In September, Lee Gettler and colleagues published the paper “Longitudinal evidence that fatherhood decreases testosterone in human males” in the Proceedings of the National Academy of Sciences. A news storm erupted, for this research shows that becoming a father was linked to significant declines in levels of testosterone, the quintessential “male” hormone.
Time Magazine just named Gettler et al.’s research to its Top Ten Stories on Parenting in 2011, and ably captures the good and bad of the media coverage all in one. Here is the sensationalistic side, right from the opening:
Testosterone levels plunging? Blame it on fatherhood, according to research from Northwestern University that found that the male hormone drops in men once they have children. The hormone dips most precipitously in men who throw themselves into the details of child rearing.
Becoming a father comes across as losing something essential about being a real man – testosterone plunges, fatherhood is to blame, particularly if men throw themselves into it.
On the positive side, Time acknowledges some of the nuances of the research:
[This] finding … helps make the case that women aren’t the only ones who are biologically wired for raising children. Decreased levels of testosterone may play a role in helping a man respond more sensitively to his children’s needs and those of his entire family. “If this weren’t something that had been normative in humans for the last 100,000 or more years, there would be no reason to expect this decline in testosterone,” says the study’s lead author, Lee Gettler.
I have known Lee for many years now. He was an undergraduate at Notre Dame, where I used to work, and then went on to do his graduate studies at Northwestern with friends of mine from graduate school.
So I emailed Lee to get the real story behind this research, and over a period of weeks, we put together a great interview. We cover fatherhood, sex, biomarkers, applied implications, interdisciplinary research, and more. Enjoy it below, after I provide more background on Lee and the research itself.
Lee is a doctoral candidate in anthropology at Northwestern, and works in the Laboratory of Human Biology there. He specializes in biological anthropology and human biology, particularly how “male physiology is responsive to a variety of shifting socio relational cues and contexts, including pair-bonding status and becoming a father.” For a graduate student, he already has a long and impressive list of publications.
This research on testosterone over the male lifespan is part of the larger Cebu Longitudinal Health and Nutrition Survey (also described on the Northwestern Human Biology Laboratory site). One reason I admire this project is because of the collaboration between public health researchers and anthropologists, as well as between the US and the Philippines to execute the research. These sorts of long-term field sites are increasingly important to be able to answer fundamental questions about human development and human/environment interactions at multiple levels. As the main Cebu site says:
The CLHNS was originally conceptualized as a study of infant feeding patterns, particularly the overall sequencing of feeding events (i.e., of both milk and non-milk items), the various factors affecting feeding decisions at each point in time, and how different feeding patterns affect the infant, mother, and household. The idea was to study these topics within as natural a setting as possible and to analyze how infant feeding decisions by the household interact with various social, economic, and environmental factors to affect health, nutritional, demographic, and economic outcomes.
The cohort of children born during that period, their mothers, other caretakers, and selected siblings have been followed through subsequent surveys conducted in 1991-92, 1994, 1999, 2002, and 2005. Research is now focused on the long-term effects of prenatal and early childhood nutrition and health on later adult outcomes, including education and work outcomes and development of chronic disease risk factors.
The complete citation for the PNAS paper is Lee T. Gettler, Thomas W. McDade, Alan B. Feranil, and Christopher W. Kuzawa (2011). Longitudinal evidence that fatherhood decreases testosterone in human males. Proceedings of the National Academy of Sciences 108(39): 16194-16199. The PNAS page is here, and a pdf available here. Here’s the abstract:
In species in which males care for young, testosterone (T) is often high during mating periods but then declines to allow for caregiving of resulting offspring. This model may apply to human males, but past human studies of T and fatherhood have been cross-sectional, making it unclear whether fatherhood suppresses T or if men with lower T are more likely to become fathers.
Here, we use a large representative study in the Philippines (n = 624) to show that among single nonfathers at baseline (2005) (21.5 ± 0.3 y), men with high waking T were more likely to become partnered fathers by the time of follow-up 4.5 y later (P < 0.05). Men who became partnered fathers then experienced large declines in waking (median: −26%) and evening (median: −34%) T, which were significantly greater than declines in single nonfathers (P < 0.001). Consistent with the hypothesis that child interaction suppresses T, fathers reporting 3 h or more of daily childcare had lower T at follow-up compared with fathers not involved in care (P < 0.05). Using longitudinal data, these findings show that T and reproductive strategy have bidirectional relationships in human males, with high T predicting subsequent mating success but then declining rapidly after men become fathers. Our findings suggest that T mediates tradeoffs between mating and parenting in humans, as seen in other species in which fathers care for young. They also highlight one likely explanation for previously observed health disparities between partnered fathers and single men.
Lee Gettler and his colleagues already wrote up a nice overview of the research on the Scientific American site, with the post titled Fatherhood, Childcare, and Testosterone. They note two critical reactions to their research, Tarzan the Diaper Man at Slate and NYT: Will Graying Editors Believe in a Drop in Testosterone? at Knight Science Journalism Tracker. I found a third over at Big Think, Testosterone Study Doesn’t Prove Men Are “Meant” To Do Childcare.
The Scientific American piece by Gettler et al. is a great complement to the PNAS article itself:
We would like to contribute to the discussion [of the research] by providing more scientific detail and context for our findings. We welcome this opportunity to discuss, for example, the previous research that motivated our question, exactly what we found in our study, and why we interpret our findings as we do. We will also discuss the gaps in current understanding that leave open important questions.
Finally, onto the interview with Lee.
Lende: What is the main take away message you hope people get from this research?
Gettler: A few fundamental facts about humans and human evolution are useful for framing our paper. First, humans produce children that are completely dependent on caregivers for a decade or more, and, despite that, we have children every few years (in natural fertility populations), or, at least, all signs suggest we would have in the evolutionary past. Because of these factors, raising human children is necessarily a cooperative endeavor. Mothers would have cooperated with others to raise multiple children at once and to ensure their survival and well-being.
Depending on the ecology/circumstances, these allo-caregivers would likely have included grandmothers, other female kin, perhaps even older siblings, and fathers, who were likely in a good position to participate in caregiving during human evolution, as they often are now. Cross-species comparisons suggest that if paternal care is indeed an evolved behavior in humans, men’s biology would likely accommodate the transition to fatherhood/caregiving in specific ways, including changes in testosterone.
What we see, specifically, in our research is that men have the biological capability to “attune” to fatherhood, responding to the transition to fatherhood with large declines in testosterone. We also see that fathers who are the most involved with physically taking care of their children have the lowest testosterone.
This does not mean that this pattern and its predicted relationships to behavior will occur in every man everywhere, but simply that, within a normative range of variability, male human reproductive biology has the capacity to respond in this way. Individual personalities and cultural norms can certainly affect, mitigate, even dictate, in some cases, how or if these testosterone patterns come to fruition and how they relate to male’s behavior, if they do at all.
Classic models of human evolution have often emphasized the role of men as hunters and providers, without much (or any) attention given to men’s possible contributions to childcare. Our findings help revise this model by showing that human male biology can specifically adjust to the demands of fatherhood and suggest an important role for fathers’ direct care of their children in that accommodation process.
Lende: Your paper got a lot of press, and some of that coverage went the sensationalist route. What are some of the common mistakes you have seen in the popular reporting on this research?
Gettler: Some examples of headlines associated with our article:
“Less Macho, More Daddy” and “Fatherhood Lowers ‘Manly’ Hormone, Keeps Dad at Home” and “Fatherhood: The ultimate libido-killer?”
I think many news agencies, whose goal is obviously and unapologetically to attract readership, ran with the notion that masculinity, testosterone, and sex drive are all equatable or synonymous, which they clearly are not. Is some testosterone necessary for libido? I think research on men with clinically low testosterone provides evidence that, yes, it is, but once we are talking about the “normal range” of testosterone the relationship between testosterone and libido becomes much weaker and the factors that influence a man’s sexual desire go well beyond one hormone.
There is, however, research showing that a couple’s sex life changes when they have young children, but, again (and all the parents out there are probably vigorously nodding along) the factors that influence sexual activity/desire among new parents are much more complex than the “fatherhood effect” on testosterone. It might even be worth noting that in the study of which the PNAS paper is a part, the Cebu Longitudinal Health and Nutrition Survey, fathers were more likely to report having had sex in the month prior to their interview, compared to non-fathers.
Part of the reason that there was so much media interest in our article is that testosterone is one of the few biomarkers explored by researchers like us that resonates strongly with the public. That said, at least in part, the public connects with “testosterone” because they are constantly barraged with images of “testosterone-fueled aggression” or the “testosterone-laden environments” of male locker rooms, etc. I cannot claim specific expertise on cultural models of masculinity in our society or how they have emerged or have changed, particularly with the ever-morphing role of mass media in our lives, but in response to our article there seemed to be a strong desire to attribute masculinity and what “makes the man” to an irreducible, primordial component- testosterone.
This monolithic characterization fails to consider the extent to which one’s cultural setting determines what characteristics are “masculine” and how one’s developmental experiences help determine where an individual falls on his own culture’s scale of “masculinity.” Moreover it ignores the reality that the relationships between human biology, personality, and behavior are incredibly complex, thus making it rather naive and myopic to claim that testosterone = manliness.
Given the diversity of the US, I am not sure there is a “prevailing” model” of masculinity in our culture, but the media portrayal seems to imply that being an involved father and experiencing a drop in testosterone are antithetical to manhood. If that’s the case, what’s the model of masculinity? Don Draper of Madmen infamy?
Perhaps our findings- which indicate that human males have an evolved capacity to accommodate the demands of fatherhood, including childcare, with potentially adaptive and beneficial biological changes- can help revise the notion of “manliness” to a broader formulation that more appropriately matches onto the scope of experiences in men’s lives.
Lende: You contrast your approach – a focus on men’s experiences and life events in conjunction with hormonal function – with the simplistic notion that hormones, or any biological cause, drive what we do in a primordial way. Can you explain some more about how this type of anthropological approach works?
Gettler: First off, I think there is an ongoing, complex, sometimes contentious anthropological discussion regarding biology and behavior, which greatly pre-dates my existence as a scholar (and a human), to the extent that there are tensions between acknowledging that biology does influence human behavior and recognizing the degree to which much of human behavior is not biologically-determined.
All of human behavior is mitigated physiologically- i.e. through the actions of neuronal pathways and neurotransmitters- so there’s really no way of divorcing biology and behavior, which are in constant “flux” and “conversation” with one another. One challenge for anthropologists and other scholars studying these domains is trying in some coherent way to disentangle “the chicken” and “the egg” in the transactional relationship between biology and behavior.
Throughout the history of our field, anthropologists have demonstrated that there is amazing variability in human biology, culture (especially), and the relationship between the two across space and time. Thus, for our research on male reproductive ecology and physiology in Cebu, our research team drew on diverse lines of pre-existing evidence to inform our methodological approaches, while working within the pragmatic constraints of logistic and financial feasibility.
Notably, there was very little ethnographic information available to us that described fatherhood in Cebu or even the Philippines, more broadly. However, in the case of anthropological work on fatherhood and testosterone, it was fortuitous for us that, though there are few scholars conducting research on this topic, there was an existing body of literature to help inform our hypotheses.
Dr. Peter Gray has studied marriage, fatherhood, and testosterone in cultural groups around the world, including the US, China, Kenya, and Jamaica, and, noting that I am providing an overly-simplistic synopsis of Peter’s work, he has shown that testosterone-fatherhood patterns vary quite substantially based on marital and residence patterns and expectations of fathers (for more information on Peter’s work and human fatherhood and evolution, more broadly, see Peter’s recent book Fatherhood with Dr. Kermyt Anderson). A particularly elegant study was published in 2009 by Dr. Martin Muller and colleagues, which showed that in two samples of men hailing from distinct cultural groups in Tanzania, testosterone was lower among fathers (compared to non-fathers) in the group where at least some paternal care was culturally normative (Hadza men) whereas fathers and non-fathers did not differ for testosterone in the group where fathers did not and were not expected to perform care (Datoga men).
So, although all of these prior studies were cross-sectional, eliminating any potential to identify causation between fatherhood and testosterone, they highlight the interplay between cultural models of behavior and men’s biology. Thus, as an a priori anthropological perspective on human physiology would suggest and as these prior studies confirm, understanding the cultural context of fatherhood in the Cebu metropolitan area- including what men did as fathers and why- was abundantly important to our research, which began in the early 2000s.
Two of the more obvious challenges in approaching this kind of work – using an integrative anthropological approach that employs both biomarker collection and some aspect of interview/ethnography- are that there’s a) only so much funding available to scholars (particularly dissertation students, such as myself) and b) only so much time to conduct the research (again, for me, I was [and still am] trying to defend/fund/conduct/produce a dissertation project).
As I mentioned above, our PNAS paper tested hypotheses using data collected as part of the Cebu Longitudinal Health and Nutrition Survey (CLHNS), a large population-based birth cohort study that began in 1983-1984. I think it is worth noting that much of the funding, data collection, and laboratory work necessary to produce our PNAS paper actually pre-dated my time at Northwestern University and resulted from the efforts of Drs. Chris Kuzawa, Linda Adair, and Thom McDade as well as many collaborators at the Office of Population Studies Foundation, University of San Carlos (Cebu City, Philippines), including Dr. Judith Borja and Alan Feranil.
Lende: Tell me more about the specifics of the research, in particular the data collection.
Gettler: The collection of these questionnaire and biomarker data required that almost 1000 men be located, interviewed, and visited multiple times over a 5 year period, in both rural and urban areas, in a metropolitan center that is home to millions of people, not to mention the time required to process the questionnaire and biological samples for analysis. This was a vast undertaking that provided us with highly detailed, standardized information on many aspects of our subjects’ lives. These data allowed us to, for example, test for longitudinal relationships between fatherhood and testosterone while controlling for measures of sleep quality and psychosocial stress, although we did not have open-ended ethnographic interviews that might be more traditionally associated with anthropological study.
In 2010, I also traveled to and resided in Cebu City, where I conducted a smaller study that focused on acute (over 30-60 minutes) changes in men’s hormones while playing with their toddlers in their homes. In my time in Cebu, again working with scholars at the University of San Carlos, we were able to conduct semi-structured group-based discussions on the role of fathers and meaning of fatherhood in this cultural setting, which have helped inform our research in this domain, both for our PNAS paper and another recent publication at Hormones and Behavior.
These two publications are available for download here and my co-authors and I wrote a thorough guest blog walking through our PNAS paper, so I will not delve into an especially thorough discussion of the studies’ results here.
Lende: Can you provide some highlights from the research?
Gettler: Our results provide a noteworthy example of behavior/lifestyle causing males’ biology to change in showing that becoming a partnered father caused a dramatic decline in T, compared to staying single and childless. Similarly, our findings also demonstrate that fathers who chose to become involved caregivers ended up with the lowest testosterone. Our statistical analyses suggest that childcare caused testosterone to go down, but that issue requires additional research. These results conformed to our predictions, which were based on prior research and the results of our questionnaire- and group- interviews, the latter of which showed that many men in this setting valued physically caring for their children.
We also found some evidence that biology may influence behavioral/reproductive patterns, as single non-fathers with higher testosterone at age 21 were more likely to be partnered fathers at age 26, though we were not able to determine the pathways through which this transpired. In our Hormones and Behavior paper, in which we analyzed the results of our study that focused on men’s hormonal changes during father-child play, we found that men’s perceptions of themselves as fathers predicted how their prolactin (a protein hormone with diverse physiological functions) responded to their interactions with their toddlers. In total, we have multiple lines of evidence from our studies in Cebu that behavior/personality influence biology and vice versa, reflecting the mutually-regulatory, interactive relationship I mentioned above.
Finally, I think I would be remiss if I failed to acknowledge that there are multiple brilliant examples of scholars in our field doing really tremendous “biocultural” work- with some prominent examples being Dr. Thom McDade’s research on lifestyle incongruity, stress, and immune function, Dr. Lance Gravlee’s work on skin color and markers of health/stress, Dr. Bill Dressler’s research integrating cultural consonance methods and objective measures of health, and Dr. Robin Nelson’s studies of kinship and biomarker/anthropometric indices of health. I do not mean to specifically privilege these approaches, at the expense of others, but they provide accessible, tangible examples of the ways in which both biological and cultural anthropological methods can be operationalized together.
Lende: Those are great examples, and what you said shows how this type of integrative work, whether biocultural human biology research or neuroanthropology, builds on so much that has come before.
One final question. What are the applied implications of this integrative approach, and in particular, of your research on fatherhood?
Gettler: I think it is important to note from the outset that the applied implications of our findings (that fatherhood causes testosterone [T] to decline in fathers in the CLHNS and that T is lowest among fathers heavily involved in childcare) are as yet unclear and require further longitudinal research.
That said, men’s health is one of the most obvious domains in which our findings might have applied relevance. First, I think there is a widely held notion that T is implicitly suppressive to the immune system. There are multiple pathways through which this type of trade-off between reproductive effort (high T) and survivability (immune function) might transpire. T promotes energetically expensive somatic investments and behavioral patterns, which may detract from the energy available for costly immune functions.
Alternatively or in addition, T may directly inhibit aspects of immunity. I would point readers to the 2005 review by Drs. Michael Muehlenbein and Richard Bribiescas (Testosterone-Mediated Immune Functions and Male Life Histories) for a thorough discussion of these issues, but the simple message I would like to highlight here is that there is not a rigid negative relationship between T and immunity, rather their interactions are likely highly dependent on energetic status and the nature of a given immune challenge (e.g. acute infection, parasitism, etc). Among other scholars, Dr. Muehlenbein and colleagues at Indiana University are continuing to expand our understanding of these domains.
Consequently, I argue that it is too simplistic to conclude that men who experience a dramatic decline in T after transitioning to parenthood are necessarily implicitly healthier than single childless men and such a conclusion would give short shrift to the effects of T on men’s health. On the one hand, there is some evidence that low T is a risk factor for some morbidities, such as Type II diabetes and cardiovascular disease, and that men’s T and adiposity are negatively related. Moreover, there is growing evidence that some men experience an increase in adiposity and body mass index upon entering long-term romantic relationships or becoming parents.
Although, to my knowledge, no studies have examined whether changes in men’s body fat result from their T declining after becoming married and/or fathers, it seems possible that this could contribute to the observed increases in adiposity during these transitions, with long-term, chronic ramifications for men’s health. On the other hand, married men and fathers have been shown to have lower all-cause mortality risk compared to single childless men, which may be in part mediated through behavioral pathways. Thus, it is plausible that fatherhood-related decrease in T help reduce the expression of risky behaviors that contribute to these differences in mortality risk. In addition, high T (likely through conversion to 5-alpha-dihydrotestosterone) has been shown to increase the risk of prostate cancer, which is a prominent mortality concern for males, particularly in long-lived populations.
The men we studied for our PNAS paper were approximately 21.5 years old at baseline and 26 at follow-up, thus for us to test the relevance of our findings for possible health implications will require further longitudinal research, which we hope to pursue if the subjects wish to continue participating in the study and we can secure additional funding. In addition, I have discussed the ways in which this pattern (T changes with life history stage transitions) seems to vary based on cultural setting and expectations of men’s roles in those capacities— if there are long-term health implications of these findings it will be important to consider how they may come to fruition differently in Cebu compared to other locales, based on things like developmental experiences, diet, activity, availability of healthcare, and other societal resources.
Lende: Thanks, Lee. What a great interview.
Photo Credit of Cebu Father and Child: F. Legardo.
And for more fun, check out this Bill Maher video “Real Men”, which provides an entertaining discussion of the research and what testosterone drops might really mean.