Another cause of the differences existing between individuals is difference in race inheritance. In causing differences in physical traits this factor is prominent. The American Indians have physical traits in common which differentiate them from other races; the same thing is true of the Negroes and the Mongolians. It has always been taken for granted that the same kind of difference between the races existed in mental traits. To measure the mental differences caused by race is an extremely difficult problem. Training, environment, tradition, are such potent factors in confusing the issue. The difficulty is to measure inborn traits, not achievement. Hence the results from actual measurement are very few and are confined to the sensory and sensorimotor traits. Woodworth, in summing up the results of these tests, says, "On the whole, the keenness of the senses seems to be about on a par in the various races of mankind.... If the results could be taken at their face value, they would indicate differences in intelligence between races, giving such groups as the Pygmy and Negrito a low station as compared with most of mankind. The fairness of the test is not, however, beyond question."[14] The generality of this conclusion concerning the differences in intelligence reveals the lack of data. No tests of the higher intellectual processes, such as the ability to analyze, to associate in terms of elements, to formulate new principles, and the like, have, been given. Some anthropologists are skeptical of the existence of any great differences, while others believe that though there is much overlapping, still differences of considerable magnitude do exist. At present we do not know how much of the differences existing between individuals is due to differences in remote ancestry.