Already, while showing that among inferior creatures, pleasures and pains have all along guided the conduct by which life has been evolved and maintained, I have pointed out that since the conditions of existence for each species have been occasionally changing, there have been occasionally arising partial misadjustments of the feelings to the requirements, necessitating readjustments. This general cause of derangement, operating on all sentient beings, has been operating on human beings in a manner unusually decided, persistent, and involved. It needs but to contrast the mode of life followed by primitive men, wandering in the forests and living on wild food, with the mode of life followed by rustics, artisans, traders, and professional men in a civilized community, to see that the constitution, bodily and mental, well-adjusted to the one, is ill-adjusted to the other. It needs but to observe the emotions kept awake in each savage tribe, chronically hostile to neighboring tribes, and then to observe the emotions which peaceful production and exchange bring into play, to see that the two are not only unlike, but opposed. And it needs but to note how, during social evolution, the ideas and sentiments appropriate to the militant activities carried on by coercive co-operation have been at variance with the ideas and sentiments appropriate to the industrial activities, carried on by voluntary co-operation, to see that there has ever been within each society, and still continues, a conflict between the two moral natures adjusted to these two unlike modes of life. Manifestly, then, this readjustment of constitution to conditions, involving readjustment of pleasures and pains for guidance, which all creatures from time to time undergo, has been in the human race during civilization especially difficult, not only because of the greatness of the change from small nomadic groups to vast settled societies, and from predatory habits to peaceful habits, but also because the old life of enmity between societies has been maintained along with the new life of amity within each society. While there co-exist two ways of life so radically opposed as the militant and the industrial, human nature cannot become properly adapted to either.