also due in part to differences in environment, circumstances, training—one sort of home-life being more favorable than another to progress through school, for example. Each advance in the study of individual
differences, however, shows that differences in maturity and differences in the circumstances of nurture account for only a small fraction of the differences actually found in individuals of the same general environment of an American city in 1900-1912. Long before a child begins
his schooling, or a man his work at trade or profession, or a woman her management of a home—long indeed before they are born—their superiority or inferiority to others of the same environmental advantages is determined by the constitution of the germs and ova whence they spring, and which, at the start of their individual lives, they are.
Of the score or more of important studies of the causes of individual
