The unphilosophical character of such a conception of facts has now become apparent, at least to a few. The true positive of the two forces is change, variation. This is the one, fundamental, essential characteristic of living matter. Every element of an organism that is not ceaselessly changing ceases to be living, vital. “Hereditary,” therefore, is a merely negative expression. It means a diminution, not a cessation of change. Inherited traits are those in which the rate of variability has been so reduced that they reappear by repetition in several or many generations. Every one of them began in some single individual, was due to a definite exciting cause, and was transmitted by the route of reproduction. Hence inherited traits have been properly termed “secondary variations.” The long discussion whether acquired characters can be inherited has virtually been decided in favour of the opinion that every character, whether racial or specific, was originally acquired by a single person or persons and transmitted by them. The data of pathology admit of no doubt on this point, and pathology is but one of the aspects of general organic development. That not every acquired character can be transmitted goes without saying; and it is equally true that hereditary traits vary widely in their capacity for survival. So evident is this that they have been classified by observers into “strong” and “weak” traits, the latter betraying a feebleness of self-perpetuation compared to the former. I have been discoursing of physical heredity and some of its observed laws. This has not been beside the mark; for I repeat that the correlation between body and mind is absolute. Psychical traits are passed down from generation to generation hand in hand with physical peculiarities. Men are what they are in good measure because they are born so. About this the students of heredity are unanimous and positive. Hence the necessity in ethnic psychology of learning the laws of physical heredity and applying them to the history of the mind. An example will illustrate this. There is a curious manifestation of transmission called “homochronous” heredity. The adjective signifies that a trait which appears first at a certain age in the parent will also appear first at about the same age in the offspring. A familiar physiological example is the date of the beginning and the end of the reproductive period in women. Inherited tendencies to disease will recur in the offspring at the age they revealed themselves in the parent. This is strikingly true of mental traits, especially those which are degenerative.