29 April 2014
Hip width and risk of birth-related trauma may play a role in a woman’s decision to have sex
Women who were more inclined to have one-night stands have wider hips according to a researcher from the University of Central Lancashire (UCLan) who has teamed up with scholars at the University of Leeds for a new study.
UCLan senior psychology lecturer Dr Gayle Brewer has worked with lead author Dr Colin A. Hendrie and Victoria J. Simpson from the University of Leeds on a study into how a woman’s build influences her sexual behaviour, published in Springer’s journal Archives of Sexual Behaviour.
The study into whether hip width or waist-to-hip ratio was a better predictor of a woman’s sexual behaviour was conducted among 148 women between 18 and 26-years-old. The participants all had at least one sexual partner previously. Their hip width (defined as the distance between the upper outer edges of the iliac crest bones of the pelvis) was measured, as well as their hip circumference at the widest point and their waist circumference at its narrowest point. Participants also completed a questionnaire about their sexual histories, including the age at which they lost their virginity, the number of sexual partners they had had, and information about emotionally significant sexual relationships they had had.
The results show that the number of sexual partners a woman had is largely driven by one-night stand behaviour. This, in turn, correlates with a woman’s hip width and not waist-to-hip ratio.
“Hip morphology has a direct impact on women’s risk of childbirth related injury and mortality. Women’s sexual behaviour reflects this risk, with narrow hipped women being more sexually cautious than those with wider hips.”
Overall, women in this study with hips wider than 36 centimetres (14.2 inches) had more sexual partners and more one-night stands than women with hips under 31 centimetres (12.2 inches) wide. More specifically, the women for whom one-night stands accounted for three out of every four of their sexual relationships had hips at least two centimetres (0.8 inches) wider than their counterparts in whose lives such fleeting relationships were not as prevalent.
The researchers surmise that women with wider hips are more likely to engage in sex because the birth process is generally easier and less traumatic for them than for smaller-hipped women (below 31cm).
UCLan senior psychology lecturer Dr Gayle Brewer commented: “Hip morphology has a direct impact on women’s risk of childbirth related injury and mortality. Women’s sexual behaviour reflects this risk, with narrow hipped women being more sexually cautious than those with wider hips.”
This, in turn, relates back to how humans learned to walk upright and the subsequent development of narrower hips to make it easier to walk. In the process, female hips have become just wide enough to allow childbirth. Infants are born at a less developed stage than most other primates because of this restriction, and therefore need much more care and investment after birth from their mothers and fathers.
Dr Hendrie added, however, that statements about causality cannot be made using the current data and it remains to be seen if these conclusions can be generalized to other populations and cultures.