Psychobiological mechanisms of gender differences in social approach behavior

Abstract

By modulating social approach behavior, oxytocin critically affects the formation and maintenance of monogamous relationships. A seminal study showed that in men, oxytocin increases trust and hence approach behavior towards unfamiliar others. In women, however, oxytocin’s effects on trust are still unknown. Furthermore, the decision whether to trust a potential romantic partner or not is strongly influenced by facial features such as attractiveness and threat. The former acts as a signal of good reproductive fitness, the latter as a signal of potential trust abuse, both being highly relevant in a mating context. This dissertation thus studies largely unknown gender differences in the relevance of attractiveness and threat by using a refined trust game with interaction partners that vary in these facial features. It furthermore addresses the research gap of gender differences in oxytocin’s effects on trust by systematically comparing single men and women in the luteal phase. In Chapter 1, literature is reviewed on the psychobiological factors and gender differences in social approach behavior and trust, and on possible ways to measure trust. Chapter 2 presents a refined, incentivized trust game, which includes photos of interaction partners that vary in facial attractiveness and threat. Results from 93 participants (all singles; 46 women during their luteal phase) with romantic interest in the opposite sex show that both women and men trusted attractive and unthreatening interaction partners more often. Moreover, women’s trust behavior was more strongly affected by threat than by attractiveness, whereas men’s trust behavior was equally affected by both features. From an evolutionary perspective, it might be advantageous for women to be more vigilant towards threat cues due to a higher parental investment. For men, on the other hand, it might be more beneficial to approach women whose attractiveness signals a good reproductive fitness, as men can produce more offspring than women can. To study gender differences in oxytocin’s effects on trust, Chapter 3 first reviews the literature on oxytocin, with a focus on gender differences in oxytocin’s effects. Then, it presents data from 144 participants (all singles with romantic interest in the opposite sex; 73 women during their luteal phase) who played the trust game after intranasal administration of oxytocin or placebo in a randomized, double-blind procedure. We find that oxytocin, compared to placebo, increased trust behavior to a larger degree in men than in women. Furthermore, this gender difference in oxytocin effects was more pronounced when participants interacted with unattractive and unthreatening interaction partners. We therefore demonstrate for the first time that there are gender differences in oxytocin’s effects on trust behavior towards potential romantic partners, and that this effect is dependent on facial features. Gender differences in the oxytocin system and its interaction with gonadal hormones might explain the gender-specific oxytocin effects on social approach behavior. Finally, Chapter 4 integrates the findings from both studies and provides a general discussion of gender differences in approach behavior both with and without oxytocin, as well as limitations and implications of this dissertation. Taken together, this dissertation reveals gender differences in the importance of facial attractiveness and threat, and in oxytocin’s effects when singles approach potential romantic partners. Future studies could utilize this refined version of the trust game to investigate oxytocin’s effect on approach behavior in homosexual participants, in friends, and in clinical samples like participants with social anxiety disorder or autism. Furthermore, our findings emphasize that more research including both genders is necessary to understand the mechanisms and evolutionary purpose of oxytocin’s effects on social cognition and behavior