Being a dad comes naturally

From Toronto at the annual meeting of the Endocrine Society

Men’s hormone concentrations shift significantly throughout the course of their wives’ pregnancies and after the baby is born, according to a small, new study. While the study’s research team didn’t monitor parenting behaviors, animal studies indicate that hormones affect a male’s willingness to take care of his offspring, says lead researcher Katherine E. Wynne-Edwards of Queen’s University in Kingston, Ontario.

Wynne-Edwards found that concentrations of the male sex hormone testosterone in saliva were, on average, significantly lower in 13 first-time, expectant fathers compared with 14 childless guys. Testosterone concentrations began to rise in the dads soon after their wives gave birth, she says, but remained lower than those in the men who did not have children.

More soon-to-be dads had detectable amounts of estrogen, a female sex hormone, in their saliva than did men whose partners were not expecting, she reports. Estrogen concentrations rose after the birth of their children, Wynne-Edwards says.

The men in the study spat into test tubes at the same time every day. The researchers collected the vials and analyzed the contents for testosterone, estrogen, and cortisol, a stress hormone. Cortisol concentrations were lower in expectant dads than in the other men and did not change after the birth.

Fluctuations in hormone concentrations may trigger behavioral change, Wynne-Edwards says, but changes in behavior also lead to changes in hormone concentrations. She plans to explore this link by studying hampsters, a species in which low testosterone concentrations have already been linked with normal parental behaviors.