several nervous systems are much alike. In love of life, in desire for food, in social feeling, &c., the different species resemble one another, but in this or that particular, in the nest-building, the fighting, the slavegetting, or other instincts, they differ. In them, a difference in nervous tissue, so minute as to be inappreciable to us, results in mental products that differ greatly. Now the huge brain of man, in which, as we cannot doubt, various tracts subserve definite functions, is subject to great variations in size (as shown by differences in the cranial capacity) and in the complexity and amplitude of the convolutions. Surely, if minute differences in the nervous systems of. other animals result in mental differences so vast, it is possible to account for much less fundamental and important differences in human faculties, as manifested in different individuals, by supposing that they likewise are due to more or less slight differences in the systems, especially when we remember how small a mass of nerve tissue—e.g. the thermal and breathing centres—may subserve important functions.
Much, very much, has been written concerning man's moral nature. Numerous authors, especially theologians, have assured us that there is inborn in him a knowledge of good and evil, that, in fact, this knowledge is instinctive, not acquired. But all the evidence points the other way. On both à priori and à posteriori grounds we are forced to the conclusion that man's moral nature is acquired, not inborn. In the first place, it is impossible to conceive how the possession of a high moral tone can have so affected the survival rate as to secure to the possessors of it such advantages in the struggle for existence, that there was thereby brought about an evolution in moral tone by the survival of the morally high. In the second place, young infants certainly give no indication
