Original articles
The Scent of Symmetry: A Human Sex Pheromone that Signals Fitness?

https://doi.org/10.1016/S1090-5138(99)00005-7Get rights and content

Abstract

A previous study by the authors showed that the body scent of men who have greater body bilateral symmetry is rated as more attractive by normally ovulating (non-pill-using) women during the period of highest fertility based on day within the menstrual cycle. Women in low-fertility phases of the cycle and women using hormone-based contraceptives do not show this pattern. The current study replicated these findings with a larger sample and statistically controlled for men's hygiene and other factors that were not controlled in the first study. The current study also examined women's scent attractiveness to men and found no evidence that men prefer the scent of symmetric women. We propose that the scent of symmetry is an honest signal of phenotypic and genetic quality in the human male, and chemical candidates are discussed. In both sexes, facial attractiveness (as judged from photos) appears to predict body scent attractiveness to the opposite sex. Women's preference for the scent associated with men's facial attractiveness is greatest when their fertility is highest across the menstrual cycle. The results overall suggest that women have an evolved preference for sires with good genes.

Section snippets

Fluctuating asymmetry

A potentially important phenotypic marker of good genes is low fluctuating asymmetry (FA). FA is nondirectional deviation from perfect bilateral symmetry in traits that are, on average, bilaterally symmetric. FA reflects ability to deal with stresses, both genetic and environmental, during ontogeny. Individual FA, then, is developmental maladaptation owing to the individual's inability to achieve perfect symmetry given environmental and genetic perturbations during traits' ontogeny (review in

Body scent and fa

In addition to the three lines of evidence mentioned indicating that sex pheromone is involved in the human sexual selection system, a previous study by the authors provided data supporting the hypothesis that olfactory stimuli pertaining to men's phenotypic and genetic quality, measured by degree of body FA, positively affect men's sexual attractiveness to women (Gangestad and Thornhill 1998a). That study showed that non-pill-using women's preferences for the scent of male symmetry is directly

Methods

Research participants were 80 men and 82 women. Ages ranged from 17 to 33 years for men (mean and SD = 20.4 and 2.9) and 17 to 53 years for women (mean and SD = 22.3 and 6.8). Self-reported ethnicities of men were 55% Caucasian, 30% Hispanic, 8% African American, 4% Asian, 4% Native American; of women, 52% Caucasian, 32% Hispanic, 6% African American, 2% Asian, and 7% Native American. Participants received experimental course credit in an introductory psychology course in return for their

Results

Although unsigned FA tends to be non-normally distributed (Swaddle et al. 1994), Monte Carlo analyses reveal that significance tests on parametric correlations involving FA are robust (Gangestad and Thornhill 1998b); hence, we performed standard parametric analyses. For predicted effects, we used directed tests (Rice and Gaines 1994), which use a p value of .04 for a predicted relationship and .01 for a relationship opposite of prediction (rather than .025 for each, as with a two-tailed test).

Discussion

This research used T-shirts worn by each sex for 2 nights of sleep and then smelled by the opposite sex to examine the relationship between heterosexual attractiveness of one's body odor and one's body FA. The results indicate a sex difference in this relationship. Compared to the body scent of relatively asymmetric men, relatively symmetric men's scent is more attractive to normally ovulating (non-pill-using) women during their period of peak fertility based on menstrual cycle point. Yet

Acknowledgements

We thank Melissa Benedetti, Joel Fellis, Carol Frost, Alena Gallegos, Katrina Ganster, Jill Merritt, Emilie Miller, Robert Nofchissey, Kim Schancer, and Robert Stallman for their assistance in measuring participants, collecting other data, and data entry. C. Wedekind gave useful advice about the T-shirt protocol. John G. Manning provided valuable assistance with the literature on olfaction and androstenes. For useful criticisms of the manuscript, we thank M. Daly, I. Folstad, M. Wilson, and two

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