The biology of dads

Our first study involved recruiting a large group of fathers with children one to three years of age. We found that compared with non-fathers, fathers had 20 per cent less testosterone, the primary male sex hormone, often abbreviated as T.

We asked mothers to tell us how involved fathers were in caring for their toddler children, and found that men with higher testosterone tended to be less involved, whereas men with lower testosterone were more involved.

Despite having lower testosterone compared with non-fathers, fathers in our study actually had higher levels of another hormone that is classically identified with motherhood: oxytocin. In contrast with testosterone, oxytocin appears to promote paternal caregiving.

There is evidence for a decline in fathers’ testosterone even during the partner’s pregnancy, so cues from the mother could be important. There is also evidence that postnatal contact with the infant can both lower T and increase oxytocin. Perhaps something about the appearance, the odour or actual tactile contact with the infant is responsible.

A notable 2015 study showed that skin-to-skin contact with premature infants increases both parental and infant oxytocin levels. These findings predict that human fathers should become more strongly bonded to their children if they spend more time in close proximity to them as infants, and this has indeed been demonstrated.

(…) particular set of physical characteristics, called the baby schema, that tend to ‘release’ adult caregiving. These include large heads, protruding foreheads, large eyes, high brows, small lower faces and short, stubby limbs (…) one important study showed that if you morph an infant’s picture to give it more baby schema (ie, you make the baby cuter), adults report stronger motivation to care for it and show stronger neural activation in the striatum.

The more the midbrain was activated, we found, the more involved the father was in caring for the child. This could mean that fathers who were more rewarded by their child became more involved in caregiving, or it could mean that, as fathers became more involved and formed stronger bonds with their child, they came to find the child more rewarding.

(…) infant crying, that aversive stimulus that effectively forces the caregiver to share in an offspring’s pain or figure out a way to alleviate it. Paradoxically, we found that fathers who activate the anterior cingulate the most when listening to infant crying report the most negative emotional responses to those cries (…) a phenomenon known as ‘empathic overarousal’, in which an observer takes on the distress of another individual to such an extent that they become mired in personal distress

(Many men) override impulses that evolution has programmed into their brains, impulses that evolved because they enhanced the reproductive success of their ancestors. They do so out of love and respect for their partners and their children, and out of respect for social and cultural norms. But how do they do what males of other species seem incapable of? The answer, I believe, is that they rely on the crowning achievement of human brain evolution: the prefrontal cortex. (It) is what allows us to override ancient, evolved impulses in the service of honouring commitments, abiding by social norms, and exercising our moral responsibilities. We are privileged to have this remarkable organ, and we fathers would all do well to make use of it.