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.