Marc Breedlove argues prenatal testosterone levels set brain architecture for romantic attraction before birth.
Each older brother raises a man's odds of being gay by 33%, known as the fraternal birth order effect.
The fraternal birth order effect is a biological bias from prior male pregnancies, not a result of social upbringing.
Andrew Huberman notes the 2D:4D finger ratio, a marker of prenatal testosterone, impacts sexual orientation.
Lesbians often show more masculinized finger length ratios than heterosexual women.
Lesbians also produce fewer inner-ear sounds than heterosexual women, mirroring the typical male pattern.
Breedlove says physical evidence from fingers and ears convinced him orientation is biological, not socially learned.
Brain regions like the OVLT lack full blood-brain barriers, letting neurons directly sample salt levels in the bloodstream.
When salt concentrations spike, the OVLT triggers the pituitary to release the hormone vasopressin.
Vasopressin signals the kidneys to retain water, an anti-diuretic response that prevents dehydration.
Osmotic thirst is triggered by high salt concentration, while hypovolemic thirst responds to blood volume loss from sweating or bleeding.
Huberman states that low sodium levels can be misinterpreted by the brain as a sugar or carbohydrate craving.
This misreading can drive unnecessary calorie consumption to solve what is actually a mineral deficiency.
Performance hydration depends on sodium, which enables the body to effectively use the water you drink.
The kidney's Loop of Henle executes neural commands, filtering blood and deciding what to retain based on hormonal signals.