This paper will examine the phenomenon of close relationship infidelity through the lens of evolutionary psychology. While personality predictors of infidelity are relatively more idiosyncratic, such that there are many personality characteristics that predict infidelity and no two people that are likely to commit infidelity have to necessarily have the same combination of personality traits. The evolutionary psychology theory speaks in terms of broad human tendencies that explain population trends. This paper will examine these theoretical tendencies, and suggest that based on the evolutionary theoretical framework of infidelity, men, at any point in time, will find more women acceptable for sexual relations. Furthermore, by applying basic human exchange behaviour to the previous claim, this paper will argue that men find each potential alternative mate to be less valuable than women find each of their potential alternative mates. In order to present a clear picture, key concepts will be explained first (Parental Investment Model, availability of alternatives, perceived susceptibility to infidelity (PSI)), along with evidence for those concepts. Finally, all the concepts and evidence will be pulled together to support the two hypotheses.
Parental Investment Model. The evolutionary psychology theory, as described by Guerrero, Anderson and Afifi (2007) in Close Encounters: Communication in Relationships, is based on theoretically derived gender differences in mate selection and attraction evolved through time in order to maximize reproductive success. According to the evolutionarily based parental investment model, women risk more than men in a sexual encounter (Trivers, 1985; as cited in Guerrero, Anderson & Afifi, 2007). The rationale is that women will have to go through nine months of pregnancy and nurse the child, while men will not. Therefore, women should be more careful, and pickier about the men that they engage in sexual relations with, in the case that they do get pregnant. On the other hand, men should be less picky than women because they do not risk nearly as much. Kenrick, Groth, Trost & Sadalla (1990; as cited in Guerrero, Anderson & Afifi, 2007), conducted research supporting this notion by looking at the minimum levels of attractiveness, dominance, status, intelligence and other characteristics that each gender would require in order to go on a date with, have sex with, date steadily, and marry a person. Results indicate that men hold lower standards than women in all relational situations (date, sex, steady dating, and marriage) except for attractiveness.
Availability of Alternatives. In this paper, availability of alternatives will refer to the number of opposite-gender individuals that a person considers to be acceptable for sexual relations. If men have lower standards than women, then they may perceive a wider range of women acceptable for sexual relations; therefore, they may have a higher availability of alternatives. Women on the other hand, should perceive a smaller range of men acceptable for sexual relations. Therefore, women should have a lower availability of alternatives. Further support for the gender difference in availability of alternatives stems from research done on male to female ratios in a population. A study done by Stone, Shackelford & Buss (2007), supported the notion that when there are more females in a society, males will lower their standards in order to secure more short-term dating. Furthermore, Stone et al. hypothesized and supported the notion that in that same context, women, instead of lowering their standards due to competition, will raise their standards in order to counter-act the male’s tendency to seek out short-term relationships. According to a report done by the U.S. Census Bureau (Smith & Spraggins, 2001), the U.S. 15 – 24 year old population has more females than males1. Therefore, based on the work done with gender ratios, American males should have lower standards than American females. One last piece of evidence indicating that males perceive to, or actually have more alternatives, comes from the report done by Center of Disease Control (Fryar, Hirsch, Porter, Kottiri, Brody & Louis, 2007), showing that American males self-reported a median of seven partners in their lifetime, while American women self-reported four. Taking into consideration the three pieces of evidence, 1) the support found for the parental investment model that indicates higher availability of alternatives for men 2) the supported gender-ratio relationship with mate-selection standards combined with the statistic showing that more men than women live in the U.S. also indicate lower standards for American males, and 3) that men self-reported more partners in their lifetime than women, it is likely that males perceive to have a higher availability of alternatives than women.
Perceived Susceptibility to Infidelity (PSI). PSI is a measure that can be used to assess the extent that an individual feels that he or she may commit infidelity in the future (PSI; Buss & Shackelford, 1997). Usually, it is measured by asking participants to indicate the possibility of them engaging in each of the six types of infidelity behaviors on a scale from zero to 100 percent in increments of 10 percent for a total of 11 possible responses to each type of infidelity. On the scale used by Buss and Shackelford (1997), the six types of infidelity are flirting, passionately kissing, going on a romantic date, having a one-night stand, having a brief affair and having a serious affair.
Availability of Alternatives and PSI. Assuming that at least some of the opposite-gender friends that a person has can be considered as available alternatives, then there should be a relationship between the number of opposite-gender friends and availability of alternatives. When an individual is single and has a high availability of alternatives, then it would be expected that on average, that person would have more sexual activity. However, when that individual is in a relationship, making use of those alternatives would be considered cheating. Nonetheless, the temptation to make use of these alternatives may remain. PSI may capture some of that temptation in terms of the person’s perception about his/her likelihood of committing infidelity. Therefore, the number of opposite-gender friends, which should be related to the number of available alternatives, should also be related to an individual’s PSI.
Supporting the Availability of Alternatives and PSI Relationship. Because males have a higher availability of alternatives than females, the number of friends that males have should be correlated to PSI more strongly and consistently than for females. Biec (2008) measured the ratio of opposite-gender friends to same-gender friends that each subject had with the following question: “Roughly what percent of your friends are of the gender that you would be interested in sexually?” The answers ranged from 1 to 5 with 1 indicating “0%” and 5 indicating “100%” (Males: M = 2.69, SD = .65. Females: M = 2.70, SD = .81). The results showed that males and females have nearly identical ratios of opposite-gender friends. In order to investigate the possibility that the gender difference in the availability of alternatives exists, a correlation was conducted between PSI and the ratio of opposite-gender friends. It is expected that the ratio of female friends that males have will be more strongly correlated with PSI than for females due to higher availability of alternatives. However, before the results of the correlation could be interpreted, an estimate for the actual numbers of opposite-gender friends that males and females have was required in the case that one gender happens to average more friends than the other. In a very large study conducted (10,000 participants) in the UK, both genders had the same average number of friends. Therefore, if the British study can be generalized to the U.S., then it can be said that both males and females in Biec’s (2008) study had the same number of opposite-gender friends (same ratio of male to female friends, and same total number of friends). Biec’s (2008) finding was consistent with the evolutionary approach to an extent. Males had a strong correlation between the ratio of opposite-gender friends and PSI (r = .29, p Economic Principles Applied. If in fact there is a gender difference in the number of available alternatives as it would be implied by evolutionary psychology, then basic economic principles of supply and demand can help further explore the consequences of such a dynamic. Economic concepts have been previously applied in psychology as in the Social Exchange theory (Zafirovski, 2005). Furthermore, economic principles are based on human behavior (humans trade goods), therefore, they may be applicable in psychology. The laws of supply and demand say that the more a specific commodity is available, the cheaper it becomes and less valuable to possess. The inverse is also true, when there is less of a commodity, the more expensive and prized it becomes and more valuable to possess (Henderson, 2004). The same idea may be applicable to the evolutionarily psychological notion that men have more alternatives than women, and that women have fewer alternatives than men. Because men have more alternatives than women (more of a commodity), they perceive each individual alternative to be relatively valued less, lowering their gender-relative quality of alternatives (each individual alternative is less tempting in terms of infidelity). On the other hand, if a woman finds an acceptable alternative, that alternative is worth more to her than an acceptable alternative for a man (due to less of a commodity). Therefore, for women, an average acceptable alternative will be perceived to be of a higher quality (each individual alternative is more tempting in terms of infidelity) than an average acceptable alternative for men. Because the supply of a commodity is directly related to the price one is willing to pay for it and the supply of acceptable alternatives for women is lower than for men, women are willing to ‘pay’ more to get that alternative, which may be at the price of risking the current relationship through infidelity. Men on the other hand, are not willing to ‘pay’ as much as women for each acceptable alternative because there are more of them, so their chance of infidelity with one particular woman is lower. However, the amount of alternatives that they have is greater. Therefore, it is important to note that this kind of a gender difference is not necessarily indicative of which gender cheats more, but what situation may lead a male or a female to infidelity. In order to estimate which gender cheats more from this perspective, it would be necessary to know the average chance that a man and a women have of cheating with an acceptable alternative (PSI) and the average number of alternatives that a man and woman have. Based on the rationale presented in this paper, it may be possible that men have a higher availability of alternatives but a lower quality of the perceived alternatives, while women have a lower availability of alternatives but a higher quality of the perceived alternatives.
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1Generally, all age brackets have more females than males. However, the 15-24 year old bracket was chosen because it best resembled the age groups used as subjects in some of the other studies mentioned in this paper in order to construct the argument. This bracket also happens to have the biggest difference in the number of males and females in the U.S. population.
Student of Psychology and Mental Health Counseling at Columbia U.
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