Sex differences in morphological predictors of sexual behavior: Shoulder to hip and waist to hip ratios

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Abstract

Differences exist between males and females in fat distribution, skeletal morphology, muscle mass, and body shape. We investigated sex differences in shoulder to hip ratios (SHR) and waist to hip ratios (WHR), and their relationships to different features of sexual behavior. Males with high SHR and females with low WHR reported sexual intercourse at an earlier age, more sexual partners, more extra-pair copulations (EPC), and having engaged in more instances of intercourse with people who were involved in another relationship (i.e., having themselves been EPC partners). The predictive value of these morphological features was highly sex-specific.

Introduction

There is growing evidence that individual differences in digit ratios (Robinson & Manning, 2000) and fluctuating asymmetry (Thornhill & Gangestad, 1994) are correlated with differences in sexual behavior. Other morphological features show variance not only among individuals, but are sexually dimorphic. One such trait is the waist to hip ratio (WHR), the circumference of the waist relative to the hips. WHR is an indicator of a female's hormonal profile and reproductive status and is linked to such things as age, fecundity, and the capacity to sustain pregnancy and nurse a child (Singh, 1993). Another sexually dimorphic feature is shoulder to hip ratio (SHR), the circumference of the shoulders relative to the hips. Broad shoulders and narrow hips tend to be a masculine trait related to testosterone (Kasperk et al., 1997).

In the present study, we examined WHR and SHR and their relationship to different aspects of sexual behavior in males and females.

Section snippets

Methods

Undergraduate students (56 females and 60 males) from the State University of New York at Albany participated in this study, which was approved by the University Institutional Review Board. Mean age was 19.6 years (S.D.=2.8), range 18–44. Subjects were not informed about the purpose of the study.

Subjects first completed an anonymous questionnaire concerning their sexual history. Two subjects reported being homosexual, three had children, and four were married; each of these subgroups was too

Results

Male SHRs (M=1.18±0.071, range 1.03–1.40) significantly (t=10.41, P<.01) exceeded female SHRs (M=1.03±0.066, range 0.90–1.22). Here and subsequently, M signifies mean±standard deviation.

Male SHR was negatively correlated with reported ages of first masturbation and first sexual intercourse, and positively correlated with reported numbers of sex partners, EPC partners, and persons for whom one had been an EPC partner (Table 1). Female SHR was not significantly correlated with any sexual behavior

Discussion

We found striking differences between males and females in features of the shoulders, waist, and hips that predict different dimensions of sexual behavior. Since high SHR in men is linked to androgen, while female fertility is related to WHR, these features may be important parameters of mate choice. In fact, both SHR and WHR influence judgements of attractiveness Dijkstra & Buunk, 2001, Singh, 1993.

Female WHR conveys information about hormonal profile, reproductive maturity, fecundity, and

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