Genetic Opposites Do Attract
Valentine's Day is just around the corner, so I thought it would be appropriate to discuss some psychological research about romantic relationships. I found an article from the October 2006 journal Psychological Science (Vol 17. No. 10, 830-835) particularly interesting. This research springs from a controversial theory of human and animal behavior called sociobiology, which is based on Darwin's principles of evolution and natural selection. The main idea of sociobiology is that humans and animals behave in ways that improve their individual biological fitness, which results in social behavior that enhances the genetic fitness of the entire species. The term "fitness" as used here refers to characteristics that improve the chances of successful reproduction. Sociobiologists suggest that dating and sexual behaviors that give humans a greater chance of surviving and reproducing are more likely to be "selected" (passed on) and repeated from generation to generation.
If the idea that your romantic and sexual relationships are driven by your biologically mandated urges makes you uncomfortable, you are not alone. Most people would like to think that their love life is not driven by their genes, particularly when it comes to choosing with whom they will remove their jeans. Some scientists also have problems with the theory of sociobiology, arguing that something as complex as human behavior cannot be explained by evolution and natural selection alone.
The work of Dr. Christine Garver-Apgar and her colleagues has provided research support for the theory of sociobiology as it relates to human sexual behavior. Her team studies MHC (major histocompatiblity complex), a set of genes that helps the immune system to distinguish between pathogens (disease causing agents) and our own bodies. In other words, MHC helps our bodies to recognize and attack illness-causing agents rather than our own cells.
Previous research has shown that humans tend to prefer partners with different MHC makeup. From a Darwinian point of view, this makes perfect sense. Close family members often have a similar MHC, and this preference for a different MHC in a reproductive partner helps to prevent inbreeding (which can cause medical problems, intellectual impairment, and decreased fertility). Children born of parents with dissimilar MHC profiles have immune systems that are more effective at getting rid of a wider variety of pathogens than do children of parents with a similar MHC. Therefore, when you are mysteriously "drawn" to a romantic partner with a different MHC, you are strengthening your children's ability to resist diseases.
Surprisingly, Dr. Garver-Apgar and her team found that the degree of MHC similarity between romantic heterosexual human partners is related to the quality of their sexual relationship! The couple's degree of MHC similarity was related to the female partner's levels of adventurousness, her responses to her partner's attempts to initiate sex, her number of orgasms, and her ratings of satisfaction with the sexual relationship. MHC similarity was also related to "cheating;" in that it influenced the number of sexual partners the female partner pursued outside the couple (e.g., in addition to her regular romantic partner), as well as her level of attraction towards other men during the fertile phase of her menstrual cycle (e.g., when she is most likely to become pregnant).
Specifically, as MHC similarity between partners increased, women's levels of sexual adventurousness, responsiveness, and satisfaction decreased. On the other hand, as MCH similarity increased, women's cheating also increased. In English, then, the more a woman and her partner share similar genes, the less likely she is to find him a satisfying sexual and romantic partner, and the more likely she is to seek out other sexual partners. Again, if you think about this from a sociobiologist's perspective (e.g., from the perspective of the theory of evolution), it makes sense for us to be less satisfied with potential sexual partners who have similar MHC genes. If we are more motivated to pursue relationships with partners who can contribute a MHC complex different from our own, we can then go on to create stronger, healthier children.
This study is one of the first to show that compatible genetics can influence the sexual relationships of romantic heterosexual couples, as well as an interesting twist on the notion that "opposites attract."
Do Opposites Attract: Article - Evan Nassau - Nov 18th 2010
I have recently written an article about whether opposites attract, and if so, how does this relate to the fact that people also are attracted to those who are like themselves? -> http://www.evannassau.com/do-opposites-attract/