Secular trends in cranial size and shape among black South Africans over the late 19th and 20th centuries

Abstract

Background

Previous studies of secular change in cranial size among black South Africans have produced conflicting results.

Aim

We re-examined cranial size change in this population during the 19th and 20th century by evaluating its relationship with individual year-of-birth, and the significance of trends among eight decennial cohorts.

Subjects and methods

This study is based on 102 male and 89 female adults born between 1865 and 1959. Linear regressions were employed to evaluate possible relationships between year-of-birth and cranial dimensions; ANOVAs were used to evaluate the significance of long-term trends among decennial cohorts.

Results

No analysis revealed a secular change in cranial length in either sex; however, the ANOVA for cranial length in the combined sex sample was significant. There is no secular trend in female cranial breadth, but males display a negative trend in this dimension. This results in a secular trend for increased male dolichocephaly.

Conclusions

The factors that underlie the negative secular trend in male cranial breadth and the absence of a secular trend in overall cranial size in this population are unclear. Nevertheless, these observations accord with findings related to stature and long bone strength in this population and are consistent with observations for other sub-Saharan African populations.

Keywords:

• Cranial breadth
• cranial length
• cranial index
• decennial cohort
• dolicocephaly

Acknowledgements

We thank the School of Anatomical Sciences, University of the Witwatersrand for permission to access the Raymond A. Dart Collection of human skeletons, and we acknowledge the selfless generosity of those who donated their bodies for teaching and research. We thank Tea Jashashvili and Queen Letsoalo for assistance with the CT scanning, and Brenna M. Henn for insightful discussions about southern African population genetics. We are grateful to the anonymous reviewers, whose comments have significantly improved this contribution.

Disclosure statement

No potential conflict of interest was reported by the author(s). The authors alone are responsible for the content and text of this article.

Author contributions

FEG designed the study, IW, BKB and VM conducted the CT scans, CL and CM acquired the measurements, and CM performed the statistical analyses. FEG drafted the manuscript and all authors edited the manuscript for intellectual content, provided critical comments and reviewed the submitted manuscript.

Additional information

Funding

This work received financial support from the Leakey Foundation and the College of Arts and Sciences, Stony Brook University.