An Evolutionary Understanding Towards the Differences Between Males and Females:
In Terms of Sexual Attitudes and Sexual Behaviors
Abstract
From huge amount of studies in psychology, scientists have found numerous differences between men and women regarding their sexual attitudes and behaviors. In this paper, I try to explain these differences from an evolutionary point of view and evaluate to what extent can it help us to reach a thorough understanding on this question. I summarize the differences between men and women from five main interrelated aspects – “sexual desire and satisfaction”, “sexual role playing”, “single-person sexual behavior”, “sexual attitudes toward casual sex, premarital sex and infidelity”, “sexual coercion” – and offer evolutionary explanations toward these differences using theories and concepts including “parental investment theory”, “good genes hypothesis & dual mating strategy” and “paternity uncertainty”. The limits of other theories and the advantages of the evolutionary theory is included in the discussion.
Keywords: sexual difference, sexual attitude, sexual behavior, evolutionary psychology
Introduction
In our daily life, we can find various differences existing between men and women. There is romantic love joining them together; however, there are also conflicts in their interests, attitudes or values that frequently separate them. Many people generally believe that men and women differ significantly, like two different “species”, which is shown by the fact that books like Men Are From Mars, Women Are From Venus usually captivate mass media and general public by arguing that “men and women differ in all areas of their lives” (Gray, 1992; Gray, 2005). Nevertheless, the truth is, although males and females are different in some ways, they are, for the most part, similar (Hyde, 2005).
In this paper, I will focus on the existing differences between men and women that have been reliably suggested by scientific psychology researches and studies. And for explanations, among so many existing competing and complementary psychology theories, I find the ones proposed by evolutionary psychology most persuasive and thorough. Therefore, I will mainly focus on these explanations and, at the same time, examine to what extent can evolutionary theory help us to understand the differences between males and females.
Sexual Selection
In the mid-nineteenth century, Charles Darwin (1859) first formulated the theory of evolution by natural selection. In his great work On the Origin of Species, he defined natural selection as the “principle by which each slight variation [of a trait], if useful, is preserved".
However, after the completion of this great work, “Darwin became dissatisfied with natural selection as the sole mechanism for evolutionary change” (Buss & Barnes, 1986) since he found that there were traits and characteristics that impair survival but nonetheless promote reproductive success. One typical example is that he discovered that the existence of the plumage of male peacocks seemed to be unreasonable since it appeared to violate the “survival of the fittest” theory. With plumage, the male peacocks are easier to attract predators andcannot move quickly. The only possible explanation is that this characteristic has some other advantages that can compensate for this loss. Therefore, he further proposed the concept of sexual selection.
Darwin’s sexual selection subsumed intrasexual selection and intersexual selection, which are closely related to each other:
Intrasexual selection refers to the “competition between members of the same sex for mating access to members of the opposite sex” (Buss, 1988). Certain characteristics can be strength, body size or agilitythat directly help them to win in the combat. They can also be producing successful mate-attracting signals or acquiring resources desired by the opposite sex, which indirectly help them to get access to mate members. This is exactly the explanation for the existence of plumage in male peacocks. Plumage acts as a mate-attracting signal that can increase the reproductive success of them. When more female peacocks are attracted to the male peacock that has the most attractive plumage, this male peacock has a greater chance to pass on its genes to the next generation.
Intersexual selection, in the opposite, involves “preferential choices exerted by members of one sex for members of the opposite sex possessing certain qualities”. (Buss, 1988). These qualities or characteristics can be appearance, health or, as the case for human beings, resources and social status. Since Darwin observed that females of many species were more discriminating and choosy in their mating process than were males, he termed intersexual selection also as the “female choice”. Using the same example, the intersexual selection in the peacock’s case is that female peacocks have the preference for “beautiful” plumage. And this preference acts as a pressure for the male peacocks to compete on this axis in the evolution process, leading them to evolve “beautiful” plumage to meet with this preference.
“After the selection process, some individuals have better reproductive success, either from being more attractive or preferring more attractive partners to produce offspring” (Buss, 1988). As a result, these beneficial traits are preserved within the different sexes.
Differences Between Males and Females in Terms of Sex: A Phenomenal Description
Not surprisingly, the sexual selection theory applies to human beings as well. Women preferring men with muscular body, more resources and higher social status is an example of intersexual selection; on the other hand, men competing with each other in these aspects, aiming at better careers and more social resources, is an example of intrasexual selection (Sprecher et al., 1994; Buss & Barnes, 1986).
In terms of the differences between men and women, there are huge amount of similar findings in evolutionary psychology. In order to present the sexual differences in a clearer and more structured way, I divided these differences into some subcategories. However, they are actually interrelated with each other. For instance, the experiments and researches used to illustrate people’s sexual behaviors can also be used to suggest people’s sexual desires. While these divisions are artificial, by dividing them into these categories, I believe we can reach a more structured understanding toward this problem.
Sexual Desire and Satisfaction
Several researches have confirmed people’s general belief that men are on average more eager for sexual intercourse then women are (Clark, 1989; McCormick, 1979; Hatfield, 1983; Peplau, 1983). Men think about sex more often than women do (Fisher et al., 2012). A study of young adults found that men on average reported sexual desires 37 times a week (Regan, 2013). Sprecher’s studies in 1995 and 2002 have also confirmed that men typically want to begin having sex at an earlier age and want to have sex more often than women do. Regarding to the sexual satisfaction they have, men tend to feel more dissatisfied with the amount of sex they get because they have greater desires (Sprecher et al., 1995; Sprecher, 2002).
Sexual Role Playing
In Burchinal & Ehrmann’s (1960) study of dating couples, they found men and women usually played different roles in their sexual relationships. Men typically exercised positive control in the sexual relationships, which means that it was typically men who proposed sexual activities. On the other hand, women were more likely to exercise negative control by refusing sex. This is actually a major reason of conflicts between husbands and wives after they enter their 50s or 60s. Men still have sexual desires; nevertheless, comparing to men, women’s sexual instincts are becoming weaker and weaker. By frequently refusing men’s sex proposals, conflicts have been created and the overall satisfaction of sex also decreases (Schwartz et al., 2014). This phenomenon also suggests possible reasons for the following single-person sexual behaviors and infidelity in men.
Single-Person Sexual Behavior
Regarding to sexual behaviors, let us mainly focus on single-person sexual behaviors, including masturbation and watching pornography.
Not surprisingly, males view pornography and masturbate more often their entire lives (Das et al., 2011). “Compared to women, men were exposed to pornography at a younger age, consumed more pornography as measured by time and frequency, and used pornography more often during sexual activity on their own” (Hald, 2006). Also, in Philip Zimbardo’s book Man (Dis)connected: How the Digital Age Is Changing Young Men Forever (2016), there are some impressive statistics from UK about excessive porn use in boys. According to the statistics, it shows that PornHub was the thirty-fifth most visited website for children aged from 6 to 14 in UK in 2013. One in three boys is now considered a ‘heavy’ porn user, watching more times than they can count. A survey in UK found that the average boy watches nearly two hours of porn per week.
Men also spend more money on sex, buying more sex toys and porn (Laumann et al., 1994) and even paying to obtain sex. 23 percent of men had paid for sex at least once according to an Australian study by Pitts et al. (2004).
Sexual Attitudes Toward Casual Sex, Premarital Sex and Infidelity
In Halpern and Kaestle’s (2014) study, they found that men are more likely to view sex without love as acceptable; instead, women are more willing to view sex as part of the romantic relationship, as a companion of love. This can also be shown by the result of a famous experiment asking men and women about whether emotional betrayal or sexual betrayal is more unacceptable. It turns out that men on average view sexual infidelity as more unacceptable; instead, women on average view emotional infidelity as more unacceptable (Buss et al., 1992).
Also, Galperin and Haselton’s (2013) study has shown that men and women regret about their past sexual experiences in different ways. Women are more likely to regret for their actions, things they have done, such as having a hookup; however, men tend to regret for their inactions, things they have not done, such as miss to have sex with potential sexual partners. Furthermore, there is a sexual double standard existing. Although the situation is much better currently, traditionally, people view women who are sexually experienced as indecent; nevertheless, when a man has many sexual partners and is very sexually experienced, it seems acceptable and he may even be admired. Now, we tend to disapprove anyone, either man or woman, who has pre-martial sex frequently (Miller, 2017; Allison & Risman, 2013).
This leads us to the discussion of infidelity. Most people strongly opposites engaging in extradyadic sex when someone is already in a committed relationship with his or her mate (Widmer et al., 1998). Therefore, in the nowadays society, people generally value their mates’ fidelity. Nevertheless, sexual infidelity seems common. A compilation of several studies have found that “21 percent of the women and 32 percent of the men had been sexually unfaithful to their romantic partners at least once” (Miller, 2017; Tafoya & Spitzberg, 2007). From the data and statistic results, psychologists find that men are more likely to be unfaithful to their mates. Of course, it is just an average result; it definitely does not mean men are all likely to cheat on their partners and here are actually great individual differences. In order to measure the individuals’ beliefs and behaviors that describe their feelings about sex, the concept of sociosexual orientation has been raised and a Sociosexual Orientation Inventory was developed (Simpson et al., 2004; Simpson et al, 1991). People who believe that sex must be a companion of love and should not happen between two people without love and commitment are described as “restricted”. On the other hand, people who believe that sex does not require the two people to be in a close, romantic relationship are described as “unrestricted”. Actually, the result of the study carried out by Schmitt (2005), using this inventory, confirms the previous finding: males are more “unrestricted” on average than females are. And Ostovich’s study (2004) has shown that people with “unrestricted” orientations have more sexual partners and are more likely to cheat on their primary lovers comparing to “restricted” people.
Sexual Coercion
By sexual coercion, we basically mean inducing, pressuring or forcing someone to engage in unwanted sexual intercourse or sexual behaviors. These coercions can be in various forms, either verbal coercion, or physical force. Although it is common belief that most people never coerce the other sex to have sex, this kind of sexual coercion is actually quite common.
“Specific counts depend on the precise definitions employed, but one out of every six college women encounters coercion in some form every 2 months (Gidycz et al., 2008), and most women (56 percent) suffer such interactions during their college careers (Crown & Roberts, 2007). Ten percent of the women in Great Britain have, through pressure or force, had sex with someone against their will (Macdowall et al., 2013). Overall, men use more physical force than women do—they are more likely to be the perpetrators than the victims in quadrants 3 and 4—but women are just as likely as men to verbally coerce reluctant partners to have unwanted intercourse; about 25 percent of both men and women have done so (Spitzberg, 1999).” (Miller, 2017) Also, there is a scary fact that the males conducting sexual coercions tend to think of females as animals and objects instead of human beings, persons (Rudman & Mescher, 2012).
Evolutionary Explanations
From an evolutionary point of view, males and females have faced really different adaptive problems in the history of evolution. In order to solve them, the selection pressure caused them to develop different strategies, preferences and mechanisms in mating and sex. In order to explain the previous phenomena, I want to introduce some main streams of theories: “parental investment theory”, “good genes hypothesis & dual mating strategy” and “paternity uncertainty”.
Parental Investment Theory
“Parental investment theory” was famously proposed by Trivers (1972). According to the natural selection theory introduced previously, animals, including human beings, inherit some characteristics which insure that they can pass on as many genes to the next generations as possible. Therefore, it is both advantageous for men and women to reproduce and give birth to as many surviving children as possible. Nevertheless, men and women actually differ in this level. In the reproduction process, although they aim to achieve the same goal, they have different strategies since there are differences regarding their “investment”.
For males, giving birth to a baby does not require too much energy, time or effort. Males only need to have sexual intercourse with females, consume small amount of energy and provide some sperms. Therefore, the investment for is really trivial. A single man actually has the possibility of becoming the father of unlimited amount of children. Nonetheless, the situation is extremely different for females. After having a sexual intercourse and receiving some sperms, a zygote will be formed inside the females’ bodies. The most important thing is that females need to spend almost a year to take care of the babies inside their bodies. In this period of time, their physical abilities are reduced and they also become weaker; fighting against the possible enemies in the nature is becoming an impossible task. After that, they also need to suffer from the extreme pain of giving birth to the new lives. Furthermore, they even need to take the responsibility of nurturing these children and make sure that they can survive in that highly competitive natural environment… From these aspects, we definitely recognized the differences of “parental investment”.
As a result, men ought to have more sex in order to achieve the evolutionary goal. By having sex with as more females as possible, he will have as many children as possible and therefore increase the possibility of survival of their progeny. Instead, women need to carefully select which male to have sex with because, for the same purpose, they have a different strategy, which is to focus on the quality instead of the quantity of their children (e.g., making them healthier and more attractive). They can only have limited children in their lives; therefore, they need to insure that the male they have sex with has good genes and has the commitment to devote his energy and resources on rearing these children in the future. When the children have more resources, they typically are more likely to survive.
From this parental investment theory, the research findings introduced previously can be explained:
Men think about sex more, desire sex more and have sex more because this is their evolutionary strategy. This explains why it is typically men who takes the positive control in the sexual relationship and holds a more “unrestricted” sociosexual orientation. However, constantly and freely having sex with many females is not accepted in the current societies and cultures. Social values have constrained men’s sexual behaviors and lowered men’s chances of having normal sexual intercourses that they used to have in the history. Therefore, it can be reasonably argued that men consume pornography and masturbate more as substitution or catharsis for the lack of sex. On the other side, men cheat on their partners more because monogamy is actually a quite modern regulation set by human beings. The period of existence of monogamy, comparing to the long evolutionary history, is too short to have an influence on our innate mechanisms designed for us to deal with the complex, competitive natural environment in the past. Men have the tendency to have sexual relationships with as more women as possible; focusing on one single woman and devoting all the sexual desires, all the resources on her and the children for the entire life was not the norm in the hunter-gatherer era.
Furthermore, the explanation for men on average desiring to begin having sex at an early age than women do is actually related to the reproductive values of females, which can be defined in units of expected future reproduction: the extent to which people of a given age and sex will contribute, on average, to the ancestry of future generations (Fisher R. A., 1930). Youth symbolizes reproductive value; therefore, males, for the purpose of improving the viability of their children, generally desire to have sexual relationships with younger females.
Good Gene Hypothesis & Dual Mating Strategy
Then, how can we explain females’ cheating behavior on their mates? What is the reproductive advantage for females? For explaining this phenomena, other theories were raised, including the good gene hypothesis & dual mating strategy (Pillsworth & Haselton, 2006).
In Pillsworth and Haselton’s (2006) paper, they suggest that there are mainly two evolutionary goals for females: one is to get good genes, which are the genes that help the children to become healthier and more attractive, and the other one is to gain more resources provided by their mates.
Obviously, the best mate option will be a man who is muscular, strong, young, healthy and, at the same time, has high fidelity toward the woman, promising to devote all the resources he has to the women and the children in the future. Nonetheless, not every male is like the one in the description. Most of the time, females need to face trade-offs in the mate selection. She may find a man with great resources but not so healthy and strong; she may also choose a healthy and strong man without much resources. Is there a better choice evolutionarily speaking? Yes.
Under the pressure, a dual mating strategy has developed for some women who have less desirable mates. They may pursue partners who are willing to devote and invest their resources to their offspring and, at the same time, surreptitiously try to seek better genes from other men. Applying this strategy, they can reach both the two evolutionary goals and have the best offspring theoretically.
However, on the other side, the existence of this strategy means that some of the males will be rearing someone else’s children instead. And this is actually supported by a meta-analysis study of Anderson (2006), which found that “2 percent of the world’s children, on average, are being raised by men who don’t know that someone else is the child’s biological father”. Also, there is study showing that females’ preference of male appearance is influenced by their menstrual cycles. “If they are not using hormonal contraception and are cycling naturally, they tend to find rugged, manly features somewhat more appealing when they are fertile, just before they ovulate, but they’re more attracted to youthful boyishness the rest of the month” (Little et al., 2002, Miller, 2017) [See Photo Attached Below]. It is a reasonable guess that females are more inclined to have sex and reproduce with males with rugged, manly features; on the other side, they are more inclined to find males with youthful boyish features more attractive since these males tend to appear more kind and loyal.
This is intuitively a worse situation for males, especially when males are devoting all the resources on rearing children who are someone else’s. How can they make sure that the children are theirs and they are the real fathers? This is clearly a problem faced by males and there is also psychological mechanism designed by the nature in order to deal with this problem. Actually, we have already seen some evidences in the phenomenal description section of this paper.
Paternity Uncertainty
The main problem faced by males is the problem of paternity uncertainty. In order to avoid the possibility that their mates are having someone else’s children, the most direct way is to avoid letting other males to have sex with their mates. Therefore, the hypothesis following is that males will be more sensitive to sexual betrayals of their mates. And this is supported by the research result introduced previously: men on average consider sexual infidelity as more unacceptable comparing to emotional infidelity. From women’s point of view, since they need to make sure their mates are loyal and will devote their resources to them, they have evolved the psychological mechanism to view love and emotional loyalty as more important. And this is supported by both the study discussed above and the fact that women tend to view sex more as part of the romantic relationship, as a companion of love (Halpern, C. T., & Kaestle, C. E., 2014).
Conclusion
Recent studies in psychology have suggested multiple differences between men and women. In this paper, I briefly offered a phenomenal description of the sexual differences in terms of sex and introduced several evolutionary theories to explain these phenomena. It turns out that the explanations from the Darwinian point of view are thorough and coherent. They can logically explain most of the phenomena psychologists have found regarding this topic. Also, more impressively, findings related to the innate biological factors can also be reasonably explained. The most obvious examples of this are the studies of Little et al. (2002) and Thornhill (2003), suggesting that females’ mate preferences are affected by their menstrual cycles.
Concluding, I think considering human psychology from an evolutionary point of view can significantly help our understanding toward ourselves. Combining with studies in anthropology, archeology and biology, the evolutionary theory is supported by numerous evidences and it is gradually gaining a greater power of explanation. Especially for the connection between biological & neurological mechanisms and psychological mechanisms, the evolutionary theory is providing very insightful ideas for the field of psychology. As suggested by Steven Pinker, it is “no exaggeration to say that contemporary research on topics like sex, attraction, jealousy, love, food, disgust, status, dominance, friendship, religion, art, fiction, morality, motherhood, fatherhood, sibling rivalry, and cooperation has been opened up and guided by ideas from evolutionary psychology” (Buss, 2015).
Finally, I would like to mention the importance of the studies related to the current topic. Through these findings, men and women can know the existing differences between them and better understand each other. When people are in a relationship, they must face both the sweetness of romantic love and the bitterness of conflicts. It is necessary for them to have better communications with each other and deal with the conflicts together. For example, regarding sexual intercourse, now they both understand men’s sexual desire is on average stronger than women’s. In order to avoid the possible conflicts in this aspect, avoid the possible infidelity and more single-person sexual behaviors by men, they can reach a consensus or an agreement about what is the optimal number of sexual intercourse in a certain amount of time. With better mutual understanding between men and women, the overall happiness of human beings will significantly increase. In the United States, the current divorce rate is so high that about one in two couples will divorce eventually, around 50% (Miller, 2017). Therefore, there is sufficient reason for us to refocus on the relationship between men and women, to provide them helpful guides and to try our best increasing their happiness in relationships and marriages. Increasing people’s happiness and apply psychology into our lives is clearly one of the ultimate goals of the subject of psychology.
References
Allison, R., & Risman, B. J. (2013). A double standard for “hooking up”: How far have we come toward gender equality? Social Science Research, 42, 1191–1206.
Anderson, K. G. (2006). How well does paternity confidence match actual paternity? Evidence from worldwide nonpaternity rates. Current Anthropology, 47, 513–520.
Burchinal, L., & Ehrmann, W. (1960). Premarital Dating Behavior. Marriage and Family Living, 22(2), 194.
Buss, D. M., & Barnes, M. (1986). Preferences in human mate selection. Journal of Personality and Social Psychology, 50(3), 559–570.
Buss, D. M. (1988). The evolution of human intrasexual competition: Tactics of mate attraction. Journal of Personality and Social Psychology, 54(4), 616–628.
Buss, D. M., Larsen, R. J., Westen, D., & Semmelroth, J. (1992). Sex differences in jealousy: Evolution, physiology, and psychology. Psychological Science, 3, 251–255.
Buss, D. M. (2015). The handbook of evolutionary psychology. Hoboken, NJ: John Wiley & Sons, Inc.
Clark, R. (1989). Gender Differences in Receptivity to Sexual Offers. Journal of Psychology & Human Sexuality, 2(1), 39–55.
Crown, L., & Roberts, L. J. (2007). Against their will: Young women’s nonagentic sexual experiences. Journal of Social and Personal Relationships, 24, 385–405.
Darwin, Charles (1859). On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life (1st ed.). London: John Murray.
Das, A., Waite, L. J., & Laumann, E. O. (2011). Sexual expression over the life course: Results from three landmark surveys. In J. DeLamater and L. Carpenter (Eds.), Sex for life: From virginity to Viagra, how sexuality changes throughout our lives (pp. 236–259). New York: NYU Press.
Fisher, R. A. (1930). The genetical theory of 'natural selection. Oxford, England: Clarendon Press.
Fisher, T. D., Moore, Z. T., & Pittenger, M. (2012). Sex on the brain? An examination of frequency of sexual cognitions as a function of gender, erotophilia, and social desirability. Journal of Sex Research, 49, 69–77.
Galperin, A., & Haselton, M. G. (2013). Error management and the evolution of cognitive bias. In J. P. Forgas, K. Fiedler, & C. Sedikides (Eds.), Social thinking and interpersonal behavior (pp. 45–63). New York: Psychology Press.
Gidycz, C. A., Van Wynsberghe, A., & Edwards, K. M. (2008). Prediction of women’s utilization of resistance strategies in a sexual assault situation: A prospective study. Journal of Interpersonal Violence, 23, 571–588.
Gray, J. (2005). John Gray, Ph.D. is the best-selling relationship author of all time. Retrieved May 20, 2017, from http://www.marsvenus.com
Gray, J. (1992). Men are from Mars, women are from Venus. New York: HarperCollins.
Hald, G. M. (2006). Gender Differences in Pornography Consumption among Young Heterosexual Danish Adults. Archives of Sexual Behavior, 35(5), 577-585.
Halpern, C. T., & Kaestle, C. E. (2014). Sexuality in emerging adulthood. In D. L. Tolman, L. Diamond, J. Bauermeister et al. (Eds.), APA handbook of sexuality and psychology (Vol. 1, pp. 487–522). Washington, DC: American Psychological Association.
Hatfield, E. (1983). What do women want from love and sex? In E. R. Allgeier & N. B. McCormick (Eds.), Changing boundaries (pp. 106-134). Palo Alto, CA: Mayfield Publishing Co.
Hyde, J. S. (2005). The Gender Similarities Hypothesis. American Psychologist, 60(6), 581–592.
Laumann, E. O., Gagnon, J. H., Michael, R. T., & Michaels, S. (1994). The social organization of sexuality: Sexual practices in the United States. Chicago: University of Chicago Press.
Little, A. C., Penton-Voak, I. S., Burt, D. M., & Perrett, D. I. (2002). Evolution and individual differences in the perception of attractiveness: How cyclic hormonal changes and self-perceived attractiveness influence female preferences for male faces. In G. Rhodes & L. A. Zebrowitz (Eds.), Facial attractiveness: Evolutionary, cognitive, and social perspectives (pp. 59–90). Westport, CT: Ablex.
Macdowall, W., Gibson, L. J., Tanton, C., et al. (2013). Lifetime prevalence, associated factors, and circumstances of non-volitional sex in women and men in Britain: Findings from the third National Survey of Sexual Attitudes and Lifestyles (Natsal-3). Lancet, 382, 1845–1855.
McCormick, N. B. (1979). Come-ons and put-offs: Unmarried students' strategies for having and avoiding sexual intercourse. Psychology of Women Quarterly, 4, 194-211.
Miller, R. (2017). Intimate Relationships. S.l.: McGraw-Hill.
Ostovich, J. M., & Sabini, J. (2004). How are sociosexuality, sex drive, and lifetime number of sexual partners related? Personality and Social Psychology Bulletin, 30, 1255–1266.
Pillsworth, E. G., & Haselton, M. G. (2006). Women’s sexual strategies: The evolution of long-term bonds and extrapair sex. Annual Review of Sex Research, 17, 59–100.
Pitts, M. K., Smith, A. M. A., Grierson, J., O’Brien, M., & Misson, S. (2004). Who pays for sex and why? An analysis of social and motivational factors associated with male clients of sex workers. Archives of Sexual Behavior, 33, 353–358.
Regan, P. C. (2013). Sexual desire in women. In D. Castañeda (Ed.), The essential handbook of women’s sexuality (Vol. 1, pp. 3–24). Santa Barbara, CA: Praeger.
Rudman, L. A., & Mescher, K. (2012). Of animals and objects: Men’s implicit dehumanization of women and likelihood of sexual aggression. Personality and Social Psychology Bulletin, 38, 734–746.
Schmitt, D. P. (2005). Sociosexuality from Argentina to Zimbabwe: A 48-nation study of sex, culture, and strategies of human mating. Behavioral and Brain Sciences, 28, 247–275.
Schwartz, P., Diefendorf, S., & McGlynn-Wright, A. (2014). Sexuality in aging. In D. L. Tolman, L. Diamond, J. Bauermeister et al. (Eds.), APA handbook of sexuality and psychology (Vol. 1, pp. 523–551). Washington, DC: American Psychological Association.
Simpson, J. A., & Gangestad, S. W. (1991). Individual differences in sociosexuality: Evidence for convergent and discriminant validity. Journal of Personality and Social Psychology, 60, 870–883.
Simpson, J. A., Wilson, C. L., & Winterheld, H. A. (2004). Sociosexuality and romantic relationships. In J. H. Harvey, A. Wenzel, & S. Sprecher (Eds.), The handbook of sexuality in close relationships (pp. 87–112). Mahwah, NJ: Erlbaum.
Spitzberg, B. H. (1999). An analysis of empirical estimates of sexual aggression, victimization, and perpetration. Violence and Victims, 14, 241–260.
Sprecher, S., Sullivan, Q., & Hatfield, E. (1994). Mate selection preferences: Gender differences examined in a national sample. Journal of Personality and Social Psychology, 66(6), 1074–1080.
Sprecher, S., Barbee, A., & Schwartz, P. (1995). “Was it good for you, too?” Gender differences in first sexual intercourse experiences. Journal of Sex Research, 32, 3–15.
Sprecher, S. (2002). Sexual satisfaction in premarital relationships: Associations with satisfaction, love, commitment, and stability. Journal of Sex Research, 39, 190–196.
Tafoya, M. A., & Spitzberg, B. H. (2007). The dark side of infidelity: Its nature, prevalence, and communicative functions. In B. H. Spitzberg & W. R. Cupach (Eds.), The dark side of interpersonal communication (2nd ed., pp. 201–242). Mahwah, NJ: Erlbaum.
Thornhill, R. (2003). Major histocompatibility complex genes, symmetry, and body scent attractiveness in men and women. Behavioral Ecology, 14(5), 668-678.
Tooby, J., & Cosmides, L. (2015). The Theoretical Foundations of Evolutionary Psychology. The Handbook of Evolutionary Psychology, 1-85.
Trivers, R. L. (1972). Parental investment and sexual selection. In B. Campbell (Ed.), Sexual selection and the descent of man, 1871-1971 (pp. 136-179). Chicago: Aldine.
Widmer, E. D., Treas, J., & Newcomb, R. (1998). Attitudes toward nonmarital sex in 24 countries. Journal of Sex Research, 35, 349–358.
Zimbardo, P. G., & Coulombe, N. D. (2016). Man (dis)connected: how the digital age is changing young men forever. London: Rider Books.