THE INFLUENCE OF IMMEDIATE ANCESTRY OR FAMILY. A factor that is, on experimental evidence, rated to be of high importance in the determination of the differences of the mental make-up of human beings, is "immediate ancestry" or family. Stated in the most simple and general terms this means that children of the same parents tend to display marked likenesses in mental traits, and to exhibit less variation among themselves than is exhibited in the same number of individuals chosen at random. A great number of experiments have been conducted to determine how far resemblances in mental traits are due to common parentage. The correlation between membership in the same family and resemblances of social traits has been found to be uniformly high. The inference was made that children of the same family would show great resemblances in mental traits, when accurate experiments showed marked similarity in physical traits under the same conditions. The coefficient of correlation between brothers in the color of the eye, is, according to the results obtained by Karl Pearson, .52.[1] The coefficient of fraternal correlation in the case of the cephalic index (ratio of width to length of head) is .40. The correlation of hair color is found to be .55. The fact of high correlation between resemblance of physical traits and membership in the same family is of crucial importance, because these traits are clearly due to ancestry, and not to environmental differences. If physical traits show such a correlation, it is likely that mental traits will also, mental traits being ultimately dependent on the brain and the nervous system, which are both affected by ancestry. [Footnote 1: These facts are based on the reports of Karl Pearson in his _On the Laws of Inheritance in Man_. What is meant by coefficient of correlation may be explained as follows: If the coefficient of correlation between father and son is .3 and the coefficient of correlation between brother and brother is .5 we may say: a son on the average deviates from the general trend of the population by .3 of the amount of his father's deviation, a brother by .5 of the amount of his brother.] Measurements of measurable traits and observations of less objectively measurable ones, have revealed that immediate ancestry is in itself an influential factor in producing likenesses and differences among men with respect to mental traits. One interesting case, interesting because it was a test of a capacity that might be expected to be largely environmental in its origins, was that of the spelling abilities of children in the St. Xavier School in New York. Thorndike thus reports the test: