The intertrochanteric line on the proximal human femur has been the focus of paleoanthropological study for several decades, as it is thought to be a defining characteristic of bipedalism. Expression of this trait is highly variable in human fossils. However, the relatively narrow range of modern human groups in which its expression has been documented limits understanding of its variability and interpretation of its meaning. Our study analyzed variation in the expression of the intertrochanteric line in a population comprising young, middle and old age groups living in the 19th–20th centuries in Kunming city, southwestern China. Results showed that this trait was not equally present in all age groups. Statistical analyses revealed significant differences in frequencies of absence between the age groups, and also highlighted strong correlations between age and the degree of expression of the intertrochanteric line. It was more frequently absent or subtly expressed in young individuals, while individuals in the middle and old age groups tended to exhibit a more pronounced expression of this feature. The degree of expression of the intertrochanteric line also differed significantly between sexes, and it was significantly positively correlated with body size. Interestingly, the degree of expression of the intertrochanteric line rarely exhibited significant correlations with magnitudes of cross-sectional geometric properties of the femoral diaphysis, used as proxy measurements for physical activity patterns.
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