What happened in this episode?
Steven Bartlett interviews developmental psychologist Dr Darby Saxbe about biological and behavioural changes around the transition to parenthood, with a focus on fathers. Saxbe describes research suggesting new fathers show grey matter volume reductions—“shrinking”—especially in brain networks linked to social cognition and reading infants’ cues, arguing the changes may reflect increased neural efficiency rather than impairment. She says her lab found greater brain changes among fathers who reported stronger bonding and more hands-on involvement.
Saxbe also discusses hormonal shifts, saying longitudinal studies indicate hands-on fathers typically experience about a 25% fall in testosterone, with some rebound as children age. She cautions against simplistic “testosterone equals masculinity” narratives and says her lab observed associations between higher post-birth testosterone and poorer relationship outcomes, while very low testosterone was linked with higher paternal postpartum depression symptoms.
On relationships, Saxbe outlines a lab methodology that included recording couple conflict during pregnancy. She says more negative conflict behaviours predicted more medically complex births based on later medical records and more stressful birth appraisals. She also describes findings on stress physiology, including associations between stronger couple cortisol linkage and lower marital satisfaction.
The conversation turns to declining fertility rates and to policy: Saxbe argues humans evolved as cooperative “alloparents” and says lack of universal paid parental leave in the US increases stress and constrains choices around childcare. Bartlett also discusses his own plans for fatherhood, including embryo freezing, and asks for practical advice on preparing for parenthood.
