The authors are psychologists at the Northwestern University of Chicago and they utilize 535 pages, collecting in one book the important facts and conclusions in the broad field of the psychology of individual differences.

The fact that differences of various kinds exist in the herd of homo sapiens is a truism. Even as low down, if down it may be so called, as Amoeba, differences exist. If we had better instruments for observation the greater the number of these differences will be found. Even lowly animals show by their behavior that they recognize differences. As