Tuesday, June 23, 2015

How fathers are shaped by their children

We wish all Dads a Happy Father's Day :

Popular convention may dictate that the father's role in the early development of his children pales in comparison to the mother's, but author Paul Raeburn is shedding new light on the science behind the vital contributions of the often overlooked male parent.

During pregnancy, mothers experience a variety of profound hormonal and physical changes that help to prepare them for the substantial task of carrying and nurturing the foetus and new baby. That's not news; what is news is that men also undergo hormonal turmoil.

One of the most obvious changes is the weight gain that many men experience along with their wives during pregnancy. Many women experience cravings and of course require more food during pregnancy. The men's weight gain could be occurring simply because they are tempted by all that extra food in the house. We don't need hormones to explain that.

Anthropologists have discovered that this phenomenon, called couvade (from the French word meaning 'to hatch"'), occurs not only in Britain and the United States but in non- Western societies, too, sometimes to an even more extreme and incapacitating degree.

In Papua New Guinea, some men, while waiting for their babies to be born, "retire to bed with unremitting nausea and incapacitating back problems, demand to be looked after, and otherwise raise an emotional fuss during the last months of their wives' pregnancies."

One of the key hormones that's affected is the sex hormone testosterone. And the other is prolactin, a hormone involved in the production of milk by nursing mothers. Men have prolactin, too, even though they don't nurse children. Why its levels should change in men has been a mystery.

Behavioural changes

We've known that hormonal changes occurred in some animal species in which the fathers participated in rearing their offspring; prolactin levels rise in primates, in male birds just before they become parents, and in rodent species in which fathers help to care for their offspring. But nobody had shown much interest in looking at human fathers, to see whether something similar might be going on.

In a paper published in 2000, Anne E. Storey, Katherine E. Wynne-Edwards, and their colleagues at Memorial University in Newfoundland began their study by acknowledging that lack of research: "Little is known about the physiological and behavioural changes that expectant fathers undergo prior to the birth of their babies," they wrote.

Based on the findings in animals, Storey and company predicted they would find similar changes in male humans, beginning during their partners' pregnancy and continuing after birth. And they predicted that the variation in hormonal levels in any individual would be related to men's symptoms during pregnancy and their responsiveness to their infants.

They recruited thirty-four couples taking prenatal classes at a nearby hospital and took blood samples from the men before and after the births of their babies. All but three of the couples were first-time parents. The couples were asked whether the men had experienced any of the typical symptoms of pregnancy- nausea, weight gain, fatigue, increased appetite, and emotional changes.

The couples who were tested were exposed to their newborns, or to blankets that had been in the nursery, and to a film about breast-feeding to see whether the infant cues would cause any short- term change in hormone levels.

The tests revealed significant changes in each of the three hormones Storey and Wynne-Edwards measured-testosterone, cortisol, and prolactin. And the pattern in men was similar to what happens in pregnant women. Men's testosterone levels fell 33 percent when they had their first contact with their babies, compared to measurements taken near the end of their wives' pregnancies.

What could explain this change in testosterone? Many scientists believe that a rise in testosterone is associated with competitive behavior in animals and in men. The drop that occurs with the birth of a baby might be nature's way of encouraging men to drop their fists, at least temporarily, and nuzzle their babies.

Paternal care-giving

From an evolutionary perspective, this is smart. Competitiveness is incompatible with nurturing. And men who are more bonded to their babies are more likely to stick around and support them.

Indeed, in September 2013, James K. Rilling and his colleagues at Emory University reported in the Proceedings of the National Academy of Sciences that testosterone levels in the blood were inversely correlated with paternal care-giving-that is, testosterone was highest in fathers who devoted less effort to child care, and lowest in those who invested more effort in child care. They also found that the fathers who devoted more resources to their children had smaller testicles. The results provide evidence for the supposition that there is a trade-off between the effort devoted to mating and to parenting. Some males choose to devote more effort to mating and less to child care; others choose the opposite course.

(Excerpted from Do Fathers Matter? What Science Is Telling Us About the Parent We've Overlooked, by Paul Raeburn -Scientific American/FSG, 2014)