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Facial symmetry, masculinity and shoulder-to-hip ratios in men convey information to mates about reproductive/genetic quality, the so-called “good genes” hypothesis. On the other hand waist-to-hip ratio conveys important reproductive information about women to men. Here using fMRI, men showed activation in neural reward centers when they viewed and rated the attractiveness of surgically optimally configured female bodies.
Physical attractiveness serves as a biologically honest signal to members of the opposite sex and is a key element of successful mating and reproduction. Women rate men with masculine, symmetrical faces as more attractive mates than men with feminine and asymmetrical faces. Women also rate men with a high shoulder-to-hip ratio (SHR) as attractive. Attraction to symmetrical and masculine faces, and high SHR males appears to be tightly linked to ovulation in women supporting the idea that these characteristics indicate “good genes”.1–7
The ability to differentiate the virile from weak is not limited to the female sex; men similarly identity fertile and healthy mates based on morphology. Men prefer women with lower waist-to-hip ratio (WHR) because this is positively correlated with “good genes” indicators. For example, lower WHR women are at a lower risk of developing heart disease, cancer and depression, in addition to having healthier full-term pregnancies and complication- free deliveries when compared to high WHR women. It is well known that optimal WHR is rated as attractive, the world over,8–11 but the proximate neural mechanisms are not at all understood. In this study,12 we hypothesized that optimal WHR in women would activate neural reward centers men. Specifically, we anticipated activation in reward centers that that have been linked to sexual reward (pleasure) in species with low conception rates (e.g., nucleus accumbens).
Pre- and post-surgical pictures of 7 naked female bodies were shown to 14 men (Mage = 25.21, S.D. = 6.30). Female subjects in the pictures had undergone an elective cosmetic surgery to optimize their WHR. Pre-surgical pictures show a variety of body types from the well-known pear and apple shape to an ectomorphic tube shape. Post-surgery, all 7 bodies displayed the optimized WHR with well-defined buttocks, smaller waists and proportioned thighs: the perfect hour-glass shape.
Images of the rear and oblique rear position of the pre- and post-surgical females served as the stimuli for male participants. These images were randomly presented to male participants 15 times for 1 second with variable interstimulus intervals (2–15 s). Participants used a 5 button fMRI-compatible response pad to rate each picture on attractiveness from very unattractive to very attractive.
Surprisingly, changes in body mass index (BMI) only activated low-level visual areas, while changes in WHR activated areas associated with pleasure, reward13,14 and judgment.15,16 Viewing post-surgical (i.e., optimally designed WHR) bodies revealed activation in the right orbital frontal cortex (OFC), lateral occipital cortex, and the anterior cingulate gyrus. Further examination of OFC activation revealed that the left and right OFC became activated with the post-surgical and not the pre-surgical pictures. Finally, participant’s ratings of attractiveness were regressed on their brain activation for postsurgical (optimal WHR) body images and we found activation in subcortical brain substrates associated with reward, namely the nucleus accumbens. The nucleus accumbens is highly sensitive to rewards and is the seat of addictive behavior. This suggests that men see optimally designed women’s bodies as highly rewarding; neurologically they likely stimulate appetitive, sexual behaviors. We can assume from these findings that so long as WHR hovers around the optimal 0.7, a woman’s BMI can vary without compromising her attractiveness to men.
Previously published online: www.landesbioscience.com/journals/cib/article/11560