歯の形質に関する人類学的な問題点

Abstract

The physical traits of human teeth have suffered changes in the long span of evolutionary ages and have developed even specific types characteristic of certain ethnic differences. If evolution of teeth is assumed to have taken place phylogenetically, the first thing to be studied is how have the teeth of reptiles been transformed into those of mammals as they are seen today. Although many and confusing theories have been advanced about this topic, the present author would like to favor the tritubercular theory of Cope and Osborn. Using the materials of the author's own and other investigators, the present author studied the human adult and deciduous molars with regard to the primitive traits that are considered to be of special significance phylogenetically. Results showed that many factors were involved for the evolutionary changes to occur in the teeth. Of these factors, the following three were considered important, 1) the time factor on the change of traits, 2) the change of traits according to ethnic difference, and 3) the fact that the evolutionary traits developing in the same individual did not necessarily appear as such in the full line of teeth, but followed certain definite pattern in their appearance. It follows, therefore, that although the fundamental traits of human teeth from the fossil down to the modern ages have not suffered much change, there can be seen accumulation of varying factors which resulted in the ethnic differences and even in differences among individual subjects with regards to the teeth.