Why You Really Can Judge a Book by Its Cover

In an earlier post, I discuss the adage, “You can’t judge a book by its cover,” as one of the very few stereotypes that are not empirically true. Indeed, virtually all other similar stereotypes empirically are true—nice people look nice, and nasty people look nasty.

A 2006 study neatly illustrates this point and shows that women can successfully tell which men would make good fathers just by looking at them.

For an article published in the Proceedings of the Royal Society of London, Series B, James R. Roney, Katherine N. Hanson, Kristina M. Durante, and Dario Maestripieri first measured men’s interest in infants. They showed 10 pairs of pictures to 39 male students at the University of Chicago. In each pair, one was a picture of an infant and the other a picture of an adult. For each pair, the men indicated which of the pictures they preferred. The more pictures of infants they chose, the higher their level of interest in infants was gauged to be.

Then the pictures of these 39 men were shown to female students halfway across the country, at the University of California, Santa Barbara. Twenty-nine women rated each man’s picture based on how interested they judged he was in children. It turned out that their ratings were significantly positively correlated with men’s actual interest in infants, as judged by their preference for pictures of infants to pictures of adults.

In other words, women can tell which men are interested in children and which are not, simply by looking at them!

The women were then asked which men they found attractive as mates. Women who had expressed that they were interested in long-term relationships found men who were interested in children more attractive, whereas women who were interested in short-term relationships found men who had higher levels of testosterone more attractive. Yes, women can also tell which men have higher levels of testosterone simply by looking at them—but this is less surprising, because there are certain facial features, such as large jaws and strong brow ridges, that indicate higher levels of testosterone.

This latter finding is consistent with previous research in evolutionary psychology showing that women who are ovulating (and are thus at a higher risk of conception) find masculine men with higher levels of testosterone more attractive, whereas women who are not ovulating (and are thus at a lower risk of conception) find men with lower levels of testosterone more attractive. This shift in mate preference through the menstrual cycle aids in women’s overall evolutionary goal of marrying nice, resourceful men (“dads”), and potentially cuckolding them with handsome, masculine men who have higher levels of testosterone (“cads”).

At any rate, Roney et al.’s study is another indication that you can indeed judge a book by its cover. Men who would make good fathers look like they do, and women can tell just by looking at them.