Assessment and improvement of current sex estimation standards for application in Holocene San and Khoekhoe populations
Skeletal sex estimation is important in biological anthropology. Population-specific sex estimation standards do not exist for southern African Holocene San and Khoekhoe (HS-K) population. Due to their markedly small stature, skeletal gracility, and physically active lifestyle, they exhibit reduced sexual dimorphism. In this study I aimed to assess the accuracy of current sex estimation methods, and to optimise the assessed methods for population-specific application in the HS-K population. Seven morphological traits (cranial and mandibular) and six metrical parameters (mandibular, humeral, and femoral) were analysed in 175 adult HS-K skeletons. Accuracy was determined by comparison with pelvic sex estimates. Results were analysed using chi-squared tests, univariate statistics, and cross-validated discriminant function analysis. Trait/parameter preservation rates were assessed and reported: Of the traits, supra-orbital margin and glabella were best preserved (90% and 88% respectively), and mandibular shape least (71%). Of the metrical parameters assessed, femoral and humeral vertical head diameters (FVHD and HVHD) were best preserved (89% and 80% respectively), and bicondylar breadth (BB) least (44%). The highest sex classification accuracies obtained were for mastoid process (73%) and mandibular shape (72%), whilst the lowest were for mental eminence (53%) and nuchal crest (53%). Following categorisation by pelvic sex, the highest accuracies in females were for nuchal crest (98%) and mental eminence (95%), and in males, mandibular shape (80%) and gonial eversion/flaring (81%), illustrating differential sexual dimorphic expression for certain traits. All six metrical parameters were sexually dimorphic, with dimensions of FVHD and HVHD being the most discriminatory. The highest discriminant function accuracy for a single measurement (univariate) was 75% for FVHD, and for combined measurements (multivariate) were 77% for direct combination of BB, FVHD and HVHD, and 73% for stepwise combination of FVHD and HVHD. Whilst all traits/parameters assessed were sexually dimorphic, they produced lower accuracy rates than in other populations. This confirms that the range of sexual dimorphism exhibited by the HS-K does not conform to existing standards, illustrating the need for methodological adjustments. This study identified the most accurate areas to target for sex estimation in the HS-K and generated the first population-specific discriminant functions for sex estimation with known accuracies.
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