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HerzCahill.1997.Olfactory(2)

HerzCahill.1997.Olfactory(2) - DIFFERENTIAL USE OF SENSORY...

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Unformatted text preview: DIFFERENTIAL USE OF SENSORY INFORMATION IN SEXUAL BEHAVIOR AS A FUNCTION OF GENDER Rachel S. Herz and Elizabeth D. Cahill Monell Chemical Senses Center Olfactory information is critical to mammalian sexual behavior. Based on parental investment theory the relative importance of olfaction compared with vision, touch, and hearing should be different for human males and females. In particular, because of its link to immunological profile and offspring viability, odor should be a more important determinant of sexu- al choice and arousal for females than for males. To test this hypothesis a questionnaire was developed and administered to 332 adults (166 males, 166 females). Subjects used a 1-7 scale to indicate how much they agreed with a series of statements concerning the importance of olfactory, visual, auditory, and tactile information for their sexual responsivity. The data reveal that males rated visual and olfactory information as being equally important for selecting a lover, while females considered olfactory infor- mation to be the single most important variable in mate choice. Addi- tionally, when considering sexual activity, females singled out body odor from all other sensory experiences as most able to negatively affect de- sire, while males regarded odors as much more neutral stimuli for sexual arousal. The present results support recent findings in mice and humans concerning the relation of female preferences in body odor and major histocompatibility complex (MHC) compatibility and can be explained by an evolutionary analysis of sex differences in reproductive strategies. This work represents the first direct examination of the role of different forms of sensory information in human sexual behavior. may wonos: Evolutionary principles; Gender differences; Odor; Sensory information; Sexual behavior. Received: January 27, 1997; accepted: March 15, 1997. Address all correspondence to Rachel S. Herz, Monell Chemical Senses Center, 3500 Market 51., Philadelphia, PA 19104. E—mail: [email protected] Copyright © 1997 by Walter de Gruyter, lnc., New York Human Nature, Vol. 8, No. 3, pp. 275-286. 1045-6767/97/51.w+.10 275 276 Human Nature, Vol. 8, No. 3, 1997 Gender differences in human reproductive strategies are typically char- acterized by males having more sexual partners, and being less moti- vated by commitment and more motivated by physical attractiveness, than females (see Buss and Schmitt 1993 for review). In humans, as in most mammals, females invest more than males do in reproduction and offspring survival (Trivers 1972). Females are also always certain of ma- ternity. By contrast, the cost of reproduction for males is low and pater- nity is never certain. According to sexual selection theory (Darwin 1871; Trivers 1972), then, males should mate with as many fertile females as possible, while females should choose mates who are most likely to secure offspring survival. Buss and Schmitt (1993), among others, have proposed that the eval- uation of female fertility is most simply assessed on the basis of physical indications of youth and health (e.g., full lips, clear and smooth skin, clear eyes, high activity level). Importantly, these signs of physical at- tractiveness are determinable on the basis of visual inspection. That is, male mate-search strategies are predominately based on the evaluation of biological cues to fitness, with visual information being the most important sensory variable for choice and interest. Females, on the other hand, have been characterized as primarily concerned with evaluating males’ behavioral displays of commitment and contribution of resources towards herself and her potential offspring (Buss and Schmitt 1993; Greenlees and McGrew 1994; Landolt et al. 1995). That is, female mate- search strategies have traditionally been described as primarily based on the evaluation of nonbiological cues to a male’s paternal potential. A notable omission in current writing on sex differences in reproduc- tive strategies is the evaluation of biological characteristics of male mates by females. Indeed, in keeping with an evolutionary analysis of mate selection parameters, parental investment theory (Trivers 1972) predicts that females should be more concerned than males about physiologically adaptive mating because females invest more in their offspring than do males. Physiologically adaptive mating entails genetic compatibility be- tween a specific mating couple such that allele combinations in offspring will maximize disease protection from invading micro-organisms, and minimize deleterious recessive mutations. It therefore follows that fe- males should be most sensitive to biological cues that are indicative of a male’s immunological genotype. Products of the MHC (major histocompatibility complex) play an im- portant role in immune recognition (Hedrick 1994; Klein 1986). Several studies have shown that MHC identity influences mate choice in mice (Egid and Brown 1989; Potts et al. 1991; Yamazaki et al. 1976). Mice who are genetically identical except for minor variations in MHC loci will preferentially select mates who are dissimilar at these same loci. Impor- tantly, the basis for this discrimination has been shown to be entirely Sensory Information and Sexual Behavior 277 based on the odor-type of the mice (Boyse et al. 1987; Egid and Brown 1989; Yamazaki et al. 1979), and it is the female mouse who makes these odor-based selections (Eklund et al. 1992). Recent research has shown that human MHC type is an important variable in human female mate choice, and that as with rodents, it is demonstrated in response to body odor. Wedekind and colleagues (1995) typed female and male students for their human leukocyte antigens (:A, -B, and -DR), which correspond to the mouse MHC. Each male subject then wore a T—shirt for two consecutive nights, after which the shirts were collected and placed in identical cardboard boxes for the female subjects to sniff and evaluate. For each female, half of the boxes con- tained T-shirts from men who were similar to her in MHC-type, and half contained T-shirts from men who were dissimilar. The results revealed that females preferred the smell of males who were most dissimilar from them in MHC—type, indicating that female preferences for male body odor correlate with MHC complementarity. Data from fertility clinics has also shown that MHC similarities between couples are associated With a greater likelihood of infertility and spontaneous abortions (Ho et al. 1990; Koyama et al. 1991; Thomas et al. 1985; Weckstem et al. 1991): Thus MHC complementarity, as detected by body odor, has direct bearing on human reproductive fitness. Despite its obvious importance, the concept of female mate-search ‘ strategies based on the evaluation of biological/sensory cues has been overlooked in the psychological literature on human mate chorce. The primary purpose of the present research was thus to examine the use of various types of sensory information in mate selection and sexualhrnter— est among males and females. Based on the revrewed literature, it was hypothesized that olfactory stimuli would be relatively more important for female mate choice and sexual interest than for male mate chorce and sexual interest. To evaluate this hypothesis, a questionnaire was devel- oped which examined the importance of tactile, visual, olfactoryaa-nd auditory qualities in evaluating potential sexual partners and in elrcrtmg sexual arousal. METHOD Materials To assess how different types of sensory information are used by males and females for evaluating sexual partners and inducrng sexual arousal, a questionnaire entitled the Sensory Stirnuli and. Sexuality Survey was developed (see Appendix). The questionnaire consrsted of 18 scalar questions grouped under three topics: lover/potential lover chorce, sex- r-r n~.:.w""‘ 278 Human Nature, Vol. 8, No. 3, 1997 ual arousal during sexual activity, and sexual arousal during nonsexual activity. The questions under each topic assessed the subjective impor- tance of the sensory characteristics of sight, hearing, touch, and smell to subjects’ behavior regarding the topic in question. Subjects used a 1—7 likert scale (1 = strongly disagree and 7 = strongly agree) to indicate their responses. General information regarding age, race, and education level were also obtained from all subjects. Subjects The questionnaire was administered to 332 college students (166 fe— males, 166 males) solicited from the University of Pennsylvania and Drexel University. The average age of subjects was 19.75 years. Students were approached by a female experimenter at various campus locations (bookstore, class, library, and indoor and outdoor gathering places) and asked if they would be willing to complete a short survey. Upon comple- tion of the survey subjects were thanked for their participation. RESULTS To examine the overall response levels of males and females, all of the ratings were first analyzed by gender. For each item topic it was found that males used higher numeric ratings than did females, indicating that they rated themselves as more strongly agreeing with each of the state- ments than did females. This effect may be due to greater conservatism in sexual attitudes among females (Hendrick et a1. 1985; Sprecher 1989). Nevertheless, because these gender differences were found it was con- sidered statistically necessary to analyze the data from males and fe- males independently. One—way ANOVA tests on the various sensory stimuli within each topic (lover choice, arousal during sexual activity, arousal during nonsexual activity) were conducted separately on the male and female data. The mean responses (’5 s.e.) given by males and females for each question are shown in Table 1. Where significant effects were obtained, Newman-Keuls (p < 0.05) post hoc comparisons were performed. Lover choice. A significant main effect was found for both males and females: F (3, 495) = 47.47; F (3, 485) = 44.95, respectively. Post hoc comparisons indicate that for males, when selecting a lover, looks and smells are equally important, while for females, how someone smells is the single most important variable in mate choice; in fact, smell is signifi— cantly more importantthan how someone looks, feels, or sounds. More- over, for females, the sound of someone’s voice and how their skin Sensory Information and Sexual Behavior 279 Table 1. Mean Ratings for the Importance of Various Sensory Experiences in Sexual Partners’ Interest and Arousal Males s.e. Females s.e. _____________.______—._—-—— Lover Choice Sight 5.79 0.083 5.15 0.080 Sound 4.93 0.083 4.48 0.116 Smell 5.79 0.079 5.58 0.089 Feel 5.27 0.104 4.63 0.108 Arousal during Sexual Activity Sight 6.33 0.069 5.26 0.115 Imagine 5.36 0.120 4.73 0.135 Sexual Sounds 5.68 0.105 4.67 0.159 Music 4.40 0.094 4.99 0.130 Body Smells 4.95 0.121 4.41 0.142 Non-Body Smells 4.93 0.118 4.78 0.139 Touch/Feel 6.12 0.088 6.00 0.104 Arousal during Nonsexual Activity Sight 5.53 0.106 4.59 0.124 Imagine 5.60 0.098 4.75 0.128 Sexual Sounds 4.52 0.124 3.55 0.135 Music 3.64 0.128 4.43 0.132 Body Smells 3.88 0.121 3.62 0.128 Non—Body Smells 4.13 0.114 4.10 0.136 Touch/Feel 4.41 0.138 4.53 0.146 _____,_____.___———-—————--—-—'—— feels did not differ in importance, while for males, the feel of skin was more important than the sound of a voice. During sexual activity. The first question under this topic asked wheth— er subjects had previous sexual experience, and if not then respondents were told to skip to the next item topic (question 13). Twenty-six females (15.7%) and fifteen males (9%) answered negatively. Therefore the num- ber of males and females who responded to the questions under this topic differed. A significant main effect was obtained for both males and females: F (6, 900) = 48.47; F (6, 828) = 22.70, respectively. Post hoc comparisons indicate that what males see and what they feel/touch are most arousing during sex, and there was no statistical difference be- tween these means. MaIes rated human sexual sounds to be the next most arousing sensory experience, followed by what they could imag- ine, which in turn was more arousing than olfactory experience. Fra- grances and body odors were moderately arousing for men, and there was no statistical difference between the ratings given to these two types of olfactory experience. Music was the least arousing sensory experience for males in the context of sex. Females rated what they feel/touch to be the most arousing stimulus during sexual activity, followed by what 280 Human Nature, Vol. 8, N0. 3, 1997 they can see. The mean ratings given to these two experiences were significantly different. Following visual stimuli, the next most arousing experiences were music, sexual sounds, non-body smells, and imagined scenarios, which all affected female arousal equally. Notably, females rated fragrances (non-body smells) to be significantly more arousing than body smells. Indeed females rated body smells as the least arousing sensory experience during sexual activity, and significantly more nega- tive than any of the other sensory experiences. When not engaged in sexual activity. A significant main effect for both males and females was obtained: P (6, 978) = 62.28 and F (6, 954) = 22.30, respectively. Post hoc comparisons indicate that for males and females visual experience, both imagined and real, was most arousing. Next most arousing for males were hearing human sexual sounds and tactile stimuli. These two means did not differ from each other. Olfactory stimuli were not especially arousing to males out of the context of sex, and fragrances and body odors did not differ in this regard. Males rated music to be the least arousing of all the sensory experiences assessed. For females, following visualexperience, the next most arousing stimuli were touch and music. These two means did not differ from each other. Non-body smells were significantly more arousing than body smells to females, and hearing human sexual sounds was the least arousing sen- sory experience. DISCUSSION The Sensory Stimuli and Sexuality Survey revealed that males rated visual and olfactory information as being equally important for selecting a lover, while females considered olfactory information to be the single most important variable in mate choice. Additionally, when considering sexual activity, females singled out body odor from all other sensory experiences as most able to affect desire negatively, while males re- garded odors as much more neutral stimuli for sexual arousal and were most aroused by visual and tactile experience. These results support the hypothesis that olfactory information is relatively more important for female mate choice and sexual arousal than for male mate choice and sexual arousal. Vision and olfaction do not have the same functional significance for the behaviors involved in human reproduction. We have equated olfac- tory information as relevant to offspring viability, and visual information as relevant to fertility. There are also physical range differences in the information that can be conveyed by vision versus olfaction. Vision provides distal information to attract males and females to each other over some physical distance (e. g., across a crowded room), while olfac- Sensory Information and Sexual Behavior 281 tion provides proximal information for screening against incompatible mating partners when in close physical range. The consequences of relying on visual relative to olfactory information for mate selection are predicted to be different for males and females owing to the different costs and limitations of reproduction for each sex (Trivers 1972). Accord- ingly, sex differences in the importance of olfaction versus vision in sexual behavior are expected. The data reported here support this proposition. Our survey results show that female sexual interest is more affected by body odor than any other sensory stimulus. Earlier research has shown that human female olfactory acuity varies with menstrual cycle phase, with highest sensitivity shown at ovulation and lowest during menstruation (Doty et al. 1981). The coincidence of ovulation with olfac- tory peak acuity is further indirect evidence for the importance of olfac- tion in human female sexual behavior. Our data also reveal that males are interested in olfactory information about females during mate choice. This finding suggests that males are also invested in offspring viability. Notably, the present study did not contrast biological/sensory characteristics with resource status and commitment potential. Thus, it is not known whether or how sensory variables outweigh behavioral variables in mate selection for females in contrast to males. The Sensory Stimuli and Sexuality Survey showed that during the context of sexual activity, males considered visual and tactile stimuli to be most arousing, but that females were more aroused by tactile stimuli than any other sensory experience. When not engaged in sexual activity, both men and women were most aroused by actual or imagined visual stimuli. Aspects of these results are both consistent with and divergent from previous literature. Research on sexual arousal in women has re- ported that women are typically most aroused by tactile stimulation during sexual activity (Ellis and Symons 1990; Faust 1980; Symons 1979), and that males are most affected by visual cues (Buss 1987, 1994; Ellis and Symons 1990; Feingold 1990, 1992; Greenlees and McGrew 1994; Landolt et al. 1995). The present results show that men are strongly affected by tactile stimuli as well, and that when not already sexually engaged, women and men become most aroused by visualizable stimuli. A differentiation between men and women in arousal produced by arti- ficial odors versus body odors, and music versUs human sexual sounds, was also revealed by the data. Women were less aroused by body odors and human sexual sounds both in and out of the context of sex than by fragrances and music. By contrast, males rated body odors and fra- grances equally and rather neutrally. Additionally, males could be quite aroused by human sexual sounds both in and out of the context of sex, but not by music. One way to conceptualize these findings is that fe- males prefer auditory and olfactory stimuli that are not directly sexual, 282 Human Nature, Vol. 8, No. 3, 1997 whereas males are more aroused by explicitly sexually associated stimu- li. Other research has reported that males have more explicit sexual fantasies than do females (e.g., Hardin and Gold 1989). The present findings might also reflect gender differences in sexual conservatism (Hendrick et al. 1985; Sprecher 1989). Sex differences in social/grooming behavior regarding the use of fra- grances are consistent with the finding that females are more aroused by fragrances than by natural body odors. Females are far more likely to buy and use artificial fragrance than are males. Two-thirds of all fra- grance sales (a $5.1 billion industry) are for female products, and fe— males do most of the purchasing (Annette Green, president, Fragrance Foundation and Olfactory Research Fund, personal communication 1996). Moreover, in the prestige end of male fragrances it is primarily women who buy fragrances for men as a gift item (Allan Mottus, pub- lisher, The lnformationist, a cosmetic trade journal, personal communica- tion 1996). Women buy fragrances for themselves and for men because of their interest in odors. By contrast, men are less concerned with scenting themselves or smelling scent on women because they are less intensely (either positively or negatively) affected by body odors. The Sensory Stimuli and Sexuality Survey did not indicate whether the interpersonal relationships referred to opposite sex or same sex part— ners. Rather it was presumed that subjects would select their average tendency....
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