There is no doubt that a cheerful mental disposition is in itself a defence against the attacks of disease. Seeland, in his anthropologic studies of the question, found that persons of a cheerful temperament are, in an extended series, physically stronger than those who are melancholic, in the proportion of 148:135; though whether this should be regarded as cause or consequence is open to construction; and, while fully recognising the actuality of national temperaments, he adds that an analysis of them, with a view to defining their causes, is still far from practicable. The important conclusion which he reaches, however, is that the happier temperament corresponds to the higher degree of health, and that, in comparison, that which tends to the melancholic is morbid, a pathologic product, an indication of degeneration. Regarded as a national question, we derive from this that the calm and the cheerful temperaments are those which promise most success and permanence. CHAPTER II _ETHNIC MENTAL DIVERSITY FROM COGNATIC CAUSES_ In the last chapter I have considered the individual in his relation to the group simply as an isolated unit, with his own powers and weaknesses. Both of these, however, he derives largely from his ancestors, through the fact that he is born a member of a particular species, race, and family. Such traits react powerfully on his mental life, and, indeed, in themselves force him into relation with a human group, his cognatic or kindred associates. The ethnic psychologist must therefore devote to them insistent attention. For convenience of study the facts may be grouped under three headings, Heredity, Hybridity, and Racial Pathology. _Heredity._—In body and mind, the child resembles his parents, the individual his ancestors. This is the principle of fixity of type, the permanence of species. Neither in body or mind is the child ever exactly like his parents or either one of them. Differences are always visible. This is the principle of constant variation, at the basis of the unending transformations of organic forms. On these two principles rests the law of Evolution, which may be progressive or regressive, that is, toward greater complexity and specialisation or toward simplicity and homogeneity. Of these two principles, one is real, the other merely apparent,—the negative or minus quantity of the other, as cold is to heat or darkness to light. Which is the real? The question is not idle, for upon its correct decision depends the accuracy of our views of organic life. So long as the doctrine of the immutability of species was accepted, everyone believed in the fixity of type as the prime law. When Lamarck and Darwin had undermined that position, and up to a very recent date, the two principles were considered somehow equal, dual conflicting forces, the fixity of type being a passive result of the action of the “environment.”