I am away on vacation this week. I have decided to share my most popular post to date with the Scientific American audience, in the hopes of getting a few more people excited about physiology, women’s health, and culture. Enjoy!
When I was thirteen years old, I got my period. Soon after, I remember going with my mother to the nurse practitioner’s office — her name was Debbie. Debbie told me that once girls got their periods, they were more likely to be anemic, and I would have to watch out for it. She suggested I start to take an iron supplement.
Something about that conversation irked me, even when I discovered that I was slightly anemic a few years later. I disliked the implication that one could be pathological just by being female. And I didn’t understand how it was that menses, which is only about thirty milliliters of blood loss per menses, could have such a profound impact on women’s iron status.
When I was in college, I studied this in a bit more depth in my undergraduate thesis. I discovered two important studies:
First, most people assume that the sex difference in iron stores in males and females, which begins at puberty, is due to the onset of the period and looks like this:
|Figure 1. Made-up data to visually represent the assumed way the sex difference in hemoglobin is produced. No, I can’t find real data in the literature but yes, if you find any send it along and I’ll update the post.|
However, the sex difference in iron status in males and females derives from an increase in male iron stores at puberty, not a decrease in female iron stores. This has to do with oxygen transport and testosterone (Bergstrom et al 1995). This means that the difference that occurs at puberty actually looks like this:
|Figure 2. Made-up data to visually represent the actual way the sex difference in hemoglobin is produced. See caveat from Figure 1.|
Second, the main culprit for iron-deficiency anemia (IDA) in men is upper-gastrointestinal bleeding, so when men present with IDA the first thing they do is an endoscopy. When women present with IDA they give her iron supplements and tell her to go home because it’s just her ladybusiness. Kepczyk et al (1999) decided to actually do endoscopies on women for whom a gynecological source was diagnosed by a specialist for their IDA. They found a whopping eighty-six percent of these women had a gastrointestinal disease that was likely causing their IDA. Therefore, menses likely had nothing to do with their IDA, and the assumption that menses made them pathological actually obstructed a correct diagnosis.
When I went to graduate school, I wanted to study menstrual and endometrial functioning because the assumption that it inherently causes disease seems to lead to a life of frustration with the medical system for many women. I figured it would be good for us to better understand variation in this part of the body… so that’s what I did. I went to rural Poland, where my colleague Dr. Grazyna Jasienska has a lovely field site perfect for testing my questions about the endometrium: I wanted a non-industrial population, but couldn’t choose one so remote that I didn’t have access to a hospital, since the women would need to do ultrasounds for me to image their endometria. Then, I didn’t set out to test specific questions about IDA, but Dr. Jasienska wanted to do some blood tests on my subjects for a related study, and happened to do a full work-up on them.
Without meaning to, I ended up with two very useful pieces of evidence: measurements of their endometrial thickness, and their iron status. I also knew their dietary iron intake since I did 24-hour diet recalls. I realized that I had the evidence in front of me to test the relationship between menstruation and anemia directly, rather than indirectly like other studies I had read.
It was a matter of some simple correlations (Clancy et al 2006):
|Figure 3. Red blood cells (RBC) and hemoglobin (Hg) are positively correlated with endometrial thickness (from Clancy et al 2006). Click to embiggen!|
Take a look at the p-values for the relationship between endometrial thickness (ET) and red blood cells (RBC), and ET and hemoglobin (Hg): both are statistically significant. What’s more, the relationships are positive. That means that the thicker the endometria, the better the iron status. I’ll admit, when I ran these stats my hypothesis was simply that there would be no relationship, likely meaning that the effect of ET on iron status was at most neutral. But a positive effect? At least in this test, there is no support for the prevailing medical assumption that menses is correlated with IDA.
I was reminded of this study of mine recently, because it was cited by someone else studying something a bit different (vanity Google Scholaring will get you that). Elizabeth Miller at the University of Michigan wrote a very interesting paper on maternal hemoglobin depletion, which is the situation where pregnancy and lactation deplete iron stores. Miller (2010) studied this phenomenon in two populations in northern Kenya, a settled population and a more pastoral one, as a way to understand the differential impact of interbirth interval, energetic constraint, and dietary iron intake on maternal depletion. I’m going to focus just on the part of this study related to issues of menses and IDA.
Miller found that iron stores slowly increase in lactating mothers with months since birth, but also that the more children these women had, the lower their hemoglobin. This makes sense in terms of where iron needs to be allocated during pregnancy and lactation, and how women with many children might not have enough time or resource to replete their iron before having their next kid.
But the really cool finding, to me, was that resumption of menses after pregnancy was positively associated with hemoglobin. Resumption of periods after pregnancy is highly variable, and largely dependent on energy availability and lactation practices. These results, that iron stores increase once you start getting your period again, indicate again that menses is not having a negative effect on iron stores. So this is the second study I know of to show a positive relationship between menses and iron status.
Ladies, unless you are menorrhagic (bleeding more than 120 milliliters each cycle) your period is not doing you wrong. If you have iron-deficiency anemia and your doctor is insisting it’s because you slough off your endometrium from time to time without doing a single test to confirm it, you may want to insist on an endoscopy. It could save your life.
Bergström E, Hernell O, Persson LA, & Vessby B (1995). Serum lipid values in adolescents are related to family history, infant feeding, and physical growth. Atherosclerosis, 117 (1), 1-13 PMID: 8546746
Clancy, K., Nenko, I., & Jasienska, G. (2006). Menstruation does not cause anemia: Endometrial thickness correlates positively with erythrocyte count and hemoglobin concentration in premenopausal women American Journal of Human Biology, 18 (5), 710-713 DOI: 10.1002/ajhb.20538
Kepczyk, M. (1999). A prospective, multidisciplinary evaluation of premenopausal women with iron-deficiency anemia The American Journal of Gastroenterology, 94 (1), 109-115 DOI: 10.1016/S0002-9270(98)00661-3
Miller EM (2010). Maternal hemoglobin depletion in a settled northern Kenyan pastoral population. American journal of human biology : the official journal of the Human Biology Council, 22 (6), 768-74 PMID: 20721981
Academic journals often solicit book reviews from faculty. Faculty get a publication and a free book out of it, so it’s especially worth it for those of us clawing our way up the tenure track. Last year I reviewed Wenda Trevathan’s Ancient Bodies, Modern Lives: How Evolution has Shaped Women’s Health, and the issue finally came out yesterday (if you cannot access the issue for free and want to read my review, it is legal to email the author of the article for a copy. Hint, hint).
Overall, I loved the book, and think it’s great for anyone with an interest in women’s health or evolutionary medicine. So yes, I think you should buy it.
But Trevathan was provocative in a few places. In particular, Trevathan uses the terms health-rich and health-poor to describe populations, when the more common terms are often industrial and traditional, or western and non-western. Recently, I have even seen some populations referred to as post-industrial, since what many people are doing in places like the US are now different from industry and manufacturing.
There are some good reasons to try and make these distinctions between human populations. People who live as foragers, as agriculturalists, people who live in rural areas and in cities all get their food differently (hunting it, growing it, or buying it) and this has a profound impact on lifestyle. Many people think that understanding the different lifestyles and health of people who live differently will help us understand some of the big questions of human evolution. What selection pressures led to humans putting on fat as easily as we do? How is it that we can survive on just about any diet? How much physical activity was normal for early humans?
Making these distinctions also help those of us in countries like the United States figure out why we are seeing an increase in some health problems, like diabetes, obesity, cardiovascular disease and cancer. Making comparisons between those of us whose work consists of typing at a computer, harvesting barley or slowly stalking a giraffe help us understand modern diseases better than saying that Americans eat too much. There is something about the transition to sedentary jobs, to energy dense foods, something about the huge changes in the composition of our diets and how we live from day to day that needs to be better understood. And then we need to figure out what changes we could realistically implement in our society to change our health.
But are these the right distinctions to make? Trevathan is referring in part to access to health care when she uses terms health-rich and health-poor. But are Americans health-rich? We do a good job with childhood illness, with vaccinations, and with treatable or preventable illness, and with sanitation and clean water. We certainly have a lot that we take for granted.
But we have a high rate of premature babies, low birth weight babies, birth complications and maternal and infant mortality compared to other developed nations, not to mention the other health concerns I described above. So among the health-rich nations, if we were to use Trevathan’s terms, we are health-poor when it comes to maternal and metabolic health.
I also can’t help but think of how heterogeneous, or variable, health and health access is within the United States. Many low income women get little to no prenatal care. Race is a major determinant not only of access to health care, but health problems, homicide, addiction and other issues, based on discrimination and internalized racism.
It doesn’t make sense to put all the blame on Trevathan’s terms. Post-industrial/industrial/traditional have their own sets of problems, as do western/non-western. Trevathan is simply trying to find a better terms for the same old categories. So how do we define these different populations? And can we find better words for them?
Part of the point of anthropology is to try and understand the causes and consequences of human variation. One of the problems here is that we are trying to bin all human kind into only two or three categories. Where do we draw the line, and how do we draw it? Because wherever it gets drawn we’ll have to be comfortable with the variation we are ignoring in order to do it. If we bin people into any of these groupings, are we just making the best of a bad situation, relying too much on old dichotomies, or doing our field a disservice?
What kind of terms do you think we should use? What would be the more appropriate way for us to understand how different populations end up with different health profiles? And when we use these terms, what are the implications for how we do research and outreach?
September 10, 2005. The temperature was warm, but not hot. The sky was wild with sunshine.* All my friends and family were seated before me, and I walked down an aisle between them, arm in arm with my parents.
As I embarked upon my marriage, I thought about the life we would build: where we would live, what we would do, and how we might raise children together. I thought of how we would communicate and share our lives, and I looked forward to working to have a satisfying, enjoyable, equal marriage.
Apparently, what I should have been doing was making sure that I didn’t overdo it on the hors d’oeuvres.
Meltzer and colleagues (2011) recently published an article entitled “Marriages are more satisfying when women are thinner than their husbands.” The authors used a previously collected sample of 165 couples to assess age, depression, BMI and marriage satisfaction every six months over four years. When controlling for depression, income, education and divorce, Meltzer et al (2011) found that women were more satisfied with their marriages if they stayed thin; men were more satisfied if they married thin. The BMI, or change in BMI of husbands didn’t impact satisfaction of either spouse.
So, if a wife stays thin both spouses are more likely to report satisfaction with their marriage.
The data and findings are interesting (even though, controlling for divorce? Really? When studying marriage satisfaction?). The conclusions, however, are troubling. To put it another way: if you write an evolutionary psychology article but the only author you cite who even pretends to be evolutionary is David Buss, I’m probably going to blog about it.
Data and interpretation
Let me first explain the measurement they used as a proxy for thinness. BMI, or body mass index, is a simple calculation based on height and body weight (weight/height2). A BMI of 18-25 is considered healthy, 25-29 overweight, and over 30 obese. However age, ethnicity and sex significantly impact the meaning of these numbers (Gallagher et al 1996). Sex differences are particularly relevant here: on average women have more fat mass, and men more muscle mass, which means that a BMI of 25 in a man and a woman of similar height don’t mean the same thing (Gallagher et al 1996).
A few other issues worth noting: while the authors don’t say much about their study sample, aside from the fact that they are newlyweds, another paper on the same dataset describes it as urban and relatively well-educated (Davila et al 2003). The subjects are also almost entirely white. And while the title sounds like the authors are saying that wife thinness causes marriage satisfaction, they only run statistics that allow them to make associations.
There is an added problem in asking men and women about satisfaction in their lives and correlating it with their BMI. BMI doesn’t just mean something different physiologically, it means something different culturally! Thinner women report higher satisfaction with their lives. Men? Don’t tend to care either way (Sira and Ballard 2011). Is it possible that marriage satisfaction is partly a reflection of broader satisfaction in life?
The authors also present the data in a way I found troubling. Here is their graph of husband and wife satisfaction. The three lines are when the husband has a higher BMI than his wife, when their BMIs are equivalent, and when the husband has a lower BMI than his wife. They only show survey results of the first and last time points, so at zero and four years, in order to draw their lines.
I wonder how much satisfaction fluctuates in all the data they didn’t bother to show – survey results for time points 2 through 7. I also wonder how much variation they found around the average points displayed (also called error bars, to demonstrate standard deviation or standard error).
Last but not least, here is the final paragraph of the article:
“Finally, the current findings also have important practical implications. Specifically, given that men have a stronger preference for and are more likely to choose thin partners than women (Chen & Brown, 2005; Legenbauer et al., 2009), women may experience increased pressures to achieve a thin physical appearance. Indeed, women strive harder than men to be thin for their partners and are, consequently, more prone to developing body dissatisfaction than men (Sanchez & Kwang, 2007). Nevertheless, the findings of the current study indicate that the absolute levels of thinness for which women strive do not actually influence their relationships. Rather, women of any size can be happy in her relationship if they find the right partner. Accordingly, educating women about these findings may help alleviate the pressures to be extremely thin that plague women today. Of course, other adverse effects of absolute overweight and obesity continue to highlight the importance of maintaining a healthy weight” –Meltzer et al (2011: 422)
What astounded me about this paragraph was how the authors finally acknowledged the possibility that sexism and culture may play a role in their results, but in a backhanded way. They use it to say that all women can find a happy marriage if they just find the right man, and that while women shouldn’t try so hard to be thin, they should be careful not to be fat, either. Of course, with a university account I didn’t have to pay for this advice, because if I had I would want my money back.
I think there are times when people who study human behavior throw in the word “evolutionary” as shorthand for something else. Here, I suspect the authors are using the word to discuss assumed preferences between men and women that they think were once adaptive in promoting reproductive success of the individual. What I don’t think they realize is that their perspective is decidedly western, and thus can’t be assumed to apply to all humans.
This sample is young, white, urban, well-educated and American. So, I have two questions. What influences mate choice in young North Americans, and what kind of mate choice do we see in other populations?
Spitzer et al (1999) looked at an enormous dataset of ethnically diverse 18-24 year old North Americans and compared them to Playboy, Playgirl, and Miss America pageant winners from the 1950s to the present. They did this to understand how cultural expectations of beauty have changed over time, and how well cultural expectations of body size match with reality over time. They found Miss America pageant winners became dramatically thinner, Playboy models remained at a low body weight, and Playgirl models increased in size over time (the authors suspect this was due to an increase in muscle, not fat). However, the sample of North American men and women increased significantly over this time, and mostly due to an increase in fat mass, not muscle. This sets up cultural expectations that women be smaller and men bigger in a way that is nearly impossible to achieve in reality (Spitzer et al 1999).
Compare these cultural expectations, and the satisfaction in marriages based on those expectations, to marriage patterns in the Hadza. The Hadza are a population of hunter-gatherers in Tanzania that live in a pretty marginal environment, but still serve as a good example of human foragers. Male or female BMI does not appear to impact marriage patterns – individuals didn’t choose their spouses based on how much they weighed, their height or their body fat (Sears and Marlowe 2009). The authors weren’t asking questions about marriage satisfaction, of course, but the fact that in their sample husbands were not on average taller or heavier than their wives tells us something about cultural ideals of mate choice and how they might influence satisfaction.
Alternative hypothesis: it’s the culture, stupid
To me, what is more interesting about mate choice, and even marriage satisfaction, is our amazing flexibility of behavior. There is no one ancestral diet, no one way to get married, no one way to be socialized through adolescence, because we have been occupying a huge portion of this planet, different niches with differing climate, food availability and resources, for a very long time. During that time cultural traditions and behaviors were being passed down within these populations. And therefore the elements of marriage satisfaction (in populations that have marriage, at least) evolve, but not necessarily biologically. And even if it were biological, that doesn’t render it immutable. Both biology and culture are changeable, and as humans we have the cognitive capacity to operate against them at times.
While wife BMI may play a role in marriage satisfaction in some subsamples of the American population, not only does this not necessarily apply to other cultures, it doesn’t have to apply to Americans. Humans can be masters of their environments, and with the right access to information and social support, can choose to be happy in spite of cultural expectations of size.
So you can hold the mayo** if you want. But there are far too many important elements of communication and compatibility that drive marriage satisfaction for me to believe that a few pounds make the difference between a happy marriage and one that ends in divorce.
Davila, J., Karney, B., Hall, T., & Bradbury, T. (2003). Depressive Symptoms and Marital Satisfaction: Within-Subject Associations and the Moderating Effects of Gender and Neuroticism. Journal of Family Psychology, 17 (4), 557-570 DOI: 10.1037/0893-318.104.22.1687
Gallagher D, Visser M, Sepúlveda D, Pierson RN, Harris T, & Heymsfield SB (1996). How useful is body mass index for comparison of body fatness across age, sex, and ethnic groups? American journal of epidemiology, 143 (3), 228-39 PMID: 8561156
Meltzer, A., McNulty, J., Novak, S., Butler, E., & Karney, B. (2011). Marriages Are More Satisfying When Wives Are Thinner Than Their Husbands Social Psychological and Personality Science, 2 (4), 416-424 DOI: 10.1177/1948550610395781
Sear, R., & Marlowe, F. (2009). How universal are human mate choices? Size does not matter when Hadza foragers are choosing a mate Biology Letters, 5 (5), 606-609 DOI: 10.1098/rsbl.2009.0342
Sira, N, & Ballard, SM (2011). Gender differences in body satisfaction: an examination of familial and individual level variables Family Science Review, 16 (1), 57-73
Spitzer, B., Henderson, K., & Zivian, M. (1999). Gender Differences in Population Versus Media Body Sizes: A Comparison over Four Decades Sex Roles, 40 (7/8), 545-565 DOI: 10.1023/A:1018836029738
1- My own photograph.
3-Found in Meltzer et al 2011, full reference above.
*The quote is one of my favorites from The Color Kittens, one of the books I most enjoy reading to my daughter.
**Hold the mayo is slang for “hold the mayonnaise,” which means to eat a sandwich dry. It is often used to imply someone should be trying to lose weight.
Welcome to Context and Variation! My name is Kate Clancy, and I am an Assistant Professor of Anthropology at the University of Illinois.
Within the field of anthropology, my work focuses on understanding human biological variation, particularly in women. A lot of people have developed this idea – from the one biology class they took in high school, what they read on the internet (er…), or what they hear from a medical professional – that there is one right way for a body to be. And if you don’t fit into this narrow interpretation of right, or normal, you are pathological or subclinically pathological.
The way anthropologists study the body challenges this idea, and this is where the title of my blog comes in (by the way, I hope you noticed the beautiful new banner, created by Jacqueline Dillard). We see the body as existing in a way that is context-dependent. And the contexts that impact our body certainly include genes and hormones and sex, but they also include how much physical activity we get in a day, how much fiber we get in our diet, what cultural expectations impact our life decisions, and the degree of social support we get from friends and family.
All of these different contexts? Well, they produce a lot of variation. Not only that, but you vary over the course of your life, and you can see variation within and between different human populations. If you add in my particular field of study – which I fondly refer to as ladybusiness anthropology – reproductively-aged women have all sorts of additional factors that compete to produce their body’s variation, from whether they are pregnant or lactating, to the kind of contraception they use, if any, to how they and their culture define their own gender and sexuality.
What this means is that you’ll see me write quite a bit on the fields of evolutionary medicine and human reproductive ecology, because they support the idea I’ve described above. But I also write about evolutionary psychology, because it often doesn’t. And since I take my position as a role model and mentor seriously, I do write about how being a scientist intersects with other aspects of my life, particularly as a woman and a parent.
Who am I?
Originally from the East Coast, my husband, daughter and I moved to the corn fields of central Illinois for tenure-track jobs. Those of you still on one of the coasts or in a large city: you would be surprised at how great it is to live out here. We’re across the street from a beautiful park and playground, live less than a mile from our offices, and are able to eat local eggs, dairy, meat, fruit and vegetables year round.
Oh, and the jobs are pretty nice too.
I love to travel, especially to my field site in southern Poland, but the cycle of grantwriting and childrearing limits my frequency these days. I love to hike, but the lack of topography in central Illinois makes that challenging. I’ve taken up roller derby to fill the void. You’ll find I won’t talk about that here, but it will likely come up on Twitter.
Some representative posts
- Iron deficiency is not something you get just for being a lady
- Why we shouldn’t prescribe hormonal contraception to twelve year olds
- Mate magnet madness: when the range of possible explanations exceeds your own hypothesis
- If I objectify you, will it make you feel bad enough to objectify yourself? On shopping, sexiness and hormones
A scientist’s life
And this summer, I’ll be talking a lot about the birth control pill, because the majority of my questions from women (and men) come from that topic.
I’m often inspired to write on particular topics or news stories because of my readers. So let me know in the comments or over email if there is anything you wish for me to cover.
|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