Infants Prefer Female Body Phenotypes; Infant Girls Prefer They Have an Hourglass Shape

Abstract

Adolescents and adults show preferences for male and female body shapes consistent with evolutionary theories of reproductive fitness and mate selection. However, when these preferences for females with narrow waists (i.e., 0.7 waist-to-hip ratio) and men with broad shoulders (i.e., mesomorphic body shape) emerge during the lifespan is largely unknown. To address this knowledge gap, eye-movements were tracked in 146 infants (3–18 months of age) during computer presentation of three-dimensional human figures varying in body features thought relevant for reproductive success (e.g., secondary sex characteristics, waist-to-hip ratio). When presented with pairs of figures differing in apparent sex, male and female infants looked significantly longer at the female figure compared to the male figure, a new finding that extends previous research showing preferences for female faces in infancy. When presented with same-sex figures differing in characteristics associated with mate value, male and female infants looked longer at a low mate value male (i.e., an endomorphic body type) compared to a high mate value male (i.e., a mesomorphic body type), a finding that replicates the results of previous research. In addition, the novel use of high and low mate value female figures showed a sex difference in visual attention, such that female infants looked longer at the high mate value female figure compared to the low mate female figure whereas male infants showed the opposite pattern of results. In sum, these findings suggest that infants generally do not possess preferences for adult-defined attractive male body shapes. However, infant girls’ greater attention to a female figure with an adult-preferred waist-to-hip ratio raises the possibility that evolved preferences for 0.7 waist-to-hip ratio influence girls’ later preference for toys representing females with an hourglass shape, perhaps supporting elaboration of adult social behaviors that enhance reproductive success (e.g., cooperative breeding).

Waist‐to‐Hip Ratio Sensitivity in Early Infancy

“…Such sensitivity to WHR early in life is in direct contrast with previous work suggesting that such preferences do not emerge until childhood (Johnson et al, ). However, it should be noted that the WHR was not the only feature of the stimuli that differentiated the high and low mate value images in Alexander et al (). For example, the low mate value images had higher BMIs than the high‐mate value images meaning that in addition to the WHR changing between the images, the shapes of other body parts (e.g., arms and legs) also changed and could have influenced infants' preferences.…”

“…Previous research suggests that sensitivity to WHR develops in childhood between 4 and 5 years of age, implying that such sensitivity is a function of years of socialization and is possibly reliant on conceptual development (Johnson, Lurye, & Tassinary, ). However, a recent study by Alexander, Hawkins, Wilcox, and Hirshkowitz () found that female, but not male, infants show preferences for ‘ideal’ body types. This finding suggests not only that sensitivity to WHR may be acquired much more rapidly than previous reports, but also that such development varies by the sex of the observer.…”

“…Furthermore, Alexander et al () demonstrated that female, but not male, infants display preferences for female body types considered ideal by adults. Specifically, it was found that 3‐ to 18‐month‐old female infants displayed a bias to look towards computer generated images of females designated as having high‐mate value compared to those designed to have low mate value.…”

“…For example, the low mate value images had higher BMIs than the high‐mate value images meaning that in addition to the WHR changing between the images, the shapes of other body parts (e.g., arms and legs) also changed and could have influenced infants' preferences. Moreover, during analyses, Alexander et al () collapsed performance across 3‐ to 6‐month‐old infants; thus it is unclear whether infants at the younger end of this age range displayed a significant preference for the high‐mate value exemplar. Given that studies have shown development of body processing skills in similar age ranges (Zieber, Kangas, Hock, & Bhatt, , ), it is possible that performance in the 3‐ to 6‐month‐old age group was driven by infants at the higher end of the age range.…”

“…Finally, as a follow‐up to the results of Experiments 1 and 2, male infants were tested in Experiment 3 to determine whether they exhibit a preference for the ideal WHR if tested with images of real females, although they did not exhibit a preference with computer generated images in Alexander et al (). Evidence of a preference for the 0.7 WHR would indicate that male infants are also able to detect subtle changes in body morphologies but require a higher level of detail and realism than female infants to do so.…”