Sexual dimorphism in human cranial trait scores: Effects of population, age, and body size

Abstract

Sex estimation from the skull is commonly performed by physical and forensic anthropologists using a five-trait scoring system developed by Walker. Despite the popularity of this method, validation studies evaluating its accuracy across a variety of samples are lacking. Furthermore, it remains unclear what other intrinsic or extrinsic variables are related to the expression of these traits. In this study, cranial trait scores and postcranial measurements were collected from four diverse population groups (U.S. Whites, U.S. Blacks, medieval Nubians, and Arikara Native Americans) following Walker's protocols (total n = 499). Univariate and multivariate analyses were utilized to evaluate the accuracy of these traits in sex estimation, and to test for the effects of population, age, and body size on trait expressions. Results revealed significant effects of population on all trait scores. Sample-specific correct sex classification rates ranged from 74% to 94%, with an overall accuracy of 85% for the pooled sample. Classification performance varied among the traits (best for glabella and mastoid scores and worst for nuchal scores). Furthermore, correlations between traits were weak or nonsignificant, suggesting that different factors may influence individual traits. Some traits displayed correlations with age and/or postcranial size that were significant but weak, and within-population analyses did not reveal any consistent relationships between these traits across all groups. These results indicate that neither age nor body size plays a large role in trait expression, and thus does not need to be incorporated into sex estimation methods.

Sexual dimorphism in cranial morphology among modern South Africans

“…Additionally, the glabella, mastoid process, and nuchal crest contributed the highest proportional odds to the logistical regression formulae. Moreover, the glabella, mastoid process and nuchal crest showed the highest classification accuracies for all the groups, which is similar to findings from other studies [5,8,23]. The high and moderately high, positive polyserial correlations between the craniometric (e.g., mastoid height and basion-nasion length) and ordinal variables (e.g., mastoid and glabella) suggest a strong relationship between size and shape of the cranium (Tables 6-7), which corroborates findings from a North American study assessing the accuracy, correlation and corroboration of metric and nonmetric sex estimation [12].…”

“…Sexual dimorphism is population specific due to the differences in geographical location, as well as in the evolutionary influences and experiences of these groups [23,25,26]. Thus, the standards derived from the South African population increased overall classification accuracies.…”

Sexual Dimorphism of North Indian Crania and its Forensic Application

“…Previous studies on bones have shown that the performance of sex determination outside the reference population group for As evident from the past studies, skull is the most dimorphic and easily sexed portion of skeleton after pelvis, providing accuracy up to 94% [4][5][6][7]. Nevertheless, the two important parts, pelvis (95%) and skull (94%), are regarded as best indicators of sex identification in most situations owing to prominent dimorphic features in their architecture [4,7].…”

“…Nevertheless, the two important parts, pelvis (95%) and skull (94%), are regarded as best indicators of sex identification in most situations owing to prominent dimorphic features in their architecture [4,7]. Commonly employed considerations in sex determination of skull are size differences and robusticity [8].…”

“…Commonly employed considerations in sex determination of skull are size differences and robusticity [8]. But Garvin, et al [7], found that neither age nor body size plays a major role in trait expression, and thus does not need to be incorporated into sex estimation methods.…”