Men undergo significant hormonal and neurological changes when becoming fathers, preparing them to be as nurturing and protective as mothers, according to a growing body of scientific research.
These biological shifts, which can begin months before a child is born, suggest that the nurturing father is a deeply rooted biological trait rather than a modern cultural phenomenon, reports BBC.
Hormonal shifts
Research into the physical transformation of fathers began with observations of mammalian males and primates, which showed shifts in hormones typically associated with motherhood, such as testosterone, vasopressin, and prolactin.
In 2000, Canadian scholars Katherine Wynne-Edwards and Anne Storey published the first study demonstrating similar hormonal changes in human men.
Lee Gettler, director of the Hormones, Health, and Human Behavior Laboratory at the University of Notre Dame, furthered this research through a decades-long project in Cebu City, Philippines.
Testing 624 men, his team found that those who became fathers experienced significantly larger drops in testosterone compared to non-fathers. The decrease was most pronounced in fathers who spent more hours in childcare or shared a bed with their infants.
Early preparation
Recent evidence suggests these changes occur even before birth. James K Rilling, director of the Laboratory for Human Social Neuroscience at Emory University and author of Father Nature, found that expectant fathers showed lower levels of testosterone and vasopressin just four months after conception. His research indicates that the lower a father’s testosterone, the more involved he becomes with the mother and infant postnatally.
Furthermore, Darby Saxbe, an American clinical psychologist and author of Dad Brain, found that expectant fathers with stronger bonds to their unborn children had higher levels of prolactin, a chemical usually linked to lactation.
Neurological transformation
The transition to fatherhood also involves a “rewiring” of the brain. Saxbe compares this period to adolescence, noting that first-time fathers show neural changes as their brains adapt to new experiences.
A 2014 study led by Ruth Feldman demonstrated this by scanning the brains of primary-care fathers. While “helper” fathers in heterosexual couples showed activity in social brain areas, gay men acting as primary caregivers showed activity in the amygdala – an area related to deep instinctual responses – similar to that of primary-care mothers.
Societal implications
Experts argue these findings should influence public policy, particularly regarding parental leave. Gettler suggests that involving men early in pregnancy through medical appointments and ultrasounds helps bring this “paternal biology” online.
The benefits of active fathering extend to the entire family. Mothers with active partners report better mental health, while a 2026 study of 292 families found that children of attentive fathers had better heart health.
Primatologist Sarah Blaffer Hrdy, author of Father Time, concludes that the capacity for primary care is a latent trait in all human brains, waiting to be triggered by the right circumstances.
