Testosterone, that most male of hormones, takes a dive after a man becomes a parent. And the more he gets involved in caring for his children — changing diapers, jiggling the boy or girl on his knee, reading “Goodnight Moon” for the umpteenth time — the lower his testosterone drops.
The study, experts say, suggests that men’s bodies evolved hormonal systems that helped them commit to their families once children were born. It also suggests that men’s behavior can affect hormonal signals their bodies send, not just that hormones influence behavior. And, experts say, it underscores that mothers were meant to have child care help.