Friday, July 1st 2011

Summer of the pill: Will the pill mess up my ability to detect my One True Love?

Should I advise recently single ScarJo to stay
off the pill to find her next beau? From here.

Imagine you are a single, heterosexual woman. You meet a nice man at the driving range, or on a blind date. You like him and he likes you. You date, you get engaged, you get married. You decide to have a child together, so you go off the pill. One morning you wake up and look at your husband, and it’s like seeing him through new eyes. Who is this stranger you married, and what did you ever see in him?

After some articles made the news when they suggested mate preferences change on hormonal contraception, this seemed to be the scenario in the heads of many women. Is my pill deceiving me? What if my birth control is making me date the wrong man?

Several articles over the years have demonstrated that women prefer men with more masculine features at midcycle, or ovulation, and more feminine features in less fertile periods. Based on body odor, women and men also often prefer individuals with MHC (major histocompatibility complex) that are different from theirs, which may be a way for them to select mates that will give their offspring an immunological advantage. These findings have been replicated a few times, looking at a few different gendered traits. And as I suggested above, other work has suggested that the birth control pill, which in some ways mimics pregnancy, may mask our natural tendency to make these distinctions and preferences, regarding both masculinity and MHC (Little et al. 2002; Roberts et al. 2008; Wedekind et al. 1995).

On the one hand, I think it’s both interesting and important to consider the implications of the birth control pill beyond just contraception. Hormones are messages, so any cells that have receptors for these messages, like specialized mailboxes, can receive them. The pill is made of synthetic versions of estradiol and progesterone, and there are estradiol and progesterone receptors in your brain. And yes, these hormones do change your brain, both during the natural cycle and on hormonal contraception; Scicurious has written well on this in the past.

Jolie, had she been on the pill and chosen her mate
differently. From here. Yes, looks to be a real pic.

On the other hand, I have a lot of questions: First and most important to me, how does any of this translate to non-straight women? I find the constant focus on mate choice between men and women a bit exhausting, and am not sure we can assume non-straight relationships to work the same way. Next, how well do preferences over the cycle map on to actual choices for mates, short term or long term? If we happen to find Brad Pitt more attractive than Justin Bieber at midcycle, does that mean no one will do but Brad Pitt? And finally, what are all the factors that we need to consider in mate choice besides a deep voice or square jawline (again, especially if you try to expand your thinking beyond straight relationships)?

I’ll start with the last two questions that deal with mate preference versus ultimate mate selection. As you all might expect, women and men choose mates for lots of reasons, not just masculinity or complementary immune systems. Bereczkei et al (1997) looked at singles ads and found women often sought mates with high parental care. In a separate singles ad evaluation, Pawlowski and Dunbar (1999) found that women mostly selected men of high resource potential who were interested in long-term relationships (either unlikely to divorce or unlikely to die within twenty years), where men selected women by markers of fecundity (ability to have babies). In a sample of 18-24 year old straight people in the US, Buston and Emlen (2003) found that most people selected mates who had similar characteristics to themselves. And a speed dating sample showed that people under those conditions selected dates based on easily observable traits, like physical attractiveness (Kurzban and Weeden 2005).

Now on to the fact that all of this research is on straight people. I found very little on lesbian women and the menstrual cycle… but what I found was very cool! Brinsmead-Stockham et al (2008) found that, like heterosexual women, lesbian women are quicker to identify unknown faces at midcycle, as long as they were the faces of the sex they preferred. So straight women were good at identifying male faces, lesbian women good at identifying female faces. Burleson et al (2002) found that sexual behavior in lesbian and straight women was mostly similar through the menstrual cycle, with both peaking at midcycle.

So, mate preference may be about telling a research assistant who is the hottest to you at a particular point in your cycle. And it is a fairly robust and consistent finding. However, when it comes to ultimate mate selection the most important thing to consider is a great point made by Pawlowski and Dunbar: finding a mate is about advertising what you have to offer while making known what you want in a mate. Then it’s all about finding some kind of compromise through a series of trade-offs based on what the individual wants, what they can offer, and what’s available in the dating pool. (So, since neither Brad Pitt nor Justin Bieber are currently in the dating pool, my previous comparison was pointless.)

Those of you who met your mate while on the pill: not to fear. I don’t think that the possibility that you may have some suppression of masculinized preferences at one point in your cycle means you’ve chosen the wrong person.

Who knows, it could have opened you up to the Mr. or Ms. Right.

Bereczkei T, Voros S, Gal A, & Bernath L (1997). Resources, attractiveness, family commitment; reproductive decisions in human mate choice. Ethology : formerly Zeitschrift fur Tierpsychologie, 103 (8), 681-99 PMID: 12293453

Brinsmead-Stockham K, Johnston L, Miles L, & Neil Macrae C (2008). Female sexual orientation and menstrual influences on person perception Journal of Experimental Social Psychology, 44 (3), 729-734 DOI: 10.1016/j.jesp.2007.05.003

Burleson MH, Trevathan WR, & Gregory WL (2002). Sexual behavior in lesbian and heterosexual women: relations with menstrual cycle phase and partner availability. Psychoneuroendocrinology, 27 (4), 489-503 PMID: 11912001

Buston PM, & Emlen ST (2003). Cognitive processes underlying human mate choice: The relationship between self-perception and mate preference in Western society. Proceedings of the National Academy of Sciences of the United States of America, 100 (15), 8805-10 PMID: 12843405

Kurzban R, & Weeden J (2005). HurryDate: Mate preferences in action Evolution and Human Behavior, 26 (3), 227-244 DOI: 10.1016/j.evolhumbehav.2004.08.012

Little AC, Jones BC, Penton-Voak IS, Burt DM, and Perrett DI. 2002. Partnership status and the temporal context of relationships influence human female preferences for sexual dimorphism in male face shape. Proceedings of the Royal Society of London Series B: Biological Sciences 269(1496):1095-1100.

Pawłowski B, & Dunbar RI (1999). Impact of market value on human mate choice decisions. Proceedings. Biological sciences / The Royal Society, 266 (1416), 281-5 PMID: 10081164

Roberts SC, Gosling LM, Carter V, & Petrie M (2008). MHC-correlated odour preferences in humans and the use of oral contraceptives. Proceedings. Biological sciences / The Royal Society, 275 (1652), 2715-22 PMID: 18700206

Wedekind C, Seebeck T, Bettens F, & Paepke AJ (1995). MHC-Dependent Mate Preferences in Humans Proceedings: Biological Sciences, 260 (1359), 245-249 DOI: 10.1098/rspb.1995.0087

Friday, June 24th 2011

Summer of the Pill: The latest fashion accessory to hit your uterus: the IUD!

Found here. IUDs are back in style.
Neon sunglasses? Not so much.

What is used by 20-26% of European, 30% of Israeli, 34% of Chinese, 34% of Egyptian, and 49% of Korean women… but only 1-2% of US women (Harper et al. 2008)? The intrauterine device, or IUD! The IUD is found in two forms: the copper IUD, and the hormone-releasing IUD that releases a tiny amount of progesterone. Both make the uterus inhospitable to pregnancy.

The modern incarnation of the IUD is possibly safer and more effective than oral contraception. Chances of pregnancy on the IUD range from 0-1.1 per 100 woman-years of use, and they get lower with each year you use it (Prager and Darney 2007). That is far better than your chances on the pill.

The IUD suffers from a bad reputation, in part due to misinformation or misunderstanding on the part of medical providers. Harper et al (2008) surveyed 816 physicians, nurse practitioners and physician assistants who each serve more than 100 contraceptive patients per year in the California State family planning program. They found that 40% of medical providers didn’t offer IUDs to patients, 36% provided infrequent counseling. Further, 46% thought nulliparous women, and 39% thought postabortion women were good candidates for the IUDs. Younger physicians were more likely than older physicians to recommend the IUD (Harper et al. 2008), which suggests a generational gap due to the overinflated descriptions of the dangers of early IUDs.

So let’s go through the actual pros and cons of this form of contraception, so that over the course of the summer you can compare this information to what you’ll be learning about the pill.

Remember, I’m just an anthropologist who studies this stuff. I am not a medical doctor.

Danger danger! Or not

The biggest danger from an IUD is that it could perforate the uterus, or be expelled from it. And that can certainly be painful, reduce fertility, or get you pregnant when you think you are protected. So let’s look at how often this happens.

Prager and Darney (2007) wrote a review on the levonorgestrel IUD (hormone-releasing, like Mirena) in nulliparous (that means no parity, or no children) women. This is important because many still carry the misconception that nulliparous women shouldn’t use IUDs, because of an increased risk of perforation, infertility, pelvic inflammatory disease risk, and difficulty in placement.

There are notable differences between the parous (has had children) and nulliparous (no kids) uterus. The parous uterus is a little bigger, and the cervix dilates a bit more easily. However, it turns out that for the most part these differences are not great enough to produce any differences in side effects or danger to the woman using it.

Prager and Darney (2007) found six studies on perforation or expulsion rates for IUDs (some copper, some hormone-releasing, which are made of plastic and are flexible). They did not find enough data to support a link either way for nulliparity and perforation, because the studies they found had anywhere from zero to two nulliparous women in them. That said, the perforation rates for each study ranged from 0-1.3% in one study, and 2.6 out of 1000 in another (Prager and Darney 2007).

Expulsion rates do not seem to differ between parous and nulliparous women, and again, are very low for all women. The annual expulsion rate among cited studies was 0-4.2 per 100, 0-1.2% per year, and 0-0.2% per year (Prager and Darney 2007). The one important point they do make is that there is a very slightly increased risk of expulsion for lactating women – perhaps this is due to the oxytocin released during nipple stimulation, which could contract muscle?

The other concern sometimes mentioned is that of pelvic inflammatory disease. PID is an infection of the uterus and is usually associated with a sexually transmitted disease. PID can increase the risk of infertility. So for women who haven’t had a kid, but want to some day, the concern about getting PID can loom large.

However, Prager and Darney (2007) surveyed the literature and found that the only studies that support a link between PID and IUDs involves an IUD no longer on the market, or was associated with high-risk sexual behavior.

Hidden benefits

In some women, copper IUDs can increase menstruation. However, the hormone-releasing IUDs tend to decrease menstruation, and many women stop getting periods altogether. Hormone-releasing IUDs can be prescribed to women with menorrhagia, or pathologically heavy menstruation, too.

Prager and Darney (2007) describe a study in which hormone-releasing IUD users were compared to oral contraceptive users. These IUD users had less dysmenorrhea (painful periods), less spotting, fewer days of bleeding, fewer cycles. Further, 88% of the IUD users wanted to continue with that method of contraception after a year, compared to 68% of pill users, and this difference was statistically significant (p = 0.003).

Romer and Linsberger (2009) also looked at satisfaction with the hormone-releasing IUD in a sample of 8680 women across 18 countries: 95% were satisfied with their method of contraception.

The fine print

Insertion of the IUD can be a little more painful in a nulliparous woman, since her cervix has not dilated before. Also, a minority of women may spot for a while after insertion of the IUD… and by a while, I mean a few months. But once those few months of light spotting are over, they often don’t get a period again until removing the IUD. And of course, the IUD is not conducive to sudden desires to start the babymaking process: you will need to schedule its removal first.

However, with the number of women who are ambivalent at best about birth control pills, but do not want to use a barrier method, the IUD offers a lot in the way of safety, efficacy and ease of use.


Harper CC, Blum M, de Bocanegra HT, Darney PD, Speidel JJ, Policar M, & Drey EA (2008). Challenges in translating evidence to practice: the provision of intrauterine contraception. Obstetrics and gynecology, 111 (6), 1359-69 PMID: 18515520

Prager, S., & Darney, P. (2007). The levonorgestrel intrauterine system in nulliparous women Contraception, 75 (6) DOI: 10.1016/j.contraception.2007.01.018

Römer, T., & Linsberger, D. (2009). User satisfaction with a levonorgestrel-releasing intrauterine system (LNG-IUS): Data from an international survey The European Journal of Contraception and Reproductive Health Care, 14 (6), 391-398 DOI: 10.3109/13625180903203154

Tuesday, June 21st 2011

C&V Shorts: Make the most of your time and energy

This is the first in a new series at Context and Variation where I will attempt to be more concise. As I continue along the Summer of the Pill series I want to make sure I still put some attention on other topics within biological anthropology. C&V shorts allows me to share something I find cool, in half the words I usually do.

What would you do if you knew you had eighty years to live? What if you knew you only had forty?

Life history theory is the idea that the timing of major life events is adaptive. That is, when to be born, when to wean, when to grow, and when to reproduce are dependent on selection pressures in the environment. The most important concept within life history theory, then, is that of tradeoffs, because when you time these events is based off how you want to allocate your resources. In your environment, would it be best to grow right now? Should you grow under the care of your mother, or should you be independent? Is it time to have a child? How about your second, or third, or fourth child?

For this reason, many people study life history transitions, which means the critical yet variable period when people move from one state to another: from growing to reproductive cycling, from cycling to gestating, gestating to lactating, even lactating back to cycling. And much of what governs these transitions has to do with energy, because energy is finite: energy you use towards one purpose, like growing, cannot be used for another, like reproducing. This is especially true in humans because we permanently transition from allocating to growth to reproduction at puberty, unlike other species that keep growing throughout their reproductive years.

But energy isn’t the only factor that enters into our physiological decision-making: time is also important. And as I hinted in the first paragraph, if you have some sense that your time on this earth will be short or long, you might make different decisions about when to do what.

Found here. Perhaps part of a
modern menarche ceremony?

A few years ago, Walker et al (2006) looked at all the available data on growth and development in small-scale societies – that means foragers and agrarian populations. They found that girls with a later age at menarche – that is the first menstrual period – are shorter in stature. If we consider only energy, this makes no sense! The later you wait to start reproducing should mean you had more time to grow, so why did Walker et al (2006) find the opposite?

The answer is timing. It turns out that mortality rates tell us something about growth and development: the higher the mortality in a population, the earlier their age at menarche and age at first reproduction. So, the higher your chances of being offed at any given moment, the more likely you are to favor reproduction over growth so you can move ahead with the whole reproductive success thing. So, constraints on time and energy affect our physiology differently, and mean we may have to make different predictions about life history transitions that are dependent on human societies. Predation or access to health care impact mortality, but so do homicide or war.

In 2011, McIntyre and Kacerosky performed a similar analysis, only this time they compared small-scale societies with industrialized ones – industrialized societies are those that are more urban, technology-driven, with greater access to modern health care, like the USA. Their analysis of small-scale societies confirmed Walker et al’s (2006) results.

But McIntyre and Kacerosky (2011) found the opposite relationship in industrialized societies: there, the later you hit menarche, the taller you were. And this makes sense if we think we can assume most industrialized populations have lower mortality than the foragers: within the industrialized pops, those who had the time and energy to grow big by holding off on menarche, did.

McIntyre and Kacerosky (2011) are hesitant to be full adaptationists in their paper, which I appreciate. So, they offer two hypotheses and suggestions for future testing. The first hypothesis falls in line with the life history theory described in this post, though their focus is more on parental investment than mortality. But still, environment, and access to time and energy, set life history trajectories for different populations. However they are also careful to point out a nonadaptive hypothesis: it could be that variability in stature is decreasing as heritability is increasing, meaning we are hitting up against biological constraints for size.

Genes and environment interact to produce phenotype, and this is something most people remember from high school biology. But sometimes it’s nice to peek under the hood and learn a little something about the life history mechanisms that are set into motion by this interaction. Early life events, perhaps even life events of our mothers and grandmothers, start our life history trajectories. Then tradeoffs at certain important transition periods nudge us a little further one way or another for the rest of our lives.


McIntyre MH, & Kacerosky PM (2011). Age and size at maturity in women: a norm of reaction? American journal of human biology : the official journal of the Human Biology Council, 23 (3), 305-12 PMID: 21484909

Walker, R., Gurven, M., Hill, K., Migliano, A., Chagnon, N., De Souza, R., Djurovic, G., Hames, R., Hurtado, A., Kaplan, H., Kramer, K., Oliver, W., Valeggia, C., & Yamauchi, T. (2006). Growth rates and life histories in twenty-two small-scale societies American Journal of Human Biology, 18 (3), 295-311 DOI: 10.1002/ajhb.20510