Sexual Dimorphism in America: Geometric Morphometric Analysis of the Craniofacial Region*

Abstract

One of the four pillars of the anthropological protocol is the estimation of sex. The protocol generally consists of linear metric analysis or visually assessing individual skeletal traits on the skull and pelvis based on an ordinal scale of 1-5, ranging from very masculine to very feminine. The morphologic traits are then some how averaged by the investigator to estimate sex. Some skulls may be misclassified because of apparent morphologic features that appear more or less robust due to size differences among individuals. The question of misclassification may be further exemplified in light of comparisons across populations that may differ not only in cranial robusticity but also in stature and general physique. The purpose of this study is to further examine the effect of size and sex on craniofacial shape among American populations to better understand the allometric foundation of skeletal traits currently used for sex estimation. Three-dimensional coordinates of 16 standard craniofacial landmarks were collected using a Microscribe-3DX digitizer. Data were collected for 118 American White and Black males and females from the W.M. Bass Donated Collection and the Forensic Data Bank. The MANCOVA procedure tested shape differences as a function of sex and size. Sex had a significant influence on shape for both American Whites (F = 2.90; d.f. = 19, 39; p > F = 0.0024) and Blacks (F = 2.81; d.f. = 19, 37; p > F = 0.0035), whereas size did not have a significant influence on shape in either Whites (F = 1.69; d.f. = 19, 39; p > F = 0.08) or Blacks (F = 1.09; d.f. = 19, 37; p > F = 0.40). Therefore, for each sex, individuals of various sizes were statistically the same shape. In other words, while significant differences were present between the size of males and females (males on average were larger), there was no size effect beyond that accounted for by sex differences in size. Moreover, the consistency between American groups is interesting as it suggests that population differences in sexual dimorphism may result more from human variation in size than allometric variation in craniofacial morphology.

Age Effect in the Morphological Traits Performance for Sex Determination in Human Skulls and Mandibles

“…Consequently, additional diagnostics along with others as observation of sexual chromatin or advanced morphometric methods is recommended. (Kimmerle et al, 2008;Toro et al, 2010;Suazo et al, 2011). …”

El Dimorfismo Sexual en Distintas Relaciones Cráneo-Mandibulares

“…Sin embargo, existen variables que influyen en el dimorfismo sexual mandibular, como el tamaño corporal (Kimmerle et al, 2008), la simetría de la cara (Little et al, 2008), y la afinidad poblacional (Franklin et al). Así mismo, existen un número desconocido de variables relacionadas con el dimorfismo sexual de la mandíbula, algunas de las cuales podría ser necesario considerar antes de hacer una estimación del sexo de un individuo.…”

Sexual Dimorphism Determination from the Lineal Dimensions of Skulls

“…Jointly they reported the impossibility of establishing the presence of sexual dimorphism starting from the classic indicators described by Krogman (1955). Complementarily, other authors have described the influence of the size and the intrasexual variations in certain populations, such as the case of the caucasian population of North America (Kimmerle et al 2008). This shows lack of accuracy in the diagnosis of the sex using the traditional methods described by Krogman.…”