What do baseball and pornography have in common?

At first glance you might think, baseball and pornography have little in common...other than that many men appear to be rather fond of both. But both baseball statistics and pornography have been used as data sources, unobtrusive behavioral measures, to test predictions and illuminate our understanding of human nature. And they have done so in two of my favorite areas of research, birth order and human sexuality.

If you happen to be interested in how birth order influences personality and behavior, you might have taken note of a study by Frank Sulloway and Richard Zweigenhaft that was published last year, Birth Order and Risk Taking in Athletics: A Meta-Analysis and Study of Major League Baseball. The authors took an evolutionary perspective on parental investment and family dynamics. In particular, they focused on niche theory (articulated elegantly by Sulloway in his book Born to Rebel) which suggests that siblings attempt to minimize direct sibling competition by diverging into different family roles or niches on the basis of such factors as age, sex, etc. Differences in parental investment also influence sibling strategies in that parents tend to favor firstborns, who have already survived the trials of early childhood and are therefore more likely to give a return (future grandchildren) on their parents' investment. But parents also favor lastborns, their last opportunity to invest in offspring. Firstborns and lastborns also benefit from typically getting windows of opportunity where they are the main focus of parental attention (the first before their siblings are born and the last after the rest have flown the nest). Middleborns seem to lose out in this Darwinian investment equation (though if you're interested in how they actually benefit in the long run, check out The Secret Power of Middle Children coming this August by me and Katrin Schumann.

Sulloway and Zweigenhaft predicted that laterborns would be more likely to engage in high-risk activities (risk-taking being facilitated by extraversion and openness to experience, which laterborns typically score highly on) than firstborns. One way they tested this was to examine the strategies of older and younger brothers that both played major league baseball. What they found was that laterborns more frequently attempted to steal bases (the effect was particularly strong for within-family comparisons) and were more successful in doing so than their older siblings. They also looked at several measures of risk-taking in batting behavior and found younger brothers to not only hit more home runs but to be more likely to be hit by a pitch. In other performance measures, older brothers excelled (more strikeouts as pitchers and less walks given up). Such publically available baseball statistics are an excellent unobtrusive measure of risk-taking behavior, providing an additional real life source of data as an alternative to survey measures of risk.

Research in sexuality also can also benefit greatly from unobtrusive approaches. While surveys have been the most common research technique, there have often been concerns about social desirability influencing the responses as well as bias in who is willing to actually participate in studies of sexual behavior and interests. Commercial erotica, both male-oriented pornography and female-oriented romance, are multi-billion dollar industries and their characteristic features have been shaped by the millions of consumers who have spent their money on those products that have the greatest appeal. In Warrior Lovers: Erotic Fiction, Evolution and Female Sexuality, Don Symons and myself suggested that the essential features of erotic genres constitute unobtrusive measures of male and female sexuality and we outlined a variety of methods for exploring this, including the distillation of essential features as well as the examination of more esoteric genres and comparison of them with mainstream erotica in order to highlight those essential features as well as to test predictions about the causes of within-sex variation in erotic preferences.

This would be the porn.

Male and female oriented erotica appear so different, have such different essential ingredients (porn being characterized by physical gratification, the absence of courtship and commitment as well as plot, focus on the sex acts themselves, etc. while romance is characterized by plot and the journey to find one worthy mate, willing to commit, and while many are explicit it is never sex simply for its own sake), because the ancestral problems faced by males and females were also quite different.

This the romance.

While the typical parental investment for men and women may have been similar, the minimum investment for males has always been less. If a man had a child in which he did not invest, if it survived, his reproductive cost was almost zero. Even if such opportunities were rare, male sexuality evolved to take advantage of those opportunities when they arose and, as a result, men find the idea of sex with novel high mate value eager women arousing (the world presented in porn). Ancestral women would have had little to gain and much to lose from impersonal sex with anonymous strangers and there was a great deal to gain by the careful selection of a mate. The romance novel is a chronicle of that careful selection of a high mate value male, able and willing to commit to the right woman and any future offspring.

While you can survey people about their thoughts and behaviors, and it's very tempting when you have lots of undergraduates looking for research credit, sometimes an unobtrusive approach will give you new (and sometimes clearer) insight.