IV. The Sentiment of Justice.—Acceptance of the doctrine of organic evolution determines certain ethical conceptions. The doctrine implies that the numerous organs in each of the innumerable species of animals, have been either directly or indirectly molded into fitness for the requirements of life by constant converse with those requirements. Simultaneously, through nervous modifications, there have been developments of the sensations, instincts, emotions, and intellectual aptitudes, needed for the appropriate uses of these organs; as we see in caged rodents that exercise their incisors by purposeless gnawing, in gregarious creatures which are miserable if they can not join their fellows, in beavers which, kept in confinement, show their passion for dam-building by heaping up whatever sticks and stones they can find.
Has this process of mental adaptation ended with primitive man? Are human beings incapable of having their feelings and ideas progressively adjusted to the modes of life imposed on them by the social state into which they have grown? Shall we suppose that the nature which fitted them to the exigencies of savage life has remained unchanged, and will remain unchanged, by the exigencies of civilized life? Or shall we suppose that this aboriginal nature, by repression of some traits and fostering of others, is made to approach more and more to a nature which finds developed society its appropriate environment, and the required activities its normal ones? There are many believers in the doctrine of evolution who seem to have no faith in the continued adaptability of mankind. While glancing but carelessly at the evidence furnished by comparisons of different human races with one another, and of the same races in different ages, they ignore entirely the induction from the phenomena of life at large. But if there is an abuse of the deductive method of reasoning there is also an abuse of the inductive method. One who refused to believe that a new moon would in a fortnight become full, and, disregarding observations accumulated throughout the past, insisted on watching the successive phases for three weeks before he was convinced, would be considered inductive in an irrational degree. But there might not unfairly be classed with him those who. slighting the inductive proof of unlimited adjustability, bodily and mental, which the animal kingdom at large presents, will not admit the adjustability of human nature to social life until the adjustment has taken place: nay, even ignore the evidence that it is taking place.