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Context and Variation

Context and Variation


Human behavior, evolutionary medicine… and ladybusiness.
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To save your marriage, hold the mayo… but only if you’re a lady

The views expressed are those of the author and are not necessarily those of Scientific American.


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Is he hoping we will communicate well throughout our marriage? Or that I skip the shrimp cocktail later that night?

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

BMI chart, source linked at end of post.

 

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.

This image shows that from one measurement at marriage to one four years later, marriage satisfaction goes down for all couples. However it started lower when the wife had an equivalent or higher BMI for husband satisfaction, and the trajectory went lower in wife satisfaction under the same conditions.

Figure 1. Click to embiggen.

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.

Invoking evolution

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.

References

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: 10.1037/0893-3200.17.4.557

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

Image credits

1- My own photograph.

2-Found here: http://www.surgeongeneral.gov/topics/obesity/calltoaction/fact_advice.htm

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.

Kate Clancy About the Author: Dr. Kate Clancy is an Assistant Professor of Anthropology at the University of Illinois. She studies the evolutionary medicine of women’s reproductive physiology, and blogs about her field, the evolution of human behavior and issues for women in science. Find her comment policy here. Follow on Twitter @KateClancy.

The views expressed are those of the author and are not necessarily those of Scientific American.





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  1. 1. EricMJohnson 2:30 pm 07/13/2011

    “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.”

    Yes, the classic “just-so” story in which Western researchers reflexively assume that their cultural biases are enough justification to pose an evolutionary hypothesis. When they find that these cultural biases are shared by others in their own culture they conclude that it must be evolution at work. I’m not surprised that Meltzer and colleagues are psychologists. While there are many good evolutionary psychologists, if there’s ever a study in which cultural biases are presented as an adaptive strategy I’ve found that 9 times in 10 it’s a psychologist responsible. As Henrich, Heine & Norenzayan (2010) demonstrated, the majority of these studies are done on American undergraduate students. A poor basis if ever there was one to understand universal features of the human species.

    Great post Kate, I look forward to many more!

    Link to this
  2. 2. comfort 2:46 pm 07/13/2011

    Wonderful. “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.”

    Here’s hoping you do!

    Link to this
  3. 3. mgmcewen 4:06 pm 07/13/2011

    BMI has been widely criticized for not actually indicating whether an individual is obese or not. There are lots of papers out there about this, but for the layman, the BMI project is interesting.

    I’d be more interested if the data was about waist to hip ratio, a variable that seems to have more cross-cultural data linking it to attractiveness as well as research linking it to health outcomes.

    I do think the Hadza are a poor example because there aren’t any obese traditionally-living Hadza! But other cultures may provide a counter-example. On some Trobriand Island cultures, for example, a woman is more desirable if she is overweight.

    I also think that we also have to consider the co-morbidity of obesity with various illnesses that could affect a relationship.

    Oh, and I don’t think shrimp cocktail makes anyone obese :) If you want to know about the foods impacting obesity I highly recommend David Kessler’s The End of Overeating.

    Link to this
  4. 4. kclancy 4:40 pm 07/13/2011

    Thanks Eric! I actually dialed back my criticism a bit because it was so obvious that the authors didn’t have any evolutionary background. But that also made their use of evolutionary theory more inexcusable, in a way — I don’t use theoretical perspectives in my papers for things I don’t have background on, you know? And, like you said, the most egregious part of this was how they used the western perspective to make a general argument about humans.

    Comfort, thanks for your kind words :) .

    mgmcewen, I agree that Hadza aren’t an ideal comparison, but it was all I could find in the literature. But remember that the point was not to find an obese comparison, but to understand whether the cultural pressures that produce some of our preferences are specific to North American post-industrial folks, or could actually be extended to a different kind of population.

    And I agree that shrimp cocktail isn’t going to make me fat, it was simply my attempt at humor :) .

    Link to this
  5. 5. marynmck 8:32 am 07/14/2011

    Great analysis, great tone! I actually wondered about the demographics of the sample as I was reading, because it certainly sounded to me like white women (NB: I am one). There’s pretty good literature about perceptions of self-image, weight and desirability being different for N. American African-American and Latina women than they are for white women. Don’t know of any studies that specifically address mate choice and wife BMI, sadly.

    Link to this
  6. 6. EricMJohnson 9:04 am 07/14/2011

    @mgmcewen Also in Mauritania. Though this is changing (BBC: http://j.mp/nae2Uk). The Efik people of Nigeria have similar “fattening rooms” as a rite of passage for young women (LA Times: http://j.mp/onCPtn).

    On a related point, I think the discussion from Smuts (1992) on body size as an example of adaptive flexibility is a fascinating one (ES: http://j.mp/oT6Au4). Her statement that “Adaptive flexibility and cultural change are two sides of the same coin” is a truth about human nature that Evolutionary Psychologists should consider more often.

    Link to this
  7. 7. Melissa Lott 10:31 am 07/14/2011

    Great post, Kate! Especially enjoyed the wrap-up:

    “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.”

    As someone who doesn’t study this subject (beyond personal interest), I liked how you broke down the conclusions made by the authors and the deficiencies in their analysis. I completely agree with your identifying the risks that the authors took (and the failure that resulted) by stepping too far away from their area of expertise. Wish they’d called in an evolution expert to give them some grounding. Who knows – that person’s perspective could have helped them to see some interesting results in their data set.

    I definitely feel like I learned something new while reading through this – Thanks!

    Link to this
  8. 8. kclancy 9:56 pm 07/14/2011

    Maryn — exactly. It’s so important for us to understand variation both within and between populations. Within pop variation does get overlooked quite a bit.

    And Melissa — thanks to you too! I really do wonder why the authors went in that evolutionary direction. It seems to me like the evolution of human behavior *seems* intuitive to many people, and so everyone feels they can have an evolutionary perspective. I think Eric’s right that you see this in psych a lot more than other fields (though I also know a ton of truly excellent psychologists), though econ sometimes does it too.

    Link to this
  9. 9. Torbjörn Larsson, OM 5:23 pm 08/8/2011

    The article seems to hit all the correct criticism.

    But for this: “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.” It _could_ have been a statistical factor. (But it likely wasn’t.) In the same way imperceptibly small differences in fitness can drive selection.

    “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.”

    I knew that. What I don’t know is how people become so fat happy that they want to pollute a perfectly healthy sandwich with it! Cultural differences indeed. :-D

    Link to this

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