Prognathism

Prognathism

Prognathism describes a projection of the jaws. Prognathous individuals also have their mouth and lips pushed forward. The shape of the lower part of the nose is altered as well. Measuring prognathism is relatively complex, and various methods have been devised (e.g. the basion-prosthion length). Most early Hominids were prognathous. The continuous reduction of jaw size probably brought advantages in that the extra off-center weight of a protrusive jaw impedes rapid turning of the head. Several tropical populations still show significant prognathism today, especially in Africa and Australia. This led some early anthropologists to describe Africans as more "primitive" compared to Europeans, who show prognathism in fewer cases. However, this would be a hasty conclusion without considering that Europeans show higher frequencies of other "primitive" traits like strong male body hair and pronounced supraorbital arches. Individuals with absence of prognathism are usually defined as orthognathous (there exist a few more detailed distinctions as well that are not considered here). The maps show regions where orthognathy and prognathy are common (yellow). The dark yellow colour shows where both traits are found in a milder form.

orthognathous

File:Prognathous Morph.png prognathous

Orthognathous: Orthognathy developed relatively early in the evolution of Homo sapiens and continuously increased in frequency, especially in colder regions. It is widespread in Europe, much of North and East Asia, as well as most parts of Polynesia and America. In Africa, orthognathy is common in the North of the continent as well as in many East Africans (Ethiopids). Orthognathy is also frequent in Khoisans of South Africa.

Prognathous: Prognathy is the typical condition in most Hominid species and was found in almost all prehistoric humans. Today centres of prognathy lie in sub-Saharan Africa as well as Native Australia. In a milder form it occurs in Melanesia and New Guinea, parts of Indonesia, South Asia, and even in mountain regions of the Middle East. In America prognathy is especially found in some Lagids and Fuegids, but hardly as strong as in Africa and Native Australia. In Europe some of the more ancient types (e.g. Paleo Atlantids) can show mild prognathy. Milder forms include alveolar prognathism.