Essay Sample on Sexual Dimorphism

By definition, sexual dimorphism is the distinct variation in appearance or the size between the sexes of an animal. Thus, in the context of sexual dimorphism in the human skeleton, although both the male and female characteristics are present in the skeletons morphologic configuration, size is not considered as the only sex indicator (Loth & Henneberg, 1996). Instead, in this regard, for a better separation of the sexes, there needs to be some sort of morphological differences which primarily arise from the genetically sex-linked growth and development. Additionally, the structural gender differences in the human bone mass are characterized by wider but not opposing sex steroid action in both the male and the females. This being said, this essay seeks to give a critical review of Loths and Hennebergs study on the new morphologic indicator of sexual dimorphism in the human skeleton.

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To begin with, this particular study acknowledges that sex differences in animals and specifically, humans, have, for a long time, been investigated in almost every part of the skeleton of both the human and non-human primates. With this out into consideration, the primary intention of this particular study is to critically analyze the human mandible which in turn, will help the two scholars in presenting a new morphologic indicator of the sexual dimorphism in the humans. To accomplish this, this study included 200 mandibles which were normatively sampled from adults who were of known sex. Therefore, when studied, the morphological features of the sampled population saw the discovery of a distinct angulation of the posterior border of the ramus of the mandibular in the 84 male adults who were sampled. The sampled females on the other hand, in a majority of them, the posterior border of the ramus was characterized by the retention of a straight juvenile shape (Loth & Henneberg, 1996).

In the course of this particular study, both the morphological features of the male and the female mandibles were extensively studied and compared so as to identify the differences in the morphologic indicators of dimorphism across the two sexes. The results of the study showed a distinct angulation of the posterior the mandibular ramus in the males. This, in essence, mainly showed the difference between the male one and the female since for most females, the posterior border of the ramus was in a straight shape. Although a fundamental difference was identified in the form of mandibular ramus in both the males and the females, it is evident that both boys and girls have a similar shape of the ramus, which is straight. Besides, in males, the flexure is, however, not consistent until the end of their adolescence. Thus, in this regard, it is concluded that the ramus flexure is initiated by the slow growth in the males. Additionally, this ramus flexure is maintained by the optimal muscle balance so as to preserve the most efficient ramus in the structural form effectively.

To conclude the study, the interpretation of the results and findings indicated that unlike most bones in the human skeleton, the mandibular ramus flexure has substantially increased the accuracy of sex assessment from the skeleton. Concerning the morphologic indicators of sexual dimorphism, the study concluded that the shape of the ramus alone resulted in a significant 99% of the correct classification, unlike the 95% classification which was produced from a complete pelvis. Also, the study gives evidence that some of the main influencers of the mandibular morphology are both the changes in the cranial shape and also the configuration of the muscles of mastication. Thus, in this regard, the morphological indicator identified relates to the creation of the flexure which is likely to result from a change in the strength, size or even the angulation of the muscles of mastication. In a nutshell, there is the conclusion that the normal function of the ramus essentially maintains the sex differences which in turn, enhances the reliability of the shape as the morphological indicator which is contrary to many other traits which are considered equivocal through ordinary usage.

According to recent literature, there is proof that the traditional concept of the sex hormones as the primary regulators of the skeletal dimorphism have been redefined. Therefore, scholars have increasingly contended that of all the human bones, the pelvis happens to be the most reliable site for sex determination when it comes to the identification of the sexual dimorphism indicators. However, as a human skeletal part, it is almost impossible to recover an intact pelvis from the prehistoric fossils and burials sites. For this reason, scholars have recommended that, owing to the fact that one may not always have the bone they intend to study in a satisfactory condition, therefore, it is crucial that one studies as many bones as possible, so as to maximize the sex determination (Garcia-Martinez, et al., 2016). Besides, studies conclude that despite the fact that it is almost impossible to recover a majority of the human bones in an entire situation, the mandible should be considered as one of the most reliable bones of study. The reason why the mandible is reliable is that it is one of the most durable bones and many at times, it is often one of the only remnants of rare fossil hominids. Besides, when the mandibular ramus is studied, it is considered that there is a possibility that a high level of dimorphism will occur in the ramus, as a natural response to the sex-specific hormones done by the receptors which are present in the susceptible skeletal sites.

Gavin & Ruff (2012), in their study on Sexual dimorphism in skeletal brow ridges morphologies, point out that various researchers have increasingly contended that there is a need for scholars to come up with ways which accurately capture the morphology of certain traits using the traditional metric techniques. For this reason, their study explores the skeletal brow ridges and the chins of sampled US males and females who are from both the white and the black ancestries which effectively gives evidence regarding the differences in the morphology. For instance, the results of their study indicate that both the sex and ancestry are considered to be of significant effects in the chin and brow morphologies. Besides, these two are also consistent with the traditional qualitative description (Gavin & Ruff, 2012).

The human skeleton, spanning from the skull to the feet is characterized by sexual dimorphism with a significant difference between those of the male and the females. According to numerous scholars studying the morphology of the human skeleton, the differences in the sexual dimorphism between the males and the females is directly linked to the sex-specific differences in the body composition. Besides, studies which make the comparison of the sex discriminant functions across different populations increasingly contend that a particular combination of a number of sex dimorphism variables can be used to effectively give a good discrimination that lies between the male and the females. This, particularly, is usually independent of the race and ancestry of the specific group within which the function is applied.

Unlike Loths and Hennebergs study which seeks to determine the morphological indicator of sexual dimorphism through the extensive study of the human mandibular ramus, various other scholars study different human bone masses in relation to forensic anthropology. For instance, Garcia-Martinez, et al. (2016) study the human respiratory apparatus and its relation to sexual dimorphism. In their studys findings, it is concluded that the size of the thorax and specifically the thorax shortening in the males is a primary indicator of the sexual dimorphism. Additionally, the study identified the difference in functional size as another morphological indicator of sexual dimorphism in both the male and the female individuals.

Finally, being the study of human skeletal remains for the determination of the identity of specific bones, forensic anthropology substantially relates to this particular study. For example, although forensic anthropology is mostly used for legal purposes, especially in realizing the identity of the deaseased, the primary concern of this particular paper, the identification of the morphologic indicators of the human skeletons sexual dimorphism is relative to forensic anthropology. Therefore, the value of this article in relation to forensic anthropology is found in the sense that, this can be used in the construction of a biological profile, especially those that relate to the morphology of the individuals skeleton. Some of the aspects that can be drawn from this study and can be used in the ancestry, age, disease, and injuries among others. All these will primarily play an important role in sex identification, which is key in forensic anthropology.

References

Garvin, H. M., & Ruff, C. B., 2012. Sexual dimorphism in skeletal browridge and chin morphologies determined using a new quantitative method. American Journal of Physical Anthropology, 147(4), pp.661-670. doi:10.1002/ajpa.22036

Loth, S. R., & Henneberg, M., 1996. Mandibular ramus flexure: A new morphologic indicator of sexual dimorphism in the human skeleton. American Journal of Physical Anthropology, 99(3), pp.473-485. doi:10.1002/(sici)1096-8644(199603)99:3<473::aid-ajpa8>3.3.co;2-d

Garcia-Martinez, D., Torres-Tamayo, N., Torres-Sanchez, I., Garcia-Rio, F., & Bastir, M., 2016. Morphological and functional implications of sexual dimorphism in the human skeletal thorax. American Journal of Physical Anthropology, 161(3), pp.467-477. doi:10.1002/ajpa.23051