Thursday, May 10th 2012
Who makes your food? Do you live alone and do everything yourself, or are you part of a partnership, roommate situation, or extended family where food is shared? Most likely, the more complicated your living situation, the more complicated the food allocation. Perhaps one person buys the food and another cooks it, or everyone shares in the acquiring and making but you don’t all like the same stuff, so sometimes you have to make an extra peanut butter and jelly sandwich for the kid who hates curry night.
Humans share both food and labor. To some extent, we allocate food based on status (“The Big Piece of Chicken” from Chris Rock’s Bigger and Blacker – warning, profanity (and a splash of sexism) ahead!):
[youtube http://www.youtube.com/watch?v=2Cn8sczZTZ4&w=420&h=315]
Maybe you’re the parent who always gets the big piece of chicken, or maybe you’re the roommate who always seems to have his leftovers stolen. The question is, why? What implications does this have for your own stress and energy stores, and ultimately your reproductive success?
The concept of pooled energy budgets
A series of papers over the last few years by Karen Kramer, Meredith Reiches, Peter Ellison and others raises exactly this question. In particular, they take on the paradox of slow human life histories – the fact that we take a long time to grow up, mature, be fully independent and have our own offspring – with fast reproduction – once we can have kids we are capable of having many overlapping, dependent offspring (Kramer and Ellison, 2010).
Consider that the age at first birth among many hunter-gatherer populations is in the late teens (Kramer et al., 2009), yet individuals in these populations often aren’t fully competent hunters and foragers until their thirties (Gurven et al., 2006; Kramer et al., 2009; Walker et al., 2002). Among industrialized populations, our average age at first birth is in the mid to late twenties (and here are CDC stats for the US only), but our average full financial independence equally late (that’s not to say there aren’t many teens and young adults fully independent from parents, but also many folks into their twenties and thirties are still getting loans, help with down payments, or gifts that help financially).
Kramer et al 2009 Figure 4 showing age at menarche and first birth among South American forager populations.
Gurven et al 2006 Fig 3b Age-dependency and hunting skill.
This gap would not do among non-human primates: most primates become independent foragers very early in their lives, and so what they collect, they eat. If they can’t get enough food to survive, they certainly won’t be allocating any of that energy towards reproduction, and so their reproductive success will be low or zero.
How do we handle the years between age at first birth and full independence? How do we take so long to mature, using up parental resources all the while, yet still manage to have a decent number of babies? Humans manage to circumvent our very slow and dependent juvenile period, and therefore have plenty of energy for reproduction, through transfers of energy (food, or in industrial societies money for food) and labor (especially childcare) between individuals.
When individuals hunt or forage, many are able to bring in more than they themselves will eat, and this gets shared among their family or community. Individuals in different reproductive states may even contribute more to their households to increase their indirect fitness, as has been found with grandmothers in Hadza foragers (Hawkes et al., 1997), and in suitors (Hawkes et al., 1997) or fathers (Marlowe, 2001), perhaps to offset potentially lower foraging capabilities of a pregnant or breastfeeding mother. And many increasingly agree that humans are a cooperatively breeding species (Hrdy, 2008), meaning that labor transfers of childcare can happen pretty often.
Hawkes et al 1997 Table 1. Time allocated to work among different age groups in Hadza men and women.
It’s great that we share, and that foraging and childcare behavior is responsive to one’s context and in the context of one’s family. This means that one’s social environment may play a significant role in the amount of energy and time you have for survival and reproduction (Reiches et al., 2009).
Why pooled energy budgets are cool
Understanding where our energy comes from – who has it easy and who has it hard in the daily labor of food acquisition – can help us understand a number of interesting things that vary among human populations. For instance, lighter juvenile workloads can contribute to faster juvenile growth. I’ve talked about the Pumé foragers before as an example of a population with relatively early reproduction. Kramer et al (2009) have shown that Pumé girls reach menarche and first birth earlier than most foragers (check out the first image in this post). These girls tend to have lower foraging expectations placed on them, which indirectly increases their energy budgets, as what would have gone towards foraging effort can now go towards maintenance and reproduction. This contributes to how they achieve faster growth and earlier reproductive maturity.
Understanding the nature of energy transfers can also help us understand cooperative breeding. In populations where pregnant and breastfeeding mothers’ foraging workloads are still high, are they getting respite from childcare to offset these costs? Who helps more: peers, fathers, maternal grandmothers or paternal grandmothers? What factors drive variation in allocare between populations? I wonder how varied these behaviors are even within a population: perhaps some mothers prefer foraging to childcare, or vice versa, and so find themselves doing more of one or the other. And I wonder if any of this could have an ultimate effect on reproductive success, depending on the environment and difficulty foraging.
But what I find really interesting is that some individuals may get more or less food through these energy transfers based on status, kinship, and friendship. That is, who you know, who your mother or father is, the kind of culture you come from and whether it treats some kinds of people better or worse, this may all have an ultimate impact on an individual’s energy budget. This is on top of the already documented impact of social environment on stress and health (e.g., Albert et al., 2008; Kiecolt-Glaser et al., 2010; Miller et al., 2002). So there are at least two very significant ways in which our social environment affects wellness and reproductive success: an energy-based mechanism and a stress-based mechanism, and they are not mutually exclusive paths.
Starting from the pooled energy budgets model resolves a lot of the bickering that can occur about which ecological factor is “most” important to reproduction. The reality is, no matter how much I and others love to talk about inflammation, stress, immune function and other stuff, all of these factors ultimately impact the body through allocation of resources – through energy. The pooled energy budget concept gives a space for all these factors, and a useful framework to understand them.
References
Albert MA, Ravenell J, Glynn RJ, Khera A, Halevy N, de Lemos JA. 2008. Cardiovascular risk indicators and perceived race/ethnic discrimination in the Dallas Heart Study. American heart journal 156(6):1103-1109.
Gurven M, Kaplan H, Gutierrez M. 2006. How long does it take to become a proficient hunter? Implications for the evolution of extended development and long life span. Journal of Human Evolution 51(5):454-470.
Hawkes K, O’Connell JF, Blurton Jones NG. 1997. Hadza women’s time allocation, offspring provisioning, and the evolution of long postmenopausal life spans. Current Anthropology 38(4):551-577.
Hrdy S. 2008. Evolutionary context of human development: the cooperative breeding model. In: Salmon C, Shackelford T, editors. Family relationships: an evolutionary perspective: Oxford University Press.
Kiecolt-Glaser JK, Gouin J-P, Hantsoo L. 2010. Close relationships, inflammation, and health. Neuroscience & Biobehavioral Reviews 35(1):33-38.
Kramer KL, Ellison PT. 2010. Pooled Energy Budgets: Resituating Human Energy Allocation Trade-offs. Evolutionary Anthropology 19:136-147.
Kramer KL, Greaves RD, Ellison PT. 2009. Early reproductive maturity among Pumé foragers: implications of a pooled energy model to fast life histories. American Journal of Human Biology 21(4):430-437.
Marlowe F. 2001. Male contribution to diet and female reproductive success among foragers. Current Anthropology 42(5):755-760.
Miller GE, Stetler CA, Carney RM, Freedland KE, Banks WA. 2002. Clinical depression and inflammatory risk markers for coronary heart disease. The American Journal of Cardiology 90(12):1279-1283.
Reiches MW, Ellison PT, Lipson SF, Sharrock KC, Gardiner E, Duncan LG. 2009. Pooled energy budget and human life history. American Journal of Human Biology 21(4):421-429.
Walker R, Hill K, Kaplan H, McMillan G. 2002. Age-dependency in hunting ability among the Ache of Eastern Paraguay. Journal of Human Evolution 42(6):639-657.
Tuesday, May 1st 2012
Anthropology is an inherently interdisciplinary field. We draw from evolutionary theory, feminist theory, critical race theory, we compare within and between primates, we even manage to work with the occasional rodent or suid species. There are anthropologists who make models, anthropologists who theorize, anthropologists in the field and the lab, anthropologists who study those long dead, recently dead, living and even those not yet alive. You can find us in anthropology departments, sure, but you can also find us in biology, sociology, psychology, community health and education departments; in businesses, hospitals, museums, zoos, and non-profits, and countless other places I’m forgetting.
So it’s interesting to me that within anthropology we have four fields: biological, cultural, and linguistic anthropology, and archaeology. Then within those four fields we have further subfields: within bio we have human biology, primatology, paleoecology, morphology, genetics to name a few, and even within those are sub-sub-fields. Some of the subfields collaborate, and some never read each other. Part of the reason I was so excited to collaborate with Katie Hinde and Julienne Rutherford on Building Babies was that I would get more of a chance to read the non-human primate literature, something we human biologists are sometimes known to ignore more than is good for us.
Then there’s biocultural anthropology. Biocultural anthropology is not actually that new, and there are some truly excellent practitioners. But more recently there has been a spate of work in anthropology claiming to take a “biocultural approach” that does not appear to be derived from these folks. I had the chance recently to chat with some colleagues about recent work on the biocultural approach, and found I was not the only one stymied, perhaps even frustrated, by this work.
Some work that claims to be biocultural doesn’t really appear to be biological, nor is it cultural, because it is atheoretical and happens to use biological and cultural methods. Some of it leans in some sort of theoretical direction, but then the methods are inscrutable.
How is it that a field that is so good at being interdisciplinary cannot do a good job interdisciplinary-ing itself?
What Does It Mean to Be Interdisciplinary?
A few of these venting sessions with colleagues just happened to be followed by a talk by Dr. Liam Heneghan, co-director of the DePaul Institute for Nature and Culture, environmental science professor, and philosophy PhD student (also, a blogger!). Heneghan’s talk was sponsored by the University of Illinois Institute for Genomic Biology, where some of us are trying to be all interdisciplinary ourselves. The talk was titled: “Interdisciplinarity: is it necessary, possible, or useful – a discussion.” In addition to several interesting books that I am going to have to dig through this summer, Heneghan offered a very hopeful picture for interdisciplinarity. Here are a few of my takeaways, as applied to the problem of the biocultural approach.
Being interdisciplinary isn’t the same as being a little good at everything, consistent with the saying “jack of all trades, master of none.” Heneghan analyzed the footnotes of one of the most popular interdisciplinary works, The Ecological Thought by Timothy Morton, and found it represents typical biodiversity quite well: the strongest influences by a few fields with, as he says, “a trailing edge of rarer species.” At least one model of being interdisciplinary, then, is to be very good in one field, pretty good in a few more, and then conversant across others. Some of the work I’ve been reading never masters that first field. And so there is something less than ideal in how we are training our students.
Students who want to become good biocultural anthropologists must first become experts in biological or cultural anthropology. Scholars need a base from which to reach out to other disciplines. If you are not thoroughly trained as one or the other, you will have a lot of trouble bridging them, or using your critical thinking skills to help ease you into a new field. This also suggests being thoughtful about undergraduate and graduate curriculum: while initial coursework should make someone an expert in their first field, learning a mixed methods approach for research probably wouldn’t hurt.
We also need to identify the essential reading for biocultural anthropology. What is the canon? What do biological anthropologists need to read to become conversant in cultural anthro? What do cultural anthropologists need to read to become conversant in bio anthro? I can probably identify most of the biological readings, but certainly not the cultural, and hope my readers do.
Next, identify the core questions that a biocultural approach can tackle better than any other. If a bio or cultural approach would satisfy the question, but you are tacking on the other field because it seems sexy, your grant proposal or manuscript submission is unlikely to make it through. But if you can recognize a problem that only this approach can solve you will be able to better develop the theory.
Finally, be ambitious. When I suggest we should make sure students and junior colleagues develop high competency in one discipline first and then thoroughly read one if not several others, I am not trying to deter people away from a biocultural approach. It’s just that the field will be better served by rigorous, developed, thoughtful research. Be ambitious in your projects, your goals, your research trajectories, and encourage ambition in those you mentor. But the lesson I have learned the hard way over and over is that ambition, excitement yet not thorough training will get you burned. I want my students, and any other budding biocultural anthropologists, to be kicking my ass in five to ten years because they know the literature and methods better than me.
What am I missing? Am I being too hard on the field? What biocultural curricula are you a part of, and what is or isn’t working? This is really just the most preliminary version of my thoughts on this, and so I welcome your comments.
Friday, April 27th 2012
This is a re-post, with slight editing, of a piece I wrote on the old blog after last year’s AAPA meetings. I would like to keep thinking on this topic so thought I would share this before I write anything new for the Sci Am space.
Variation in adolescent menstrual cycles, doctor-patient relationships, and why we shouldn’t prescribe hormonal contraceptives to twelve year olds
The United States has the highest rate of unintended teen pregnancy among industrialized nations. So I can understand why there are so many papers, and such a great effort, to get young girls on hormonal contraception (Clark et al. 2004; Clark 2001; Gerschultz et al. 2007; Gupta et al. 2008; Krishnamoorthy et al. 2008; Ott et al. 2002; Roye 1998; Roye and Seals 2001; Sayegh et al. 2006; Zibners et al. 1999).
But I’ve noticed two things: first, that hormonal contraception is used imperfectly in this population, with some estimates that 10-15% of adolescents on hormonal contraception still get pregnant (Gupta et al. 2008). Second, discontinuation rates for hormonal contraception in young girls are high, with many girls complaining about side effects, particularly breakthrough bleeding (Clark et al. 2004; Gupta et al. 2008; Zibners et al. 1999). I have to admit some concern over the fact that many of the papers I read that mentioned these discontinuation rates and side effects were almost condescending in their tone. The implication was that the side effects weren’t a big deal.
One of the ways clinicians and sexual health educators are trying to improve hormonal contraceptive use in adolescents is to emphasize their off-label use as a “regulator” – that is, the pill can regulate your cycle, regulate your mood, regulate your skin. The idea is to emphasize the positive effects of hormonal contraception to combat the side effects young girls both worry about, and actually experience. This also tends to produce campaigns and commercials with images of idealized young women that young girls would want to model themselves after – skinny, confident, and of course very feminine.
This is not my favorite idea. The pill should not regulate the cycles of adolescent girls who experience moderate variation in their cycles, which, as it turns out, is what characterizes the normal adolescent menstrual cycle. (This is independent from debilitating, pathological experiences of the menstrual cycle or menstrual bleeding, which occur in a very small percentage of women.)
Allow me to explain.
From Vihko and Apter (1984). These are from old site so you can click to embiggen.
Vihko and Apter (1984) showed that there is variation in age at menarche, and that that variation tells us something about how long it should take an adolescent to start to achieve regular ovulatory cycles. The later your age at menarche, the longer you will experience irregular cycles. However, even in girls with ages at menarche twelve and under, it still took on average five years to achieve regular cycles. This indicates that, in adolescents, irregularity is in fact regular.
Lipson and Ellison (1992) have also looked at age-related variation in progesterone concentrations. Progesterone is the sex steroid hormone secreted by the ovary after ovulation, which is in the luteal phase. Luteal phase function is the one that seems to be the most variable within and between populations, and so progesterone is a great way to understand how female bodies vary. They found that those with the lowest hormone concentrations were on the extreme ends of their sample – 18-19 year olds, and 40-44 year olds and, as you might expect, hormone concentrations were higher as you moved towards the middle of that age range. So both younger and older women have low hormone concentrations relative to women in their reproductive prime, which is 25-35 years of age. But of course, this means that low hormone concentrations when you are in those early or late age ranges means that you are normal for your age.
From Lipson and Ellison (1992). These are from old site so you can click to embiggen.
Despite these issues, there are substantial benefits to hormonal contraception in adult women. When women take hormonal contraception in adulthood, particularly in the 25-35 year range, they are very effective contraception. The pill also may reduce risk of reproductive cancers, though results are mixed (Collaborative Group 1996; Collaborative Group 2008; Kahlenborn et al. 2006; Marchbanks et al. 2002; Modan et al. 2001; Narod et al. 1998; Smith et al. 2003). And of course, off-label use to treat painful periods or premenstrual syndrome can be beneficial for many (Fraser and Kovacs 2003).
However, the benefits of hormonal contraception in adults seems to be limited to more industrialized populations. Bentley (1994; 1996) first raised these concerns. She discussed the possible genetic, ethnic and developmental differences between women that could produce variation in pharmacokinetics, which could in turn vastly change the experience and efficacy of hormonal contraception in a global context. Virginia Vitzthum and others have also shown that there are high discontinuation rates and complaints of breakthrough bleeding in rural Bolivian women on hormonal contraception (Vitzthum and Ringheim 2005; Vitzthum et al. 2001). Other studies have shown similar discontinuation rates and side effects in other non-industrial populations (de Oliveira D’Antona et al. 2009; Gubhaju 2009).
You might notice that the issues in non-industrial populations mirror what has been seen in industrial adolescent girls. This isn’t surprising, given that they also have in common fewer ovulatory cycles and lower hormone concentrations.
So, I worry about whether the clear benefits of hormonal contraception in adulthood can be applied to adolescent girls, some as young as eleven or twelve years old. With the imperfect administration and high discontinuation rates, they aren’t that great as contraception. But there are additional, physiological concerns. What are the effects of giving doses of hormones to young girls with newly developing hypothalamic-pituitary-ovarian axes? The variation I mentioned before, where irregularity is regular in adolescence, is because the feedback loop between the brain and the gonads is priming and developing in this period, and this takes time. The sensitivity of the feedback loop is being set. If we flood this feedback loop with extra hormone, does this alter its sensitivity? It is a question worth testing.
Further, if we flood this immature system that normally has irregular cycles and low hormones, are we increasing lifetime estrogen exposure? High lifetime estrogen exposure is a risk factor for breast cancer and other reproductive cancers. Is it possible that hormonal contraception in adolescence could have the opposite effect of hormonal contraception in adulthood? Again, we need to test this hypothesis.
Future work on this topic includes asking whether adolescent menstrual cycle variation is any different today than twenty to thirty years ago. The only data we have (at least that I know of) are from the aforementioned 1984 and 1992 papers, and maybe some derivative papers using the same datasets. But we all know there have been massive changes in body composition, diet and health in the last few decades that deserve consideration. So, this work needs to be re-done on a current population.
We also need to ask how adolescent reproductive functioning varies within and between populations. While this has been studied extensively in adult women, we don’t have a sense of adolescent population variation. This will give us a sense of what ecological variables produce variation not only in age at menarche, but in how long cycle irregularity persists and reproductive hormone concentrations.
Some additional, provocative thoughts
In this symposium where I gave this talk, Karen Kramer delivered a beautiful paper just before mine on teen pregnancy, and I had some great conversations with session participants and attendees, that has further evolved my own thinking on this issue. I want to say something just a little provocative:
While I think teen pregnancy should be avoided, culturally we overstate its dangers and consequences because we have a real problem with young people reproducing. This can lead young girls to overlook potentially more serious issues like sexually transmitted infections, HIV, and cervical cancer, all of which girls and women are at risk for if they use only hormonal contraception and have otherwise unprotected sex.
Let me explain two important points here. First, in most industrialized nations we are not set up well to support young mothers because of the way families are isolated, yet social support is a strong predictor of birth weight, postpartum depression, and labor progression (Collins et al. 1993; Feldman et al. 2000; Turner et al. 1990). So there are very strong and obvious reasons why teen pregnancy and motherhood can be incredibly challenging in industrialized environments. I wonder sometimes if that lack of cultural support is related to a fear that more young girls will get pregnant if they feel they have permission to procreate. This is similar to the argument in favor of abstinence-only sex ed: if they don’t know their options, or are shamed into believing this option is the worst possible one, then of course they won’t make them. But adults aren’t rational. I’m unsure why we expect adolescents to be.
Birthday gift for a Northwestern student. Image by vxla on Flickr, Creative Commons license.
We also need to consider population variation in adolescence and pregnancy. Variation in age at first birth in traditional populations is quite wide, from sixteen to almost twenty six years of age (Walker et al. 2006). In more traditional populations you see a lot of allomothering and grandmothering to support first time mothers, who are often teenagers (Hawkes 2003; Hrdy 2009; Kramer 2005; Kramer 2008). So, support systems are built in, and it does not alter the trajectory of your life in the same way teen pregnancy does in an industrialized population.
This range of variation in age at first birth, and the fact that most of those young mothers do just fine, perhaps even end up with higher reproductive success, leads me to my second point: the physiological evidence against teen pregnancy might be overstated. In her talk, Karen discussed a paper of hers in the American Journal of Physical Anthropology that described the negative health outcomes of teen pregnancy (Kramer 2008). In it, she reviewed literature that suggests that when you control for lack of prenatal care, first pregnancy, and low socioeconomic status, the common assumption that pregnancy is harmful to teens is significantly weakened.
Further, in her own work with Pumé foragers in Venezuela, mothers under the age of fourteen were the only group to have greater infant mortality than the referent group of late reproducers (Kramer 2008). Yet when we teach young girls about their bodies, we tell them that their bodies are not equipped to have babies in their teens and that there are extreme consequences (in fact, I have said exactly this in the past). The reality is that those consequences are worst for very young teens, and may not be as significant in older teens.
Am I advocating teenagers get pregnant? Absolutely and unequivocally no. But I think they need access to correct information, not skewed information. This means telling them the truth about our uncertainties about the health implications for hormonal contraception in adolescence, it means educating them about the importance of barrier methods, and it means making sure they understand the health risks associated with unprotected sex.
This is a nuanced issue that requires nuanced thinking. Despite my concerns about adolescent hormone contraceptive use, there are problems with barrier methods as well, particularly when there may be a cultural bias against their use, or in situations when women cannot safely use contraception in an obvious way with their partner (Gupta et al. 2008). Again, what is important here is conveying correct information, so that each individual can weigh the pros and cons as they relate to her own context. This means it could be an excellent idea for some twelve year olds to be on hormonal contraception, and a terrible one for other girls through the age of twenty. It is going to have to be up to them.
I hope this post generates some thinking and some conversation, and I welcome people who might push me in a different direction than where I’m currently thinking. I am sharing this now, before putting it together as a manuscript, to provoke thoughts and comments.
References (watch out! Ref list almost as long as post!)
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Clark, L. (2001). Will the Pill Make Me Sterile? Addressing Reproductive Health Concerns and Strategies to Improve Adherence to Hormonal Contraceptive Regimens in Adolescent Girls Journal of Pediatric and Adolescent Gynecology, 14 (4), 153-162 DOI: 10.1016/S1083-3188(01)00123-1
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