Testing Testosterone


There’s more to testosterone than macho muscles and mustaches. Testosterone levels drop once men become fathers, researchers at Northwestern University found in a long-term study.

The Northwestern team studied testosterone levels in more than 400 men in the Philippines, taking a measurement when they were 22 years old and again five years later. At the time of follow-up, many of the participants had entered committed relationships and had children for the first time. Their testosterone levels were lower than the men participating in the study who weren’t yet fathers. Chris Kuzawa, a Northwestern anthropologist who conducted and co-authored the study, explains the importance of cultural norms on testosterone levels and the implications of the study for our understanding of relationships.

Chris Kuzawa, associate professor of anthropolgy at Northwestern (photo: Emma Dutton/MEDILL)Chris Kuzawa, associate professor of anthropolgy at Northwestern (photo: Emma Dutton/MEDILL)To what extent are these findings culturally dependent? Does a study of Filipino men provide us with insights into American men?
Our best guess is that the hormonal response of a male to fatherhood is contingent upon local, cultural notions of what fatherhood is about. Based upon our study and past studies, it appears that being committed to child rearing is an important predictor of whether men experience testosterone decline. So it seems likely that cultural norms have a big role in shaping the nature of these responses. These are not just generic responses, but likely shaped by cultural norms and a man’s understanding of his social roles as a father.

In the Philippines, there are transitions underway in which fathers are increasingly becoming involved in child rearing, [while] that was a little less common a generation ago. Other studies that have looked at single snapshots of testosterone in fathers and single men in the U.S. report lower testosterone in fathers. There's every reason to suspect that what we see in the Philippines will apply here in the U.S. and in other societies with similar notions about the roles that fathers play in raising their children. In societies in which fathers are less involved, I’m guessing we will not see comparable hormonal changes.

How does testosterone affect male behavior?
Testosterone is a hormone that I’m guessing most men think they understand. The reality is that researchers and scientists who study testosterone can't come to much of an agreement about what effects on behavior it has. In general, you can think of it as focusing a person's attention on the social realm and perhaps providing a bit of a boost in competitiveness and confidence. Certainly, seeking mates and status are part of the activities that we tend to associate with testosterone in humans and also in other species. With respect to our study’s findings, lowering testosterone might shift a male's focus away from the social realm and more toward the child. I think this idea would resonate with many committed fathers.

Should fathers be worried about losing their masculinity when testosterone levels decline?
Our study suggests that part of male biology is oriented toward care giving and raising children. In my view, the biological changes that we document in new fathers do not represent a challenge to a man's masculinity. Instead, they are part of what we should think of as masculine. The men who started with such high testosterone likely had more than they needed. After all, male reproductive functions are maintained at much lower levels of the hormone. I think many of our notions of masculinity tend to be inspired by portrayals of young pre-adult males rather than males who have settled into mature social roles. I hope the findings of this study will generate discussion and stimulate men to rethink some of the old stereotypes and models of masculinity that many of us have learned.

One question that I’ve seen discussed is whether fathers should be augmenting their testosterone. I think that's frankly a little silly, and possibly dangerous. Why fight the body’s natural response to becoming a father?

What do these findings imply about parenting and marriage?
From our study it seems likely that testosterone will be lower in many fathers, and it is presently not clear whether this is going to have effects on traits like libido, but it could have some. To the extent that this is a result, I think it could be liberating for married couples to be aware that this is perhaps normal and expected. If there is a kind of natural progression that you can expect to experience as part of being in a pair-bonded relationship and becoming a parent, that might be good to know. Maybe this is just part of our basic biological make up as a social species with strong pair-bonding and cooperative care of young. Maybe we shouldn't take these changes as an indication that there's something wrong with our relationship or with our partner. It may simply be a predictable effect of entering a new and different social role.

Moving forward from this study, what questions do you have?
We still do not know what causes the decline in testosterone among new fathers. What specifically is it about fatherhood that drives testosterone down? Is it purely the result of a psychological and emotional commitment? Is it a result of physically interacting with the child? And is there a feedback? As testosterone declines, does that encourage the kinds of commitments and behaviors that reinforce lower testosterone and vice versa? That's how we're thinking about it now, and that's one of the important questions that needs to be teased apart in future research.


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