Skeletal variability in the pelvis and limb skeleton of humans: does stabilizing selection limit female pelvic...

This study tests the hypothesis, a correlate of the obstetric dilemma, that skeletal variability in the human female pelvic canal is limited owing to the action of stabilizing selection. Levels of variation in three skeletal regions (pelvic canal, noncanal pelvis, and limbs) of females and males are compared to each other and between sexes.

Nine human skeletal samples (total female n = 101; male n = 117) representing diverse populations were included. Osteometric data were collected from the articulated pelvis, os coxa, sacrum, femur, tibia, humerus, radius, and clavicle. Coefficients of variation, adjusted for small sample size (V*), were calculated for variables in separate samples by sex, and mean V*s were taken for the skeletal regions. Size variances were measured as V* of the geometric mean (GM) of the skeletal region variables. Using nonparametric methods, coefficients were compared between sexes and skeletal regions and correlations among V*s were calculated.

Females and males do not differ in levels of variation for any skeletal region. The pelvic canal is the most variable region in both sexes, while size variability (GM) is similar among the three skeletal regions. Across the samples, canal and noncanal pelvic regions share patterns of variability in females but not males, while variability of the limb skeleton is independent in both sexes.

The results suggest that stabilizing selection does not limit variability in the female pelvic canal. Biological plasticity may be greater in the canal than that in other skeletal regions.