Weismann, Heredity, 270, 272, 380, 384, denies Brooks’s theory that the male element represents the principle of variation. He finds the cause of variation in the union of elements from the two parents. Each child unites the hereditary tendencies of two parents, and so must be different from either. The third generation is a compromise between four different hereditary tendencies. Brooks finds the cause of variation in sexual reproduction, but he bases his theory upon the transmission of acquired characters. This transmission is denied by Weismann, who says that the male germ-cell does not play a different part from that of the female in the construction of the embryo. Children inherit quite as much from the father as from the mother. Like twins are derived from the same egg-cell. No two germ-cells contain exactly the same combinations of hereditary tendencies. Changes in environment and organism affect posterity, not directly, but only through other changes produced in its germinal matter. Hence efforts to reach high food cannot directly produce the giraffe. See Dawson, Modern Ideas of Evolution, 235-239; Bradford, Heredity and Christian Problems; Ribot, Heredity; Woods, Heredity in Royalty. On organic unity in connection with realism, see Hodge, in Princeton Rev., Jan. 1865:126-135; Dabney, Theology, 317-321. V. The Moral Nature of Man. By the moral nature of man we mean those powers which fit him for right or wrong action. These powers are intellect, sensibility, and will, together with that peculiar power of discrimination and impulsion, which we call conscience. In order to have moral action, man has intellect or reason, to discern the difference between right and wrong; sensibility, to be moved by each of these; free will, to do the one or the other. Intellect, sensibility, and will, are man’s three faculties. But in connection with these faculties there is a sort of activity which involves them all, and without which there can be no moral action, namely, the activity of conscience. Conscience applies the moral law to particular cases in our personal experience, and proclaims that law as binding upon us. Only a rational and sentient being can be truly moral; yet it does not come within our province to treat of man’s intellect or sensibility in general. We speak here only of Conscience and of Will. 1. Conscience.