Podbit · Modern Wisdom
The challenge hypothesis explains that testosterone rises during mating competition and then adaptively falls when the strategy shifts from maximizing babies to maximizing any given baby's survival. It plays out in birds, primates, rodents, and humans alike — fatherhood isn't a hormonal failure, it's a hormonal success.
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At 39:38 · chapter starts 38:50
The hormonal dimension of fatherhood is as well-documented as the neurological one, and Saxbe walks through it with the challenge hypothesis as the organising framework. [1] — Darby Saxbe "The challenge hypothesis explains that testosterone rises during mating competition and then adaptively falls when the strategy shifts from…" 39:38 Testosterone rises during mate competition — maximising opportunities to reproduce — and then adaptively falls once mating is accomplished and the strategy shifts from quantity to quality of offspring. The pattern holds across birds, rodents, primates, and humans. In new fathers specifically, the testosterone drop is linked to caregiving behaviour, not simply to the existence of a baby. The downstream effects are broadly health-protective: less risky driving, fewer fights, lower substance use, more attention to health checkups, greater investment in the pair bond. Saxbe and Chris discuss the irony of men who supplement testosterone in an attempt to signal masculinity, potentially suppressing the very adaptive shift that makes them effective fathers — with anecdotal reports from mothers suggesting the connection is real.
When men become engaged fathers, testosterone naturally drops — and that drop is adaptive. It reduces aggression, increases pair bonding, and promotes nurturing. Men who take exogenous testosterone may be overriding that system, and anecdotal reports from mothers suggest it shows up as reduced patience with their babies.
Darby Saxbe warned that men taking testosterone supplementation while becoming fathers risk suppressing the natural hormonal adaptation that promotes patience and caregiving behavior.
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