第三臼齿退化及其在人类演化上的意义

对第三臼齿退化在世界范围内各人类群体分类数据的分析表明：人类第三臼齿先天缺失是伴随整个人类进化而发生的牙齿退化现象的一部分，这一特片在居住于不同的地理区域的人类始发的时间及增加的速率不尽一致。

THE DEGENERATION OF THIRD MOLARS AND ITS SIGNIFICANCE TO HUMAN EVOLUTION

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 s-trong support for the theory of regional continuity for the modern human origin in East Asia.