Date of Award

5-2010

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Anthropology

Major Professor

Richard L. Jantz

Committee Members

Andrew Kramer, Murray K. Marks, Dawn P. Coe

Abstract

The human bony pelvis has evolved into its current form through competing selective forces. Bipedalism and parturition of large headed babies resulted in a form that is a complex compromise. While the morphology of the human pelvis has been extensively studied, the changes that have occurred since the adoption of the modern form, the secular changes that continue to alter the size and shape of the pelvis, have not received nearly as much attention. This research aims to examine the changes that have altered the morphology of the human bony pelvic girdle of individuals in the United States born between 1840 and1981.

Secular changes in the human skeleton have been documented. Improvements in nutrition, decreased disease load, exogamy, activity, climate, and other factors have led to unprecedented growth in stature and weight. The size and shape of the pelvic canal, os coxa, and bi-iliac breadth were all examined in this study. Coordinate data from males and females, blacks and whites were digitized. Calculated inter-landmark data was analyzed using traditional metric methods and the coordinate data was analyzed using 3D geometric morphometrics.

After separating the samples into cohorts by sex and ancestry, results indicate that there is secular change occurring in the modern human bony pelvis. Changes in shape are significant across the groups while only white males exhibit increases in size. The dimensions of the pelvic canal have changed over time. The birth canal is becoming more rounded with the inlet anteroposterior diameter and the outlet transverse diameter becoming longer. These diameters, once limiters, are believed to have led to an adoption of the rotational birth method practiced by modern humans. In addition, the bowl of the pelvis is becoming less flared.

Childhood improvements in nutrition and decreases in strenuous activity may be the cause of the dimension changes in the bony pelvis. The similar changes across both sexes and ancestries indicate a similar environmental cause. However, it is likely a combination of factors that are difficult to tease apart. Whether the increases continue remains to be determined.

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