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Arching the Back (Lumbar Curvature) as a Female Sexual Proceptivity Signal: an Eye-Tracking Study

  • Linnaeus University, Kalmar, Växjö, Sweden
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Abstract and Figures

It is common in studies of human mate preference to have participants judge the attractiveness of photographs in which models adopt a neutral facial expression or a neutral body posture. However, it is unlikely that humans adopt neutral expressions and postures in normal social circumstances. One way in which posture can vary is in the curvature of the lower spine. In some non-human animals, a “lordotic” posture (in which the lower spine is curved towards the belly) is associated in females with readiness to mate. In humans, this posture may serve a similar function, attracting heterosexual men. In this study, participants were presented with computer-generated images of female bodies in which the back curvature was systematically manipulated. The result showed that small changes in lumbar curvature are associated with changes in the perception of attractiveness. Specifically, the result showed that there is a relationship between the range of the back curvatures used in this study and attractiveness, such that increasing the curvature increased the perception of attractiveness. Additionally, as the curvature increased, participants looked longer and fixated more on the hip region of the female bodies. This paper argues that the attractiveness of women in lordotic posture is due to a conserved mechanism across the taxa which signals proceptivity to men.
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Arching the Back (Lumbar Curvature) as a Female
Sexual Proceptivity Signal: an Eye-Tracking Study
Farid Pazhoohi
&James F. Doyle
&Antonio F. Macedo
&Joana Arantes
Published online: 25 October 2017
#Springer International Publishing AG 2017
Abstract It is common in studies of human mate preference
to have participants judge the attractiveness of photographs in
which models adopt a neutral facial expression or a neutral
body posture. However, it is unlikely that humans adopt neu-
tral expressions and postures in normal social circumstances.
One way in which posture can vary is in the curvature of the
lower spine. In some non-human animals, a lordoticposture
(in which the lower spine is curved towards the belly) is as-
sociated in females with readiness to mate. In humans, this
posture may serve a similar function, attracting heterosexual
men. In this study, participants were presented with computer-
generated images of female bodies in which the back curva-
ture was systematically manipulated. The result showed that
small changes in lumbar curvature are associated with changes
in the perception of attractiveness. Specifically, the result
showed that there is a relationship between the range of the
back curvatures used in this study and attractiveness, such that
increasing the curvature increased the perception of attractive-
ness. Additionally, as the curvature increased, participants
looked longer and fixated more on the hip region of the female
bodies. This paper argues that the attractiveness of women in
lordotic posture is due to a conserved mechanism across the
taxa which signals proceptivity to men.
Keywords Lumbar curvature .Lordosis .Proceptive
behavior .Receptivity .Sexual behavior .Eye-tracking
Human sexuality is not unique, nor is human sexual
behavior totally different from that of other
animals.”—Alan F. Dixson 2015
There exist sex differences in courtship and mating behav-
ior. These differences in mating behavior are due to an inter-
play between endocrine and genetic factors throughout devel-
opment and life span. Behavioral sex differences are affected
by organizational hormones during all stages of organisms
lives, with critical prenatal and pubertal periods (Berenbaum
and Beltz 2011). Prenatally, hormones influence brain devel-
opment resulting in permanent and pronounced differences in
sex-typed behavior beginning at puberty and expressed in
adolescence (Berenbaum and Beltz 2011). The hypothalamic
ventromedial nucleus (VMH) is a site of ovarian hormone
action critical to the lordosis response. Sex differences in neu-
ral circuitry and neurochemistry of the VMH have been
reviewed elsewhere (Flanagan-Cato 2011). Lordosis, or the
arching of the back, is a female-specific copulatory behavior
which indicates that the female is sexually receptive (Beach
1976). In many female mammals, VMH is involved in the
display of proceptive and receptive behaviors (Flanagan-
Cato 2011; Henley et al. 2011), and lesions in this center
reduce sexual receptivity and lordosis behavior in female rats
(Clark et al. 1981), hamsters (Malsbury et al. 1977), guinea
pigs (Goy and Phoenix 1963), ferret (Robarts and Baum
2007), sheep (Clegg et al. 1958), cats (Leedy and Hart
1985), and primates (Aou et al. 1988). As lesions to the
VMH of female whiptail lizards inhibit receptive sexual
*Farid Pazhoohi
Department of Basic Psychology, School of Psychology, University
of Minho, Braga, Portugal
Stillwater, MN, USA
Vision Rehabilitation Laboratory, Department and Centre of Physics,
University of Minho, Braga, Portugal
Department of Medicine and Optometry, Linnaeus University,
Kalmar, Sweden
Evolutionary Psychological Science (2018) 4:158165
DOI 10.1007/s40806-017-0123-7
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
... Intrasexual competition in women is influenced by traits that are important in intersexual selection in men, such as desirable physical traits [1], attractive features [2], and sexual receptiveness [3]. Given the importance placed on attractive features by men, women may compete with other women to enhance specific traits in order to increase their mating success. ...
... Importantly, women are also aware of other women's attractiveness and enhancement strategies [7] and are likely to utilize retention strategies to keep their current partners [2,8]. Studies have also shown that lumbar curvature (i.e., lordosis) in women is considered attractive, due to its role in bipedal fetal load [9] and sexual receptiveness [3]. ...
... The present study is concerned with this latter factor [3,9]. While conceptually similar, there are two different evolutionary hypotheses for the attractiveness of arched-back postures, with one focusing on an arched back as a morphological adaptation in women bodies, and the other emphasizing lumbar curvature as a nonverbal behavioral adaptation. ...
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Previous research has shown that women may use self-enhancement strategies to compete with one other. Lumbar curvature in women is considered to enhance a woman′s attractiveness, potentially due to its role in bipedal fetal load and sexual receptiveness. The current study investigated the role of lumbar curvature on women’s perceptions of sexual receptiveness as well as its role in women’s intrasexual competitiveness. Study 1 (N = 138) tested and confirmed that women’s intrasexual competition influences their perception of sexual receptivity of women as a function of lordosis posture depicted in a standing posture. Study 2 (N = 69) replicated these results and extended them to other postures, namely, the quadruped and supine positions. Study 3 (N = 106), using a two-alternative forced-choice task, revealed that other women perceive relatively larger arched-back postures as more threatening to their relationship and frequently as being more attractive. Collectively, this work suggests that women consider a lordotic posture in other women as a signal of sexual receptivity and perceive it as a threat to their relationship. This research provides robust support for the sexually receptivity hypothesis of lumbar curvature, questioning the alternative morphological vertebral wedging hypothesis.
... A more recent study published by Pazhoohi, Doyle, Macedo, and Arantes [21] revealed that both male and female observers were sensitive to changes in female models' lumbar curvature, although men were significantly more responsive to a more pronounced vertebral wedging, which supports the hypothesis that an arching back serves as a signal of sexual proceptivity in women. Furthermore, male participants found pictures of women taken in a side or rear-side view to be more attractive than their front-side counterparts. ...
... According to the evolutionary hypothesis, the optimal angle of a woman's lumbar curvature is an adaptive signal, which has had an essential impact on men's mate choice preferences [15,19]. In the present study, however, women were also expected to be sensitive to this signal, considering that assessing a potential same-sex rival's reproductive value has adaptive benefits [3,21,30]. At the same time, it is likely that women do not perceive the sexual attraction of other women as a mere threat. ...
... As predicted, no gender difference was found between observers in the positive effect of high heels on perceived attractiveness (H2), which is in line with previous findings [21,30]. This supports the idea that adequately perceiving the sexually attractive features of the female body is an essential part of women's mate choice strategies and intrasexual rivalry [36]. ...
Full-text available
Previous studies have demonstrated that the angle of women's lumbar curvature affects men's attractiveness judgments of them. The theoretically optimal angle of lumbar curvature provides better resistance against both hyperlordosis and hypolordosis as biomechanical costs of a bipedal fetal load that could impair a woman's fertility. Since men find this attribute attractive, women aim to emphasize it by wearing high-heeled shoes. The primary objective of the present study was to test this evolutionary hypothesis using short videos presenting women walking by the camera. In line with previous findings based on static stimuli (photographs), dynamic stimuli (videos) presenting women walking in high-heeled shoes were expected to elicit increased attractiveness ratings as compared to women wearing flat shoes, which would be associated with the angle of lumbar curvature. Videos were taken of 52 female models walking in two conditions (i.e., wearing either high-heeled or flat shoes). A total of 108 participants (61 males, 47 females) rated the walking models' physical attractiveness in an online setting. Each model's lumbar curvature was measured both in high heels and in flat shoes using photographs taken of them prior to each video recording. The results showed that wearing high heels consistently increased the models' attractiveness, regardless of whether or not it decreased their natural difference from the theoretically optimal angle of lumbar curvature. Both male and female observers showed this positive effect. Furthermore, a negative correlation was found between the models' body mass index (BMI) and their perceived attractiveness scores in both conditions.
... To be more competitive in intrasexual competition, women manipulate and augment physical traits that are indicators of fertility, fecundity, and health (Arnocky & Piché, 2014;Arnocky, Perilloux, Cloud, Bird, & Thomas, 2016;Atari, Chegeni, & Fathi, 2017;DelPriore, Bradshaw, & Hill, 2018;Karimi-Malekabadi, Ghanbarian, Afhami, & Chegeni, 2019). These manipulations are applied to various physical traits, such as face, breasts, and waist-to-hip ratio (Bradshaw, Leyva, Nicolas, & Hill, 2019;Doyle & Pazhoohi, 2012;Singh & Randall, 2007), are expressed through clothing (Elliot, Greitemeyer, & Pazda, 2013;Grammer, Renninger, & Fischer, 2004;Keys & Bhogal, 2018;Morris, White, Morrison, & Fisher, 2013;Prokop, 2020;Prokop & Švancárová, 2020), and manifested through women's behaviors such as proceptive movements (McCarty et al., 2017;Röder et al., 2016) and postures (Pazhoohi et al., 2018(Pazhoohi et al., , 2020c(Pazhoohi et al., , 2020d. ...
As proposed by Trivers in 1972, Parental Investment Theory addresses sex differences that result from the trade-off between parenting and mating efforts. This half-century-old theory has contributed profoundly to our understanding of sexual behavior and psychology. According to Parental Investment Theory, the sex that has higher parental investment will be more selective when choosing a mate, while the sex with lower investment will compete intrasexually for mating opportunities (Trivers, 1972). Parental investment is defined as “any investment by the parent in an individual offspring that increases the offspring’s chance of surviving (and hence reproductive success) at the cost of the parent’s ability to invest in other offspring” (Trivers, 1972, p. 139), such as investment in the forms of gestation, lactation, food provisioning, protection, and the training of offspring. In many species, including humans, females invest substantially more in parenting compared to males. This chapter considers the sexual behaviors that have evolved as a function of differences in parental investment, with a specific focus on Homo sapiens.
... Research Design: Descriptive research design is used. Descriptive design involves the accurate description of characteristics of individual, situation, or group, and the frequency with which a certain phenomenon occurs in natural setting without imposing any control or manipulation (Pazhoohi et al., 2018). ...
... Posture is the position and relative arrangement of the body parts (e.g., Canales et al., 2010). It has been shown that nonverbal changes, including postural changes, reflect an individual's affective state and act as gateways in social communication (e.g., Cazzato et al., 2012;Grammer et al., 2000;Mehrabian, 1969;Pazhoohi et al., 2018;Pazhoohi et al., 2020). An enormous volume of research has mainly defined postural effects, such as postural openness and postural relaxation, on social impressions, and showed how these postural changes modulate interpersonal attractiveness and dominance (e.g., Burgoon, 1991;Hall et al., 2005;Mehrabian, 1969;Vacharkulksemsuk et al., 2016). ...
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People often try to improve their social impressions by performing “good” postures, particularly when others are evaluating them. We aimed to investigate whether such postural management to modulate social impressions are indeed effective, and in the case that they are effective, which impressions are modulated and how quickly these impressions are formed. In total, 207 participants in two different experiments (72 participants in Experiment 1; 135 in Experiment 2) reported their impressions from photographs where other people performed “good” or “bad” postures in three viewing angles (back, front, and side). Participants were presented with a total of 96 pictures without time limitation in Experiment 1; then, for Experiment 2, they were presented with the same pictures, but with time limitations (100, 500, or 1000 ms). In both experiments, participants were asked to report their impressions for each photograph related to the person’s attractiveness, trustworthiness, or dominance. Results showed that the people with “good” postures were generally rated as more attractive and trustworthy. More importantly, it was found that impressions formed after a 100 ms exposure had high correlations with impressions formed in the absence of time constraints, suggesting that the sight of a managed posture for 100 ms is sufficient for people to form social impressions. The findings suggest that people quickly make attractiveness and trustworthiness impressions based on managed postures.
Darwin found that many animals had characteristics that were difficult to explain in terms of natural selection (i.e., the gradual process in which organisms better adapted to their environment survive and reproduce more successfully over sufficiently long time periods). He proposed a new selective force, sexual selection, which refers to the process generated by differential sexual access to opposite-sex mates. The process of sexual selection, in its classic conceptualization, consisted of two components: male–male competition, resulting in built-in weapons, and female choice, resulting in ornaments. Following Darwin, sexual selection is often divided into two forms: (1) intrasexual selection, in which members of one sex, most often males, compete with one another to gain sexual access to opposite-sex mates; and (2) intersexual selection, in which individuals of one sex, most often females, choose among individuals of the opposite sex as mates. The two forms of sexual selection have been investigated in humans across cultures, producing a large body of work on psychological similarities and differences between women and men in the context of mating. Post-mating sexual selection and its effect on sexual psychology have also gained increasing research attention in the last two decades. Two post-mating strategies in sexual selection are discussed: sperm competition (the competition between the sperm of two or more males to fertilize the egg(s) of a single female) and mate guarding (behaviors used to maintain reproductive opportunities and sexual access to a mate). Previous applications of sexual selection to sexual psychology and future directions in integration of multiple perspectives in evolutionary social sciences are discussed.
Evolutionary sexual psychology posits that sexual preferences evolved in response to recurring adaptive problems faced by men and women in regard to reproduction and mating. Accordingly, asymmetries in the mating-related problems faced by the sexes should result in sex-differentiated preferences. Some asymmetries which could be expected to result in sex-differentiated preferences include: 1) the length of time during which one is able to produce offspring (much longer for men as compared to women, which is posited to result in men showing a preference for partners who display cues to fertility and reproductive viability); 2) minimum investment needed to produce offspring (much greater for women as compared to men, which is posited to result in men showing a greater preference for short-term mating relative to women); and 3) certainty of maternity/paternity of offspring (much greater for women as compared to men, which is posited to result in men showing preferences which mitigate partner infidelity and sperm competition). Consistent with the predictions of evolutionary sexual psychology, many of the physical characteristics which men find to be attractive in women are associated with fecundity (e.g., a low waist-to-hip ratio, youthfulness). Men do appear to display a greater interest in engaging in short-term mating relative to women. Men self-report more permissive attitudes toward casual sex, desire a greater number of sexual partners across various time periods, and report being more motivated by casual sex when dating or using dating apps. Large representative surveys frequently find a sizable sex difference in the number of sexual partners reported over the lifespan, although the degree to which this may reflect factors like differences in the way that men and women respond to such questions (e.g., estimating versus counting) is debated. Field experiments indicate that men are more inclined to accept offers of casual sex from opposite-sex strangers, and men appear to be more likely to pay for sex. The content of sexual fantasies and pornography also offer insights into the nature of men’s sexual preferences. Men’s sexual fantasies more frequently involve elements of sexual variety and nonmonogamy (e.g., casual sex with multiple partners). Men also appear to consume pornography more frequently than women, which may reflect pornography providing vicarious access to excellent short-term mating opportunities in the form of a myriad of virtual partners who are youthful, attractive, and display unusually high levels of sexual accessibility. The contents of pornography, and themes common to men’s sexual fantasies, also demonstrate a preoccupation with partner infidelity.
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In women, the waist-to-hip ratio (WHR) is an indicator of attractiveness, health, youthfulness, and reproductive potential. In the current study, we hypothesized that viewing angle and body postures influence the attractiveness of these forms based on the view dependency of WHR stimuli (vdWHR). Using eye tracking, we quantified the number of fixations and dwell time on 3D images of a female avatar in two different poses (standing and contrapposto) from eight viewing angles incrementing in 45 degrees of rotation. A total of 68 heterosexual individuals (25 men and 43 women) participated in the study. Results showed that the contrapposto pose was perceived as more attractive than the standing pose and that lower vdWHR sides of the stimuli attracted more first fixation, total fixations, and dwell time. Overall, the results supported that WHR is view-dependent and vdWHRs lower than optimal WHRs are supernormal stimuli that may generate peak shifts in responding. Results are discussed in terms of the attractiveness of women’s movements (gaits and dance) and augmented artistic presentations.
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There is debate regarding whether oral sex recurred over human evolution. We investigated the occurrence of oral sex (cunnilingus and fellatio) and other sexual activities among a rural Igbo community in south-east Nigeria. We found that giving and receiving oral sex was less common relative to other sexual activities in both men and women. Both sexes reported more frequent vaginal sexual intercourse (particularly ventro-ventral posture compared with dorso-ventral posture) in the past 10 days compared to oral sex. Taken together, our data suggests that vaginal sexual activities follow similar patterns as found in other parts of world and that oral sex occurred with significantly less frequency in this traditional society.
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People judge attractiveness and make trait inferences from the physical appearance of others, and research reveals high agreement among observers making such judgments. Evolutionary psychologists have argued that interest in physical appearance and beauty reflects adaptations that motivate the search for desirable qualities in a potential partner. Although men more than women value the physical appearance of a partner, appearance universally affects social perception in both sexes. Most studies of attractiveness perceptions have focused on third party assessments of static representations of the face and body. Corroborating evidence suggests that body movement, such as dance, also conveys information about mate quality. Here we review evidence that dynamic cues (e.g., gait, dance) also influence perceptions of mate quality, including personality traits, strength, and overall attractiveness. We recommend that attractiveness research considers the informational value of body movement in addition to static cues, to present an integrated perspective on human social perception.
Sexual selection may have shaped male visual sensitivity to characteristics that provide information about female mate quality. Indeed, men judge certain facial and bodily configurations of women to be attractive, possibly because those configurations signal health and fertility. Most of this evidence derives from the study of women's facial and body photographs. We tested the hypothesis that attractive female dancers receive greater visual attention from men than do unattractive dancers. Twenty-nine men viewed video pairs of pre-categorized high and low attractive female dancers. Their eye gaze was tracked and they also provided ratings of attractiveness, femininity, and dance movement harmony. High attractive dancers received greater visual attention than did low attractive dancers and men's visual attention correlated positively with their judgments of attractiveness, femininity, and dance movement harmony. We discuss our findings in the context of the ‘beauty captures the mind of the beholder’ hypothesis and the role of dance movements in human mate selection.
This article considers patterns of sexual behavior in the various nonhuman primates, and their possible relevance to understanding the origins of human sexuality. Copulatory patterns and frequencies vary, depending upon effects of sexual selection as well as natural selection, in various types of primate mating systems. Many monkeys and apes also employ sexual behavior in the wider context of social communication, and exhibit same-sex mounting in a variety of socio-sexual and bisexual contexts. Rhythmic changes in sexual behavior during menstrual cycles in the Old World monkeys and apes are discussed in relation to the human menstrual cycle and behavior.