Thoracopelvic Covariation Across Ontogeny in Humans

Abstract

Clarifying human thoracopelvic covariation patterns can contribute to an understanding of body shape evolution. Previous research has shown that although adult human males and females share a common thoracopelvic covariation pattern, males tend to exhibit mediolaterally wide thoraces and narrow pelves, and females tend to exhibit mediolaterally narrow thoraces and wide pelves (2020 Am J Phys Anthropol 173(3) 514‐534). The current study tests for sex differences in thoracopelvic covariation across ontogeny.I analyzed decedent computed tomography data from the Center for Forensic Imaging at the University of New Mexico with a sample of 44 females and 48 males, aged 0‐21 years. I used SlicerMorph to collect three‐dimensional landmark coordinate data representing thoracic and pelvic shapes as well as R geomorph and Morpho for geometric morphometric analyses. After separate Generalized Procrustes Analyses on the pelvis and thorax, I analyzed thoracopelvic covariation with two‐block partial least squares analysis. To compare covariation magnitudes, I tested effect sizes of sex‐specific two‐block partial least squares. I assessed sex‐specific covariation patterns by projecting the male data into the female two‐block partial least squares analysis and then comparing the slopes of sex‐specific data via major axis regressions and the smatr R package.Results from the two‐block partial least squares analyses indicate significant covariation between the thorax and pelvis in females and males (p=0.001). The first latent variables explain 94.47% and 94.40% of the total covariation in the female and male samples, respectively. In both sexes, as the thorax becomes less pyramidal and more barrel‐shaped with development, the pelvis becomes more anteroposteriorly elongated. The sex‐specific two‐block partial least squares analyses do not exhibit significantly different magnitudes of thoracopelvic covariation. Slope comparison between sexes does not indicate significantly different patterns of thoracopelvic covariation.Previous research suggests that adult thoracopelvic covariation is driven by sex differences. The current study shows that subadult thoracopelvic covariation tracks with growth and development in both sexes, which is expected in the ontogenetic sample. Subadult females and males do not exhibit significantly different magnitudes nor patterns of thoracopelvic covariation. Processes such as sagittal balance of the upper body over the pelvis may influence thoracopelvic covariation.