Sexual dimorphism determination from the lineal dimensions of skulls/Determinacion del dimorfismo sexual utilizando las dimensiones lineales del craneo.
It is possible to determine sex from isolated bony pieces such as the temporary bone, frontal, in jaw, in orbit, and in tooth of the skull by studying a group of traditional morphological indicators or through the calculation of general cranial dimensions and the angles formed among craniometric points (Baughan & Demirjian, 1978, Lestrel et al., 2005; Ursi et al., 1993; Olivier & Tissier, 1977; Bibby, 1979; Kalmey & Rathbun, 1996; de Paiva & Segre, 2003; Kemkes & Gobel, 2006; Celbis et al., 2001; Wescott & Moore-Jansen, 2001; Panella et al., 1988; Buschang et al., 1986; Rosas et al., 2002; Steyn & Iscan, 1998; Franklin et al., 2007; Schmittbuhl et al., 2001; Loth & Henneberg, 1998; Loth & Henneberg, 1996; Balci et al., 2005; Haun, 2000; Lam et al., 1996; Graw et al., 1999; Schleyer et al., 1971; Introna et al., 1993; Kondo et al., 2005; Abdelmalek & Michael, 1984).
The previous parameters, not so much qualitative as the quantitative ones, deserve special consideration, because the variation of the skeletal characteristics of different populations (Steyn & Iscan). In relation to these, Franklin et al. (2005) in a study of skulls belonging to South Africans evidenced indigenous, distinctive features between men and women, some of which have not been described for the caucasian population. 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.
The purpose of this study was to use dry human skulls to anthropologically determine sexual dimorphism in conventional lineal dimensions, to build a discriminant function, and to evaluate its yield; the skulls used for the study were from the Collection of the Museum of Skulls of the Universidade Federal de Sao Paulo.
MATERIAL AND METHOD
A cross sectional study was carried out using a nonprobabilistic method. From Universidade Federal de Sao Paulo's collection the collection in the (UNIFESP), 226 mature human skulls that conformed to the eligibility criterion were analyzed; the criterion was that the conservation state of the skulls should allow obtaining the proposed measurements. These skulls corresponded with mature individuals with sex and age record. In this analysis, skulls that presented asymmetries or evident dismorphosis, fracture or loss of some segment of the bony head were excluded.
The sample comprised 149 males skulls with a mean of age of 43.41 years old (DS 12.88) and 77 females skulls with a mean of age of 38.19 years old (DS 15.68). This sample considered skulls from individuals with white, brown, and black skin.
The mensurations were carried out in the museum of skulls of UNIFESP with the aid of a Willis compass (0.1mm) and a digital caliper (0.01mm). The following lineal dimensions of the skulls were determined:
- Bieuric (Eu-Eu).
- Glabela--Opisthocranion (Gl-Op).
- Basion--Bregma (Ba-Br).
- Nasion--Prosthion (Na-Pr).
- Bizigomatic (Zi-Zi).
- Maximal width of the piriform aperture (MWPA).
- Nasion--Spinal (Na-ANS).
With the obtained dimensions and using the statistical program SPSS 15.0 for Windows, descriptive statistics were calculated. The mean differences were contrasted by means of T test for independent samples, with p <0.05. With the purpose of obtaining the lineal dimensions that better allow discriminating between skulls of men and women, the analysis of the discriminant function was carried out using the inclusion method for steps and correcting the calculation in the differences in the skull sizes of both groups. Finally, to determine the combinations of lineal dimensions that better explains the variance among the groups, principal components analysis was carried out.
The means of all the analyzed lineal dimensions were bigger in the men skulls than in the women skulls. Nevertheless only Gl-Op, Na-Pr, Zi-Zi, and Na-SNA were statistically significant with p <0.05. These results are shown in Table I.
When carrying out the calculation of the lineal discriminant functions of Fischer, it was observed that in an independent way, only the distance Zi - Zi and Na-SNA allow to discriminate against. Table II shows the sample classification coefficients that compose the discriminant function; the percentage of skulls correctly classified with this function was 82.7%.
When carrying out the analysis of the principal components obtained for the first three components, the results are able to explain 76.36% of the variance in the dimensions of the analyzed male skulls and 76.9% of the variance in skulls of women. The details of these results are given in Table III.
The quantitative methods used for the determining sex based on the lineal dimensions of the skull are constantly analyzed in diverse samples, in terms of accuracy and validity, to select appropriately those that allow the quantitative methods to be applied, or, to generate parameters peculiar to populations--specifically, in the context of the medico-legal identification.
In this study, some of the classic skull dimensions used to build indexes (cephalic, facial superior, nasal) and of wide application in formulas described to classify between men and women (Da Silva, 1997; Galvao, 2008) were analyzed. Some of these measures were significantly greater in the skulls of men (Gl-Op, Na-Pr, Zi-Zi and Na-ANS); however, when supplementing the study with the analysis of the discriminant function, it was observed that only Zi-Zi and Na-ANS allow to discriminate against with a success rate of 82.7% when classifying using these variables. In addition to the above-mentioned, with regard to the first three components, the principal components analysis of the sample can explain 76.36% and 76.9% of the variance in the skulls dimensions of men and women, respectively, the first of them being related with the size and remaining strongly associated to the shape in both men and in women, that is, the differences in the dimensions of the skulls can be explained by reason of size by 37.63% in men and 40.53% in women. This fact is interesting; the cranial size determination is multifactorial and because the splanchnocranium and the calvaria of the neurocranium development reaches mature dimensions influenced by epigenetics factors of high variability among populations, geographical regions, socioeconomic strata, and so on.
On the other hand, the remaining percentage of the variance is explained by differences in shape, especially facial. This is important and it reinforces the value of the dimorphism morphologic strains. In this respect, Suazo et al. (2008 a,b,c) reported good levels of accuracy of the qualitative classic strains of sexual dimorphism in a sample comparable to this study, a situation also described for other populations (Rogers, 2005; Haralabakis et al., 2006; Hu et al., 2006).
The authors conclude that the methods for determining sex based on the lineal dimensions of the skull present a limited utility as per this sample; new methods for sex determination should be explored.
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* Daniela Alejandra Zavando Matamala; *,** Ivan Claudio Suazo Galdames & * Ricardo Luiz Smith
* Departamento de Morfologia y Genetica, Universidade Federal de Sao Paulo, Brasil.
** Departamento de Anatomia Normal, Universidad de Talca, Chile.
Correspondence to: Dra. Daniela Zavando Matamala
Table I. Statistical analysis, t Student, for dimensions by sex. Sig. Dimension Sex n Mean DS (bilateral) Bieuric Male 149 140.86 10.757 .040 Female 77 137.66 11.581 Glabella--Opisthocranio Male 149 184.09 10.529 .001 Female 77 178.81 11.931 Basion--Bregma Male 149 134.99 9.972 .362 Female 77 133.64 11.694 Nasion--Prosthion Male 149 68.846 5.4118 .000 Female 77 64.492 5.0839 Bizigomatic Male 149 127.02 5.972 .000 Female 76 119.67 5.006 Maximal width of Male 149 25.831 2.7179 .066 the piriform aperture Female 77 25.145 2.5098 Nasion--Spinal Male 149 51.250 3.8834 .000 Female 77 47.613 3.1458 Table II. Coefficients of classification of the discriminant function. Dimension Sex Male Female Bizigomatica 3.741 3.528 Nasion--Spinal 3.238 2.997 (Constant) -320.980 -283.486 Table III. The principal components analysis dimensions by sex. Male Component 1 2 3 Bieuric .717 .455 -.004 Glabella--Opisthocranio .809 .189 -.309 Basion Bregma .784 .246 -.397 Nasion--Prosthion .537 -.480 .408 Bizigomatic .344 .416 .742 Maximal width of the piriform aperture -.268 .698 .312 Nasion--Spinal .610 -.608 .284 Percentage of the variance explained 37.63% 22.33% 16.39% Female Component 1 2 3 Bieuric .924 -.067 -.206 Glabella--Opisthocranio .889 .143 -.153 Basion Bregma .887 .076 -.203 Nasion--Prosthion -.131 .846 .086 Bizigomatic .555 .042 .495 Maximal width of the piriform aperture .282 -.011 .849 Nasion--Spinal -.049 .844 -.073 Percentage of the variance explained 40.53% 20.86% 15.5%