Our Genes, Our “Chemistry”: The Search for the Perfect Match
When we say that there is “chemistry” between people, we are not probably referring to the activity of the MHC-genes. However, this mechanism might be one of the key components for finding the love of your life.
By Karen Wu
Imagine that you are speed-dating. You anxiously sit in your chair, scanning the other speed-daters and wondering how you will fare tonight. Will you find your perfect match? Your first partner approaches you. This person is simply gorgeous. However, once they sit down in front of you, everything changes. They smile charmingly and say all the right things, but you feel nothing for them. You begin to question your judgment.
Your next partner looks to be far less beautiful, and definitely not your type. You resign yourself to a mediocre speed-date. But, once this person sits across from you, butterflies begin to fill your stomach. You feel nervous and giddy and inexplicably drawn to them. Love is in the air, but you don’t know why.
Could there be an important basis for these seemingly illogical feelings? What could explain the mysterious “chemistry” that we feel with some people, but not others? Perhaps the answer lies in our genes. When we choose our partners, we use a combination of conscious processes (e.g., checking if a potential partner meets our “checklist” of qualifications), unconscious processes (e.g., gut instinct and “chemistry”), and an interaction between the two (e.g., rationalizing our instinctual preferences). Existing research points to a family of genes, known as the Major Histocompatibility Complex (MHC), as one of the major mechanisms behind our unconscious mate preferences.
In the past several decades, there has been growing evidence for the importance of MHC-genes in human mate selection. The more people differ in their MHC-genes, the more sexual attraction they appear to feel for each other. MHC-based attraction is thought to serve two main purposes. First, MHC-based attraction may function as an incest-avoidance mechanism because relatives are likely to share more MHC alleles with one another than with non-relatives (Penn & Potts, 1999). Second, preferences for MHC-dissimilar partners may result in healthier offspring who can defend against a broader array of pathogens as MHC-genes are responsible for our immunocompetence (Lie, Simmons, & Rhodes, 2010). This gene-based attraction seems to operate through our preferences for the body scent of MHC-dissimilar partners (Havlicek & Roberts, 2009; Wedekind et al., 1995; Wedekind & Furi, 1997). Although much scientific research (outlined below) substantiates the importance of MHC, we still do not know the extent to which MHC-compatibility plays a role in the mate preferences of emerging adults in a true-to-life scenario, that is, when other desirable and more salient attributes of potential partners (e.g., good looks, charm) are taken into account. In addition, we do not know how these unconscious MHC-based preferences influence our conscious perceptions of potential mates. That is, might people perceive more MHC-dissimilar others as not only better-smelling, but also more physically attractive, kind, trustworthy, intelligent, or socially-skilled?
Below, I will summarize converging lines of evidence for the importance of MHC genes in mate selection, and describe a speed-dating study that our research team is conducting with the help of an SRA Innovative Small Grant.
- MHC plays a substantial role in mate selection across species. Fish (Landry, Garant, Duchesne, & Bernatchez, 2000), lizards (Olsson et al., 2003), mice (Penn & Potts, 1998), lemurs (Schwensow, Eberle, & Sommer, 2008), and mandrills (Setchell et al., 2009) have all been found to prefer mates that share fewer MHC-genes.
- Population-based studies have found evidence for MHC-based assortment of spouses. Specifically, European American spouses have been found to be more dissimilar in their MHC-genes than expected by chance (Chaix, Cao, & Donnelly, 2008), indicating that MHC- compatibility may play a tangible role in the selection of marriage partners.
- People are more attracted to the body scent of those who differ from them in MHC-genes. To many people, a pleasing body scent is extremely important in a romantic partner. In one study, scent was rated by women as the second most important criterion in a partner (Herz & Inzlicht, 2002). It is through body scent that MHC-based assortment is thought to operate. Studies indicate that normally-ovulating women prefer the body scents of MHC-dissimilar men as opposed to MHC-similar men (Wedekind et al., 1995). Furthermore, people may perceive the body scents of MHC-dissimilar others as reminiscent of their exes (Wedekind & Furi, 1997).
- MHC-dissimilarity has been linked to greater relationship quality and sexual satisfaction in existing couples. Intriguingly, women who differ more from their partners in their MHC-genes report being less attracted to other men and are also less likely to cheat on their partners (Garver-Apgar et al., 2006). Both women and their male partners also report greater sexual satisfaction in their relationships when they are more MHC-dissimilar.
- MHC-dissimilarity has been linked to better reproductive health. Couples who differ more in their MHC-genes have less difficulty conceiving children via in vitro fertilization (Weckstein et al., 1991), shorter intervals between pregnancy (Havlicek & Roberts, 2009), higher birthweight babies (Reznikoff-Etievant et al., 1991), and lower rates of miscarriages (Ho et al., 1990; Koyama et al., 1991; Laitinen, 1993). MHC-dissimilarity between partners may also result in enhanced immunocompetence of offspring, a phenomenon that has been well-supported in mice (e.g., Penn, Damjanovich, & Potts, 2002).
To examine the role of MHC-compatibility in emerging adults’ mate preferences, we designed a speed-dating study with the aid of an SRA Innovative Small Grant. From November 2012 to May 2014, my research team and I conducted 15 speed-dating events, each consisting of approximately 20 participants. The majority of participants ranged from 18-23 years old, and speed-dating events were separated by age group (i.e., ages 18-20 and 21-23). During each event, participants, all of whom were single, went on approximately 10 3 min dates with opposite-gender partners. After each date, participants rotated and completed questionnaires about the person they just saw. In these questionnaires, participants were able to extend a second date offer to their partner. They also rated them on attributes such as mate desirability (both long-term and short-term), attractiveness of body scent, and sexual chemistry; as well as attributes that are highly valued in a romantic partner, such as physical attractiveness, kindness, trustworthiness, intelligence, and social-skills (Buss, 1994; Shackelford, Schmitt, & Buss, 2005). At the end of each session, we collected DNA samples from participants through cheek swabs.
Running these speed-dating events has proved to be both challenging and rewarding. For instance, maintaining an equal gender ratio can be very difficult, due to last minute cancellations, usually by male participants. As a result, our team has learned to be creative and varied with our recruitment methods, such as by recruiting participants through a colorful sign-up booth on campus, as well as advertising the events on popular social media sites such as Reddit.com. However, running the events has also been fulfilling, as we are able to provide participants with the potential for a new romance, or at the very least, an interesting and unusual experience. Indeed, a subset of our participants went on to date each other outside of the lab, and others described the event as “life-changing”, “super fun”, or “not as awkward as I expected”.
We are currently processing participants’ DNA samples using the GoldenGate Genotyping Assay. MHC-dissimilarity between dyads will be assessed at approximately 50 different loci, and the relationship between MHC-dissimilarity and mate choice will be examined alongside other variables that have been found to predict mate preferences, such as physical attractiveness. In addition, we will examine the relationship between MHC-dissimilarity and social perceptions of speed-dating partners. We expect to find that individuals, especially women who are normally-ovulating (Penn & Potts, 1999; Roberts et al., 2008; Wedekind et al., 1995), will rate more MHC-dissimilar partners as more attractive-smelling and desirable and will be more likely to offer them second dates. We also expect that MHC-dissimilarity will predict more positive ratings of partners as MHC-based attraction may “bleed” into peoples’ perceptions of their dates, enhancing the attributes of more MHC-compatible partners. Such findings would clarify whether a gene-based detection system may play a role in emerging adults’ mate choice, and whether our social judgments may be unknowingly influenced by genetic-compatibility.
Last, we will test the possible moderating role of oral contraceptives in females’ MHC-based mate choice, as oral contraceptives have been found to reverse women’s MHC-based preferences in laboratory paradigms (Penn & Potts, 1999; Roberts et al., 2008; Wedekind et al., 1995). This will shed light on the anecdotal tales of women who have begun or ceased using oral contraceptives, only to find that they are no longer attracted to their partners.
All-in-all, we hope to better understand the mysterious forces behind the “chemistry” that people sometimes experience with one another. Perhaps armed with this knowledge, emerging adults can decide whether or not to trust their instincts when it comes to love.
I would like to recognize the following individuals for their continued support and guidance on this project: My advisors, Drs. Chuansheng Chen, Ellen Greenberger, and Robert Moyzis; my research assistants, Jonathan B. Lim, Stephanie Nguyen, Blaise Lallathin, Ronica Senores, Justin Huft, Gabriel Corpus, Melody Lim, Jennifer Lai, Paul Phandl, and Marissa Tom.
I would also like to thank Society for Research on Adolescence and Psi Chi International Honor Society for funding this research.
Karen Wu is a doctoral candidate in the Department of Psychology and Social Behavior at the University of California, Irvine. She received her Master of Arts in Social Ecology from the University of California, Irvine, in 2012. In 2009, she graduated with High Distinction from the University of California, Berkeley, receiving her Bachelor of Arts in Psychology with a minor in Asian American Studies. Her research thus far has mainly focused on the interplay of cultural and personality factors on self-concept and close relationships. More recently she has been incorporating another important element into her research on intimate relationships—genetics.
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