HoldsUp

Huberman Lab · 2026-03-30 · Andrew Huberman (host), Marc Breedlove

How Hormones Shape Sexual Orientation & Behavior | Dr. Marc Breedlove

60 research-tied claims examined: 3 contradicted 3 overstated 3 context 48 supported 3 unverified

3 Contradicted by research
0:38:51Marc Breedlovecontradictedmoderate

Chimpanzee brain growth slows rapidly after birth, whereas human brains sustain a fetal-like rate of growth until at least six to ten years of age.

"And shortly after birth, the chimpanzee brain stops growing as fast and eventually asymptotes right away. The human brain continues that feverish fetal rate of growth until at least 6 years of age, maybe out there to 10 years of age." (said at 0:38:51)

While humans are characterized by 'secondary altriciality'—extending rapid, fetal-like rates of brain growth postnatally compared to chimpanzees and other non-human primates—this rapid fetal rate of growth is sustained only during the first postnatal year (or up to roughly 12–18 months), after which the rate of brain growth decelerates dramatically. By 5 to 6 years of age, the human brain has already achieved ~90–95% of its adult size. The speaker erroneously claims that the fetal rate of brain growth continues until 'at least 6 years of age, maybe out there to 10 years of age', confusing prolonged neurodevelopmental maturation (such as synaptic remodeling and myelination) with sustaining the rapid fetal rate of volumetric growth.

1:18:41Andrew Huberman (host)contradictedmoderate

Nattokinase supplementation can reduce LDL cholesterol levels.

"As a result, I decided to start supplementing with nattokinase, which can naturally help reduce LDL cholesterol, and it did. In a follow-up test, I could confirm that this strategy worked; my blood lipids are now back where I want them in range." (said at 1:18:41)

A 2023 systematic review and meta-analysis of randomized controlled trials (PMID 39076715) evaluating nattokinase supplementation found that nattokinase monotherapy does not reduce LDL cholesterol. In pooled RCT data, standard/low doses showed a slight increase in LDL cholesterol compared to controls, while higher doses showed no statistically significant effect on LDL levels. Although combinations of nattokinase with red yeast rice (Monascus, which contains monacolin K / lovastatin) reduce LDL, and one non-randomized study observed lipid improvements only at an exceptionally high experimental dose (10,800 FU/day; PMID 36072877), the randomized trial evidence indicates that standalone nattokinase supplementation does not lower LDL cholesterol.

1:40:30Marc Breedlovecontradictedlow

In birds, brain sexual differentiation is driven by local hormone synthesis inside the brain determined by genetic sex.

"in some cases, it's the brain itself that's making the hormone and is masculinizing itself. So in birds, there's pretty good evidence that brain sexual differentiation happens because the genetic sex of the brain determines how much hormone, including testosterone and estrogen, is getting made locally and that that then is driving sexual differentiation" (said at 1:40:30)

While research in songbirds (such as zebra finches) established that the brain synthesizes its own neurosteroids (expressing steroidogenic enzymes like CYP17 and aromatase), empirical studies do not support the claim that sexual differentiation is driven by genetic sex determining local hormone synthesis levels. Studies measuring steroidogenic enzymes (CYP17 and aromatase) in the developing avian brain found no significant sex differences in expression levels or spatio-temporal patterns between males and females. Furthermore, manipulation of steroid synthesis (such as aromatase inhibition) fails to prevent masculine brain development, and gynandromorph studies indicate that avian brain sexual differentiation is driven primarily by cell-autonomous direct genetic sex effects rather than differences in local hormone production.

3 Overstated
0:00:30Andrew Huberman (host)overstatedlow

Prenatal testosterone exposure significantly affects 2D:4D finger length ratios and is correlated with sexual orientation.

"the amount of testosterone that a fetus is exposed to while in the mother has a profound impact not only on the ratio of finger lengths, yes, you heard that right, but it also plays a meaningful role in sexual orientation. And in fact, there's a correlation there between finger length ratios and sexual orientation." (said at 0:00:30)

The speaker overstates the evidence by asserting that fetal testosterone exposure has a 'profound impact' on digit ratios and 'plays a meaningful role' in sexual orientation, alongside a definitive correlation between 2D:4D and sexual orientation. While 2D:4D is widely discussed as a putative indirect biomarker for prenatal androgen exposure, a 2024 meta-analysis of 54 studies (Kowal et al., PMID 37795916) found no consistent evidence connecting directly measured prenatal testosterone (e.g., in umbilical cord blood) to digit ratios, noting that conclusions assuming 2D:4D is a reliable proxy warrant great caution. Furthermore, while some meta-analyses report small statistical differences in 2D:4D by sexual orientation (e.g., Grimbos et al., 2010; Swift-Gallant et al., 2025), recent robust Bayesian meta-analyses accounting for publication bias (PMID 41861700) demonstrate that evidence for group differences in 2D:4D based on sexual orientation is weak and substantially diminished after bias adjustments.

0:29:34Marc Breedloveoverstatedlow

William Byne's group independently replicated the finding that the INAH3 nucleus is smaller in homosexual men compared to heterosexual men.

"So that was William Byne, who eventually—and there's an interesting aspect of it. It took him a long time to get a sample big enough, because, you know, Simon, it was such a horrible time in the AIDS epidemic... and it took longer for William Byne to gather the samples, but eventually did, and even though he was skeptical of it, he saw it, too." (said at 0:29:34)

William Byne and colleagues (2001) attempted to replicate Simon LeVay's 1991 findings regarding the size of the third interstitial nucleus of the anterior hypothalamus (INAH3) in relation to sexual orientation. While Byne's group did observe a trend toward smaller INAH3 volume in homosexual men compared to heterosexual men in the same directional pattern, the difference did not reach conventional statistical significance, and there was no significant difference in the total number of neurons within INAH3 based on sexual orientation. Describing this study as a straightforward replication that 'saw it, too' overstates a finding that was statistically non-significant.

0:40:14Marc Breedloveoverstatedlow

Studies show that testosterone levels rise in voters whose candidate wins a presidential election and fall in voters whose candidate loses.

"In elections, it's been shown that people whose candidate won the presidential election, their testosterone levels went up a little bit, and the people whose candidate lost went down a little." (said at 0:40:14)

A 2008 study examining voter salivary testosterone levels on election night (PMID 19844583, n=183) found that male voters supporting the winning candidate (Barack Obama) maintained stable testosterone levels across the evening (resisting the normal circadian decline), whereas male voters supporting losing candidates (John McCain and Robert Barr) experienced a decrease in testosterone levels. However, testosterone levels did not actually increase in winning voters, and no significant changes were observed in female voters.

3 Needs context
0:00:30Andrew Huberman (host)needs contextlow

Each male pregnancy leaves a biological trace in the mother that biases the likelihood of subsequent male offspring being homosexual.

"every time a woman is pregnant with a male, there's a biological trace of that which biases the likelihood that her next male offspring will be either heterosexual or homosexual." (said at 0:00:30)

The speaker is describing the 'maternal immune hypothesis,' which provides a biological mechanism for the well-documented 'fraternal birth order effect' (the epidemiological finding that each older biological brother increases the odds of male homosexuality by roughly 30–47%). A 2018 case-control study found that mothers of gay sons with older brothers had significantly higher concentrations of antibodies against the Y-linked neuroligin protein NLGN4Y compared to mothers of heterosexual sons or women with no sons. However, the speaker frames this as a deterministic rule occurring 'every time a woman is pregnant with a male.' In reality, this is a probabilistic hypothesis: maternal immunization occurs in some mothers and accumulates across male gestations, and the underlying birth order effect remains an area of ongoing statistical and immunological investigation.

1:33:32Marc Breedloveneeds contextmoderate

The carrier frequency for congenital adrenal hyperplasia genetic mutations is approximately 1 in 12.

"is that it's very common. It's one in 12." (said at 1:33:32)

The statement that the carrier frequency for congenital adrenal hyperplasia (CAH) mutations is approximately 1 in 12 (~8-10%) is consistent with comprehensive genetic screening studies of the CYP21A2 gene in European and selected populations when including both classic and non-classic (mild) alleles (e.g., Baumgartner-Parzer et al., 2005 reported a 9.5% carrier frequency, or roughly 1 in 10.5). However, carrier frequency depends heavily on whether both classic and non-classic alleles are counted, as well as the specific population/ethnicity: traditional newborn screening estimates for severe/classic CAH alone estimate carrier frequencies closer to 1 in 55 to 1 in 65, whereas total heterozygote frequency (including mild alleles) ranges from ~1 in 10 to 1 in 15 in some populations, and is higher in specific ethnic groups like Ashkenazi Jews.

1:51:45Marc Breedloveneeds contextlow

In mixed-sex groups of monkeys or rats, overall levels of rough-and-tumble play are intermediate between all-male and all-female groups.

"And an interesting thing happens if you put it in a mixed group, and it doesn't matter whether it's monkeys or rats, the overall play will be intermediate. It's like the girls calm the boys down and the boys ramp the girls up a little bit." (said at 1:51:45)

Juvenile male and female rodents alter their rough-and-tumble play (RTP) behavior based on the sex and composition of their play partners, but the dynamics do not neatly reflect a simple averaging or intermediate level where 'girls calm boys down and boys ramp girls up.' In rats, males show partner-dependent modifications in play behaviors (such as attacks and pinning) when paired with females, and females often initiate significantly fewer playful nape attacks in mixed-sex groups compared to all-female groups (where female play frequency can equal male levels). Because these findings are derived from preclinical animal models with nuanced context-dependent partner interactions, the claim captures the broad concept of partner-dependent modulation but oversimplifies the specific behavioral shifts.

48 Supported by research
0:00:00Andrew Huberman (host)supportedmoderate

The probability of a male being gay increases with the number of older biological brothers he has.

"The larger the number of older brothers that a male has, the higher the probability that he is gay." (said at 0:00:00)

The statement accurately reflects the well-documented 'fraternal birth order effect'. Meta-analyses of dozens of independent cohorts (totaling tens of thousands of participants) confirm that each additional older biological brother reliably increases the odds of male homosexuality, an effect unique to older brothers and not observed with older sisters or younger siblings.

0:00:00Marc Breedlovesupportedmoderate

A baby boy with no older brothers has about a 2% baseline probability of being gay, and each older brother increases the odds by roughly 33% (to approximately 2.6% for one older brother and 3.5% for two older brothers).

"if a baby boy is born today, if he has no older brothers, his odds of being gay when he grows up is about 2%. Right? Pretty low. But if he had one older brother, his odds go up by a third. Okay, 2.6. And if he has two older brothers, they go up a third again. All right, now we're at 3.5." (said at 0:00:00)

The speaker accurately describes the standard numerical model of the fraternal birth order effect established in sexual orientation research (originally formulated by Blanchard and Bogaert). In demographic and epidemiological literature on this effect, the baseline probability of male homosexuality is typically modelled around 2%, with each additional older biological brother increasing the odds of male homosexuality by roughly 33% to 38% (progressing from ~2.0% with no older brothers to ~2.6–2.7% with one, and ~3.5% with two).

0:08:17Marc Breedlovesupportedmoderate

Females produce more spontaneous otoacoustic emissions than males, a sex difference that is already present at birth.

"what Dennis knew is there's a sex difference in how many of these otoacoustic emissions are being made. Girls make more and it's present at birth." (said at 0:08:17)

Dennis McFadden's research and broader audiological literature robustly establish that females produce more spontaneous otoacoustic emissions (SOAEs) and exhibit higher OAE amplitudes than males, a sexually dimorphic trait present at birth due to differences in prenatal androgen exposure affecting cochlear amplifier development.

0:08:17Marc Breedlovesupportedlow

Dennis McFadden reported that lesbian women produce fewer spontaneous otoacoustic emissions than heterosexual women.

"And he reports that compared to straight women, the lesbians have fewer of these otoacoustic emissions than straight women." (said at 0:08:17)

Dennis McFadden and Edward G. Pasanen reported in 1999 (PMID: 10212421) that spontaneous otoacoustic emissions (SOAEs) in homosexual and bisexual females were less numerous and weaker than those in heterosexual females, showing an intermediate, partially masculinized pattern between heterosexual females and males. Earlier work by the same group in 1998 (PMID: 9482952) found an identical pattern for click-evoked otoacoustic emissions (CEOAEs).

0:10:51Marc Breedlovesupportedhigh

The ratio of the second digit to the fourth digit (2D:4D) tends to be smaller in men than in women, and this sex difference is present in children.

"Divide the length of the second digit by the fourth digit, so-called 2D:4D ratio. And a guy named John Manning was reporting that there's a sex difference there, that that ratio tends to be smaller in men than in women, and that it's present in children." (said at 0:10:51)

John Manning and colleagues have extensively documented that the second-to-fourth digit ratio (2D:4D) is sexually dimorphic, with males consistently exhibiting lower mean ratios than females. Cross-sectional and longitudinal studies in pediatric populations confirm that this sex difference is established early in development and is present in children.

0:11:52Andrew Huberman (host)supportedmoderate

The sex difference in 2D:4D digit ratio between men and women is more pronounced on the right hand.

"And the difference between men and women is more pronounced on the right hand as I recall. That's true too." (said at 0:11:52)

A large meta-analysis of 116 samples (including 13,260 females and 11,789 males) examining expert-measured 2D:4D digit ratios confirmed that while men have lower 2D:4D digit ratios than women, the sexual dimorphism (sex difference) is significantly larger and more pronounced in the right hand than in the left hand.

0:14:01Andrew Huberman (host)supportedmoderate

A 2020 study by the Environmental Working Group estimated that over 200 million Americans are exposed to PFAS chemicals through tap water.

"In fact, a 2020 study by the Environmental Working Group estimated that more than 200 million Americans are exposed to PFAS chemicals, also known as forever chemicals, through drinking of tap water." (said at 0:14:01)

A 2020 study by researchers at the Environmental Working Group (Andrews & Naidenko, published in Environmental Science & Technology Letters) evaluated publicly accessible datasets of PFAS occurrence in U.S. drinking water. They estimated that over 200 million Americans likely receive tap water with perfluorooctanoic acid (PFOA) and perfluorooctanesulfonate (PFOS) concentrations at or above 1 ng/L.

0:14:01Andrew Huberman (host)supportedlow

The Environmental Working Group demonstrated that over 122 million Americans drink tap water containing elevated levels of carcinogenic chemicals.

"The Environmental Working Group has also shown that over 122 million Americans drink tap water with high levels of chemicals known to cause cancer." (said at 0:14:01)

Research conducted by scientists at the Environmental Working Group (EWG; Evans et al., 2019/2020) evaluated cumulative cancer risk from 22 carcinogenic contaminants across US community water systems using national drinking water data from 2010 to 2017. Their cumulative risk assessments demonstrated widespread exposure to carcinogenic drinking water contaminants (such as arsenic, disinfection byproducts, chromium-6, and radionuclides) exceeding benchmark health guidelines, finding that over 269 million Americans are served by water systems with cancer risks exceeding the de minimis threshold (one-in-a-million lifetime risk), with over 100 million Americans exposed at higher cumulative risk tiers. Because these estimates derive from toxicological modeling and population-level exposure estimations rather than direct prospective clinical epidemiological outcomes, certainty is low.

0:19:38Marc Breedlovesupportedlow

On average, lesbian women have more masculine 2D:4D digit ratios than heterosexual women, a finding confirmed across multiple meta-analyses.

"But back to the digit ratios, the lesbians had more masculine digit ratios than the straight women on average. And as you say, that's been replicated by many different labs. Dave Puts at Penn State and Ashlyn Swift-Gallant and I recently published like the third meta-analysis, and I mean it's clear." (said at 0:19:38)

Multiple meta-analyses have found that homosexual/lesbian women have significantly lower (more masculine/male-typical) 2D:4D digit ratios on average compared to heterosexual women. Grimbos et al. (2010) analyzed 16 independent female datasets and found heterosexual women had higher (more feminine) 2D:4D ratios than lesbians for both hands. An expanded meta-analysis co-authored by Swift-Gallant, Puts, and Breedlove (2025) encompassing 34 female datasets confirmed lower, more male-typical digit ratios in homosexual women compared to heterosexual women (right hand g = 0.26, left hand g = 0.16). While a recent Bayesian reanalysis (2026) suggested this finding may be substantially attenuated when accounting for publication bias, the speaker's claim accurately describes the conclusions of the major published meta-analyses in this literature.

0:25:25Marc Breedlovesupportedhigh

A sex difference in the 2D:4D digit ratio is present in mice.

"The sex difference is present in mice." (said at 0:25:25)

Multiple experimental and morphometric studies have demonstrated sexual dimorphism in the 2D:4D digit ratio in mice (particularly in the rear/hind paws), driven by differential prenatal androgen and estrogen receptor signaling during digit development.

0:25:31Marc Breedlovesupportedvery low

In mice, knocking out or impairing androgen receptor function eliminates the sex difference in digit ratios, as the fourth digit possesses higher androgen receptor concentration in developing bones than the second digit.

"and it turns out that if you make the androgen receptor dysfunctional, the sex difference goes away. And they showed that in mice, at least, there's more androgen receptor in the growing bones of the fourth digit than the second digit. And then they showed that, um, that that's why the fourth digit grows a little bit more than the second digit." (said at 0:25:31)

The speaker's claim accurately describes the seminal study by Zheng and Cohn (2011) in mice. The study demonstrated that androgen receptor (AR) and estrogen receptor alpha activity is higher in developing digit 4 than digit 2, and that inactivating AR decreases the growth of digit 4 (feminizing the digit ratio by increasing the 2D:4D ratio). Because this evidence comes directly from preclinical mouse developmental models, the GRADE certainty is rated as very low.

0:27:03Marc Breedlovesupportedmoderate

Simon LeVay found that the third interstitial nucleus of the anterior hypothalamus (INAH3 / SDN-POA) is significantly smaller in gay men than in straight men and comparable in size to that in women.

"And what he found was that the nucleus in gay men was smaller than in straight men and, in fact, not significantly different from the size of the nucleus in women." (said at 0:27:03)

Simon LeVay's landmark 1991 postmortem study published in Science examined the volumes of the interstitial nuclei of the anterior hypothalamus (INAH 1-4) in women, presumed heterosexual men, and homosexual men. LeVay reported that INAH 3 was more than twice as large in heterosexual men as in women, and also more than twice as large in heterosexual men as in homosexual men, with INAH 3 volume in homosexual men being comparable to that observed in women.

0:29:34Marc Breedlovesupportedvery low

Research by Brad Cooke demonstrated that the sex difference in the medial amygdala in animals disappears within a few weeks following testosterone removal in adult males.

"In fact, even in animals, Brad Cooke showed that, you know, there's a nucleus, the medial amygdala, um, there's a sex difference there, but if you take away the testosterone in males, sex difference goes away in just a matter of a few weeks." (said at 0:29:34)

A landmark 1999 rodent study by Brad Cooke and colleagues (PMID: 10377450) demonstrated that the sex difference in the volume and neuronal soma size of the posterodorsal medial amygdala (MePD) in adult rats is maintained by circulating androgens. Castrating adult male rats caused the MePD volume to shrink to female levels within four weeks, while testosterone treatment of adult females enlarged it to male levels. Because this evidence is derived entirely from animal models, the GRADE certainty is rated very low.

0:27:04Marc Breedlovesupportedvery low

The sexually dimorphic nucleus of the preoptic area (SDN-POA) in the rat brain is significantly larger in males than in females.

"he looked in the preoptic area because in rats, there's a very prominent sexual difference, or sex dimorphism, in a nucleus in the rat brain in the preoptic area, and the nucleus got named the sexually dimorphic nucleus of the preoptic area, or the SDN-POA. And Simon knew there was a huge sex difference there in rats." (said at 0:27:04)

The speaker accurately describes the sexually dimorphic nucleus of the preoptic area (SDN-POA) in rats. First identified and named by Gorski and colleagues, the SDN-POA in male rats is several times larger in volume and contains significantly more neurons than in female rats due to perinatal testosterone-mediated inhibition of apoptosis.

0:18:27Marc Breedlovesupportedmoderate

Marc Breedlove's original 2000 study on digit ratios and sexual orientation found no significant difference in 2D:4D finger length ratios between gay men and heterosexual men.

"Anyway, so I measure these hands and I'm doing the math at the end of the day and lo and behold, I don't see any difference in the digit ratios of gay and straight men, right? Okay." (said at 0:18:27)

The claim is supported. In the seminal 2000 study on 2D:4D digit ratios and sexual orientation by S. Marc Breedlove and colleagues (Williams et al., Nature 2000, PMID 10761903), the researchers found a statistically significant masculinized (lower) 2D:4D ratio in homosexual women compared to heterosexual women, but no significant overall difference in digit ratios between heterosexual men and gay men (differences in men only emerged after stratifying by fraternal birth order). Subsequent reviews by Breedlove and early meta-analyses confirmed that overall 2D:4D ratios showed a robust difference between lesbian and heterosexual women, whereas the overall difference in men was absent in the initial dataset.

0:35:32Marc Breedlovesupportedhigh

The difference in digit ratios (2D:4D) between men and women has an effect size of approximately half a standard deviation.

"Well, this sex difference in digit ratios is half a standard deviation, so a quarter that." (said at 0:35:32)

Large-scale meta-analytic evidence confirms that the sexual dimorphism in human 2D:4D digit ratios (lower in men than in women) has a moderate effect size corresponding to approximately half a standard deviation (Cohen's d ~ 0.4 to 0.6, typically averaging around d = 0.5 for right-hand expert measurements).

0:38:43Marc Breedlovesupportedmoderate

Prior to birth, the rate of brain size increase compared to body size is approximately identical in humans and chimpanzees.

"So up until birth, the rate at which the brain size increases compared to body size is about the same in humans and chimps." (said at 0:38:43)

Comparative developmental and evolutionary anthropology studies show that prenatal brain growth allometry relative to body size is conserved across anthropoid primates, including humans and chimpanzees. In both species, the prenatal rate of brain mass increase relative to fetal body growth follows nearly identical scaling trajectories. The major divergence between human and chimpanzee brain-to-body scaling occurs postnatally: chimpanzees decelerate brain growth rapidly around birth (expanding brain size by ~2.5x from birth to adulthood), whereas humans maintain rapid brain growth rates into early postnatal life (expanding by ~3.3x).

0:40:07Marc Breedlovesupportedmoderate

In competitive contests, winners experience an increase in testosterone levels post-event while losers experience a decrease.

"In competitions, the winners afterwards are more likely to have higher testosterone and the losers will have lower." (said at 0:40:07)

Meta-analytic evidence supports the claim (often referred to as the 'winner-loser effect' within the biosocial model of status). An updated meta-analysis of 60 effect sizes and over 2,500 participants found that winners experience a significantly larger relative increase in testosterone concentrations compared to losers (d = 0.20 overall, and d = 0.43 in real-world sport settings). Systematic review data in specific sports (e.g., soccer) also show a divergence where winners typically display an increase and losers a decrease relative to pre-match baselines.

0:41:27Andrew Huberman (host)supportedvery low

A population of POMC appetite-suppressing neurons in the hypothalamic arcuate nucleus can undergo late-stage plasticity to express neuropeptide Y (NPY).

"I saw a paper just the other day that, um, the neurons that control suppression of appetite, these POMC neurons in the arcuate nucleus, there's a population of them that are sort of undifferentiated that can become, let's just call it pro-hunger, and by expressing a different peptide, neuropeptide Y, and that there's a lot of late-stage plasticity." (said at 0:41:27)

Animal and developmental neurobiology studies support the claim that hypothalamic POMC (pro-opiomelanocortin) progenitors and differentiated neurons exhibit developmental and phenotypic plasticity, with a subset able to adopt an orexigenic neuropeptide Y (NPY) phenotype. Studies manipulating microRNAs (such as Dicer/miR-103/107) and transcription factors (such as Tbx3) have shown that immature POMC progenitors and terminally differentiated neurons can switch or differentiate into NPY-expressing neurons. Because evidence is currently derived from animal and in vitro cellular models, certainty is graded as very low for direct application to humans.

0:44:54Marc Breedlovesupportedvery low

In male rats, removing testosterone causes mounting behavior to cease within a few weeks, and administering testosterone restores mounting behavior.

"In animals, at least, we know that that there's a relationship there, that in in males, in males of most species, let's take rats, uh, if you take away the testosterone, within a few weeks, they'll they'll stop mounting altogether. And if you give them testosterone, after a few weeks, they they start mounting again" (said at 0:44:54)

Extensive experimental animal literature demonstrates that castration (removal of endogenous testosterone) leads to the gradual decline and eventual cessation of mounting and copulatory behavior in male rats over several weeks, and that exogenous testosterone replacement reinstates mounting and copulatory behavior over subsequent weeks. Because this claim is grounded entirely in animal experimental data, the GRADE certainty is rated as very low.

0:45:18Marc Breedlovesupportedvery low

Exposure to the odors of a receptive female causes a spike in testosterone levels in male animals.

"we've known for a long time that if a male is exposed to the odors of a receptive female, that causes a spike in their testosterone." (said at 0:45:18)

The claim is supported by decades of mammalian neuroendocrinology research in rodents (e.g., mice, rats, and hamsters). Exposure to receptive female olfactory cues (such as urine, pheromones, or vaginal secretions) rapidly stimulates the hypothalamic-pituitary-gonadal axis via medial amygdala and kisspeptin pathways, triggering rapid surges in luteinizing hormone (LH) and a corresponding spike in circulating testosterone. Because the claim is supported entirely by animal experimental data, the GRADE certainty is rated very_low.

0:49:48Marc Breedlovesupportedvery low

Male rats castrated on the day of birth and treated with estrogen and progesterone in adulthood display female-typical lordosis posture when mounted.

"Now I drop into the cage a a male rat who I castrated on the day of birth 90 days before and I've given him the same hormones I gave the female to make her receptive. Romeo hops on, and sure enough, a beautiful lordosis, right, of the sort that the control male never showed." (said at 0:49:48)

The speaker accurately describes a foundational finding in neuroendocrinology (the organizational-activational hypothesis of sexual differentiation): male rats deprived of perinatal testicular androgens via castration on or near the day of birth fail to defeminize and retain the neural circuitry necessary to display the female-typical lordosis posture in adulthood when primed with ovarian hormones (estrogen and progesterone) and mounted by a male. Intact control males do not display this receptive behavior. Because the evidence is derived exclusively from animal experiments, the GRADE certainty is very low.

0:54:27Marc Breedlovesupportedmoderate

A small percentage of domestic rams exclusively court and mount other rams and show no sexual interest in females even after prolonged exposure.

"Chuck did these tests where he would put a bunch of females that are in stocks so they can't move and they're all ready for mating. And he put a ram in with them, and most rams, of course, will mount the females. He puts in these rams that prefer males. If there's a variety of sheep's butts sticking out at him, he'll mount males... and he never mounts a female. In some cases, they'll have one of these—I'm going to call them gay rams... He'll put the gay ram where there's a dozen females, and he might be in that paddock for 12 hours and never mount a single female." (said at 0:54:27)

Extensive research by Charles (Chuck) Roselli and colleagues has established that approximately 6–10% (commonly cited as ~8%) of domestic rams naturally display an exclusive sexual preference for other males, actively courting and mounting rams while showing no sexual interest in estrous females during standardized partner preference testing.

0:57:19Marc Breedlovesupportedvery low

Male-oriented rams show structural and neurochemical differences in the preoptic area of the hypothalamus compared to female-oriented rams.

"Chuck eventually dissected the preoptic areas of these various rams. And he found a difference between the preoptic area of gay rams and straight rams, a difference in how they process testosterone in exactly that part of the brain, the preoptic area where Simon saw a difference between gay and straight men." (said at 0:57:19)

Charles Roselli and colleagues demonstrated that male-oriented domestic rams exhibit distinct structural and neurochemical characteristics in the preoptic area/anterior hypothalamus compared to female-oriented rams. Specifically, the volume of the ovine sexually dimorphic nucleus (oSDN) is approximately twofold larger in female-oriented rams than in male-oriented rams (in which volume is comparable to ewes). Additionally, the oSDN neurons express cytochrome P450 aromatase (the enzyme converting testosterone to estrogens), with female-oriented rams demonstrating significantly higher aromatase mRNA expression than male-oriented rams. GRADE certainty is very low because the evidence is derived from animal neuroanatomical studies.

1:00:35Marc Breedlovesupportedmoderate

Women display greater longitudinal fluidity and plasticity in their sexual attractions and orientation than men do.

"And we know there are plenty of women who are straight in one part of their lives, and later they fall in love with a woman and now they feel like they're gay, right? So females, women, are more plastic in terms of their sexual longings and sexual orientation than men are." (said at 1:00:35)

Extensive empirical and theoretical literature in sexology (notably pioneered by Roy Baumeister and Lisa Diamond) supports the finding that women generally display greater erotic plasticity and sexual fluidity over time compared to men. Evidence from psychological reviews, daily diary studies, and longitudinal cohort analyses shows that female sexual desire, attractions, and orientation identities are more responsive to situational, relational, and sociocultural factors across the lifespan than male sexual orientations, which tend to be more categorically fixed.

0:36:59Marc Breedlovesupportedmoderate

Demographic surveys show that a higher proportion of young people currently identify as bisexual compared to previous generations.

"if you do surveys now, especially for among younger people, there are more people who report that they are bisexual than there were then." (said at 0:36:59)

Demographic and population-based surveys in the United States and internationally consistently show that younger cohorts report higher rates of bisexual identification compared to previous generations (particularly driven by pronounced increases among younger women). For example, analysis of the National Survey of Family Growth across birth cohorts from 1966 to 1995 demonstrated significant cohort increases in self-reported bisexual identity.

1:08:11Marc Breedlovesupportedhigh

In congenital adrenal hyperplasia (CAH), impaired synthesis of adrenal steroids causes the pituitary to overstimulate the adrenal glands, leading to hypertrophy and excess production of testosterone and other androgens.

"these are individuals where the fetus itself is not able to make some of the adrenal steroids that are important for staying healthy. And so the brain, detecting, "Hey, where are the adrenal steroids that we need here?" drives the pituitary to tell the adrenal gland, "Hey, we need more steroids." The adrenal gland gets the message. It hypertrophies, but the machinery isn't there to make those steroids. And so instead, the adrenal gland makes testosterone and other androgens." (said at 1:08:11)

The speaker accurately describes the classic pathophysiology of congenital adrenal hyperplasia (CAH), most commonly caused by 21-hydroxylase deficiency. In CAH, enzymatic defects impair cortisol synthesis, eliminating normal negative feedback to the hypothalamus and pituitary. This results in elevated secretion of adrenocorticotropic hormone (ACTH), driving adrenal cortical hyperplasia and shunting accumulated steroid precursors into the androgen synthesis pathway, leading to excess production of androgens such as androstenedione and testosterone in utero and postnatally.

1:13:00Marc Breedlovesupportedmoderate

Women with congenital adrenal hyperplasia are more likely to report same-sex sexual attraction than the general population, with the reported percentage of lesbian orientation increasing with age.

"if you look at groups of women with CAH, they are more likely to be same-sex attracted, to be lesbians, than the population at large, but most of them are straight. But what's interesting about that is the older they get, as you keep surveying them, the higher the percentage of them that report having a lesbian orientation." (said at 1:13:00)

Evidence from clinical cohort studies and reviews confirms both aspects of the claim. Women with congenital adrenal hyperplasia (CAH), exposed to atypical levels of prenatal androgens, consistently demonstrate higher rates of non-heterosexual (bisexual/homosexual) attraction and orientation compared to control populations (e.g., ~15-40% depending on genotype/virilization severity vs. ~2-7% in controls), while the majority remain heterosexual. Longitudinal and cross-sectional survey data across adulthood have also documented that rates of reported same-sex attraction and lesbian orientation tend to increase over time as individuals age and gain adult relationship experience.

1:13:52Marc Breedlovesupportedhigh

The gene encoding the androgen receptor is located on the X chromosome.

"And it turns out the gene for the androgen receptor that responds to testosterone and other androgens is on the X chromosome." (said at 1:13:52)

The gene encoding the human androgen receptor (AR) is located on the X chromosome (specifically at cytogenetic locus Xq11–q12). This is a well-established fact of human genetics confirmed across extensive literature and genomic mapping.

1:14:38Marc Breedlovesupportedhigh

In complete androgen insensitivity syndrome, XY individuals have testes producing anti-Müllerian hormone (preventing uterus and oviduct formation), elevated testosterone, and typical female external genitalia.

"The testes will secrete two hormones that are going to guide sexual differentiation in the periphery, one of them being anti-Müllerian hormone, which is going to suppress the development of the Müllerian ducts, and therefore no oviduct, no uterus will form... and so she'll eventually go to an OB-GYN who will first do an exam, a vaginal exam, and he'll notice that the vagina is relatively short because the inner part of the vagina is normally derived from the Müllerian ducts. Well, in this woman, in this teenage girl, the Müllerian ducts never develop because of anti-Müllerian hormone. So, there'll be no cervix that can be seen in the exam. And if he takes blood plasma levels, he'll see that this very feminine-looking girl, teenage girl, has very high levels of testosterone... And yes, there are testes in there, typically in the abdomen." (said at 1:14:38)

The speaker's explanation accurately describes the pathophysiology and clinical presentation of Complete Androgen Insensitivity Syndrome (CAIS). In 46,XY individuals with CAIS, functional testes develop and secrete anti-Müllerian hormone (AMH) and testosterone. AMH causes the regression of Müllerian duct structures, preventing the development of the uterus, fallopian tubes (oviducts), and the upper part of the vagina/cervix. Due to complete androgen receptor insensitivity, external genitalia differentiate along typical female lines, and circulating testosterone levels are normal-to-elevated (in the male reference range or higher due to lack of androgen feedback on LH).

  • supports: Molecular pathogenesis, diagnosis, and management challenges in complete androgen insensit… (Frontiers in endocrinology 2025) · cited 5x in the literature
    "Primitive bipotent gonads in CAIS differentiate into testes producing androgens and antimüllerian hormone (AMH). However, androgens cannot stimulate embryonic wolffian ducts into male internal reproductive organs owing to AR defect and hormone resistance, while AMH induces the regression of müllerian ducts with the absence of uterus, fallopian tubes, and upper third of the vagina. Thus, with male sex chromosome and testes, individuals with CAIS present with a typical female phenotype... Endocrinological hormone assay is helpful for the identification of CAIS which reveals normal or elevated T levels" (abstract)
    pubmedfull study (doi)
1:16:58Marc Breedlovesupportedmoderate

The vast majority of individuals with complete androgen insensitivity syndrome identify as women and are sexually attracted to men.

"what's the sexual orientation of these women? And the vast majority of them grow up to be straight. They are attracted to men, and they might be very—they're often very interested in having a family." (said at 1:16:58)

Published clinical and psychosexual outcome studies consistently show that the vast majority of individuals with 46,XY complete androgen insensitivity syndrome (CAIS) identify as female/women and have an androphilic (heterosexual, attracted to men) sexual orientation. Because androgen receptor dysfunction prevents prenatal and postnatal androgen signaling, brain and psychosexual development follow a typical female trajectory.

1:22:41Marc Breedlovesupportedmoderate

Each additional older biological brother increases the probability of a male being homosexual by approximately 33%.

"if a baby boy is born today, if he has no older brothers, his odds of being gay when he grows up is about 2%. Right? Pretty low. But if he had one older brother, his odds go up by a third. Okay, 2.6. And if he has two older brothers, they go up a third again. All right, now we're at 3.5." (said at 1:22:41)

The speaker accurately describes the well-established 'fraternal birth order effect' first quantified in landmark studies and meta-analyses by Ray Blanchard and colleagues. Research demonstrates that each additional older biological brother increases the odds of male homosexuality by approximately 33% (odds ratio ~1.33). The numerical illustration given by the speaker (baseline odds starting around 2%, increasing to ~2.6% with one older brother, and ~3.5% with two older brothers) precisely aligns with the mathematical application of this ~33% relative odds increase per older brother.

1:23:55Marc Breedlovesupportedhigh

In the general human population, the secondary sex ratio is approximately 105 male births for every 100 female births.

"So it turns out in the general population, there are about 105 boys born for every 100 girls, right? That's also very consistent." (said at 1:23:55)

Extensive demographic and epidemiological registry data establish that the natural secondary sex ratio (the sex ratio at birth) across human populations is approximately 105 male births for every 100 female births (typically falling within the standard biological range of 103–107 males per 100 females). Large population records, such as national vital statistics across England and Wales (105.3 per 100) and Sweden (105.9 per 100), confirm this ratio.

1:24:17Marc Breedlovesupportedmoderate

Gay men have an older brother to older sister ratio of roughly 140 to 100, compared to approximately 105 to 100 in heterosexual men.

"For straight men, you total up all the older brothers they have and all the older sisters, and there's a ratio of about 105 older brothers to 100 older sisters. For the gay men, it turned out there were 140 older brothers for every 100 sisters." (said at 1:24:17)

The speaker's statement accurately summarizes the biodemographic research on the fraternal birth order effect in male sexual orientation, primarily pioneered by Ray Blanchard and colleagues. In the general population and among heterosexual men, the ratio of older brothers to older sisters mirrors the standard human secondary sex ratio (approximately 105 to 106 males per 100 females). In cohorts of homosexual men (particularly right-handed homosexual men), studies consistently find an excess of older brothers relative to older sisters, with ratios across classic datasets typically reported between ~130 and ~140 older brothers per 100 older sisters.

1:25:50Marc Breedlovesupportedmoderate

Statistical modeling estimates that approximately one in seven gay men are homosexual due to the fraternal birth order effect.

"Ray Blanchard has done the statistics, and their estimate is of all the population of gay men, about one in seven are gay because their mother carried brothers before them." (said at 1:25:50)

Ray Blanchard and colleagues derived population attributable fraction (PAF) calculations modeling the fraternal birth order effect. In their 2002 publication (PMID: 11910793), they explicitly calculated that roughly 1 gay man in 7 (approx. 15%) owes his sexual orientation to having older brothers (hypothesized to occur via maternal immune response to male fetuses). Subsequent estimates from probability samples have ranged from approximately 15% to 29% (PMID: 14994314, PMID: 15302549).

1:28:24Marc Breedlovesupportedlow

Older stepbrothers do not increase a male's odds of being gay, whereas biological older brothers from the same mother increase the odds regardless of whether they were raised together.

"Tony Bogaert started looking at these data, and he started asking, well, what about stepbrothers? Do older stepbrothers make any difference in the odds of sexual orientation? And the answer was a clear no. On the other hand, older brothers who came from the same mother but were raised apart had just as much of an effect as those that were raised with it." (said at 1:28:24)

Anthony Bogaert's 2006 study examined 944 homosexual and heterosexual men, including individuals raised in blended or nonbiological families (e.g., step-siblings, half-siblings, or adoptees). The study found that only biological older brothers predicted male sexual orientation, whereas nonbiological older brothers (such as stepbrothers) had no effect, and the biological older brother effect was independent of whether siblings were reared together or apart. As this is observational research, the GRADE certainty is rated as low.

1:29:44Marc Breedlovesupportedlow

Mothers of gay sons with older brothers have higher concentrations of antibodies against the male-specific protein neuroligin 4Y (NLGN4Y) than control mothers.

"And the strong evidence they found in favor of this is that in women who have sons where there's this pattern that looks like that might have happened, it turns out they have higher levels than control mothers of antibodies to a male-specific antigen, quite specifically an antigen to a protein called neuroligin 4Y." (said at 1:29:44)

A 2018 study by Bogaert et al. (PNAS) tested maternal immune responsivity to Y-linked proteins (PCDH11Y and NLGN4Y). They found that mothers of gay sons, particularly those with older brothers, had significantly higher concentrations of antibodies against the male-specific protein neuroligin 4 Y-linked (NLGN4Y) compared with control mothers, including mothers of heterosexual sons. As an observational case-control finding in a single cohort, the evidence grade is low certainty.

1:15:56Marc Breedlovesupportedhigh

The inner portion of the human vagina is embryologically derived from the Müllerian ducts.

"the inner part of the vagina is normally derived from the Müllerian ducts. Well, in this woman, in this teenage girl, the Müllerian ducts never develop because of anti-Müllerian hormone. So, there'll be no cervix that can be seen in the exam." (said at 1:15:56)

Standard human embryology establishes that the female reproductive tract is formed from dual embryonic origins: the fused paramesonephric (Müllerian) ducts form the fallopian tubes, uterus, cervix, and the upper (inner) portion of the vagina, while the lower (outer) portion develops from the sinovaginal bulbs of the urogenital sinus. In genetic males or conditions with intact Anti-Müllerian Hormone (AMH) secretion (such as Complete Androgen Insensitivity Syndrome), AMH causes regression of the Müllerian ducts, resulting in the absence of the uterus, cervix, and upper vagina, leaving only a shallow lower vaginal pouch derived from the urogenital sinus.

1:30:03Marc Breedlovesupportedhigh

Neuroligins are cell adhesion molecules involved in synapse formation, and humans have distinct homologous copies on both the X and Y chromosomes (NLGN4X and NLGN4Y).

"You know that neuroligins are important for synapse formation. And this one, neuroligin 4, there's one on the X chromosome and one on the Y chromosome, and they're slightly different." (said at 1:30:03)

The claim accurately reflects established molecular genetics and neuroscience. Neuroligins are a family of synaptic cell adhesion molecules involved in synapse formation and maturation. In humans, neuroligin-4 exists as homologous pairs on the sex chromosomes: NLGN4X on the X chromosome and NLGN4Y on the Y chromosome, which share approximately 97% sequence identity but exhibit distinct functional properties.

1:22:32Marc Breedlovesupportedmoderate

The fraternal birth order effect on male sexual orientation was first identified and reported by Ray Blanchard.

"It's really one of the rock-solid findings in human sexuality that was first noticed by Ray Blanchard at Toronto and has been seen in many populations all over the world." (said at 1:22:32)

The fraternal birth order effect on male sexual orientation was first identified and reported in 1996 by Ray Blanchard (at the Clarke Institute of Psychiatry / University of Toronto) and Anthony Bogaert. They established that male homosexuality is positively correlated with the number of older brothers, a biodemographic phenomenon that has since been widely replicated across diverse international cohorts.

1:32:45Marc Breedlovesupportedmoderate

Having older or younger sisters, or younger brothers, does not change a male's odds of being gay.

"Ray's looked at that very carefully, and so older sisters don't matter, and neither do younger sisters. And here's the other thing: that younger brothers don't matter, right? So no matter how many younger brothers you have, that doesn't change your odds of being gay when you grow up." (said at 1:32:45)

Extensive meta-analyses and demographic research led by Ray Blanchard on the 'fraternal birth order effect' demonstrate that having older brothers is specifically associated with increased odds of male homosexuality, whereas having older sisters, younger sisters, or younger brothers does not independently increase the odds.

1:35:23Marc Breedlovesupportedhigh

Being a heterozygote for the sickle cell anemia mutation confers a survival advantage against malaria.

"Where being a heterozygote for that gene confers an advantage if there's malaria in the area; you'll be less likely to succumb." (said at 1:35:23)

Heterozygosity for the sickle hemoglobin mutation (sickle cell trait, HbAS) is well established as conferring substantial protection against severe, life-threatening Plasmodium falciparum malaria and malaria mortality (typically ~90% protection against severe/complicated malaria), representing a classic example of balanced polymorphism and heterozygote advantage.

1:37:04Marc Breedlovesupportedhigh

Nicole Le Douarin conducted experiments transplanting embryonic neural system tissue between quail and chick embryos.

"Nicole Le Douarin, did these experiments where she would open up chick embryos and quail embryos, and she could scoop out part of the nervous system from one and implant it in the other, and she'd know when she had done it right that she had a way of telling the cells apart under a microscope." (said at 1:37:04)

Nicole Le Douarin pioneered the quail-chick chimera marking system in avian developmental biology. By microsurgically transplanting portions of the developing nervous system (such as the neural tube, neural crest, and rhombomeres) between Japanese quail and chick embryos in ovo, she tracked cell migration and fate. Quail and chick cells can be distinguished microscopically due to distinctive histological features (condensed heterochromatin associated with the quail nucleolus).

1:39:13Marc Breedlovesupportedvery low

In gynandromorphic songbirds, the brain region HVC is larger on the genetically male side of the brain than on the female side.

"when Art Arnold and others looked at the brains of gynandromorphs, sure enough, the sex differences where this region, HVC, for example, tends to be larger in males than females. In these animals, it was larger on one side of the body than on the other." (said at 1:39:13)

In a landmark 2003 study by Art Arnold and colleagues (Agate et al., PNAS), the researchers examined a rare bilateral gynandromorphic zebra finch that was genetically male (ZZ) on the right side and genetically female (ZW) on the left side. Despite both hemispheres being exposed to the same circulating hormonal environment, the neural song circuit (including HVC and Area X) had a distinctly more masculine, larger phenotype on the genetically male right side than on the genetically female left side. GRADE certainty is very low because the evidence comes from an animal case study.

1:44:05Marc Breedlovesupportedmoderate

Julian Davidson at Stanford conducted double-blind, placebo-controlled trials showing testosterone administration improves energy, mood, and libido in hypogonadal men.

"Julian Davidson at Stanford, actually in the physiology department there, uh was among the first to do these double-blind, placebo-controlled studies in men who had lost their testes for one reason or another, accident or cancer, things like that... And they concluded uh that in fact the men who were getting testosterone definitely reported feeling better, feeling more energetic, having a higher libido" (said at 1:44:05)

Julian M. Davidson (Professor of Physiology at Stanford University) conducted pioneering double-blind, placebo-controlled crossover trials in the late 1970s and early 1980s evaluating testosterone replacement in hypogonadal men. His landmark 1979 trial in the Journal of Clinical Endocrinology and Metabolism demonstrated that testosterone administration reliably restored libido, spontaneous erections, and sexual behavior compared to placebo, while subsequent work with mood inventories (e.g., Profile of Mood States) also documented reductions in fatigue and improvements in mood/well-being.

1:47:10Marc Breedlovesupportedhigh

Age-related testosterone decline in men is much more gradual than the hormonal changes occurring in women during menopause.

"for the decline in testosterone levels in men, uh first of all, it's so much more gradual compared to what happens to women at menopause, right? There's no comparison whatsoever" (said at 1:47:10)

The speaker's assertion is fully supported by established endocrinological evidence. In women, menopause represents a relatively rapid and universal transition marked by the cessation of ovarian follicular activity and a steep decline in estrogen levels over a few years. In contrast, age-related testosterone decline in men (often termed andropause or late-onset hypogonadism) is a subtle, progressive process occurring over several decades (typically declining at a rate of approximately 1% per year after early adulthood) without abrupt cessation of testicular function.

1:50:44Marc Breedlovesupportedmoderate

Scientific studies searching for social and family correlates of male sexual orientation, such as an absent father or an overprotective mother, have failed to find reliable empirical support.

"in terms of sexual orientation, I I can tell you people looked really hard for any social correlates. You know, you talked earlier about the the dad that's missing or or even Freud talked about the overly coddling mother and and the the dismissive father that that might make a boy more likely to be gay. And so people have looked for those sorts of correlates. The data just aren't there." (said at 1:50:44)

Extensive empirical research assessing psychoanalytic and social-environmental hypotheses regarding the development of male sexual orientation—specifically theories involving overprotective/coddling mothers, absent or rejecting fathers, or other post-natal family dynamic factors—has consistently failed to find reliable empirical support. Comprehensive reviews of sexual orientation etiology (such as Bailey et al., 2016) confirm that early developmental social hypotheses lack robust predictive power, whereas biological and prenatal factors (such as prenatal hormonal influences, fraternal birth order, and genetic markers) account for the observed patterns.

2:07:05Marc Breedlovesupportedmoderate

Research by Melissa Hines demonstrated that male monkeys show significantly more interest in wheeled toys than female monkeys, while female monkeys show more interest in doll-like toys.

"Melissa Hines showed it first. Even among monkeys, if you put in wheeled toys, it's the male monkeys that are much more interested in that than the females. And the female monkeys are much more interested in in the dolls, etc." (said at 2:07:05)

Research by Gerianne Alexander and Melissa Hines (2002) in vervet monkeys first reported that male monkeys showed significantly more contact time with male-typed toys (such as a car and a ball) than females, whereas female monkeys showed greater contact time with female-typed toys (such as a doll and a pot). Subsequent research in rhesus macaques (Hassett et al., 2008) similarly found that male monkeys exhibited a strong preference for wheeled toys over plush toys, while females showed more flexible interactions. Although a more recent study testing monkeys in isolation (PMID: 36737809) questioned whether these preferences hold outside group social dynamics, Hines's landmark research did demonstrate the sex-differentiated toy preferences described.

3 No source found (not proven false)
0:06:07Marc Breedloveunverifiedvery low

Human brains continue growing at a fetal rate of growth until approximately nine or ten years of age.

"we have this long stretch of time where our brains are still growing at a fetal rate of growth until like nine or 10 years of age and we're taking in so much information." (said at 0:06:07)

No publication matching the claim could be fetched and verified within the search session. Standard neurodevelopmental literature indicates that while the human brain undergoes rapid growth in early life, the rapid fetal rate of brain growth only continues for approximately the first year of postnatal life (secondary altriciality), with total brain volume reaching ~80-90% of adult volume by early childhood rather than maintaining a fetal growth velocity through age 9 or 10; however, without a fetched record to cite in this verification session, this finding is classified as unverified.

0:34:34Marc Breedloveunverifiedlow

The difference between male and female adult human height averages is approximately two standard deviations.

"And that that's because those two averages in those two populations are about two standard deviations apart, the standard deviation being a measure of how much variability there is in something." (said at 0:34:34)

No matching published record directly evaluating or citing this exact effect size for human height was retrieved from the search queries within the search constraints. This does not mean the statement is false; standard anthropometric datasets (such as CDC/NCHS or UK Biobank data) show that adult male and female average heights typically differ by approximately 13 to 14 cm, with a standard deviation within each sex of roughly 6.5 to 7.0 cm, corresponding to an effect size (Cohen's d) of approximately 2.0 standard deviations.

2:05:32Andrew Huberman (host)unverifiedvery low

A study found that the more children people have, the more they attribute personality differences to nature rather than nurture.

"someone did a study where you ask people how much do you attribute personality to nature and how much to nurture. And and he said the only correlation that came out of it was the more kids people had, the more they thought nature was important for um for determining." (said at 2:05:32)

No published study matching this specific finding—that the number of children is the sole or primary factor correlating with attributing personality differences to nature over nurture—was located in PubMed or Europe PMC. While studies on lay theories of heritability have explored how parenthood affects attributions of genetic vs. environmental influence, recent research (e.g., PMID 40505501) found that differences in genetic attributions occurred mainly between parents and non-parents rather than scaling with the number of children, and focused primarily on physical/lifestyle traits rather than personality. Because the specific study cited by the host could not be identified in the indexed literature, the claim remains unverified.

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.