Developing Subadult Sex Estimation Standards Using Adult Morphological Sex Traits and an Ontogenetic Approach
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Authors
Cole, Stephanie J.
Issue Date
2022
Type
Dissertation
Language
Keywords
Growth and Development , Juvenile , Puberty , Sex Estimation , Skeletal Maturity Indicators , Subadult
Alternative Title
Abstract
A persistent theme in the anthropological literature is that sex estimation can only be conducted on “adults,” a term associated with the culturally and legally defined chronological age of 18 years and older. Consistently low accuracy rates published in the subadult sex estimation literature causes these beliefs to persist even though observable differences in some sex traits exist as early as the prenatal period, while others have different developmental trajectories that result in increasingly dimorphic expression throughout ontogeny. Because biological sex differences arise prior to the completion of skeletal development and maturation, sex estimation should be possible in individuals prior to the cultural and legal definition of adulthood, and therefore, could be included as part of the subadult biological profile to facilitate identification.Major developmental milestones in ontogeny are the foundation for most sex differences observed in adults. For example, adult sex estimation primarily relies on the morphological evaluation of the skull and pelvis, and it is understood that sex differences in these regions are linked to hormone mediated changes occurring at puberty. However, little is known regarding the age or maturation stage at which skull and pelvic morphological traits useful in discriminating between the sexes become dimorphic or reach full expression. Investigating the ontogenetic trajectories of the most commonly used traits for adult sex estimation will allow for the determination of their true capacity to estimate sex in subadults, rather than assuming sex estimation can only be conducted on individuals estimated to be 18 years of age or older. Data were collected from a large sample (n = 625: m = 386, f = 239) of American individuals between the ages of eight and 20 years from the Subadult Virtual Anthropology Database, which is comprised of high-resolution computed tomography scans of contemporary, known subadults to address three specific research aims: Specific Aim #1: Determine the age at which sex traits of the skull and pelvis become dimorphic and reach full expression and quantify the predictive power of each trait throughout ontogeny. To meet Aim #1, traditional morphological sex trait descriptions and scoring procedures of the skull and pelvis that are routinely used for adult sex estimation were modified to be more appropriate for use with subadult remains. The skull traits include: supraorbital margin, glabella, nuchal crest, mastoid process, and mental eminence. The pelvic traits include: pubis morphology, presence/absence and degree of expression of the ventral arc, medial aspect of the ischiopubic ramus, subpubic contour, greater sciatic notch, preauricular sulcus, and obturator foramen. Specific Aim #2: Determine when during maturation the skull and pelvic sex traits become dimorphic using various skeletal maturity indicators associated with puberty to serve as a guide for forensic practitioners in deciding if an immature individual is sufficiently mature for a sex estimate to be made without needing to rely on age. Although Aim #1 is crucial in debunking the persistent belief that sex estimation can only be conducted on individuals 18 years of age and older, using age as the parameter on which to decide whether to estimate sex is problematic because individuals enter puberty at different ages and move through puberty at different tempos. Since dimorphism in the skull and pelvis is associated with puberty, a better way of knowing if an immature individual is sufficiently mature for sex to be estimated using these anatomical regions is to evaluate skeletal maturity indicators associated with various stages of puberty. The maturity indicators include: humeral proximal epiphysis, humeral distal epiphysis, humeral medial epicondyle, ulnar proximal epiphysis, radial distal epiphysis, iliac crest, ilio-ischial epiphysis, calcaneal tuberosity, and the permanent mandibular canine. Specific Aim #3: Develop sex classification models for the creation of a new two-step method for subadult sex estimation that is based in ontogeny through incorporating skeletal maturity indicators associated with puberty and modified skull and pelvic sex trait descriptions and scoring procedures specifically for use with subadults. The results indicate that 1) most skull and pelvic traits express dimorphism, with many also attaining full expression, prior to adulthood, 2) skeletal maturity indicators associated with puberty provide a valid way to estimate maturity status, thus removing a reliance on chronological age when deciding whether subadult sex estimation should be attempted, and 3) subadult sex estimation can be as accurate as adult sex estimation when using appropriate samples and taking an ontogenetic approach. To have the largest impact on the field, the new subadult sex estimation method is freely available as a graphical user interface, The Ontogenetic Subadult Sex Estimation (OnSEt) System. The OnSEt System allows practitioners to easily include sex as part of the subadult biological profile, ultimately helping to facilitate identifications and improve outcomes in medicolegal death investigations involving the young.