The Physiology of Fatherhood

Phew! I took a break from posting while I was on paternity leave (I just had my second son... or rather my wife did). Father's Day also just happens to be this weekend. So what better way to celebrate my return to public life than to post about the physiology of fatherhood?

”Father and son on beach” (CC BY-SA 4.0) by Gugatchitchinadze

We all know that new mothers go through numerous and varied physiological, hormonal, anatomical and psychological changes after they give birth, but you may not know that men also go through many similar (although not as dramatic) changes when they become new dads.

First of all, new dads have substantial changes in their hormones. Testosterone, the quintessential "man" hormone, drops by as much as a third in new dads. Logically this makes sense. Testosterone is the culprit behind many not-helpful-for-a-new-dad tendencies: higher aggression, risk-taking behavior, increased libido, lower empathy, etc.

The thinking is that a lower testosterone level probably helps men to settle down into a more nurturing role where they will be less preoccupied with having sex with as many people as possible while skydiving and crushing the skulls of their enemies.

Interestingly, testosterone isn't the only hormone to change for new dads. Oxytocin and vasopressin, two hormones that are often co-released from the posterior pituitary, have been linked to the sensation of love and affection. They are released in a burst after orgasm for both men and women, which some think is what induces the desire to cuddle. They are also released in women when breastfeeding, and (it turns out) in men when they interact with their children.

And even more interesting is that this effect seems to be strongest in men who interact with their children more. Meaning that men who are not very involved parents do not get the same reward-center activation when interacting with their children then men who are. Involved fathers get strong bursts of oxytocin and vasopressin when interacting with their children, which in turn positively reinforces the behavior--it's a self-sustaining process. Similarly, prolactin, which seems to signal satisfaction, is higher in new fathers.

 Father Daughter Daddy Fatherhood Happy Father's Day

But it doesn't stop there! A new dad's brain physically changes as well. Using MRI scans, researchers have shown that new dads' brains actually grow over the first few months of fatherhood in the areas associated with nurturing and empathy. However, unlike women, the changes don't happen immediately, but by about 4 months out, a new dad's new circuitry mimics that of a new mother.

So, I know what you're asking yourself. What should I get for that special someone in my life for Father's Day? Well, apparently new babies make men feel pretty happy and satisfied, so... another baby? No, that can't be right...