Rich, Sexy, Lots: A modern 3D life-history trade-off

In response to the evolutionary puzzle of modern low fertility, I’ve suggested that the patterns in various times and places can require their own explanations—so, for example, in the U.S., high 19th century fertility likely requires a different mix of explanations than high 1950s fertility, and low 1930s fertility likely requires a different mix of explanations than low 21st century fertility. I’ve suggested that the explanations for 21st century fertility in the U.S. probably can’t rely on the view that women generally don’t actually want to have kids, because even young women in college usually really do.

In my previous post, I discussed a three-way trade-off for women that is relevant to modern low fertility—it’s not the answer to everything, but it’s a piece of the puzzle. This complex modern trade-off involves having children who are likely to end up being relatively rich, having children who are likely to end up being physically attractive and sexy adults, and having lots of children. Call it the rich-sexy-lots trade-off.

This trade-off is in three dimensions. There are pretty straightforward rich/lots trade-offs—for example, getting a college education typically increases wealth but also delays childbearing, women’s careers often go on a less-lucrative path when they have more children, having more kids decreases one’s investments in each kid, and so on. But there are also trade-offs involving sexy.

Women’s sexy conundrum involves a theme that has been popular in women’s fiction for centuries, the old cad/dad dilemma—how to balance preferences for promiscuous men with preferences for reliable husbands. One of Jane Austen’s recurring plot points is the short-term appeal but long-term risk of sexy men. The Wickhams, Willoughbys, and Henrys of Austen’s early-19th-century world are attractive and immediately charming, but turn out to be dishonest seducers, lovers-and-leavers, and cheaters—in short, not great husband material. More recently, Sex and the City is at heart a story about modern professional women navigating mating terrain where Wickhams, Willoughbys, and Henrys are particularly sought after, with the best of them being hard to find and harder to tame. And very low fertility follows in the modern story—two of the main characters end up with one child each, and the other two have none.

The 3D trade-off gets real

Sex and the City is fiction, of course. But it’s not too far off the mark on similar women’s fertility outcomes. It’s well known that low modern fertility is particularly concentrated among women with the most education. That’s related to the rich-lots part of the trade-off. But what’s not as well known is that sexy is also a big deal—within educated women, very low modern fertility is concentrated among the more sexually adventurous.

In the chart below, I show completed fertility averages for the Baby Boom generation of American women (born from 1946 to 1964). I’ve plotted their average number of children according to two features—how much education the women got, and how many men they slept with since age 18. It’s basically the rich-sexy-lots trade-off in a single chart. The very highest fertility (with averages in the 2.5 to 3 children range) is among those women who combine little education with more monogamous sexual histories. And the very lowest fertility (with averages around 1 child) is essentially the Sex and the City profile.

GSSEdSexFert(Technical notes: The sample size is 3,588. Results are weighted. Number of children was capped at 8. Education had a floor of 9 and a cap of 19. Number of male sex partners since age 18 was capped at 15. The displayed results are from a regression equation predicting number of children with education and sex partners, including, to show non-linear trends, squared terms for both as well as the interaction between the two predictors.)

Not only is fertility lower as both education and sex partners rise, but there is an interaction as well. Number of sex partners doesn’t have as much to do with fertility among the less educated as it does among the college educated.

Back in college

In an earlier post, I described my sample of over 1,300 young women at six normal American universities. There we saw that most really wanted to get married in their mid-20s to faithful sorts of guys, and to have two or more kids beginning in their late-20s.

To see how sociosexual differences related to their marriage and fertility plans, I created a Sex and the City variable combining various items on how they feel about casual sex and how much they party and hook up. (For those of you who follow these things, it’s an expanded version of Sociosexual Orientation Inventory, adding three items about recent non-intercourse hook ups, getting drunk, and enjoying wild parties.)

This sociosexual variable was basically uncorrelated with how many children these young women eventually wanted to have and with how important having kids was to them—on the whole, the college women who were more abstinent and sociosexually restricted didn’t want children any more or less than unrestricted Sex and the City types did.

But sociosexual differences did relate to how important getting married was to them and the age at which they’d prefer to get married. Restricted women thought marriage was a bit more important and saw themselves getting married a bit earlier than unrestricted women.

And there were differences in what they wanted from future partners. As I described previously, I had almost half the sample rate a long list of features in terms of how desirable the features would be in a future partner. Some of these ratings varied significantly between more restricted and more unrestricted college women. Restricted women gave higher average ratings than unrestricted women to faithful-and-nice traits in future mates: someone you trust; who wouldn’t cheat on you; who’s kind; will be with you forever; has good morals; is patient. On the other hand, unrestricted women gave higher average ratings than restricted women to Sex and the City traits in future mates: has an exciting personality; has many friends; has an active social life; will have a high income; is physically attractive. It’s in large part an inherent sociosexual trade-off for women—and an enduring theme in stories especially popular among young women—namely, it’s tough to find men who combine faithful and sexy.

So how does sociosexuality end up relating to differences in fertility? These college women mostly started off looking to end up in a similar fertility neighborhood, but intending to take different roads with different kinds of guys. And, it appears, the nice-guy road to Fertville ends up being the more reliable one. But, again, it’s a trade-off—nice guys are less likely to father sexy sons.

Are people who open restaurants trying to lose money?

A big chunk of new restaurants—perhaps as many as 60%—fail within a year. So what’s up with people opening restaurants? Do they not care about making money? Are they trying to go bust?

Obviously, there’s sense in which phrasing the questions this way misses the point. They’re not trying to go bust. They’re trying to establish successful restaurants, something that would be really cool if it happened. But it’s an especially tough market. In short, they’re pursuing a high-risk high-reward venture.

We could ask similar kinds of questions about why any young person would ever put in lots of time and energy trying to be a professional athlete or a popular musician. Or about people who borrow a ton of money to go to college. Or about politicians or military officers who have extramarital affairs. Or about venture capitalists or stock-pickers. High-risk high-reward stuff happens a lot.

Now, saying that something is a high-risk high-reward strategy doesn’t mean that it’s rational in any specific case. People have limited knowledge and might genuinely misjudge their chances. They might be suckers. But they might also in some cases have real shots at getting things that they want—things that lots of people might want under the right circumstances—even if those things are difficult to pull off and potentially very costly when they don’t work out. There’s no general mystery in the fact that some people in some circumstances attempt things that have big potential upsides when they succeed and also have big potential downsides when they don’t.

Maybe the Sex and the City pattern is in this high-risk high-reward category. The big potential upside is something many young women would love to end up with—rich, sexy offspring. (The heroine’s prize in fairy tales, after all, is often both a prince and charming.) The big potential downside is something many young women want to avoid—having no offspring. Does that make it in some sense a rational strategy? Clearly not in all cases, but it sometimes works. Life is competitive and risky; it has trade-offs.

Again, I don’t want to say that the rich-sexy-lots trade-off fully explains the evolutionary puzzle of modern low fertility. It doesn’t. Indeed, it might not really hold together on closer inspection. But I’m proposing it as a possible piece of the puzzle that has received insufficient attention. The very lowest fertility rates these days are particularly concentrated among educated-and-unrestricted women. And it doesn’t look like they generally start off wanting very low fertility. Recognizing the complexity of the real-world trade-offs at least gets us closer.

So far in these fertility posts I haven’t been very explicit about the big picture. I’ve been busy getting some key empirical themes out. I’ll do a couple of concluding posts in this series that try to draw some of this together—that try to give a more general sense of how I think we might integrate evolutionary work on strategic pluralism and life-history trade-offs, while paying closer attention to the specifics of a given population’s actual circumstances and trade-offs.