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