In the tropics, the home of the anthropoid apes of to-day and, probably, of the animal we have named the man-ape, war between man and nature scarcely exists. Nature is not hostile to man. There is no occasion for clothing and little for habitation. Food is abundant for the sparse populations. Little exertion is called for to sustain life. Mental stagnation is very likely to supervene. Yet there, as elsewhere, conflict has had much to do with such mental progress as exists. Mastery in warfare is due to superior mental resources, which gradually arise from the exigencies of conflict, and manifest themselves in greater shrewdness or cunning, superior ability in leadership, better organization, fuller mutual aid, and the invention of more destructive weapons and more efficient tools. War acts vigorously on men's minds, peace acts sluggishly. In the former case man's most valued possession, his life, is in jeopardy, and his utmost powers are exerted for its preservation. Every resource within his power is brought to bear to save himself from wounds or death and to destroy his enemies. If the foes are equal physically, victory is apt to come to those which are superior mentally, which are quicker at devising new expedients, more alert in providing against danger, more skilful in the use of weapons, abler in combining their forces to act in unison. In short, the whole story of mankind tells us that mental evolution has been greatly aided by the influences of warfare, the reaction upon the mind of the effort at self-preservation, the destruction of those at a lower level of intellectual alertness, the preservation of the abler and more energetic, the effect of conflict in bringing into activity all the resources of the intellect, and the hereditary transmission of the powers of mind thus developed. It is, undoubtedly, to war between man and man, and the conflict with the adverse conditions of nature in the colder regions of the earth, that man's development from his lowest to his highest intellectual state has been largely due. This is by no means to say that war is still necessary for this result. Other influences are now at work, of equal or superior potency, and while the conflict with nature and the conditions of society is still of importance, war between man and man is no longer necessary as a mental stimulant. The time was, and that not very far in the past, when it was an essential element in human development.