Romantic partners often experience jealousy (see our previous post on jealousy and Facebook), but interestingly, who makes us jealous may lie in how long our fingers are!
Evolutionary psychologists have found that men prefer partners who are physically attractive (which is a sign of health and fertility) because it increases his chances of passing on his genes. Women, on the other hand, prefer partners who have high social status because it is a signal that he can provide resources to her children, again increasing the chances of her childrens' survival.1 Thus, men should be jealous if their partners show interest in more prototypically masculine men, whereas women should be jealous if their partners show interest in more prototypically feminine women.
How do we know how masculine or feminine someone is? If they camped out overnight to see the movie Fast Five, they are probably masculine; if they freely chose to go see Something Borrowed, they are probably feminine. In all seriousness, one clever way to answer this question is by examining individuals’ finger length (seriously, their fingers!). It turns out that the presence of prenatal testosterone influences the length of individuals’ fingers.2 In particular, more prenatal testosterone results in index fingers (our “2nd digit”) to be shorter than ring fingers (our “4th digit”), or what is called a lower 2D:4D ratio. Go ahead, check it out. Done looking at your fingers? Here's what it means: more “masculine” individuals have index fingers that are slightly shorter than their ring fingers, whereas more “feminine” individuals have index and ring fingers that are about the same length.
So how does this affect jealousy? Researchers scanned images of individuals' hands and measured their 2D:4D. Individuals then imagined a scenario in which their romantic partner was flirting with someone else and indicated how jealous they would be if the rival was more socially dominant and physically attractive than themselves. Consistent with the researchers' predictions, men with more “feminine” 2D:4D reported greater jealousy when their partners were flirting with a socially dominant (“masculine”) man, whereas women with more “masculine” 2D:4D reported greater jealousy when imagining their partners flirting with a more physically attractive (“feminine”) woman!3
So the next time you’re on a first date and want to know if the person is the “jealous-type”, take a tape measure with you and check out his/her fingers. And if the tape measure doesn’t scare your date off, you’ve got it made!
For more posts on evolutionary psychology, click here.
1Buss, D. M., & Schmitt, D. P. (1993). Sexual strategies theory: An evolutionary perspective on human mating. Psychological Review, 100, 204-232.
2Manning, J. T. (2002). Digit ratio: A pointer to fertility, behavior and health. New Brunswick, NJ: Rutgers University Press.
3Park, J. H., Wieling, M. B., Buunk, A. P., & Massar, K. (2008). Sex-specific relationship between digit ratio (2D:4D) and romantic jealousy. Personality and Individual Differences, 44, 1039-1045.
Dr. Brent Mattingly - Science of Relationships articles | Website/CV
Dr. Mattingly's research, broadly conceptualized, focuses on the intersection of romantic relationships and the self. His specific lines of research all examine how individual-level constructs (e.g., motivation, attachment, self-regulation) are associated with various relational processes.