Why taller-wife couples are so rare

Originally published on TheAtlantic.com.

It’s not just because women are, on average, shorter than men.

Keith Urban and his wife Nicole Kidman arrive at the 2009 American Music Awards. (Chris Pizzello/AP Images)

Men are bigger and stronger than women. That generalization, although true, doesn’t adequately describe how sex affects our modern lives. In the first place, men’s and women’s size and strength are distributions. Strong women are stronger than weak men, so sex doesn’t tell you all you need to know. Otherwise, as retired colonel Martha McSally put it with regard to the ban on women in combat positions, “Pee Wee Herman is OK to be in combat but Serena and Venus Williams are not going to meet the standard.”

Second, how we handle that average difference is a matter of social construction: We can ignore it, minimize it, or exaggerate it. In the realm of love and marriage, we so far have chosen exaggeration.

Consider height. The height difference between men and women in the U.S. is about 6 inches on average. But Michael J. Fox, at five feet, five inches, is shorter than almost half of all U.S. women today. On the other hand, at five-foot-ten, Michelle Obama is taller than half of American men. So how do people match up romantically, and why does it matter?

Because everyone knows men are taller on average, straight couples in which the man is shorter raise a problem of gender performance. That is, the man might not be seen as a real man, the woman as a real woman, if they don’t (together) display the normal pattern. To prevent this embarrassment, some couples in which the wife is taller might choose to be photographed with the man standing on a step behind the woman, or they might have their wedding celebrated with a commemorative stamp showing her practically on her knees—as the British royals did with Charles and Diana, who were both the same height: five foot ten.

 But the safer bet is just to match up according to the height norm. A new study from Britain—which I learned of from the blogger Neuroskeptic—measured the height of the parents of about 19,000 babies born in 2000. They found that the woman was taller in 4.1 percent of cases. Then they compared the couples in the data to the pattern found if you scrambled up those same men and women and matched them together at random. In that random set, the woman was taller in 6.5 percent of cases. That means couples are more often man-taller, woman-shorter than would be expected by chance. Is that a big difference? I can explain.

For illustration, and to compare the pattern with the U.S., I downloaded the 2009 Panel Study of Income Dynamics, a U.S. survey that includes height reported for 4,600 married couples.* These are the height distributions for those spouses, showing a median difference of 6 inches.

Clearly, if these people married (and didn’t divorce) at random we would expect the husband to be taller most of the time. And that is what we find. Here is the distribution of height differences from those same couples:

The most common arrangement is the husband five to six inches taller, and a small minority of couples—3.8 percent—are on the left side of the red line, indicating a taller wife.

But does that mean people are seeking out taller-husband-shorter-wife pairings? To answer that, we compare the actual distribution with a randomized outcome. I made 10 copies of all the men and women in the data, scrambled them up, and paired them at random. This is the result:

Most couples are still husband taller, but now 7.8 percent have a taller wife—more than twice as many.

Here are the two distributions superimposed, which allows us to see which arrangements are more or less common in the actual pairings than we would expect by chance:

Now we can see that from same-height up to “man 7 to 8 inches taller”, there are more couples than we would expect by chance. And below same-height—where the wife is taller—we see fewer in the population than we would expect by chance. (There also are relatively few couples at the man-much-taller end of the spectrum—at 9 inches or greater—where the difference apparently becomes awkward, a pattern also seen in the British study.)

Humans could couple up differently, if they wanted to. If it were desirable to have a taller-woman-shorter-man relationship, it could be much more common. In these data, we could find shorter husbands for 28 percent of the wives. Instead, people exaggerate the difference by seeking out taller-man-shorter-woman pairings for marriage (or maybe the odd taller-woman couples are more likely to divorce, which would produce the same result).

What difference does it make? When people—and here I’m thinking especially of children—see men and women together, they form impressions about their relative sizes and abilities. Because people’s current matching process cuts in half the number of woman-taller pairings, our thinking is skewed that much more toward assuming men are bigger.

* I must note that Dalton Conley and Abigail Weitzman have a forthcoming paper for the 2013 Population Association of America conference on height differences, which also uses the PSID data, as well as the National Longitudinal Survey of Youth. I haven’t seen the paper, but the abstract is here.

All hands dimorphic: Gnomeo and Juliet edition

I previously complained about Tangled‘s 75%-male cast and extreme sex dimorphism in the romantic leads, as seen in this hand shot:

Keeping to my policy of two-year delays in movie reviews, let me add the same complaint about Gnomeo and Juliet, the charming adaptation from Disney’s Touchstone imprint. Here, a writing team of 8 men and 2 women (including Shakespeare) gives us a named cast of 14 men and 7 women, in a love story featuring these two adorable garden gnomes:

He’s only a little taller, and (judging by the gray beard) a little older. And in the movie she demonstrates bravery and feats of strength, as is now the norm. But look at those hands! Take a closer look:

What is it about hands that makes it so essential for men and women to have such differences? In the “man hands” episode of Seinfeld we learned how distressing it can be for a man to find out the woman to whom he was attracted has large hands.

That scene required a hand double. In real life, men’s and women’s hands differ on average but with a lot of overlap in the distributions — lots of men have hands smaller than lots of women. But in animation the gloves are off — and Disney is free to pair up couples who are many standard deviations apart in hand size. If real people commonly had this range of hand sizes, would such an extreme difference be considered desirable?

Delusions of dimorphism

Add to the list of new books to read Delusions of Gender: How Our Minds, Society, and Neurosexism Create Difference, by Cordelia Fine, due out soon. Feeding my interest in the issue of sexual dimorphism in humans — which we work so hard to teach to children — the book is described like this:

Drawing on the latest research in neuroscience and psychology, Cordelia Fine debunks the myth of hardwired differences between men’s and women’s brains, unraveling the evidence behind such claims as men’s brains aren’t wired for empathy and women’s brains aren’t made to fix cars.

Good reviews here and here report that Fine tackles an often-cited study of newborn infants’ sex difference in preferences for staring at things, by Jennifer Connellan and colleagues in 2000. They reported:

…we have demonstrated that at 1 day old, human neonates demonstrate sexual dimorphism in both social and mechanical perception. Male infants show a stronger interest in mechanical objects, while female infants show a stronger interest in the face.

And this led to the conclusion: “The results of this research clearly demonstrate that sex differences are in part biological in origin.” They reached this conclusion by alternately placing Connellan herself or a dangling mobile in front of tiny babies, and timing how long they stared. There is a very nice summary of problems with the study here, which seriously undermine its conclusion.

However, even if the methods were good, this is a powerful example of how a tendency toward difference between males and females is turned into a categorical opposition between the sexes — as in, the “real differences between boys and girls.”

To illustrate this, here’s a graphic look at the results in the article, which were reported in this table:

They didn’t report the whole distribution of boys’ and girls’ gaze-times, but it’s obvious that there is a huge overlap in the distributions, despite a difference in the means. In the mobile-gaze-time, for example, the difference in averages is 9.7 seconds, while the standard deviations are more than 20 seconds. If I turn to my handy normal curve spreadsheet template, and fit it with these numbers, you can see what the pattern might look like (I truncate these at 0 seconds and 70 seconds, as they did in the study):

Source: My simulation assuming normal distributions from the data in the table above.

All I’m trying to say is that the sexes aren’t opposites, even if they have some differences that precede socialization.

If you could show me that the 1-day-olds who stare at the mobiles for 52 seconds are more likely to be engineers when they grow up than the ones who stare at them for 41 seconds (regardless of their gender) then I would be impressed. But absent that, if you just want to use such amorphous differences at birth to explain actual segregation among real adults, then I would not be impressed.