Sexual peak: Socially shared cognitions about desire, frequency, and satisfaction in men and women

Transcription

1 Personal Relationships, 9 (2002), Printed in the United States of America. Copyright # 2002 ISSPR /02 Sexual peak: Socially shared cognitions about desire, frequency, and satisfaction in men and women ALICIA BARR, a ANGELA BRYAN, b AND DOUGLAS T. KENRICK c a South Plains College; b University of Colorado at Boulder; and c Arizona State University Abstract Is a man s sexual peak earlier than a woman s? Three studies were conducted to examine (a) whether the perception that men achieve their sexual peak at a younger age than do women is shared across individuals of different ages and sexes, (b) whether sexual peak is defined differently for men and women, and (c) whether differences between definitions contribute to differences in the age at which men and women are perceived to reach sexual peak. Study 1 suggested that participants believed that females reach their sexual peak at an older age than do males. Study 2 indicated that the defining feature of sexual peak for males was sexual desire and for females was sexual satisfaction. Study 3 suggested that predictions of male sexual peak coincided with participants predictions of male age of highest desire and frequency, but not satisfaction, and that female sexual peak coincided with participants predictions of female age of highest satisfaction but not frequency or desire. Discussion focuses on potential reasons for differences between the perception of male and female sexuality, as well as the social and evolutionary importance of each of the dimensions of sexuality for both males and females. One of the tragedies which appears in a number of marriages originates in the fact that the male may be most desirous of sexual contact in his early years, while the responses of the females are still underdeveloped and while she is still struggling to free herself from the acquired inhibitions which prevent her from participating freely in the marital activity. But over the years most females become less inhibited and develop an interest in sexual relations, which they may maintain until they are in their fifties or even sixties. But by then the responses of the average male may have dropped so considerably that his interest in coitus, and especially coitus with a wife who had previously objected to the frequencies of his requests, may have sharply declined. (Kinsey, Pomeroy, Martin, & Gebhard, 1953, pp ) The above quotation from Alfred Kinsey et al. embodies a pair of assumptions about male and female sexuality: that human beings experience a sexual peak at a predictable point during their lives and that the sexual peaks for men and women occur at different times during the Alicia Barr and Angela Bryan share credit for first authorship of this manuscript. The authors thank Charles Judd for his helpful comments on an earlier draft of this manuscript. Correspondence should be addressed to Alicia Barr, South Plains College, Reese Campus, 528 Gilbert Ave., Lubbock, TX 79416; abarr@spc.cc.tx.us. lifespan. Perhaps because the assumption of differential sexual peak is so much a part of the conventional wisdom, it has been the subject of surprisingly little careful analysis. Kinsey et al. s statement on the topic is not completely enlightening; it is inexact about when the sexual peak occurs in either sex. Because Kinsey et al. collected data on actual behaviors rather than desires, because the marital activity (i.e, intercourse) of one participant in a sexual coupling is necessarily constrained by that of the other, and because sexual activity encompasses far more than heterosexual intercourse 287

2 288 (e.g., masturbation), the data do not fully elucidate matters. An examination of Kinsey et al. s words reveals that (a) several different definitions of sexual peak are conflated and (b) different definitions are assigned to the two sexes. Note that young men are described as being desirous of sexual contact, whereas young women are described in terms of underdeveloped responses, acquired inhibitions, and limited participation. In discussing older people, Kinsey et al. described the responses of men as having dropped and the objections of women as having lessened. Thus, they described sexual behavior as multidimensional, and they applied the dimensions differently to males and females. If the same definitional criteria were used for both sexes, perhaps the apparent tragedy of different sexual peaks would disappear. Imagine, for example, that both men and women perceive the most satisfaction with their sex lives in their early 30s, but the most desire for sexual contact during their early 20s. If male peak is implicitly defined in terms of desire, and female peak in terms of satisfaction, then the two sexes will appear to have different peaks, even though they may be identical in their psychological and/or physiological responses across the lifespan. In this work, we examine several related questions about shared social cognitions regarding sexual peak. First, are there commonly shared perceptions about a differential sexual peak in men and women? Second, are those perceptions different among individuals who have actually passed through the socalled sexual peak? Third, is the sexual peak defined in different ways for women than for men? For example, is sexual peak in women commonly defined more in terms of satisfaction, and for men defined in terms of desire, as hinted in the quotation from Kinsey et al.? If so, does the difference disappear if one equates the definitions? The issue of a perceived sex difference in sexual peak might seem to be of little social significance. However, on a practical level, both the quality and quantity of sexual activity are important to the stability of a relationship. The data collected in Blumstein and Schwartz s (1983) study of sexual behavior among couples lead to the overwhelming conclusion that a good sex life is central to a good overall relationship (p. 201). Furthermore, miscommunication or incompatibility between the sexes with regard to sexual desires often appears as one of the primary causes of relational instability and divorce (Notarius & Markham, 1993). Since successful reproduction is at the core of evolution, it may be of theoretical significance that the two sexes are on a different life course with regard to sexual behavior (Geary, 2000; Kenrick & Luce, 2000). Before assuming there is a puzzle here, however, the first question is: Is there a phenomenon here to be explained? Overview of the research program To examine socially shared beliefs about sexual peak, we conducted a series of three studies. The first study included three samples of participants of different ages who were asked about their perceptions of the age at which men and women reach sexual peak. In the second study, half of the participants were asked to define sexual peak for women, and the other half were asked to define it for men. Those responses were coded into definitions emphasizing desire, satisfaction, or frequency of sexual activity, and spontaneously generated definitions for women versus men were compared. In the final study, participants were asked about the ages at which people of each sex reached their peaks of either desire, satisfaction, or frequency of sexual behavior. This approach was used to examine whether any perceptions of differences would remain when people were constrained to using the same definitional criteria for both sexes. Study 1 Method A. Barr, A. Bryan, and D. T. Kenrick Participants Participants in the first study were drawn from three different samples: Sample 1 participants included 60 members of the Psychology Department (graduate students and faculty) at Arizona State Uni-

3 Differential sexual peak 289 versity. Participants (63% women) ranged in age from 22 to 77 years (M = 34.6, SD = 14.8). Sample 2 participants included 54 undergraduate students enrolled in introductory psychology courses at Arizona State University. Study participation contributed to partial fullfillment of course requirements. Participants (77% women) ranged in age from 17 to 23 years (M = 18.6, SD = 1.1). Sample 3 participants included 73 acquaintances of undergraduate students enrolled in introductory psychology courses at Arizona State University. Students were instructed to ask an acquaintance over the age of 35 years to voluntarily complete a short questionnaire. Participants (54% women) ranged in age from 38 to 59 years (M = 46.9, SD = 4.9). Procedure Participants from Sample 1 received the anonymous survey in their office mailboxes. They were instructed to complete the survey, then place the form in the mailbox of one of the three authors. Participants from Sample 2 completed the survey in classrooms, in groups of 5 to 15. Again, the questionnaire was anonymous. Participants from Sample 3 were recruited by undergraduate students and asked to voluntarily complete the anonymous survey in private. Instructions on the survey asked these particpants to seal their completed surveys in an envelope provided by the student. Upon return of the sealed envelope, students received extra class credit. Materials The survey administered to Samples 1 and 3 included two demographic questions (age and gender) and the following two questions: At what age do you think a female experiences her sexual peak? And at what age do you think a male experiences his sexual peak? Participants were instructed to give a single age, rather than an age range. The order of the two questions was counterbalanced to control for order effects. Sample 2 participants completed questions identical to those administered to Samples 1 and 3 as part of a larger survey. Results of Study 1 A2 2 mixed ANOVAwas conducted on each sample. Perceived age at sexual peak for target sex (male, female) served as the withinsubjects factor, and participant sex (male, female) served as the between-subjects factor. Within each sample, the same main effect of target sex was found. Specifically, males were perceived to peak at an earlier age than females (Sample 1: F(1, 57) = 70.87, p <.001; Sample 2: F(1, 54) = 34.81, p <.001; Sample 3: F(1, 65) = , p <.001). See Table 1 for means and standard deviations for sexual peak by sample. There was no main effect of the participant s sex in Samples 1 or 2. In Sample 3, however, this effect was significant (F(1, 65) = 9.76, p <.01), with women predicting an older sexual peak for both male and female targets compared to men. Nevertheless, the interaction effect between participant sex and target sex was not signficant in any of the samples. Thus, although women in Sample 3 predicted higher ages for female and male sexual peaks relative to men, they still predicted that males reach their sexual peak at a significantly younger age than females. We were also interested in determining whether participant age affected perceptions of male and female sexual peak. To examine the effect of a continuous variable such as participant age, a regression analysis was necessary. For this analysis the data from the three samples were collapsed. Because we wanted to determine whether the perceived difference between female and male sexual peak is affected by the age of the participant, we created a criterion variable by subtracting the predicted age at sexual peak for males from that of females. Perceived difference in sexual peak was then regressed on participant age (centered), participant sex, and the interaction between the two (Aiken & West, 1991). Results indicated that participant sex was not a significant predictor of the difference between the perceived ages of males and females at sexual peak (b =.51, SE b = 1.18, ns). The main effect of participant age, however, was significant (b =.12, SE b =.05, p <.05), and this main effect was modified by a

4 290 A. Barr, A. Bryan, and D. T. Kenrick Table 1. Mean (and standard deviation) for predicted age of males and females at sexual peak Predicted age at sexual peak for Males Females Study 1 Sample 1 (faculty and graduate students) Male participants (n = 22) (4.26) (8.00) Female participants (n = 37) (3.39) (5.56) All participants (3.73) (6.51) Sample 2 (undergraduate students) Male participants (n = 12) (3.40) (6.05) Female participants (n = 42) (6.91) (6.99) All participants (6.25) (6.73) Sample 3 (adults over 38) Male participants (n = 34) (3.17) (5.98) Female participants (n = 39) (5.87) (6.29) All participants (4.97) (6.48) Study 2 (undergraduate students) Male participants a (4.12) (4.50) Female participants (4.12) (4.34) All participants (4.21) (4.35) Study 3 (adults over 40) Male participants (n = 22) (7.83) (7.22) Female participants (n = 35) (8.23) (7.93) All participants (8.01) (7.61) a Participants in Study 2 were asked about either the male or female sexual peak. There were 15 male participants who answered the question regarding male sexual peak, 15 male participants who answered the question regarding female sexual peak, 20 female participants who answered the question regarding male sexual peak, and 21 female participants who answered the question regarding female sexual peak. significant interaction between participant age and sex (b =.22, SE b =.08, p <.01). Exploration of this interaction indicated that older women participants 1 believed that the difference between female and male age at sexual peak was greater compared to their younger counterparts (b =.12, SE b =.05, p <.05). On the other hand, older men believed that the difference between female age at sexual peak and male age at sexual peak was smaller 1. To probe the effect of participant age on perceptions of male and female age at sexual peak, regression analyses were conducted at one standard deviation above the mean of age (approximately 49 years), and one standard deviation below the mean (approximately 20 years). See Aiken and West (1991) for further elaboration of this statistical procedure. compared to their younger counterparts. This trend for men was not significant however (b =.10, SE b =.06, ns). Finally, older men and women reported significantly different perceptions of the discrepancy between age of male and female sexual peak (b = 3.54, SE b = 1.51, p <.05). Older women believe that females reach their sexual peak approximately 10.5 years later than males, and older men believe that females reach their sexual peak about 7 years later than males (see Figure 1). No differences were found between men and women at the mean of participants ages or one standard deviation below the mean of participants ages. In summary, the older the woman, the larger she believed the discrepancy between male and female sexual peak to be, and the opposite was true for men. Although these

5 Differential sexual peak 291 Figure 1. Effect of participant age and participant sex on perceived difference between the male and female sexual peak, collapsing samples 1, 2, and 3 from Study 1 (total n = 187). results indicate that participant age affects perceptions of the male and female sexual peak, and does so differently for males and females, all participants reported that females reach their sexual peak later than males. Study 1 Discussion The results of Study 1 suggest that men and women of various ages share similar perceptions about the sexual peak of males and females specifically, that females experience their sexual peak later in life. What do observers sense about women in their late 20s and men in their early 20s that leads to this widely shared perception of differential sexual peaks? More important, are observers basing their conclusions about male and female sexual peak on the same behaviors? Intuitively, one might think that sexual peak reflects frequency of sexual behavior, but a sole focus on frequency might paint an incomplete picture; for example, one could desire sexual intercourse but have no willing partner. A focus on frequency would not, by itself, therefore yield an accurate characterization of the individual s sexual experience. Kinsey et al. s own discussion of sexual peak focuses mainly on sexual desire or lack thereof ( desirous of sexual contact, declined interest in coitus ). But knowledge about lifespan changes in frequency and desire would still not yield a complete picture. Imagine a couple, both of whom are highly libidinous, but who, because of inhibition or inexperience, are not completely satisfied with their sex lives. Certainly such limiting factors might well vary with age, and might well vary in ways that differentially affect sexual satisfaction for the two sexes. Given the various dimensions of sexuality, it is possible that definitions of male and female sexual peak are based on different aspects of sexual behavior. To determine whether sexual peak is defined differently for males and females, we conducted a second study in which participants were asked to define what they meant by sexual peak in either men or women. Study 2 Methods Participants Participants included 73 undergraduate students enrolled in a social psychology course at Arizona State University. Study participa-

6 292 tion was voluntary. Participants (58% women) ranged in age from 18 to 36 years (M = 22.7, sd = 3.7). Procedure and materials Particpants were asked to voluntarily complete the survey during the first five minutes of a social psychology class period. Again, the survey included two demographic questions, age and gender. Following these questions, participants were asked either At what age do you think a female experiences her sexual peak? or At what age do you think a male experiences his sexual peak? Participants were instructed to provide a specific age, rather than a range of ages. Participants were then asked, in an open-ended format, to define sexual peak for the gender of the target whose age at sexual peak they had just estimated. Coding scheme. Participants open-ended definitions were given a score on each of three dimensions of sexuality. These dimensions included (a) frequency of sexual activity, (b) desire for sexual activity, and (c) satisfaction with sexual activity. If the definition mentioned one of the above dimensions, the participant received a score of 1 for that dimension. If the definition did not mention one of the above dimensions, the participant received a score of 0 for that dimension. Thus, if a participant s definition read, The male sexual peak occurs when he most desires sex, the participant would receive a score of 1 for desire, and a score of 0 for frequency and satisfaction. Inter-rater reliability among three coders was calculated via percentage agreement (or agreement rate, AR), and was equal to.82. Results of Study 2 A 2 2 between-subjects ANOVA was conducted to test the effect of participant sex (male, female) and target sex (male, female) on predictions of age at sexual peak. Similar to Study 1, predicted age at sexual peak was not affected by participant sex (F(1, 67) = 1.82, ns), or by the interaction effect between participant sex and target sex (F(1, 67) < 1.00, ns). We replicated the main effect of A. Barr, A. Bryan, and D. T. Kenrick target sex obtained in Study 1, such that females were perceived to reach their sexual peak at an older age (M = 29.28) compared to males (M = 20.60) (F(1, 67) = 69.74, p <.001; see Table 1). To determine whether sexual peak is defined differently for males and females, chi-square analyses were conducted. These analyses indicated that (a) frequency of sexual intercourse was equally likely to be used in participants definitions of male and female sexual peak ( 2 (1) < 1.00, ns), (b) desire for sexual activity was more likely to be used to define male sexual peak ( 2 (1) = 7.98, p <.01), and (c) high satisfaction with sexual activity was more likely to be used to define female sexual peak ( 2 (1) = 9.29, p <.01). Study 2 Discussion In Study 2 we investigated the possibility that people use different definitions of sexual peak for males and females. The evidence suggests that participants did indeed define female sexual peak differently from male sexual peak. Definitions of female sexual peak were more likely to include concepts related to sexual satisfaction, whereas definitions of male sexual peak were more likely to focus on sexual desire. In fact, although participants were virtually equally likely to define sexual peak for women as either desire or satisfaction, the male sexual peak was almost exclusively defined in terms of sexual desire. There are a number of explanations for this finding. If we loosely define sexual satisfaction as orgasm during sexual activity (Laumann, Gagnon, Michael, & Michaels, 1994), it could be that males sexual satisfaction does not vary much across the lifespan. Data on actual sexual behavior indicate that, though males achieve orgasm virtually every time they have intercourse regardless of age, women have orgasms less frequently (Laumann et al., 1994), and the rate of female orgasm may vary considerably due to age and relationship status (Kinsey et al., 1953). Interestingly, frequency of sexual activity was not often cited as the definition of sexual peak for either males or females.

7 Differential sexual peak 293 Study 3 To determine whether the different definitions of male and female sexual peak used by these participants might have contributed to the differences in perceived age at sexual peak, we conducted one final study. In Study 3, we asked participants about the age at which they believed males and females experienced their highest sexual desire, satisfaction, and frequency. We hypothesized that, if male sexual peak is defined in terms of sexual desire and female sexual peak in terms of satisfaction, the age at which they are believed to experience peaks in these dimensions of sexuality should coincide with the age at which they are believed to experience their sexual peaks. Furthermore, if the differences in the perceived ages of men and women at their sexual peaks are due to different interpretations of sexual peak, then constraining comparisons of male and female targets to a single dimension of sexuality might diminish or erase perceived age differences between the sexes. Methods Participants Undergraduate students enrolled in a social psychology course at Arizona State University were instructed to recruit study participants over the age of 35 years for extra class credit. The 57 participants (61% women) ranged in age from 40 to 62 years (M = 46.3, SD = 4.5). Procedure and materials Participants were asked to voluntarily complete the survey in private, then seal the survey in an envelope provided by the researcher. Again, the survey included two demographic questions, age and gender. Participants were asked the following questions for both male and females targets: At what age do you think a male/female experiences his/her sexual peak, At what age do you think a male/female experiences his/her highest frequency of sexual activity, At what age do you think a male/ female experiences his/her highest rate of sexual satisfaction, and At what age do you think a male/female experiences his/her highest rate of sexual desire? The questions regarding age at sexual peak appeared on the first page, and the remaining questions appeared on the second page and were counterbalanced to diminish any potential order effects. For all questions, participants were instructed to provide a specific age, rather than a range of ages. Results of Study 3 Four 2 2 mixed-factor ANOVAs were conducted with participant sex (male or female) as the between-subjects factor and target sex (male or female) as the within-subjects factor. The first ANOVA used age at sexual peak as the dependent variable. As in Studies 1 and 2, females were believed to reach sexual peak at a later age than males (F(1, 55) = 38.34, p <.001; see Table 1), and there was no effect of participant sex. The second, third, and fourth ANOVAs used age at highest frequency of sexual activity, age at highest rate of sexual satisfaction, and age at highest rate of sexual desire as the dependent variables. Results from each of these ANOVAs indicated that participants believed that females experience their highest frequency of sexual activity, highest sexual satisfaction, and highest sexual desire at an older age than do males (F (1, 56) = 10.43, p <.002; F (1, 54) = 14.10, p <.001; F (1, 56) = 19.11, p <.001, respectively). Means for all four ANOVAs are shown in Figure 2. To determine whether predicted age on any of the dimensions of sexuality coincided with predicted age at sexual peak, we conducted two repeated-measures ANOVAs, one for male targets and one for female targets. The first repeated-measures ANOVA used participants reports of male age at sexual peak, highest sexual desire, highest sexual satisfaction, and highest sexual frequency as the repeated measures. Results showed a significant difference among the predicted ages at sexual peak and the dimensions of sexuality, F (3, 162) = 7.54, p <.001. Post hoc pairwise comparisons were conducted to determine whether predicted male age at sexual peak was significantly different from predicted male age at the peak in each dimension of

8 294 A. Barr, A. Bryan, and D. T. Kenrick Figure 2. Predicted age at sexual peak overall and for each dimension of sexuality from Study 3 (n = 57). sexuality. 2 These analyses indicated that participants did not think male age at sexual peak was different from male age at highest desire (F(1, 54) = 2.51, ns) or male age at highest frequency (F(1, 54) < 1.00, ns). Participants did report significantly different ages for male sexual peak and male peak in sexual satisfaction (F(1, 54) = 7.14, p <.01). The second repeated-measures ANOVA used participants reports of female age at sexual peak, highest sexual desire, highest sexual satisfaction, and highest sexual frequency as the repeated measures. Results indicated that there was a significant difference among the predicted ages at sexual peak and the dimensions of sexuality, F (3, 165) = 14.10, p <.001. Again, post hoc pairwise comparisons suggested that participants did not think that 2. Because the pairwise comparisons were post hoc in nature, Dunnett s alpha-inflation correction for pairwise tests was used for each of the comparison analyses. For the comparison between age at male sexual peak and age at male peak in sexual satisfaction, Dunnett s criterion F-value was equal to 5.95 at p <.05. For the comparison between age at female sexual peak and age at female peak in sexual desire and frequency, Dunnett s criterion F-value was equal to 9.55 at p <.01. female age at sexual peak was different from female age at peak in sexual satisfaction, F(1, 55) < 1.00, ns. However, participants reported significantly different ages between female sexual peak and female peak in both sexual desire, F(1, 55) = 15.99, p <.01, and sexual frequency, F(1, 55) = 17.55, p <.013. General Discussion In our final study, we showed that participants beliefs regarding female sexual peak coincided with their beliefs regarding the age at which females reach their peak in sexual satisfaction, but not with their beliefs regarding the age at which females reach their peak in sexual frequency or desire. On the other hand, participants beliefs regarding male sexual peak coincided with their beliefs regarding the age at which males reach their peak in sexual frequency and desire, but not with their beliefs regarding the age at which males reach their peak in sexual satisfaction. Across five samples, men and women of different ages converged on the belief that males experience their sexual peak earlier than females. Some of the discrepancy in this perception was perhaps due to participants use of different definitions

9 Differential sexual peak 295 for male and female sexual peak. That is, male sexual peak is more likely to be defined as a high sexual desire relative to female sexual peak, and female sexual peak is more likely to be defined as high sexual satisfaction relative to male sexual peak. Yet, even when participants comparisons were constrained to the same dimension of sexuality (i.e., desire, satisfaction, or frequency), men were always expected to experience a peak before women. Constraining participants comparisons to the same dimension of sexuality did not erase perceived differences between the sexes, but there is some evidence that definitional differences do affect the perception of a sex difference in sexual peak. Specifically, if participants think of male sexual peak as his highest level of desire and female sexual peak as her highest level of satisfaction, the differences between male and female sexual peak may be exaggerated. For instance, Study 3 participants believed that a male s highest sexual desire (the dimension apparently central to male sexual peak in our participants minds) occurred at about age 22 years, and a female s highest sexual satisfaction (the dimension more closely connected to female sexual peak) occurred at about age 32 years a 10-year difference. When participants were constrained to a single dimension of sexuality, however, the largest perceived age difference between the sexes was approximately 5.5 years (for sexual desire). The consistent differences in perceptions of male and female sexual peak may well affect the way sexual partners relate to one another. These perceptions or stereotypes of male and female sexual behavior may lead to expectations regarding one s sexual partner. For instance, men might expect women in their 30s to be more desirous and more easily satisfied than women in their 20s and 40s. Likewise, the female partners of men in their 20s might expect these men to initiate most or all of the couples sexual contact. When expectations such as these are not realized, men and women might become disappointed in their relationships or concerned about their attractiveness and abilities as a sexual partner. Thus far we have concentrated only on the perception of a gender difference in sexual peak. Our data support the conclusion that men are perceived to reach their sexual peak earlier than women. This perception seems to be little influenced by the perceiver s age or gender, but is somewhat related to different definitions used for sexual peak for the two sexes. These shared perceptions of a differential sexual peak are interesting in themselves, but lead to the obvious question of what, if anything, they have to do with actual sexual behavior. We turn now to a discussion of what is known about actual gender differences in sexual development across the lifespan, and examine the possibile etiology of these differences. Is the differential sexual peak a behavioral reality? A review of the extant literature on sexuality and aging suggests that this reality of a differential sexual peak is difficult to measure. Most research on sexuality over the lifespan reports a summary or descriptive statistic that describes a trend (e.g., a negative correlation between sexual frequency and age; Hawton, Gath, & Day, 1994; Mulligan & Moss, 1991), but ignores details such as where a peak in sexuality might occur. Other researchers have grouped their participants into such large age categories that important age-related changes may be obscured. For example, a survey by Hunt (1974) grouped participants into age categories spanning 6 to 10 years, and showed simply a decline in marital coital frequency with increasing age. There are a few studies in which a discernable peak in sexual behavior is reported, however. For instance, Kinsey et al. s (1948, 1953) data on male and female orgasm charted responses for men and women up through age 50 years. Kinsey et al. asked participants whether they had ever experienced an orgasm, and, as noted earlier, orgasm might reflect one s sexual (physiological) satisfaction (Laumann et al., 1994). The results indicated that by their late teenage years more than 95% of men had experienced an orgasm and only 20% of women of the same age had experienced an orgasm. The women appear to peak on this measure of satisfaction around age 35 years when roughly 90% indicated that they had experienced an orgasm. These values do appear

10 296 to coincide with our participants perception of male and female satisfaction. Other possible support for this peak in sexual satisfaction among females in their 30s also comes from Hunt who found that 88% of women in the under-25-years age group in his sample reported marital coitus to be either mostly pleasurable or very pleasurable. The percentage increased to 93% in the years age group, dipped slightly to 91% for the years age group, then dropped to 83% for the over-55-years age group (Hunt, 1974, p. 215). Gagnon (1977) reported on the frequency of sexual intercourse for males and females from the ages of early 20s through mid 50s. He found that both males and females between the ages of 25 and 29 years report engaging in sexual intercourse more frequently than any other age group. Laumann et al. (1994) also reported this same peak of sexual frequency. Interestingly, this is the dimension of sexuality that our participants were least likely to use to define sexual peak. But when forced to predict peak frequency for males and females, our participants still indicated an older age for females, which according to behavioral data, may not accurately reflect reality. Research concerning sexual desire seems to be the most sparse. One possible indirect index of the desire for sexual stimulation, unconfounded by the need to find a willing partner, is masturbation frequency. Gagnon (1977) presented masturbation frequency data for men and women, ages 24 to 53 years. By this admittedly imperfect criterion, males are most desirous of sexual stimulation from ages 24 to 29 years, and women from ages 34 to 39 years. In sum, existing data sources suggest that although rates of heterosexual intercourse are almost necessarily the same for the two sexes, women begin experiencing orgasm, and reach a peak of masturbatory activity, later in their lives. What are the roots of possible gender differences in peak sexual desire and satisfaction? Questions about the roots of gender differences in peak desire and satisfaction are A. Barr, A. Bryan, and D. T. Kenrick interesting at two levels. At the proximate level, we can ask what specific environmental and intrapersonal factors might account for these differences. At the ultimate level, we can ask (a) What reproductive advantage, if any, would ancestral females have gained from a late peak in sexual satisfaction?, and (b) What reproductive advantage, if any, would ancestral males have gained from an early peak in sexual desire? Regarding proximate causes, a number of possibilities exist. One obvious set of environmental candidates are the behaviors of the opposite sex. Sexual desire in men occurs at an age earlier than the peak of men s desirability to women. Around the world, women are interested in slightly older men, arguably because these men have had time to establish themselves in terms of resources and social status (Buss et al., 1990). Teenage men, by contrast, are significantly less attractive to women as romantic partners (Kenrick, Gabrielidis, Keefe, & Cornelius, 1996; Kenrick & Keefe, 1992). Thus, men s peak of desire precedes the age at which women find them most attractive. On the other hand, women in their 20s and early 30s are highly attractive to men of all ages, including teenage men (Kenrick & Keefe, 1992; Kenrick et al., 1996). This unrequited desire that young men have for women in their 20s and early 30s may make these women seem even more attractive and these young men even more desirous. Because potential sexual opportunities are fewer and less frequent for young men than for young women, the young male s high level of motivation increases the likelihood that those opportunities will not be missed. One possible explanation for the female delay in peak satisfaction is that it may take several years for males to learn how to please a partner, or for a women to feel comfortable enough to achieve orgasm. Given Kinsey et al. s data that 75% of men ejaculate in less than two minutes, and given the relationship between male age and ejaculation latency, it may certainly be the case that older males are more likely to continue intercourse for sufficient time for the female to achieve orgasm. Along the same lines, since females often

11 Differential sexual peak 297 orgasm from manual or oral stimulation (Blumstein & Schwartz, 1983), older males may be more likely to learn techniques of lovemaking that are satisfying to their partners. Furthermore, older women, like older men, are more experienced lovemakers, which may also contribute to sexual satisfaction among women. Older women may feel more comfortable with their sexuality and be more willing to communicate with their partners regarding their preferences. In searching for a possible ultimate explanation for these differences, there are some data on male and female sexual behavior which are consistent with the notion that high sexual desire among young men and high sexual satisfaction among older women could have been reproductively advantageous during our evolutionary past, and therefore selected for and passed on to later generations. For instance, males are, in general, more desirous of, and less discriminating about, sexual contact than are females. In a study by Clark and Hatfield (1989), more than 70% of college men approached by a strange female on campus expressed a willingness to go to bed with her, whereas none of the college women accepted a similar offer from a male college student. Likewise, college men reported much lower standards for sexual partners, and a desire for more sexual partners, than did women (Buss & Schmitt, 1993; Kenrick, Groth, Trost, & Sadalla, 1993; Kenrick, Sadalla, Groth, & Trost, 1990; Regan, 1998; Simpson & Gangestad, 1991). Indeed, across vertebrate species, males more often compete for sexual partners, and females more often mate very selectively (Daly & Wilson, 1983; Gould & Gould, 1989; Trivers, 1972). Evolutionary biologists have linked this difference to an inherent difference in parental investment (Trivers, 1972). In the majority of mammalian species, minimum female investment (extended periods of internal gestation and lactation) is higher than minimum male investment (copulation). But humans are actually somewhat unusual among mammals in that males do contribute substantially to the offspring (Geary, 2000). This suggests that both sexes will be somewhat selective in choosing partners. But since males and females contribute different resources, they will be selective about different things. Females, as noted above, may choose males based on either evidence of good genes or on their ability to provide resources (Gangestad & Simpson, 2000, Gangestad & Thornhill, 1997; Kenrick et al., 1993), whereas males are more likely to choose females based on cues associated with fertility, such as physical attractiveness, and youthful sexual maturity (Cunningham et al., 1997; Kenrick & Keefe, 1992). Thus, research adopting an evolutionary perspective on human mating predicts that men will maximally value, and compete for, women at the peak of fertility (highest during their 20s), whereas women will maximally value men who have had sufficient time to establish themselves as resource providers. Such reasoning could provide some hints about the ultimate roots of the sex difference in sexual desire. Young women have very little need for high levels of desire because they are in high demand, and it is in their interest to be as discriminating as possible. Young men are not yet highly desirable, hence they might profit from a high level of motivation. Indeed, male testosterone levels, linked both to success-striving and to sexual desire (Dabbs & Morris, 1990; Mazur & Booth, 1998), peak during their early 20s (Dabbs, 1990). Another way to think about the ultimate causes of the late peak in sexual satisfaction among females is to focus on the possible reproductive function of orgasm in females. Recent research (Baker & Bellis, 1993) indicates that during sexual intercourse, the muscle contractions from female orgasm, as long as they occur between 1 minute before and 45 minutes after the male ejaculates, cause the cervix to dip down into the pool of sperm that has accumulated in the female s vagina. This bathing of the cervix in sperm aids the progression of the sperm to any egg awaiting fertilization. There is some evidence that this function is associated with selective sperm competition, favoring sperm of higher genetic quality (e.g., Shackelford, Weekes- Shackelford, LeBlanc, Bleske, Euler, & Hoier, 2000; Thornhill, Gangestad, & Comer, 1995).

12 298 Perhaps another plausible function among older women is to increase fertility more generally. If female orgasm can enhance sperm uptake during intercourse, a female may unconsciously battle her decreased fertility via higher rates of orgasm. Although the notion of unconscious control over such physiological processes seems hard to imagine, there is increasing evidence that women may indeed exert unconscious control over their orgasms during specific situations in which it might be more advantageous to conceive (Baker & Bellis, 1993; Bellis & Baker, 1990). Singh, Meyer, Zambarano, and Hurlbert (1998) showed that women who desired to conceive were more likely to orgasm after their partner than women who did not desire to conceive, further supporting the link between orgasm and an unconscious or even conscious desire to increase fertility. Limitations and future directions There are some obvious limitations to our data. First, we report only perceptions of sexual peak, not actual behavioral data. In order to fully answer the questions we have posed, we would need a longitudinal cohort study assessing frequency of sexual intercourse and levels of sexual desire and satisfaction across the adult lifespan. To our knowledge, no such study exists. A second problem is that our data are exclusively from the United States, and thus could simply be a shared western cultural stereotype. It would be useful to conduct cross-cultural studies of both perceptions of sexual peak and actual behavior. We attempted to sample a wide range of ages to ensure that some of our participants would have already moved through the ages at which sexual peak is thought to occur. Further, the fact that we replicated our effect in five separate samples suggests that our conclusions about sex differences are quite reliable. Nevertheless, we utilized convenience samples, and larger, more representative samples should be sought in future work. Finally, the methods we used to uncover participants definitions of sexual peak highlight the fact that the concept of sexual peak is not very concrete, and may differ depending A. Barr, A. Bryan, and D. T. Kenrick on whether we are thinking of male or female sexual behavior. An examination of the measurement and latent structure of the sexual peak construct using techniques such as factor analysis might further elucidate how people think of male and female sexuality across the lifespan. Our assertion about the functionality of orgasm in older women also suggests future lines of research. For example, since the timing of orgasm is crucial in terms of increasing fertility, it would make sense to ask both older women and younger women about their frequency of coital orgasm as well as the timing of coital orgasm when it occurs. There may also be important individual differences apart from gender that influence perceptions of sexual peak that we did not assess. Cultural mores, race/ethnicity, and sexual orientation are all likely to influence judgments of gender differences in sexual peak. A potentially important future direction would be to examine how beliefs regarding age-related changes in male and female sexuality affect people s expectations of and satisfaction with their sexual partners. Conclusions This research suggests that Kinsey et al. s perception of a tragic difference in the age of sexual peak is widely shared, even by those who have lived through the years of sexual peak and the years of relative sexual liberalization in this country. Although Kinsey et al. s use of shifting definitions in referring to male versus female sexual peak may not have been intentional, it was intuitively correct. Male sexual peak is defined almost solely in terms of sexual desire, whereas sexual satisfaction is given relatively more weight in shared definitions of female peak than of male peak. When respondents are constrained to common definitions, the relative difference between men and women narrows, but does not disappear. Although sex differences in sexual peak may seem, at first, to be a somewhat trivial topic, its examination raises deeper theoretical questions, linked to the evolution of differential mating strategies in our male and female ancestors.

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