A natural shot of female estrogen appears to jump-start nurturing spirits in new fathers

Joseph Hall
Toronto Star

For Father's Day, this "guy" deserves a really expensive tie – though he'd probably just chew it up or sleep on it.

The hamster in biologist Katherine Wynne-Edwards' lab is such a doting dad that he actually plays midwife at the birth of his many, many children.

He helps pull them out of the birth canal; he cleans them up once they're out. He even tidies up (well, eats) the afterbirth placenta at the end of the delivery, reports Wynn-Edwards, who works out of Queen's University.

And by studying such rodent behaviour, scientists are hoping to figure out just why and when a peculiar physiological change occurs in new or expectant fathers of the human variety.

"There are hormonal changes in men when they become fathers," says Wynne-Edwards, whose work is funded by the Canadian Institutes of Health Research. "Those specifically are an increase in (female) estrogen, a temporary decrease in testosterone, and an increase in prolactin, which is a hormone associated with the nursing process."

New dads need not worry, however, about developing breast tissue or losing their beards, adds Wynne-Edwards.

She says the spikes and dips are small in terms of the entire male hormone balance, and that the levels in new fathers remain well within the typical ratios seen in most men.

Still, the changes are pronounced enough to easily register in saliva samples.

And they could be playing an important role in how welcoming and attentive dads are to their newborn offspring, Wynne-Edwards says.

She points out that previous research has shown the magnitude of the hormonal shift is associated with the intensity with which fathers are affected by their baby's presence.

The more pronounced a father's reaction to his child is, the greater that shift is likely to be, Wynne-Edwards says.

But regardless of the degree of the hormonal flip-flop, it's not likely a primary driver of the nurturing instincts that men may exhibit, or the intensity of their fatherly involvement.

Instead, Wynne-Edwards says, the hormone alterations likely contribute to the psychological receptiveness of men to their infants.

"The hormones just make it easier or harder for certain kinds of responses to come out.

"There is no prospect anywhere on the horizon," she continues, "of a (hormonal) treatment that will turn a man into a doting father."

According to Wynne-Edwards, no one knows exactly when or how the hormonal shift takes place – hence the current hamster studies.

But in the end, work in the area helps show that testosterone is not the be all and end all of men's hormonal reality.

"One of the benefits of this research," she says, "is that it teaches us that testosterone in not the measure of a man.

"In fact, estrogen is likely to be an important hormone in men, just as we are growing to understand that testosterone is going to be an important hormone in women."

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