High assimilation of the sacrum in a sample of American skeletons: Prevalence, pelvic Size, and obstetrical and evolutionary implications

Document Type

Article

Publication Date

4-1-2009

Abstract

High assimilation sacrum is fusion of the caudal-most lumbar vertebra to the first sacral vertebra. Previous studies have shown that high assimilation is associated with clinical problems, including obstetrical difficulty. This study used adult American males(n = 1,048) and females(n = 1,038) of the Hamann-Todd and Terry skeletal collections to determine the prevalence of high assimilation and its effect on pelvic size, and to consider the obstetrical and evolutionary implications of high assimilation. The prevalence of high assimilation in this sample is 6.3%, with males and females not differing significantly from one another in their prevalence. This prevalence is near the median for that reported in 41 other samples. In both males and females, individualswith high assimilation have significantly longer antero-posterior and posterior sagittal diameters of the inlet, and shorter sacrum compared to those with a nonassimi-lated sacrum. Females with high assimilation have a significantly narrower sacral angulation(i.e., reduced inclination of ventral axis of sacrum), and shorter posterior sagittal diameter of the outlet compared to those with a nonassimilated sacrum. A short posterior sagittal diameter of the outlet is associated with childbirth difficulty. As high assimilation is partial homeotic transformation of a lumbar vertebra, this study supports previous research that homeotic transformation of vertebrae is selectively disadvantageous. Am J Phys Anthropol 138:429-438, 2009. © 2008 Wiley-Liss, Inc.

Publication Source (Journal or Book title)

American Journal of Physical Anthropology

Number

664

First Page

429

Last Page

438

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