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.