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Recent studies have examined various aspects of human physical attractiveness. Attractiveness is considered an evolved psychological mechanism acquired via natural selection because an attractive body reflects an individual's health and fertility. The length of the legs is an often-emphasized aspect of attractiveness and has been investigated using the leg-to-body ratio (LBR), which reflects nutritional status of the infant, health status, fecundity, and other factors that are predictive of physical fitness. However, previous studies of leg length and physical fitness have produced mixed results. The present study investigated the relationship between LBR, defined as the height to perineum divided by total height, and perceived attractiveness. Three-dimensional stimuli (11 male and 11 female) were constructed with various LBR features. Each stimulus was rated by 40 women and 40 men in Japan on a 7-point scale. The results showed that the values closest to the average LBRs were rated as the most attractive. Furthermore, by fitting a quadratic curve on the relationship between attractiveness and LBR, an inverted U-shaped curve with the peak located at the average LBR was observed. In addition, high LBR values were rated as more attractive in females, whereas the opposite was true for males. These results suggest that average LBR is indicative of good health and good reproductive potential, whereas more extreme values are avoided because they could be indicative of diseases and other maladaptive conditions.

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Life history theory is useful for taking an evolutionary approach to individual differences. An individual’s life history strategy (LHS), based on life history theory, can be measured using the Arizona Life History Battery or a part of it—the Mini-K—as the K-factor. In this study, I examined two research questions regarding the Japanese version of the Mini-K (i.e., Mini-K-J). First, I assessed the construct validity and invariance between sexes of the Mini-K-J because there existed issues with the factor structure of the original Mini-K. These issues were addressed in the original Mini-K, but not in the Japanese version. In particular, I examined whether the instrument consists of a single higher order factor (K-factor) and whether sex invariance exists in the factor structure, following Richardson et al. Second, I assessed criterion validity of the Mini-K-J. In particular, I examined whether the Mini-K-J could capture fast LHS traits in Japanese undergraduates because the Mini-K-J has been validated only using slow LHS traits. The results showed that (1) the Mini-K-J generated a single higher order factor (i.e., K-factor) and five first-order factors, (2) there existed sex invariance of the factor structure, and (3) the higher order K-factor mean might have a different meaning between sexes. These results predominately support Richardson et al. Further, the higher order K-factor of the Mini-K-J could capture fast LHS personality traits. These results suggest that the Mini-K-J would be useful for future studies related to LHS.