Here we shall assume it to be an inevitable inference from the doctrine of organic evolution, that the highest type of living being, no less than all lower types, must go on molding itself to those requirements which circumstances impose. And we shall, by implication, assume that moral changes are among the changes thus wrought out.
The fact that when surfeit of a favorite food has caused sickness, there is apt to follow an aversion to that food, shows how, in the region of the sensations, experiences establish associations which influence conduct. And the fact that the house in which a wife or child died, or in which a long illness was suffered, becomes so associated with painful states of mind as to be shunned, sufficiently illustrates, in the emotional region, the mode in which actions may be determined by mental connections formed in the course of life. When the circumstances of a species make certain relations between conduct and consequence habitual, the appropriately-linked feelings may come to characterize the species. Either inheritances of modifications produced by habit, or more numerous survivals of individuals having nervous structures which have varied in fit ways, gradually form guiding tendencies, prompting appropriate behavior and deterring from inappropriate. The contrast between fearless birds found on islands never before visited by man, and the birds around us, which show fear of man immediately they are out of the nest, exemplifies such adaptations.
By virtue of this process there have been produced to some extent among lower creatures, and there are being further produced in man, the sentiments appropriate to social life. Aggressive actions, while they are habitually injurious to the group in which they occur, are not unfrequently injurious to the individuals committing them; since, though certain pleasures may be gained by them, they often entail pains greater than the pleasures. Conversely, conduct restrained within the required limits, calling out no antagonistic passions, favors harmonious co-operation, profits the group, and, by implication, profits the average of its individuals. Consequently, there results, other things equal, a tendency for groups formed of members having this adaptation of nature, to survive and spread.
Among the social sentiments thus evolved, one of chief importance is the sentiment of justice. Let us now consider more closely its nature.
Stop an animal's nostrils, and it makes frantic efforts to free its head. Tie its limbs together, and its struggles to get them at liberty are violent. Chain it by the neck or leg, and it is some time before it ceases its attempts to escape. Put it in a cage, and