Duration of Cunnilingus Predicts Estimated Ejaculate Volume in Humans: a Content Analysis of Pornography
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Evolutionary Psychological Science (2016) 2:220–227 DOI 10.1007/s40806-016-0057-5 RESEARCH ARTICLE Duration of Cunnilingus Predicts Estimated Ejaculate Volume in Humans: a Content Analysis of Pornography Michael N. Pham1 & Austin John Jeffery1 & Yael Sela 1 & Justin T. Lynn2 & Sara Trevino2 & Zachary Willockx1 & Adam Tratner1 & Paul Itchue1 & Todd K. Shackelford1 & Bernhard Fink3 & Melissa M. McDonald1 Published online: 10 May 2016 # Springer International Publishing 2016 Abstract Humans perform copulatory behaviors that do not a relationship between the time spent performing cunnilingus contribute directly to reproduction (e.g., cunnilingus, and ejaculate quality. prolonged copulation). We conducted a content analysis of pornography to investigate whether such behaviors might Keywords Cunnilingus . Prolonged copulation . Content contribute indirectly to reproduction by influencing ejaculate analysis . Pornography . Ejaculate volume volume—an indicator of ejaculate quality. We coded 100 pro- fessional pornography scenes depicting the same male actor copulating with 100 different females, affording control for “Ejaculate quality” is a composite of ejaculate traits (e.g., between-male differences in estimated ejaculate volume. sperm motility, sperm viability, sperm number) that affect fer- Coders visually estimated ejaculate volume and recorded the tilizing ability (Simmons and Fitzpatrick 2012). Ejaculate vol- time the actor spent engaged in cunnilingus, penile-vaginal ume is another trait indicator of quality. For example, non- penetration, and in any physical contact with his partner. We sperm substances in semen—which comprise the majority of found support for the hypothesis that a man who spends more the ejaculate’svolume—may promote fertilization by promot- time performing cunnilingus produces an ejaculate with great- ing sperm motility, reducing the risk of preeclampsia and sup- er estimated volume, even after controlling statistically for the pressing the female immune response that would otherwise age and attractiveness of the actress, and time spent in physical attack foreign bodies—including sperm (Burch and Gallup contact with his partner. Additionally, we tested the ejaculate 2006; Davis and Gallup 2006). According to the World adjustment hypothesis for prolonged copulation and found no Health Organization (WHO 2010), low volume ejaculates in- support. Prolonged copulation does not facilitate production dicate infertility. of an ejaculate with greater estimated volume, even after con- In humans, sexual arousal influences ejaculate volume be- trolling statistically for time spent in physical contact with a tween ejaculates within men, with greater sexual arousal as- partner. This research is the first to use content analysis to sociated with increased ejaculate volumes (WHO 2010). For document that pre-ejaculatory copulatory behavior predicts example, men produce ejaculates with greater volume from estimated ejaculate volume and also is the first to document copulation (i.e., more arousing) than from masturbation (i.e., less arousing; Zavos 1985; Zavos and Goodpasture 1989), and during copulation uninterrupted until ejaculation (i.e., more arousing) than during coitus interruptus (i.e., less arousing; * Michael N. Pham Zavos et al. 1994). Men produce higher quality masturbatory [email protected] ejaculates when they spend more (versus less) time sexually aroused (Pound et al. 2002) and when they view more (versus 1 Department of Psychology, Oakland University, Rochester, MI, USA less) sexually arousing stimuli (Kilgallon and Simmons 2005; 2 Department of Psychology, California State University, Leivers et al. 2014;Josephetal.2015). Men who report great- Fullerton, CA, USA er sexual arousal report more intense orgasm, more forceful 3 Institute of Psychology and Courant Research Center Evolution of ejaculation (Pham et al. 2013), and produce an ejaculate with Social Behavior, University of Göttingen, Göttingen, Germany greater volume (van Rouen et al. 1996). Evolutionary Psychological Science (2016) 2:220–227 221 Because there are non-trivial costs to producing ejaculates cunnilingus on high fertility females than on low fertility fe- (WHO 2010), men experience greater arousal when the repro- males, including dogs (Dunbar 1977; Kiddy et al. 1978), ham- ductive benefits outweigh the costs of producing a higher sters (Mesocricetus auratus:Murphy1973;Johnston1974), quality, larger volume ejaculate. For example, men are sensi- bovine (Nishimura et al. 1991; Sankar and Archunan 2004), tive to behavioral, visual, auditory, and olfactory cues to fe- ring-tailed lemurs (Lemur catta: Palagi et al. 2003), and pyg- male fertility (Haselton and Gildersleeve 2011). Men exposed my marmosets (Cebuella pygmaea: Soini 1987). Male Indian to a woman’s scent produced at high (versus low) fertility flying foxes (Pteropus giganteus) that spend more time experience a testosterone surge and report greater sexual in- performing cunnilingus on a female also spend more time terest (Doty et al. 1975; Miller and Maner 2009;Cerda- copulating with her (Maruthupandian and Marimuthu 2013), Molina et al. 2013), consistent with the idea that men are and Maruthupandian and Marimuthu have interpreted this re- sexually aroused by high-fertility cues. Additionally, men lationship with respect to sperm competition theory. Thus, are aroused by cues to sperm competition; Pham and among mammals, cunnilingus may influence sexual arousal Shackelford (2014) review evidence that men are sensitive and consequent sperm competition tactics (e.g., mounting be- to sociosexual, personality, visual, and olfactory cues to sperm haviors, copulatory thrusting, and ejaculate adjustment). competition. For example, pornography depicting two men Much evidence suggests an evolutionary history of cunni- with a woman is more arousing (Pound 2002;McKibbin lingus in humans. Cunnilingus occurs in many cultures (e.g., et al. 2013) and leads men to produce more competitive mas- Iwawaki and Wilson 1983; Lurie et al. 1995; Guadamuz et al. turbatory ejaculates than pornography depicting multiple 2010), including pre-industrial cultures (Hewlett and Hewlett women (Kilgallon and Simmons 2005). Men exposed to 2010), indicating that cunnilingus is not a culture-specific sperm competition cues (relative to men not exposed to sperm practice. Cunnilingus is depicted frequently in pornography, competition cues) report greater sexual interest (Shackelford and pornography appeals to evolved mechanisms: Humans do et al. 2002, 2007; Camilleri and Quinsey 2009; Pham and not possess adaptations to experience sexual arousal in re- Shackelford 2013a), greater sexual arousal (Pound 2002; sponse to viewing computer images, but to viewing “real-life” McKibbin et al. 2013), and produce higher quality ejaculates humans with whom they can copulate (Malamuth 1996). (Baker and Bellis 1993; Kilgallon and Simmons 2005; Some ancestral cave paintings depict humans engaged in be- Leivers et al. 2014;Josephetal.2015). Thus, men experience haviors that resemble cunnilingus, but Angulo and García greater sexual arousal in sociosexual circumstances (e.g., (2005) caution that these depictions are ambiguous and, there- higher conception risk, higher sperm competition risk) in fore, may be interpreted in other ways. Cunnilingus occurs which the reproductive benefits outweigh the costs of produc- across many species (Soini 1987; Nishimura et al. 1991; ing higher quality, greater volume ejaculates. Palagi et al. 2003; Maruthupandian and Marimuthu 2013), Although humans and non-humans perform sexual behav- and behaviors that occur across species indicate the possibility iors that do not contribute directly to reproduction (e.g., cunni- of convergent adaptations. lingus, prolonged copulation), such behaviors might contribute In humans, men may perform cunnilingus to increase their indirectly to reproduction (e.g., affecting sexual arousal and sexual arousal and consequent ejaculate volume, particularly consequent ejaculate volume, more effective semen displace- in sociosexual circumstances (e.g., high conception risk, high ment, increasing likelihood of female orgasm). Sexual arousal sperm competition risk) in which the reproductive benefits fluctuates during the course of a single sexual event (Zavos outweigh the costs of producing higher quality ejaculates. et al. 1994). The current research investigates whether ejaculate The nationally representative National Health and Social volume is predicted by cunnilingus and by prolonged copula- Life Survey found that while 71 % of men find performing tioninhumans. cunnilingus either very appealing or somewhat appealing,and Males of many mammalian species perform cunnilingus in only 19 % find it not at all appealing, 60 % of women find sociosexual circumstances (e.g., higher conception risk, receiving cunnilingus very appealing or somewhat appealing, higher sperm competition risk) in which the reproductive ben- and 28 % report that it is not at all appealing (Laumann et al. efits outweigh the costs of producing higher quality, greater 1992), which suggests that men may also perform cunnilingus volume ejaculates. For example, males perform cunnilingus to to make their partner more receptive to penile-vaginal sex. assess a female’s fertility by sniffing and licking her genitals Men who report spending more time performing cunnilingus (i.e., cunnilingus) to gather scent cues to her fertility status. during their most recent sexual encounter report greater sexual Male cotton-top