How Hormones Shape Sexual Orientation & Behavior | Dr. Marc Breedlove
Andrew Huberman talks with neuroscientist Marc Breedlove about how prenatal hormones shape sexual orientation, covering finger length ratios, the older brother effect, gay rams, and why group differences can't predict any one person's orientation.
The gist
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Breedlove's street fair study found lesbians have more masculine finger length ratios than straight women on average, suggesting more prenatal testosterone exposure.
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Breedlove says each older brother raises a boy's odds of being gay by a third, but stepbrothers don't, pointing to the mother's body.
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Some rams never mount females and differ in the brain's preoptic area; Breedlove reads this as aversion, not just attraction, shaping partner choice.
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Women with congenital adrenal hyperplasia, exposed to extra prenatal testosterone, are more likely to be lesbians, and that share rises as they age.
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Behavior shifts hormones too, Breedlove notes: winners' testosterone rises after competitions, yet researchers have found little evidence that parenting or social factors set orientation.
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