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Shape variation in the human pelvis and limb skeleton: Implications for obstetric adaptation
Helen K Kurki1, Sarah-Louise Decrausaz2
1Department of Anthropology, University of Victoria, Victoria, BC, V8P 5C2, Canada.
American Journal of Physical Anthropology
|December 25, 2015
Summary
Human pelvic canal shape is highly variable within populations, exceeding variation in other pelvic and limb regions. This significant variation in females may balance the demands of childbirth and bipedalism.
Area of Science:
- Human paleontology
- Evolutionary anatomy
- Bioanthropology
Background:
- The obstetrical dilemma (OD) hypothesis posits conflicting selective pressures on the female pelvis: one for birthing large-brained neonates and another for efficient bipedal locomotion.
- Despite stabilizing selection, female pelvic canal dimensions show considerable variability, suggesting shape variation may be key to accommodating diverse obstetric and locomotor needs.
Purpose of the Study:
- To investigate within-population variation in human female pelvic canal shape compared to non-canal pelvic regions and limb morphology.
- To determine if pelvic canal shape variation differs significantly between sexes within populations.
Main Methods:
- Analysis of nine skeletal samples (101 females, 117 males) representing diverse body types.
- Application of principal components analysis (PCA) to size-adjusted skeletal region variables.
- Calculation of multivariate variance and F-ratios to compare within-population shape variation between sexes and skeletal regions.
Main Results:
- Multivariate shape variance of the pelvic canal is significantly greater than that of non-canal pelvis and limb regions in both sexes.
- Limb variance exceeds non-canal pelvis variance in some populations.
- No consistent significant differences in multivariate shape variation were found between sexes across skeletal regions.
Conclusions:
- High pelvic canal shape variation, particularly in females, may be influenced by diverse selective pressures (obstetrics, locomotion, load carrying) and factors like genetic drift and developmental plasticity.
- This variability likely serves to maintain obstetric sufficiency while accommodating other functional demands.
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