Dr. Darby Saxbe

And so there's been a lot of work on both human fathers and then in biparental animals like birds and

and primates and rodents, finding that testosterone does drop around a transition to fatherhood.

And Gettler's study was really clever because he had this long-term design.

So he could answer the question of, is it that lower testosterone men are selecting into fatherhood?

And so testosterone starts low and will stay low in these men, or is there something about becoming a father that changes our testosterone level?

And what he found is actually that the higher testosterone men were more likely to become fathers across the study observation time period, but they then showed lower testosterone if they were partnered and living with children.

And men who were spending more time in hands-on care showed the lowest testosterone levels of all.

And so we think that testosterone is tied to our reproductive strategy and our caregiving motivation.

And some of the first work on this was actually done in birds and found that testosterone levels are high at the start of breeding season and typically drop after mating has been accomplished and chicks are hatching.

And it's that it's somewhat costly for the body to maintain really high testosterone levels in perpetuity.

And we don't necessarily need them if our objective is to invest in caring for children.

So we need high T if we're competing for lots of mating opportunities.

And we want to maximize our odds.

But if we're shifting from a mating-oriented reproductive strategy to more of a nurturing-oriented reproductive strategy, testosterone will not necessarily play as essential of a role.

Well, I mean, there's a pretty solid literature at this point.

And like I said, across both humans and animals, linking testosterone to reproductive transitions in men.

And I think the subtlety to sort of keep in mind is we're not talking about medically low kind of risky levels of dampened testosterone that will interfere with men's well-being.

We're talking about sort of natural fluctuations.

And those fluctuations appear to kind of reflect our social role.

And so tea might drop in early parenthood, it might rebound maybe when a dad is thinking about having additional children.