animal species that have overt estrus signals, humans conceal their ovulation.
"One of the things that's really unique and interesting about humans is we conceal our ovulation. So that makes us different from a lot of other animals where when a female is fertile, you know, because she changes color, she starts dancing in a certain way, she smells different, right? Like there are all these really obvious cues and as a result, males sort of know exactly what window to jump in on. And because we conceal our ovulation as humans, it's always a little bit murky." (said at 1:01:45)
The speaker accurately describes a well-established biological and evolutionary characteristic of humans: unlike many non-human animal and primate species that exhibit overt, conspicuous estrus signals (such as sexual swellings, prominent olfactory cues, or behavioral displays), humans possess concealed ovulation and extended sexual receptivity throughout the menstrual cycle. Large empirical studies confirm that human males do not reliably detect or track ovulatory timing.
- supports: 'Concealed ovulation' and sexual signals in primates. (Folia primatologica; international journal of primatology 1992) · cited 43x in the literature
"The absence of conspicuous sexual signals in some primates, particularly humans and vervets, has been interpreted as evidence that females of these species are 'concealing' ovulation from males." (abstract, results, passage verified)
pubmedfull study (doi) - supports: Men are not aware of and do not respond to their female partner's fertility status: Eviden… (Hormones and behavior 2022) · cited 14x in the literature
"In a large, preregistered online dyadic diary study (384 heterosexual couples), we found no compelling evidence that men notice women's fertility status (as potentially reflected in women's attractiveness, sexual desire, or wish for contact with others) or display mid-cycle increases in mate retention tactics (jealousy, attention, wish for contact or sexual desire towards female partners). These results extend our current understanding of the evolution of women's concealed ovulation and oestrus" (abstract, results, passage verified)
pubmedfull study (doi)
Research indicates that psychological stress makes it harder to conceive.
"There is research on reducing stress for sure, right? Like we know that stress makes it harder to conceive." (said at 1:04:08)
Prospective cohort studies examining couples attempting to conceive naturally have demonstrated that biological markers of stress (specifically salivary alpha-amylase, an indicator of sympathetic adrenomedullary system activation) are associated with reduced fecundability, lower per-cycle conception probability across the fertile window, and a longer time to pregnancy (e.g., a 29% reduction in fecundity and a >2-fold increased risk of infertility in the LIFE cohort). While self-reported perceived stress questionnaires have sometimes shown mixed results compared to physiological stress biomarkers, the overall body of epidemiological research supports the statement that stress is associated with greater difficulty conceiving.
- supports: Stress reduces conception probabilities across the fertile window: evidence in support of … (Fertility and sterility 2011) · cited 186x in the literature
"Stress significantly reduced the probability of conception each day during the fertile window, possibly exerting its effect through the sympathetic medullar pathway." (abstract, conclusions, passage verified)
pubmedfull study (doi) - supports: Preconception stress increases the risk of infertility: results from a couple-based prospe… (Human reproduction (Oxford, England) 2014) · cited 203x in the literature
"After adjustment for female age, race, income, and use of alcohol, caffeine and cigarettes while trying to conceive, women in the highest tertile of alpha-amylase exhibited a 29% reduction in fecundity (longer TTP) compared with women in the lowest tertile [fecundability odds ratios (FORs) = 0.71; 95% confidence interval (CI) = (0.51, 1.00); P < 0.05]. This reduction in fecundity translated into a >2-fold increased risk of infertility among these women [relative risk (RR) = 2.07; 95% CI = (1.04, 4.11)]." (abstract, results, passage verified)
pubmedfull study (doi)
Research on depression shows that having a strong social support network is one of the best buffers against depression.
"So, you know, we know when we look at depression research that having a strong social support network is one of the best buffers." (said at 1:10:30)
Extensive meta-analytic and systematic review evidence confirms that strong social support and robust social networks act as major protective factors and buffers against depression across various populations (including youth, perinatal women, and older adults). A large meta-analysis of 341 studies (N = 273,149) demonstrated a consistent protective association between perceived social support and lower depressive symptoms, evaluating both general benefit and stress-buffering models. Systematic reviews in older and perinatal populations similarly show that larger, more supportive networks significantly mitigate depression risk.
- supports: A meta-analytic review of the association between perceived social support and depression … (Psychological bulletin 2016) · cited 931x in the literature
"This meta-analysis evaluated the relation between social support and depression in youth and compared the cumulative evidence for 2 theories that have been proposed to explain this association: the general benefits (GB; also known as main effects) and stress-buffering (SB) models. The study included 341 articles (19% unpublished) gathered through a search in PsycINFO, PsycARTICLES, ERIC, and ProQuest, and a hand search of 11 relevant journals. Using a random effects model, the overall effect size based on k = 341 studies and N = 273,149 participants was r = .26 (95% CI [.24, .28]), with robust support for the GB model and support for the SB model among medically ill youth." (abstract, results, passage verified)
pubmedfull study (doi) - supports: The association of social networks and depression in community-dwelling older adults: a sy… (Systematic reviews 2024) · cited 39x in the literature
"Previous research has identified that social networks have a buffering effect on depression... In total, 127 studies were included. The study categorizes structural network aspects into seven domains and finds that larger and more diverse networks, along with closer social ties, help mitigate depression." (abstract, results)
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Studies across both animal models and humans find that males tend to gain weight when they become fathers.
"it's been found across both animal and human studies that males tend to gain weight when they become fathers." (said at 1:16:14)
Both animal models (specifically biparental primates such as marmosets and tamarins) and longitudinal human cohort studies demonstrate that males tend to gain weight/BMI during their partner's pregnancy and following childbirth as they transition into fatherhood.
Prolactin levels rise in men around the transition to fatherhood.
"prolactin is a hormone we haven't talked much about, but that is rising, sleep deprivation, um changes in physical activity, changes in our diet, right, because of stress and some of the dietary choices that we're making." (said at 1:16:27)
Observational and neuroendocrine studies demonstrate that prolactin levels are elevated in men around the transition to fatherhood and during early infant care compared to non-fathers. Longitudinal and cross-sectional studies in expectant and new fathers indicate that prolactin rises during the perinatal period, correlating with maternal prolactin levels, infant bonding, and paternal responsiveness.
- supports: Prolactin, fatherhood, and reproductive behavior in human males. (American journal of physical anthropology 2012) · cited 61x in the literature
"In this sample, fathers had higher prolactin than nonfathers (P = 0.006), and fathers of infants had borderline higher prolactin than fathers of older children (P = 0.054)." (abstract, results, passage verified)
pubmedfull study (doi) - supports: Neurobiological Correlates of Fatherhood During the Postpartum Period: A Scoping Review. (Frontiers in psychology 2022) · cited 11x in the literature
"Collectively, studies published during the past 15 years suggest the existence of significant endocrine (testosterone, oxytocin, prolactin, and cortisol levels) and neurofunctional alterations... as a result of fatherhood" (abstract, results)
pubmedfull study (doi) - supports: Prenatal prolactin predicts postnatal parenting attitudes and brain structure remodeling i… (Psychoneuroendocrinology 2023) · cited 17x in the literature
"Fathers' prolactin levels were correlated with their partners' prolactin levels. Men's prolactin levels during their partner's pregnancy were associated with their self-reported antenatal bonding to the unborn infant." (abstract, results, passage verified)
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A study of expectant tamarin monkeys fed a standardized diet showed that expectant fathers gained more weight than control male monkeys who were not expecting offspring.
"So, there was a study that looked at tamarin monkeys that were expecting offspring, and um it fed them a standardized diet and it compared them to tamarin monkeys who didn't have partners that were expecting offspring. And they found that the expectant dads actually gained more weight even though they were eating the same diet as the comparison monkeys who weren't about to have a baby. And so there were these like body changes that happened even before birth in the male monkeys." (said at 1:17:01)
Studies of expectant cotton-top tamarins (and marmosets) found that expectant males show significant weight gain across their mate's pregnancy compared to control males who are not expecting offspring. Because the evidence comes from animal studies, the GRADE certainty is rated very low.
Fully monogamous animals like prairie voles exhibit virtually no male-female body size dimorphism, while harem-based species like gorillas exhibit large size differences between males and females.
"And you know, you can see that if you look at the difference in our body size, so like male humans are a little bit bigger than female humans, but they're not like twice as big. So like gorillas, male gorillas are way bigger than female gorillas. There's like a huge size differential. And you know that says that you know like the male gorilla model is one of like harem dominance, right? Fully monogamous animals are exactly the same size. Like prairie vole males and females are almost exactly the same size as each other. They have like no size differential." (said at 1:21:30)
Comparative evolutionary biology and mammalian studies support the claim. In species with intense male-male competition for mates (such as harem-polygynous primates like gorillas), sexual selection drives pronounced sexual size dimorphism, with adult males often reaching nearly double the body mass of females. In contrast, socially monogamous mammalian species, such as prairie voles (Microtus ochrogaster), exhibit minimal or no body size dimorphism between males and females, matching broad patterns correlating mating systems with sexual morphological dimorphism across mammals and anthropoids.
Strong social relationships in later life are a strong predictor of longevity.
"You know, going back to the idea that having a healthy late life is about building strong relationships and that that's a good predictor of our longevity." (said at 1:23:55)
The claim is supported by extensive epidemiological evidence. A landmark meta-analysis of 148 prospective studies comprising 308,849 individuals (Holt-Lunstad et al., 2010) found that individuals with stronger social relationships had a 50% increased likelihood of survival (OR = 1.50, 95% CI 1.42 to 1.59) compared to those with weaker social relationships, an association that held consistently across age groups, initial health status, and causes of death.
The baseline federal protection under the US Family and Medical Leave Act guarantees up to 12 weeks of unpaid leave while maintaining group health insurance.
"The baseline federal protection is the Family and Medical Leave Act. It guarantees up to 12 weeks of unpaid leave. Your employer must also maintain your group health insurance during this this time." (said at 1:26:09)
The Family and Medical Leave Act (FMLA) of 1993 is the primary federal statute governing family and medical leave in the United States. Under the FMLA, eligible employees of covered employers are entitled to up to 12 workweeks of unpaid, job-protected leave per year for qualifying family and medical reasons, during which the employer is legally required to maintain the employee's existing group health insurance coverage under the same terms and conditions as if the employee had continued working.
Bipartisan polling indicates that roughly 80% of Americans support paid parental leave.
"It's bipartisan, right? Both Republicans and Democrats say they support leave. I think it's something like 80% of Americans are in favor of it." (said at 1:26:42)
Representative national polling in the United States (including surveys from the Pew Research Center and the General Social Survey) consistently shows broad, bipartisan public support for paid parental leave, typically finding that roughly 80% of Americans (around 82% in major Pew findings for maternity leave and broadly ~70-85% across parental leave surveys) favor paid leave policies across both political parties.
- supports: Attitudes about Paid Parental Leave In the U.S. (? 2021) · cited 1x in the literature
"With the use of data from the General Social Survey, we investigated attitudes about paid parental leave availability, preferred lengths of paid leave offerings, and government funding of leave in the U.S. We found overwhelming support for paid parental leave availability, an average preference for four months of paid leave offerings, and common support for at least some government funding for leaves." (abstract, results, passage verified)
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Unverified means no publication matching the claim was located; it does not prove the claim false. Spotted an error? See the corrections policy - disputes from the people quoted are prioritized.