It is significant that the most typical specimens of working songs and dances should be met with in the tribes of Oceania. The insular life, which even in other respects has been so favourable to the development of art, has necessitated a most intimate co-operation between individuals.[412] Hence the development of canoe dances and boating songs, by help of which the movements of the rowers are adjusted according to common and fixed rhythms.[413] The same necessity has of course produced similar results, in a greater or less degree, in every community where the type of life makes collective action needful. It has not given rise to any important manifestations of art among the pastoral tribes, in which individuals can do well enough without help from each other. In agricultural societies, on the other hand, it has called forth those sowing and harvest dances or songs which are so familiar in the folklore of the civilised nations.[414] And, more than any other of life’s occupations, war has required an active coherence between the individual members of the tribe. The influence of military institutions on art is, however, in more than one respect so important that its treatment must be reserved for a special chapter. CHAPTER XIX ART AND WAR In the _Principles of Sociology_ Mr. Spencer has devoted some of his most forcible paragraphs to a treatment of the social influences of war. By adducing and comparing with each other types of social life among different tribes, he has been able to show how military customs everywhere tend to reduce the individual liberty and strengthen the central power.[415] Many other writers on sociology have perceived and commented on the truism that the internal coherence of tribes has been chiefly produced by the need of combination for defensive purposes.[416] But perhaps sufficient attention has not been paid to the share which art has had in the development of those peculiarities which are common to all military nations. And yet as a means of facilitating tribal unity of action and feeling, music and dance must be of exceptional sociological importance in warlike communities.[417]