Department of Anthropology, University of Victoria
Saturday All day, Clinch Concourse
Levels of phenotypic variability in a species are dependent on the interaction between plasticity (ability of an organism to adapt during life to stimuli) and constraint (genetic, developmental and selective limitations on morphology). Greater plasticity results in greater intraspecific variability, while greater constraint reduces it. The processes generating variation in humans are key to the study of our evolution, as this variation is the raw material for natural selection. The pelvic canal in humans displays differences in size and shape between males and females due to its differential functional roles in locomotion and obstetrics. These distinct roles in females may be postulated to result in stabilizing selection on canal morphology, which would limit pelvic canal variability. Levels of intrapopulation morphometric variability in the skeletal regions of the pelvic canal, non-canal pelvis, and appendicular skeleton were compared in females and males of nine skeletal samples (total N females = 126; males = 148). Mean coefficients of variation, corrected for sample size (V*), were calculated for each skeletal region, and then compared between regions using Wilcoxon Signed Rank tests (N = 9). Pelvic canal variability is significantly greater than non-canal pelvis and appendicular skeleton variability for both sexes. Levels of non-canal and appendicular variability do not differ. Males are more variable than females for the appendicular skeleton. These results suggest that stabilizing selection does not constrict pelvic canal variability in females. Plasticity in canal size and shape may instead enable females to accommodate obstetrically sufficient canals.
Funding provided by the Social Sciences and Humanities Research Council of Canada.