When a boy meets a girlthe role of hormones in social situations relevant to male mating

Resumen

Hormones have been found to be important in domains such as sexuality, emotion recognition, stress, competition, risk taking, and trust. Many studies have consistently shown that the release of hormones can explain in a unique way human behavior and can provide insight in the functioning of social behavior. This dissertation focuses on the hormonal responses of men to a number of social situations relevant for mating. Although there are other hormones that might play a role in such situations, this dissertation focuses on the role of cortisol and testosterone. In the first chapter of the dissertation, I will explain how and where testosterone and cortisol are secreted and I will present a short overview of how previous studies have linked cortisol and testosterone to social behavior. In chapter 2, I investigated if social contact with young women affects the release of testosterone in young men, and hypothesized that dominance as a personality trait moderates this potential change in testosterone levels. To study this, I used a similar paradigm as used by Roney et al. (2003). Some deception is included in this paradigm, because I wanted to avoid any unnatural or awkward social situation between interaction partners. In this paradigm, participants were not told that they were going to interact with another person. Instead, they were brought to a room where they were told to wait so that the experimenter could fetch the correct version of a puzzle for them. In this same room, a female or male confederate of the experimenter was also present. Participants and confederates were left alone to wait for approximately 5 min. This short period served as the contact period. Before and after the contact period participants provided a saliva sample for the measurement of their testosterone level. Participants were fully debriefed about the true nature of the experiment at the end of the study. By using this paradigm, I tried to create an everyday waiting room situation where social contact may occur. In chapter 3, I investigated if competition between men creates an increase in testosterone levels among competitors. More specifically, I tried to explain why some might increase their testosterone levels and others not. Therefore, I studied not only the effects of winning and losing, but also studied the psychological state of the competitors. As a paradigm I developed a computer task on which participants had to compete. During this task, two participants were seated opposite to each other at the same table, each behind their own computer screen. The task contained questions used in intelligence tests and the outcome was fixed by the experimenter. With this paradigm I intended to create a controlled competitive situation that reflects male intra¿sexual competition. In chapter 4, I used the same paradigm as used in chapter 2, but this time I measured the hormone cortisol. I hypothesized that contact with a woman also produces a change in cortisol levels. But because the release of cortisol has been linked to stressful and challenging situations (see chapter 1), I also studied if the release of cortisol depended on how participants perceived the interaction period. Specifically, I investigated if the participants¿ perceived attractiveness of the woman with whom they interacted moderated a change in cortisol levels. In chapter 5, I combined the paradigms used in chapter 2 (social contact) and 3 (competition). This time, I investigated if the release of male testosterone due to intra¿sexual competition also prepares men for mate attraction. To do so, I took the testosterone change produced by the competitive computer task and related this to the behavior of the participants displayed during contact with a woman. Because the social contact period occurred shortly after the competition, some participants actually had elevated testosterone levels, while others had less of an increase or even a decrease. This variation in male testosterone responses gave me the opportunity to test the hypothesis that increased testosterone levels stimulate behaviors relevant for human mating, such as courtship. In chapter 6, I investigated indirectly if the exposure to prenatal testosterone has an effect on male personality later in life. During fetal development, human brain structures are formed, and exposure of testosterone in this crucial phase masculinezes the central nervous system. Therefore, fetal testosterone exposure may affect the development of certain personality traits. I specifically investigated if this exposure to prenatal testosterone affected dominance as a personality trait, since previous studies have shown that dominance is related to testosterone levels (see chapter 2). I used the same questionnaire as in chapter 2 to measure sociable and aggressive dominance, and I obtained an indicator of prenatal testosterone exposure by measuring the ratio between the middle and ring finger (2D:4D). Finally, chapter 7 discusses the main findings of the empirical chapters and will give a new direction to future studies.