Friday, September 16th 2011

Parenting is not just for the ladies: on testosterone, fatherhood, and why lower hormones are good for you

My daughter

My daughter wearing a towel the way Mommy does.

This morning was a bit rough. “Where’s Daddy?” asked my daughter as she climbed into bed before dawn to snuggle. “It was Daddy’s turn to go to work early,” I explained. It used to be that I was the parent she turned to for everything. But the last few weeks, with preschool and a new system of pickups and drop-offs, four days a week I walk to work at six, before she usually rises. This is so that I may pick her up at 3:45 but still work a full day.

And now Daddy is the one with the morning ritual, the one who helps her pick out her clothes and make her bed. They call me at work most mornings to say a quick hello so the kiddo can tell me any dreams she had and what she is having for breakfast. Then Daddy brings her to school, helps her get into her indoor shoes and put away her lunch, helps her choose her activities during free time, and heads into work.

So we snuggle some more. I ask, “What do you want for breakfast?” She names the local restaurant we go to on the weekends. “It’s a weekday, honey, you have school soon.” She said, more forcefully this time, that she wants to go out to breakfast. Hoping to win back her love, I say, “How about I make you French toast this morning?”

“With the sprinkles.” She is referring to the dusting of powdered sugar that comes with it at the restaurant.

“How about just syrup? You don’t need both.”

“With sprinkles!”

I sigh. This is our one morning together during the week. I want it to be a good one. “Okay,” I say.

I forget to make the beds, almost forget to get her teeth brushed, have to avert several outfit disasters, and forget to call Daddy. Thankfully Daddy calls us, and we chat for a few minutes while the kiddo eats her French toast and glass of warm milk. Then I barely get her to school on time due to a power play about who gets to buckle her up, don’t know how to help her with choices for free time, and only barely manage to get her sneakers off.
Clearly, Daddy has the morning routine down.

* * *

Parenting, caring for offspring, and the work-life balance are issues usually relegated to women. There are many men who take care of their kids, and increasingly men in the US and other countries who invest at least as much or more than mothers, but these men are considered both outliers and, often, heroes. The biological imperative to parent, and the reproductive burden, is supposed to fall squarely on women, and it is only our wonderful cultural sensitivity broadening that perspective more recently.

What if there were a biological imperative to be a loving father? Or what if being a father was good for you?

Over the last decade or so, biological anthropologists have studied the biology of mating, partnering and fatherhood of men (e.g., Burnham et al. 2003; Gettler et al. 2011b; Gray et al. 2002; Gray et al. 2004). As it turns out, these different periods of men’s lives have distinct hormonal milieus, just like the reproductive states of women like fecund, pregnant, breastfeeding and grandmothering. When men are seeking mating opportunities, testosterone is high to support mating behavior, muscle anabolism, and the other secondary sexual characteristics that allow a man to display his good genes. When men are partnered in long-term relationships or become parents, testosterone often declines. And the more a man spends with his offspring, the greater the decline.

What I have noticed missing from the stories about the most recent paper on testosterone and fatherhood is the fact that, from a survival perspective, testosterone is bad for you! Look at lizards who, injected with testosterone, do pushups to attract mates until they die from the effort. Look at the health complications of men who inject themselves with steroids. Testosterone does at least two awful things to your body: it reduces your immunocompetence and it may increase your risk of male reproductive cancers (Muehlenbein and Bribiescas 2005). Further, some have studied the impact of both marriage and having children on longevity. Men almost always benefit from both (click here for a post that addresses this, albeit indirectly, at my old digs — look in particular at the second graph, from Jasienska et al 2006). The trade-off when seeking mating opportunities is that at least you’re getting the good out of testosterone: the support of the kinds of traits that may help you find a mate, despite a reduction in somatic allocation that can improve survivorship (Bribiescas 2001).

Model of the trade-off between reproductive effort and survivability in males

Model of the trade-off between reproductive effort and survivability in males (Muehlenbein and Bribiescas 2005).

But when you aren’t looking for a mate, or when those behaviors could actually be detrimental to your reproductive success, there is little reason to continue to invest energy in having high testosterone. Testosterone is one of those hormones that varies hugely (Ellison et al. 2002), because such a tiny amount is needed to support reproduction and libido yet it affects, and is affected by, behavior. Most men have loads more testosterone on a daily basis than they will ever need to make a baby the few times they may want to.

The most recent paper to come out about testosterone and fatherhood is the first to examine this relationship longitudinally, and this dataset confirms the cross-sectional data that came before it (Gettler et al. 2011a). I first learned about these data from Dr. Peter Gray, an Associate Professor of Anthropology at the University of Nevada, Las Vegas. He is one of the pioneers in the field, answering questions about the state of fatherhood from an endocrinological perspective both within and between human populations all over the world.

Because I know Peter (full disclosure: we took one class together when I was an undergraduate, and he a grad student, at Harvard), I asked him if he would answer a few questions for me about the state of the field, and what it means for men that testosterone can vary due to parenting behavior. He was kind enough to do so despite being in the field right now. His answers illuminate the importance of the current results and put them into a broader context, and also demonstrate his generousness as a scholar and dad.

* * *

What is the history of the study of this field?
In the 1980s and 1990s, a considerable amount of work on nonhuman animals, particularly North American birds, helped generate a sense of the social side of testosterone. Put simply, work on various animals illustrated the ways in which male testosterone levels shifted in response to male-male competition, courtship, longer-term bonding, and parental care. The first human testosterone and male family life studies were based on large U.S. military samples, and showed that married men had lower testosterone levels and testosterone levels increased slightly around the time of divorce. However, it was only in 2000 — a new millenium, appropriately enough — that human studies were published connecting the wider evolutionary and comparative literature. The first testosterone and fatherhood study, showing that dads shortly after birth had lower testosterone in a highly-invested Canadian sample, was published in 2000 by Anne Storey and colleagues. Since that time, more and more scholars, in more and more study populations (from Boston to Beijing, the Hadza to Jamaica), have found through cross-sectional designs that family men — men involved in long-term committed relationships and paternal care — tend to have lower testosterone levels.

Were there ever any roadblocks to you pursuing research into testosterone and mating patterns or parenting behavior?
There hasn’t been a single roadblock, but there have been recurring issues that arise in these kinds of studies. Recruiting men can be easier or more difficult, depending on the study circumstances. It can be challenging to get busy fathers of young children to go out of their way to participate. For the Jamaican fatherhood study, for example, we asked fathers to report to a testing facility with their partner and youngest child for procedures, making recruitment a significant effort. Another issue is how involved these studies are: the easier for participants, the more likely participation. That’s especially true, I think, of biological sampling. By relying on minimally invasive saliva sample (rather than blood draws) for most studies, that has probably had a huge positive impact on recruitment and ease of conducting studies. Last, I might add that my own life history realities — as a father of two young children — has posed its own juggling act, where I try to combine meaningful scholarly work with engaged family life.

What is one of the coolest findings to come out of your research? The research in this field more broadly?
I love how integrated this set of studies on human testosterone and family life is with the wider evolutionary, comparative, and endocrine work. There’s no setting humans part from nature here. We’re folded fully into its fabric, and that’s been reflected in the theoretical and conceptual foundations underlying hypothesis generation and interpretations. I also like the intersections with wider social and health concerns. When I was a postdoc between 2003-2005 working in Shally Bhasin’s Clinical Endocrine Lab, juicing baseball players were making headlines, and that folded seamlessly into the wider understanding of what androgens can do, and their respective costs and benefits. So too do discussions of male aging and efforts to quantify the risks and benefits of testosterone therapy in aging men. All of these elements — from the social side of testosterone to the health and home run angles — can be integrated within wider evolutionary and endocrine principles.

What’s something we know now because of this study (Gettler et al 2011a) that we didn’t know before? What is its main contribution?
The main contribution is the rigorous study design. In particular, this study has a large sample. It is a community-based sample from the Philippines. And, most importantly, it employs a longitudinal design. That longitudinal element demonstrates causality. While the growing pile of testosterone and family life studies were based on cross-sectional designs, one could ask whether lower testosterone men became dads or whether fatherhood caused testosterone decreases. Gettler and colleagues’ study shows convincingly that becoming a father decreases men’s testosterone. It also showed that men with higher testosterone were more lkely to initially marry and become fathers, after taking a testosterone plunge, a finding that itself is of interest and calls for more work.

If there was one thing you wanted people to understand about testosterone and fatherhood, what would it be?
There are impacts of fatherhood on men, from how they feel to their health to their physiology. This finding of testosterone declining with fatherhood makes sense in light of comparative, endocrine, and overall evolutionary considerations, not to mention the kind of day-to-day differences fathers might recount in the ways their lives are structured compared to their ‘single’ days. Fatherhood bears its stamp upon men’s testosterone in perhaps, then, some unsurprising ways.

What is a current project you are working on?
I’m involved in a collaborative fatherhood project in Jamaica, working with Maureen Samms-Vaughan, a Jamaican pediatrician. This is a new questionnaire-based national cohort study. While she and others on the project are primarily interested in mothers and child development, I’m working with her on the fatherhood arm of the study. This entails fathers during the day or two post-birth answering questions about paternal attitudes, partner relationships, sexuality, health, and more. Men’s responses can be linked with maternal and child outcomes, and some of men’s responses should be of interest in themselves. As an example, one issue concerns son vs. daughter preference, a topic that is often bracketed by male preferences among some in China and India, whereas there may be leanings toward a general daughter preference in the Caribbean, but perhaps that will be attenuated among fathers. About 1000 men have responded so far, with more yet before the study wraps up soon. This should be a really promising and exciting study, with an unusually large sample and with potential for longitudinal work as well.

I’m also working with Justin Garcia, a postdoc at the Kinsey Institute, on an integrative, evolutionary-oriented book on human sexuality. That’s plugging along well, with the manuscript’s due date the end of this year, and its gestation so far on target.

Where can people go to read more on this topic?
I would recommend the Gettler et al. PNAS article at the starting line. For general background on behavioral endocrinology, Randy Nelson’s textbook An Introduction to Behavioral Endocrinology has just been updated (a revised 2011 edition) and provides an excellent survey of the field. For work that provides general conceptual background, excellent comparative data points, and some of the most empirically-rich human findings, Peter Ellison and I coedited Endocrinology of Social Relationships, published in 2009 by Harvard University Press. And for an integrative account of human fatherhood, featuring an evolutionary perspective, comparative work, cross-cultural research, and arguably unique syntheses of topics such as male work/family/social relationships trade-offs, health and fatherhood, and sexuality and fatherhood, Kermyt Anderson and I wrote Fatherhood: Evolution and Human Paternal Behavior, published in 2010 by Harvard University Press.

* * *

Thanks to Dr. Peter Gray for his comments. What are your questions? What implications does this research have for your reproductive decisions or how you run your family life? Me, I’m going to try to not feel so guilty about my early mornings at work and our 50/50 co-parenting. My husband has chosen to be an involved father, and the love and patience he gains from the experience, not to mention the drop in testosterone, can only be a good thing for his survivorship, which will make it possible for him to be an involved grandfather.

Bribiescas RG. 2001. Reproductive ecology and life history of the human male. American Journal of Physical Anthropology 116(S33):148-176.

Burnham TC, Chapman JF, Gray PB, McIntyre MH, Lipson SF, and Ellison PT. 2003. Men in committed, romantic relationships have lower testosterone. Hormones and Behavior 44(2):119-122.

Ellison PT, Bribiescas RG, Bentley GR, Campbell BC, Lipson SF, Panter-Brick C, and Hill K. 2002. Population variation in age-related decline in male salivary testosterone. Human Reproduction 17(12):3251.

Gettler LT, McDade TW, Feranil AB, and Kuzawa CW. 2011a. Longitudinal evidence that fatherhood decreases testosterone in human males. Proceedings of the National Academy of Sciences.

Gettler LT, Mcdade TW, and Kuzawa CW. 2011b. Cortisol and testosterone in Filipino young adult men: Evidence for co regulation of both hormones by fatherhood and relationship status. American Journal of Human Biology 23(5):609-620.

Gray P, Kahlenberg S, Barrett E, Lipson S, and Ellison P. 2002. Marriage and fatherhood are associated with lower testosterone in males. Evolution and Human Behavior 23(3):193-201.

Gray PB, Chapman JF, Burnham TC, McIntyre MH, Lipson SF, and Ellison PT. 2004. Human male pair bonding and testosterone. Human Nature-an Interdisciplinary Biosocial Perspective 15(2):119-131.

Muehlenbein MP, and Bribiescas RG. 2005. Testosterone mediated immune functions and male life histories. American Journal of Human Biology 17(5):527-558.

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