Abstract: The purpose of this research is to study the frequency distribution of the degeneration of third molars in the world populations, and its significance to human evolution. The results show that the frequencies of both the agenesis and impaction of third molar are much higher in East Asian populations than all other populations around the world. The earliest occurrence and increasing rates of the agenesis of third molars varied in different geographical regions and ethnic groups, which resulted in the different frequencies of this trait among populations. The third molar impaction seems to be another expression of human orofacial degeneration, but the factors affecting the third molar impaction are much complicated than those for the agenesis. Present research reveals: the significant continuity of third molar agenesis occurred in the human populations of China chronologically. The agenesis of both third molars on Lantian Man mandible and upper right molar on Liujiang Man skull offers strong support for the theory of regional continuity for the modern human origin in East Asia.

Key words: Third molar agenesis; Third molar impaction; Modern human origin; Dental anthropology