Darby Saxbe

With mom, you can literally visibly see her body changing, right, if it's a biological pregnancy.

And with dad, there's a lot going on under the hood.

So there's research that suggests that testosterone levels drop

Oxytocin levels change.

A hormone called prolactin changes as well.

You can tell from the name.

It promotes lactation.

Okay.

So it's very good for breastfeeding, which obviously is not that helpful for dads.

And in men, surprisingly, prolactin levels before birth seem to predict...

at least this is what we found in our lab, predicted dad's kind of bonding and motivation to parent in the early postpartum period.

So we found that guys with higher prolactin levels prenatally had more enjoyment of the infant postpartum, were spending more time with the infant postpartum.

And it's interesting because in fish, and I mentioned that fish are primary caregiver fathers, if you dump prolactin into the water, fish will start acting really paternal.

So it's actually a hormone that kind of turns on fatherhood in fish.

And it turns out it might work in a similar way in humans.

Yeah, we need high testosterone if we're competing for mates.

It will help us to be competitive, to focus on our status, to be aggressive.

And it's not that useful when we have a new baby.

It's not as adaptive to sustain high testosterone levels.

And testosterone comes at an immune cost for the body.