Let it here be observed that the Moral Law is fundamental to all law. No laws in Nature ever contradict the Moral Law, but are always found acting in obedience to it. All the works of God are in accord with this Law; God is the Moral Governor of the Universe. Therefore whatever may hold good with all other laws, does not necessarily hold good with this Law. That a man should inherit his father's intellectual qualities is then no argument that he should also inherit his father's immorality. Nothing less will suffice than distinct evidence that he HAS inherited his father's immorality.
A further observation is necessary, and that is, that morality is not absolute but relative. Strictly speaking, no man is moral. God alone is absolutely moral. Nor can we compare the morality of one man with the average morality of mankind in general. To estimate a certain man's morality of conduct we must compare his conduct with the degree of the sense of responsibility which exists within him, and also his power of control over his conduct. The murderous act of a lunatic for instance is an immoral act, because we compare the act with morality in the abstract; but it would be a mistake to call the lunatic an immoral man, for the simple reason that he had no control over his conduct and was therefore not responsible for it.
Take the case of the drunkard. A certain drunken father has several drunken sons. The influence of environment, of education, or of imitation, we will suppose to be excluded. Is heredity the cause, and if so, has it invaded the moral sphere? The influence of the father's drunkenness is first made manifest in his own nervous system. The nerve centres become clogged and poisoned and fail to discharge their functions with the same healthy activity as formerly. The nervous system degenerates, and the consequence of this degeneracy is the production of that form of irritation within the system which we call the craving for drink, and which requires alcohol for its immediate satisfaction. The man will admit that he has no liking for the taste of drink; but declares that he is in a certain state of unsettlement which can only be overcome by the use of liquor. A temporary calm is induced, only to be followed by a more intense irritation or unsettlement afterwards, and thus a circle of cause and effect is at once described.