Tracking them all: exploring age-related variation in sexual dimorphism of the human pelvis

Abstract

Determining the biological characteristics of a skeleton, which include age, sex, and stature, is an integral step in skeletal analysis for bioarchaeologists and forensic anthropologists. Although sex determination in adult skeletons is highly accurate, particularly when conducted on the pelvis, this type of analysis continues to elude the field of juvenile osteology. It has been proposed that sex traits on the pelvis do not become sufficiently dimorphic until adulthood. This research examined age-related variation in the expression of sexual dimorphism in the human pelvis from an ontogenetic perspective. The main objective was to identify the age of appearance and stabilization of morphological and metric sex differences in the pelvis. This research also explored the relationship between sexually dimorphic pelvic traits and the attainment of puberty. Eighteen morphological traits and nine logistic regression equations were examined on 128 subadults (51 females and 77 males), aged 4 months to 20 years, from the Hamann-Todd and Terry Skeletal Collections. Pubertal stage assessment was also conducted based on skeletal indicators. This research showed that age-related trends exist in the appearance and stabilization of morphological pelvic traits. Three general patterns emerged from this research: traits either showed a male “default” expression, a female “default” expression, or concurrent sex expressions by birth or the time of pelvic fusion. Ten of the 18 morphological traits examined had an accuracy of 80% or above in individuals 17-20 years of age. Additionally, this research showed that the post-pubertal period is not required for the full expression of sexual dimorphism for all morphological traits. Instead, surpassing peak height velocity was shown to be more important since four traits and overall sex assessments showed substantial dimorphism occurring in the deceleration pubertal stage. Only one of the logistic regression equations tested in this research proved to be effective for sex assessment in subadults. Moreover, metric methods appeared to be best employed with age estimates as opposed to developmental (pubertal) stages. The novel strategy employed in this research to address subadult sexual dimorphism proved insightful to understand the complex nature of sexual dimorphism in the human skeleton.