The ethnic life is a mental life, and this consists not in the sameness brought about by the environment, nor even in ideas and acquirements, but in movement, comparison, and association of ideas.
The unity not merely of present traits but of future aims, not merely of ideas but of ideals, is the true unity which constitutes the ethnic mind. This is the foundation fact which must be constantly present to the student, if his researches in ethnic psychology are to be profitable.
In this it differs from racial psychology, for while doubtless each race has mental advantages and deficiencies which are its own and which largely decide the destiny of its members, these are not united in pursuit of one end. There is no unity of will and purpose.
Each individual partakes of this racial psychology as he does of many other mental unions, such as his church and his political party; but that which has pre-eminence in history and psychology is not these, but that closer and paramount union to which he is bound by a common speech, ideas, motives, and hopes.
We must not forget, however, that under whatever connotation we understand the group, it is still composed of individuals; and the relations which these bear to it require careful consideration.
The unity of a group can never be complete. The infinite variations of its individual members prevent this. And here comes in an interesting law which has lately been defined by an American scientist. He has shown that precisely that trait or those traits which are the most distinguishing characteristics of a group vary the widest in the individuals of that group.
Let us take, for instance, a given community remarkable for the average height of its members. We shall find wider variations in this dimension among them than among a community less conspicuous in this measurement.
This appears to hold equally good for the statistics of longevity, of health and disease, and other physical traits. There is little doubt it is also of general application to mental qualities. The contradictory estimates of national character largely depend upon it. Not the bias of the observers but their ignorance of the operation of this law will often explain such discrepancies.
What method should we follow to avoid such an error? In other words, what formula can we devise to correct individual variation and arrive at a true average for the group?
This work has already been done for us. Diligent students of vital statistics have as good as demonstrated that when a given characteristic of a group can be expressed in numbers and these projected by the graphic method, the resultant curve obtained will be one of those called by mathematicians binomial. Subtracting from the whole number one-tenth for aberrant forms or abnormal cases (the distribution of error), of the remainder, one-half will represent the mean, and one-fourth each will represent the plus and minus extremes. For example, suppose in a given community numbering one thousand adults the average height is 5 feet 6 inches; in it, one hundred persons (one-tenth) will be either abnormally tall or short; of the remainder, 450 will attain just about the total average height; while 225 will be above and 225 below it.