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Sons and daughters and differential parental investment
One of my favorite rhetorical tricks is asking my students a question that has an obvious answer based on cultural expectations, but is wrong. So every year, when I start to teach my students about parental investment, I ask:
Who is harder to raise, sons or daughters?
I’ve asked by a show of hands and with iClickers, over the years, and the room of 750 is almost unanimous: daughters are harder to raise. So, then I get off the stage and walk around a bit. What do you mean by that? I ask.
Girls cause more gray hairs.
Girls cause more trouble when they start to like boys.
Girls are more work, and cost more money, since they shop all the time.
Girls talk back more.
And of course, there is always the saying that girls steal some of their mother’s beauty.
So then I show them this:
|From Helle et al 2002.|
Here is a graph of maternal longevity based on the number of sons or daughters they have. This data was based on a historical population from Finland from 1640-1870 using church records (Helle et al 2002). As you can see, the more sons mothers bear, the shorter their lifespans. You see the opposite for daughters. So sons have a negative impact, and daughters have a positive impact. This same trend has been found in records from a Flemish village (van de Putte et al 2003, 2004), where sons negatively impact lifespan but not daughters. Interestingly, data from church records from the field site where I work in rural Poland provides a slightly different picture: every offspring of either sex reduced lifespan by about 95 weeks (Jasienska et al 2006).
|From Jasienska et al 2006.|
Once students see these graphs, they quickly realize what is going on. Generally speaking, girls help mothers more at home in terms of chores and alloparenting. And in many cultures, particularly the historical ones studied so far, sons are costly because parents invest more in them, to help launch their own families. Daughters, not so much. In the Polish population, there may be other factors where daughter investment is important, or it is just costly to have so many offspring and you have maternal depletion regardless of daughter help.
Sex bias in parental investment is an important part of understanding both the biology and culture of parenting, and the developmental trajectories of children. The Trivers-Willard hypothesis, which has been tested many times in humans and animals, suggests that parents should invest more in sons when conditions are good, and more in daughters when conditions are bad. That is, when you have lots of resource you should put it towards a son in order to increase the chances he will have high reproductive success, since his is assumed to be more variable and high effort could lead to high reward. But in periods of low resource, daughters are a good bet because they are more likely to have at least some reproductive success no matter what.
|From Hrdy 1990.|
Of course, differential investment based on resources is further conflated in humans due to culture and, I would contend, our almost universal favor for patriarchy (Smuts 1995). Here is an image of an Indian family waiting at a clinic. There is a mother, an older son, and a twin boy and girl. Notice the extreme difference in health between the infant boy and girl – they are twins, yet the infant girl is emaciated. This is because in this population sons are always fed and cared for first, and whatever is left over, if there’s anything, is given to daughters.
So, parental investment can have real effects on the parent in terms of lifespan, and perhaps also their own future reproductive capabilities. Further, the conditions under which you may have children can vary, but how much a parent chooses to invest in their children varies too.
The piece of this that may be toughest to parse out, particularly in humans, is how the condition of the mother (or parents) can vary, and how that variation impacts the sex ratio of their children. In some species, like red deer, it is easier to imagine a mechanism: these animals have diapause, a period where their embryos are dormant until it is a good time to gestate and bear them. It is easier to insert some kind of selection process into a period where several embryos are all “frozen” and sex has been determined. But what about humans that produce singletons and invest huge, overlapping amounts of support to their children over decades? How would a sex bias based on maternal condition operate? And is there anything the offspring can do about it?
Changes in maternal breast size during pregnancy
It turns out that measurements as easy as stepping on a scale, and knowing your bra size, can begin to unpack the answer. First, a confession: I consider the author of this paper Andrzej Galbarczyk more than a colleague, but a friend. Andrzej is the graduate student who oversaw my Polish field site last season (Mogielica Human Ecology Study Site, director Dr. Grazyna Jasienska). He has translated consent forms and surveys for me and we’ve had many valuable and important conversations about my fieldwork. He is a smart, kind and thoughtful person and scholar. So, I let him see an early draft of this post to make sure I understood his point of view.
Galbarczyk performed an internet survey in Poland with 120 women, where he asked them to report their pre-pregnancy weight and bra size, their bra size directly after giving birth, and the sex of their offspring. He found two notable differences in these women: mothers of daughters weighed less before pregnancy, but had a greater changes in breast size during pregnancy.
The evidence about maternal pre-pregnancy weight is consistent with the Trivers-Willard hypothesis, as mothers who had sons were more likely to be heavier, and thus have more resource to invest. The second significant difference, that mothers with daughters had larger breasts after pregnancy, seems could be argued either way: Galbarczyk argues that it supports Trivers-Willard because mothers of sons could have been devoting more resource to growing their offspring rather than their breasts.
In other animals and primates particularly, mothers of male infants produce more energy-dense milk, yet mothers of female infants may produce a greater quantity of milk (Hinde 2009). And breast size is a pretty noisy signal of milk quality or quantity. So, what is the meaning of this difference in breast size?
Adaptation or physiological inevitability?
Galbarczyk suggests the difference is related to the evolutionary underpinnings of human female breasts. Women develop breasts around puberty, and though they certainly change in size and shape over time, keep them their whole lives. Other animals develop their mammary glands only shortly before lactating and then they regress again. Many contend that human breasts are an honest signal of fertility. This is at least partially confirmed by the correlation between breast size and estradiol concentrations (Jasienska et al 2006).
Galbarczyk thinks that the larger breasts seen in postpartum mothers to daughters may be a way to attract a mate for parental care. Perhaps this would help where she has given birth to the less-favored sex and needs to really convince him to participate; this could be a signal from the mother or the female fetus. Or maybe by appearing more attractive, she can have another reproductive opportunity, which would give her a chance to have a son.
You all know how I feel about evolutionary storytelling. In certain ways I do find this particular argument compelling, from the perspective of the Trivers-Willard hypothesis. But the evidence for the adaptive scenario around breast size is circumstantial.
Also, I don’t want this story to detract from some very interesting data: remember that Galbarczyk found that in this population, mothers of daughters weigh less before pregnancy, and develop larger breasts afterwards. Very cool. So perhaps we should consider a mechanistic, rather than adaptive explanation?
I have two thoughts about this, both related to androgens (androgens are the class of hormone that testosterone falls under). First, I wonder if there is an effect of fetal androgens from a male fetus on breast size. If so, mothers of daughters would have larger breasts simply because they aren’t having their breast tissue growth or density suppressed by androgens. It could simply be physiology that doesn’t have adaptive meaning.
Second, the mothers of sons were heavier before pregnancy. Heavier individuals tend to have higher circulating insulin levels, and the ovary can respond to higher insulin by producing more androgens (Poretsky 1991, Dimitrakakis et al 2004). So you could have a suppressive effect on breast size from that avenue as well. You don’t need an adaptive scenario for either of these mechanisms, just a consequence of how hormones work.
I would love to see Galbarczyk or someone else follow up on these thought-provoking results by measuring women, rather than relying on self-report, and by measuring their estradiol, progesterone and androgens. Understanding the different factors and motivations that lead to sex differential investment and outcome is a great field of study, and this work gets us thinking in a new direction.
Dimitrakakis C, Jones RA, Liu A, & Bondy CA (2004). Breast cancer incidence in postmenopausal women using testosterone in addition to usual hormone therapy. Menopause (New York, N.Y.), 11 (5), 531-5 PMID: 15356405
Galbarczyk A (2011). Unexpected changes in maternal breast size during pregnancy in relation to infant sex: An evolutionary interpretation. American journal of human biology : the official journal of the Human Biology Council PMID: 21544894
Helle, S. (2002). Sons Reduced Maternal Longevity in Preindustrial Humans Science, 296 (5570), 1085-1085 DOI: 10.1126/science.1070106
Hinde K (2009). Richer milk for sons but more milk for daughters: Sex-biased investment during lactation varies with maternal life history in rhesus macaques. American journal of human biology : the official journal of the Human Biology Council, 21 (4), 512-9 PMID: 19384860
Hrdy, S. (1990). Sex bias in nature and in history: A late 1980s reexamination of the “biological origins” argument American Journal of Physical Anthropology, 33 (S11), 25-37 DOI: 10.1002/ajpa.1330330504
Jasienska G, Nenko I, & Jasienski M (2006). Daughters increase longevity of fathers, but daughters and sons equally reduce longevity of mothers. American journal of human biology : the official journal of the Human Biology Council, 18 (3), 422-5 PMID: 16634019
Poretsky L, Seto-Young D, Shrestha A, Dhillon S, Mirjany M, Liu HC, Yih MC, & Rosenwaks Z (2001). Phosphatidyl-inositol-3 kinase-independent insulin action pathway(s) in the human ovary. The Journal of clinical endocrinology and metabolism, 86 (7), 3115-9 PMID: 11443175
AAPA symposium on Evolution through the Life Course: Why we shouldn’t prescribe hormonal contraception to twelve year olds
When Dr. Grażyna Jasieńska invited me to give a talk on my thoughts around adolescents and hormonal contraceptives as part of an invited symposium on “Evolution through the Life Course,” I thought it was going to be an embarrassing experience, because I would not be presenting the quantitative data more common at the American Association of Physical Anthropology meetings. But I can’t say no to Grażyna, who has served as a wonderful mentor and cheerleader for almost ten years. Besides, if I can rant on a blog, surely I can let myself rant in a talk every now and then.
What follows is a bloggy version of the talk I gave Thursday the 14th, at the meetings in Minneapolis. Writing this post will, I hope, help me begin to turn this into a manuscript. Normally I wouldn’t dare write something on a blog that I would eventually want to publish. However, this is a piece that would benefit enormously from the kinds of conversations that happen in the science blogosphere. Further, I hope to publish it as an opinion piece well-studded with evidence. I think that by sharing my early thoughts now, my later thoughts will be more sophisticated.
* * *
Variation in adolescent menstrual cycles, doctor-patient relationships, and why we shouldn’t prescribe hormonal contraceptives to twelve year olds
|From Vihko and Apter (1984).|
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).|
Now, 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.
Despite the criticisms I’ve begun to name, 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, post-meeting thoughts
|Bristol Palin. Image from here.|
In this symposium, Karen Kramer delivered a beautiful paper just before mine on teen pregnancy, and I had some great conversation 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.
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.
Bentley GR (1994). Ranging hormones: do hormonal contraceptives ignore human biological variation and evolution? Annals of the New York Academy of Sciences, 709, 201-3 PMID: 8154705
Bentley GR. 1996. Evidence for interpopulation variation in normal ovarian function and consequences for hormonal contraception. In: Rosetta LaM-T, C.G.N., editor. Variability in human fertility. Cambridge, UK: Cambridge University Press. p 46-65.
Clark, L. (2004). Menstrual irregularity from hormonal contraception triggers significant reproductive health fears in adolescent girls Journal of Adolescent Health, 34 (2), 123-124 DOI: 10.1016/j.jadohealth.2003.11.091
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
Collaborative group (1996). Breast cancer and hormonal contraceptives: collaborative reanalysis of individual data on 53 297 women with breast cancer and 100 239 women without breast cancer from 54 epidemiological studies The Lancet, 347 (9017), 1713-1727 DOI: 10.1016/S0140-6736(96)90806-5
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Collins, N., Dunkel-Schetter, C., Lobel, M., & Scrimshaw, S. (1993). Social support in pregnancy: Psychosocial correlates of birth outcomes and postpartum depression. Journal of Personality and Social Psychology, 65 (6), 1243-1258 DOI: 10.1037//0022-3522.214.171.1243
D’Antona Ade O, Chelekis JA, D’Antona MF, & Siqueira AD (2009). Contraceptive discontinuation and non-use in Santarém, Brazilian Amazon. Cadernos de saude publica / Ministerio da Saude, Fundacao Oswaldo Cruz, Escola Nacional de Saude Publica, 25 (9), 2021-32 PMID: 19750389
Feldman PJ, Dunkel-Schetter C, Sandman CA, & Wadhwa PD (2000). Maternal social support predicts birth weight and fetal growth in human pregnancy. Psychosomatic medicine, 62 (5), 715-25 PMID: 11020102
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Gubhaju, B. (2009). Barriers to Sustained Use of Contraception in Nepal: Quality of Care, Socioeconomic Status, and Method-Related Factors Biodemography and Social Biology, 55 (1), 52-70 DOI: 10.1080/19485560903054671
Gupta, N., Corrado, S., & Goldstein, M. (2008). Hormonal Contraception for the Adolescent Pediatrics in Review, 29 (11), 386-397 DOI: 10.1542/pir.29-11-386
Hawkes, K. (2003). Grandmothers and the evolution of human longevity American Journal of Human Biology, 15 (3), 380-400 DOI: 10.1002/ajhb.10156
Hrdy SB. 2009. Mothers and others: the evolutionary origins of mutual understanding: Belknap Press.
Kahlenborn, C., Modugno, F., Potter, D., & Severs, W. (2006). Oral Contraceptive Use as a Risk Factor for Premenopausal Breast Cancer: A Meta-analysis Mayo Clinic Proceedings, 81 (10), 1290-1302 DOI: 10.4065/81.10.1290
Kramer, K. (2005). Children’s Help and the Pace of Reproduction: Cooperative Breeding in Humans Evolutionary Anthropology: Issues, News, and Reviews, 14 (6), 224-237 DOI: 10.1002/evan.20082
Kramer KL (2008). Early sexual maturity among Pumé foragers of Venezuela: fitness implications of teen motherhood. American journal of physical anthropology, 136 (3), 338-50 PMID: 18386795
KRISHNAMOORTHY, N., SIMPSON, C., TOWNEND, J., HELMS, P., & MCLAY, J. (2008). Adolescent Females and Hormonal Contraception: A Retrospective Study in Primary Care Journal of Adolescent Health, 42 (1), 97-101 DOI: 10.1016/j.jadohealth.2007.06.016
Lipson, S., & Ellison, P. (2008). Normative study of age variation in salivary progesterone profiles Journal of Biosocial Science, 24 (02) DOI: 10.1017/S0021932000019751
Marchbanks, P., McDonald, J., Wilson, H., Folger, S., Mandel, M., Daling, J., Bernstein, L., Malone, K., Ursin, G., Strom, B., Norman, S., Wingo, P., Burkman, R., Berlin, J., Simon, M., Spirtas, R., & Weiss, L. (2002). Oral Contraceptives and the Risk of Breast Cancer New England Journal of Medicine, 346 (26), 2025-2032 DOI: 10.1056/NEJMoa013202
Modan B, Hartge P, Hirsh-Yechezkel G, Chetrit A, Lubin F, Beller U, Ben-Baruch G, Fishman A, Menczer J, Struewing JP, Tucker MA, Wacholder S, & National Israel Ovarian Cancer Study Group (2001). Parity, oral contraceptives, and the risk of ovarian cancer among carriers and noncarriers of a BRCA1 or BRCA2 mutation. The New England journal of medicine, 345 (4), 235-40 PMID: 11474660
Narod, S., Risch, H., Moslehi, R., Dørum, A., Neuhausen, S., Olsson, H., Provencher, D., Radice, P., Evans, G., Bishop, S., Brunet, J., Ponder, B., & Klijn, J. (1998). Oral Contraceptives and the Risk of Hereditary Ovarian Cancer New England Journal of Medicine, 339 (7), 424-428 DOI: 10.1056/NEJM199808133390702
Ott, M., Adler, N., Millstein, S., Tschann, J., & Ellen, J. (2002). The Trade-Off between Hormonal Contraceptives and Condoms among Adolescents Perspectives on Sexual and Reproductive Health, 34 (1) DOI: 10.2307/3030227
ROYE, C. (1998). Condom use by hispanic and african-american adolescent girls who use hormonal contraception Journal of Adolescent Health, 23 (4), 205-211 DOI: 10.1016/S1054-139X(97)00264-4
Roye CF, & Seals B (2001). A qualitative assessment of condom use decisions by female adolescents who use hormonal contraception. The Journal of the Association of Nurses in AIDS Care : JANAC, 12 (6), 78-87 PMID: 11723916
SAYEGH, M., FORTENBERRY, J., SHEW, M., & ORR, D. (2005). The developmental association of relationship quality, hormonal contraceptive choice and condom non-use among adolescent women Journal of Adolescent Health, 36 (2), 97-97 DOI: 10.1016/j.jadohealth.2004.11.009
SMITH, J., GREEN, J., DEGONZALEZ, A., APPLEBY, P., PETO, J., PLUMMER, M., FRANCESCHI, S., & BERAL, V. (2003). Cervical cancer and use of hormonal contraceptives: a systematic review The Lancet, 361 (9364), 1159-1167 DOI: 10.1016/S0140-6736(03)12949-2
Turner, R., Grindstaff, C., & Phillips, N. (1990). Social Support and Outcome in Teenage Pregnancy Journal of Health and Social Behavior, 31 (1) DOI: 10.2307/2137044
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Vitzthum, V. (2001). Vaginal bleeding patterns among rural highland Bolivian women: relationship to fecundity and fetal loss Contraception, 64 (5), 319-325 DOI: 10.1016/S0010-7824(01)00260-8
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If I objectify you, will it make you feel bad enough to objectify yourself? On shopping, sexiness and hormones.
When I was younger, periods were not a fun time, and I was plagued with dysmenorrhea, which is a fancy term for really bad cramps. In high school, I would often take 1000 mg of ibuprofen every four hours to alleviate symptoms to get through all my classes, band, sports practice, and homework (what, it took you this long to realize I was, and am, a dork?).
After having my daughter in 2008, and the thirteen months of lactational amenorrhea that followed it (lactational amenorrhea means absence of periods due to lactation), my periods resumed. Pain during my periods has almost totally ceased, but I have noticed more cycle-related variation in emotion. In particular, my patience and tolerance for rude behavior, and my tendency to cry sentimentally at even the lamest greeting card, skyrocket in my premenstrual phase. I already have low tolerance for rudeness, and I already cry easily. But something about progesterone decline — which is a normal process towards the end of ovulatory cycles — seems to make it harder for me to repress these behaviors in order to fit in culturally with those around me.
I tell this to you to say, I don’t doubt that hormones, and hormonal variation through the cycle, plays some role in variation in female behavior and emotion. And I find this kind of work inherently interesting. I hate to repeat myself, but you will find echoes of my structural and methodological concerns with evolutionary psychology in this post as well.
Durante et al (2011) observe that women spend more money on their appearance than men, and claim that this sex difference is cross-culturally consistent (I wonder, is this consistent across cultures without money?). In order to understand this sex difference, they wish to see whether spending or shopping behavior is dependent on cycle phase. Therefore the authors hypothesize that women choose sexier clothing during ovulation — “even if the women themselves are not consciously aware of this biological fact” (Durante et al 2011: 922), a problematic turn of phase if I ever saw one, but I’ll get to that later. They also consider the effects of priming a shopping woman with images of attractive women and hypothesize there is a greater effect of this priming on high-fertility women.
The participants were female undergraduates and were compensated with course credit or money. The authors claim the participants had no idea the study had anything to do with the menstrual cycle, but the participants had to use LH strips at midcycle to see when she was ovulating (this is a urine test to check for a luteinizing hormone peak, which comes before ovulation).
Here’s the important part, for me:
“The first urine test was scheduled 2 days before the expected day of ovulation. If an LH surge was not detected, women came back each day until an LH surge was detected or six tests had been completed, whichever came first” (Durante et al 2011: 924).
Here are my questions: what is 2 days before the expected day of ovulation? The follicular phase — that’s from menstruation to ovulation — is the most variable phase of the menstrual cycle (Fehring et al. 2006; Lenton et al. 1984). I wonder how many ovulations they missed because of this. Perhaps even worse, how many participants had six LH tests and didn’t have a detectable LH surge? It sounds like they were included in the project. But, they either ovulated before the authors started testing, or they had an anovulatory cycle. That means the authors were including participants in their study that weren’t ovulating… in a study of behavior during ovulation.
Participants viewed a made-up shopping website on a high-fertility (near the LH surge) and low-fertility (about eight days later) day, where they had to select ten items they would like to buy that day. They were randomized into two groups: one shown a site featuring casual clothes, the other featuring clothes and accessories. The clothing on these made-up sites were “pretested to be sexy” (Durante et al 2011: 925). While that is a phrase I never expected to write on this blog, the separate validation they did to determine sexy versus nonsexy clothing seems fine.
Hypothesis 1: Near ovulation, women should be more likely to choose sexier and revealing clothing and other fashion items rather than items that are less revealing and sexy (Durante et al 2011: 923).
Women chose a greater percentage of sexy clothing and accessory items near ovulation: 59.8% ± 21.6 during ovulation, 51.3% ± 22.4 during low fertility. This was a statistically significant difference, but they did a repeated measures ANOVA, and I don’t understand why they didn’t do a paired t-test. Further, statistically significant or not, I question how meaningful it is when the averages are so close and the standard deviations almost completely overlap.
H2: Ovulation should lead women to be especially likely to choose sexier products when women are primed to compare themselves to attractive female rivals (Durante et al 2011: 924).
H3: There should be no differences in product choice between ovulating and nonovulating women when women are primed with unattractive women or men (Durante et al 2011: 924).
Follow-up studies primed sub-sets of participants (so a different cohort, same recruitment methods as above) to think about 1) attractive local women, 2) unattractive local women, 3) attractive local men, 4) unattractive local men. They did this by showing photographs of people who they claimed to be local and asking participants to rate their attractiveness.
When primed with attractive women, the percentages of sexy items chosen were 62.7% for ovulating women and 38.2% for low fertility women (I could not find standard deviations for these values so have no idea how much the two groups overlap). Priming with unattractive women, attractive men, or unattractive men produced no significant difference between low and high fertility women.
H4: Ovulation should lead women to choose sexier products when primed to think about local attractive women who constitute potential direct rivals. However, ovulation should not influence product choice when women are primed to think about women from distant locations because such women do not constitute direct rivals (Durante et al 2011: 924).
The authors used a different method for assessing fertility this time; they asked women their normal menstrual cycle length and counted back from menses to estimate when ovulation would be. So AGAIN, we don’t know how many women actually ovulated in this study, and we don’t know whether a significant portion of women were then grouped in the high-fertility group who shouldn’t have been.
This study is like the previous one in terms of photo priming, but this time the photos were said to be local or distant, and were of women only (so the four groups were local attractive, local unattractive, distant attractive, distant unattractive).
The authors claimed that the relationship between fertility, photo attractiveness and location was “marginally significant,” but the p-value was 0.09. That is, in fact, not significant, as significance is generally only considered under 0.05 unless you cheat and say your study is special and should consider a different limit (they don’t say this in their study).
That said, the only significant effect found of photo priming on high versus low fertility women was in the local attractive women group: high fertility women chose 65.8% sexy items versus low fertility’s 39.1% (I could not find standard deviations for these values so have no idea how much the two groups overlap). These results are almost identical to those found when priming women with attractive women without saying if they are local or not.
How biological are we talking here?
The authors claim a biological cause for the differences found above. And maybe there is, to some extent. But there are two major issues with the authors’ conclusions.
First, there is the major methodological flaw of including women who probably aren’t ovulating in their high-fertility group. Heads up to people who don’t study female physiology: women, even healthy women with “normal” cycle lengths, don’t ovulate every cycle. So if understanding a behavior during ovulation is important to your hypotheses, you need daily hormones on top of that LH test. Then, you know, if you can’t document ovulation, you need to exclude those women from your sample. Oh, and while we’re discussing methods, the authors don’t mention whether the participants were in a relationship or not, or what their sexualities were, or their races or socioeconomic statuses. These are all important to understanding variation in female-female competition (Campbell 2004). And since ornamentation is likely related to honest signals of health, it would be good to know waist to hip ratios, or BMI, or facial symmetry (Streeter and McBurney 2003) (hello, I’m handing someone a dissertation here! Just remember to cite me correctly).
But the second issue relates to the theme I saw throughout this paper, that changes in mood or choice behavior due to ovulation or presence of attractive women is a “biological fact.” Female-female competition is certainly found within human behavior, and behavior changes through the menstrual cycle. But is it fair to call these behaviors strictly biological, or should we have a more nuanced understanding of the interaction between biology and culture?
There are alternative cultural theories out there. Objectification theory proposes that there are consequences to living in a culture that sexually objectifies women: when women are continually appraised based on their looks, it leads to a disconnect between their body and individual (Moffitt and Szymanski 2011). This disempowers women and leads to them feeling as though their bodies exist for the pleasure of others. And if this is what women learn they have to offer others, and they seek affirmation, praise or attention from those around them, it makes sense for women to compete around attractiveness, particularly sexiness.
I would posit that shopping, particularly when primed with the image of an attractive woman, is a kind of objectification. So really, what Durante et al (2011) are measuring are the results of objectifying their study participants. Under these circumstances, a woman is more likely to start treating herself as an object to be evaluated on the basis of her appearance, so it makes sense that she would choose sexier clothing, in an effort to produce a culturally-appropriate, attractive body.
As the study stands, there is no way to parse out the impact of biology or culture — and many cultures encourage objectification, female-female competition and female attractiveness towards men. As for how that interacts with high versus low fertility samples… that’s the interesting part of this paper. If we can trust how the women are parsed. Which we can’t, since some of the high-fertility sample might not have been ovulating.
These high heels are made of deer antlers
|Antler booties from Camilla Skovgaard.|
The authors also seemed enamored with the idea of comparing their female participants to male animals. Twice they mention the idea that they want to determine whether sexy clothing is analogous to a peacock’s tail, a deer’s antlers, or a lion’s mane (really). These three examples, according to the authors, reflect a courtship function, a same-sex competition function, or both functions respectively. The authors go on to say that their results suggest that sexy dressing in women is like deer’s antlers, or, a same-sex competition function.
First, since when are a deer’s antlers only a same-sex competition function? Second, doesn’t it say something that they couldn’t find any examples of this kind of display in a female animal? This begs the question of why female humans do so much more displaying and maintenance of their appearance compared to other female animals, and again, this suggests interactions between biology and culture (Smuts 1995).
We can spin all the stories we want to explain why many human females make efforts to be physically attractive. And I do think Durante et al (2011) are on to something here as, despite methodological concerns they did find differences in high- and low-fertility choices. But if we continue to do this research on undergraduates in western contexts without sufficient hormone analysis, I’m unsure that its meaning extends beyond the participant pool.
Campbell, A. (2004). Female competition: Causes, constraints, content, and contexts Journal of Sex Research, 41 (1), 16-26 DOI: 10.1080/00224490409552210
Durante, KM, Griskevicius, V, Hill, SE, Perilloux, C, & Li, NP (2011). Ovulation, female competition, and product choice: hormonal influences on consumer behavior Journal of Consumer Research, 37 (6), 921-934
Fehring, R., Schneider, M., & Raviele, K. (2006). Variability in the Phases of the Menstrual Cycle Journal of Obstetric, Gynecologic, Neonatal Nursing, 35 (3), 376-384 DOI: 10.1111/j.1552-6909.2006.00051.x
Lenton EA, Landgren BM, Sexton L, & Harper R (1984). Normal variation in the length of the follicular phase of the menstrual cycle: effect of chronological age. British journal of obstetrics and gynaecology, 91 (7), 681-4 PMID: 6743609
Moffitt, L., & Szymanski, D. (2010). Experiencing Sexually Objectifying Environments: A Qualitative Study The Counseling Psychologist, 39 (1), 67-106 DOI: 10.1177/0011000010364551
Smuts, B. (1995). The evolutionary origins of patriarchy Human Nature, 6 (1), 1-32 DOI: 10.1007/BF02734133
Streeter, S. (2003). Waist–hip ratio and attractiveness New evidence and a critique of “a critical test” Evolution and Human Behavior, 24 (2), 88-98 DOI: 10.1016/S1090-5138(02)00121-6
Yesterday I submitted a book chapter and a journal manuscript. I have two substantial blog posts I’m working on, but neither will be ready for this week. However, I have been slowly accumulating Posts of Awesome that I’d like to share. I want to highlight people, writing, and topics that need and deserve more attention in the science blogosphere. I mention a lot of these things on Twitter, but I know a lot of my followers don’t use Twitter. So here goes.
If you have any interest in pregnancy, labor and birth, I do hope you’re reading Science and Sensibility. S&S is a evidence-based blog written by practitioners and scientists, sponsored by Lamaze International. I really like their more technical, informative posts on labor and birth, and today’s post on positioning during the second stage of labor is a winner. The writing is always accessible for layfolks, yet still provides great information for scientists and medical folk.
Remember that Wax et al (2010) article showing homebirth had a mortality rate three times higher than a hospital birth (and the sensational Lancet editorial)? A lot of folks came down hard on the article when it first came out, myself included, but two more pieces came out yesterday that call into question the authors’ conclusions. The first issue is that there were actual mathematical errors in the data (meaning, the data was probably entered into an excel sheet incorrectly), the second is that they fundamentally did the meta-analysis wrong. Wrong. As in, according to one statistician who had no stake in the story or topic, so wrong as to overlook all its other problems.
A few more spicy tidbits: cosmetic breast surgery is on the rise, and one county in Florida has a 70% cesarean rate. Seventy. Percent. Due to some smart marketing and bad decisions, a treatment to prevent pre-term birth that used to be affordable is now more expensive than gold.
Finally, this is sort of ladybusiness, but as Dr. Isis points out, it should really be family (or even just human) business: Why it’s alright to not be your mother, a guest post on AGORA.
The reverberations from Jesse Bering’s post on homophobia as an adaptation continue. And the responses have been brilliant. I especially love Jeremy Yoder’s take over at his blog, Denim and Tweed: An adaptive fairytale with no happy ending.
And then today, DeLene Beeland shared this great post on Twitter: How to Queer Ecology: One Goose at a Time over at Orion Magazine. This is a beautifully-written, thoughtful takedown of the naturalistic fallacy.
Other things to read right now
Danielle Lee has two great pieces worth reading (and I found them both because of Greg Laden): an article on the contribution of Henrietta Lacks, and the Black community, to cell culture, and a profile on Danielle in a natural hair series at Essence.com.
I read this article today by Gina Trapani on her work to make the technical world more friendly to women and other underrepresented or new folks.
A piece on Impostor Syndrome at SciAm (behind a paywall). I don’t want to pathologize all underrepresented groups in science (because frankly, these feelings make sense in the context of environment, even if it’s desirable to move beyond them), but issues around impostor syndrome resonate with me.
Things I wish I didn’t have to link to
Our amusement with Charlie Sheen just demonstrates how little we care about violence against women — especially certain kinds of women. Read The Disposable Woman.
Skepchick Rebecca Watson shares some of her hate mail, and why she doesn’t feel like internetting today: Why I deserved to be called an offensive bitch.
Pat Campbell reposted a twelve-year-old manifesto on gender and education that still holds true: The Gender Wars Must Cease.
Some LOLz and some cutes: a section I added because the last three links were so depressing
This first link doesn’t exactly bring the LOLz, but is an enjoyable read: Female Science Professor continues her series on Academic Novels.
Wax, J., Lucas, F., Lamont, M., Pinette, M., Cartin, A., & Blackstone, J. (2010). Maternal and newborn outcomes in planned home birth vs planned hospital births: a metaanalysis American Journal of Obstetrics and Gynecology DOI: 10.1016/j.ajog.2010.05.028
Editorial staff (2010). Home birth–proceed with caution. Lancet, 376 (9738) PMID: 20674705