A Geometric Morphometric Study of Sexual Dimorphism in the Human Hip Bone
Date
2013-12-13
Authors
Robertson, Heather Isobel
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Abstract
The purpose of this study was to use geometric morphometrics (GM) to investigate the relationships between non-metric traits of the human hip bone: the greater sciatic notch (GSN), the ventral arc (VA), the subpubic contour (SPC), and the ischiopubic ramus ridge (IPRR), estimated skeletal sex, and shape. Fifty-nine undocumented left hip bone specimens were visually assessed for skeletal sex using recognized standards of sex estimation for the GSN (Buikstra and Ubelaker, 1994). The VA, SPC, and IPRR were assessed according to Klales et al., (2012). The Non-metric traits were scored on a five-scale scheme. Skeletal sex was classified as either male, possible male, indeterminate sex, possible female, or female. Three-dimensional computer models were created of the hip bones using the NextEngine 3D desktop surface scanner. Thirty landmarks were selected to represent the hip bone in three-dimensional shape for GM analysis. Twenty-seven of the selected landmarks were reliable according to suggested digitizing error measurements. The apex of the auricular surface, the arcurate eminence, and the anterior gluteal line were the least precise in the test for digitizing error. Geometric morphometric analysis of the computer models were performed using MorphoJ software. Principal component analysis identified the patterns of hip bone shape within the sex categories. A Procrustes ANOVA and a Spearman's correlation tested the significance between hip bone shape and estimated skeletal sex, and between hip bone shape and non-metric trait morphology.
Patterns of hip bone shape in the ischium could not be identified by sex, however sex differences were identified in ischium size. Patterns of hip bone shape in the whole hip bone, segmented ilium and segmented pubis were distinguishable by larger sex groups (males = male and possible male categories; females = female and possible female categories). Shape patterns alluded to differences between females and possible females, however, shape patterns did not distinguish males from possible males. Individuals of indeterminate sex shared similar hip bone shapes as males and were therefore included in that larger sex group. Hip bone shape was also correlated with GSN, SPC, IPRR, and VA. However, the strength of the correlation differed between non-metric traits and certain components of hip bone shape. The GSN and SPC had the strongest correlation (p=<0.01) with the whole hip bone, the ilium and the pubis at distinguishing between larger male and female sex groups. The IPRR, and GSN had the strongest correlation (p=<0.01) with the pubis at distinguishing females and possible females.
The results of the study suggest that non-metric traits can discern patterns of female shape better than patterns of male shape. Further research into discerning patterns of male hip bone shape and non-metric trait variation using GM is suggested. The results of the study also suggest that patterns of pubis shape might exist among females and could be identifiable using pubis non-metric trait scores. This result lends credence to the practice of estimating sex on a five-scale gradient rather than on a male/female dichotomous division, in order to capture the morphological variation of female hip bone better.
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Keywords
Geometric Morphometrics, Human Osteology, Sexual Dimorphism, Bioanthropology