The view is widely held and continually referred to by many writers on war and politics, that the most fundamental of all causes of war, or the most general principle of it, is the principle of selection--that war is a natural struggle between groups, especially between races, the fittest in this struggle tending to survive. This view needs to be examined sharply, as indeed it has been by several writers, in connection with the present war. This biological theory or apology of war appears in several forms, as applied to-day. They say that racial stocks contend with one another for existence, and with this goes the belief that nations fight for life, and that defeat in war tends towards the extermination of nations. The Germans, we often hear, were fighting for national existence, and the issue was to be a judgment upon the fitness of their race to survive. This view is very often expressed. O'Ryan and Anderson (5), military writers, for example, say that the same aggressive motives prevail as always in warfare: nations struggle for survival, and this struggle for survival must now and again break out into war. Powers (75) says that nations seldom fight for anything less than existence. Again (15) we read that conflicts have their roots in history, in the lives of peoples, and the sounder, and better, emerge as victors. There is a selective process on the part of nature that applies to nations; they say that especially increase of population forces upon groups an endless conflict, so that absolute hostility is a law of nature in the world. These views contain at least two very doubtful assumptions. One is that nations do actually fight for existence,--that warfare is thus selective to the point of eliminating races. The other is that in warlike conflicts the victors are the superior peoples, the better fitted for survival. Confusion arises and the discussion is complicated by the fact that conflicts of men as groups of individuals within the same species are somewhat anomalous among biological forms of struggle. Commonly, struggle takes place among individuals, organisms having definite characteristics and but slightly variable each from its own kind contending with one another, by direct competition or through adaptation, in the first case individuals striving to obtain actually the same objects. Or, again, species having the same relations to one another that individuals have, contend in a similar manner.