The conception of man as a gregarious animal is, of course, extremely familiar; one frequently meets with it in the writings of psychologists and sociologists, and it has obtained a respectable currency with the lay public. It has, indeed, become so hackneyed that it is the first duty of a writer who maintains the thesis that its significance is not even yet fully understood, to show that the popular conception of it has been far from exhaustive. As used hitherto the idea seems to have had a certain vagueness which greatly impaired its practical value. It furnished an interesting analogy for some of the behaviour of man, or was enunciated as a half serious illustration by a writer who felt himself to be in an exceptionally sardonic vein, but it was not at all widely looked upon as a definite fact of biology which must have consequences as precise and a significance as ascertainable as the secretion of the gastric juice or the refracting apparatus of the eye. One of the most familiar attitudes was that which regarded the social instinct as a late development. The family was looked upon as the primitive unit; from it developed the tribe, and by the spread of family feeling to the tribe the social instinct arose. It is interesting that the psychological attack upon this position has been anticipated by sociologists and anthropologists, and that it is already being recognized that an undifferentiated horde rather than the family must be regarded as the primitive basis of human society. The most important consequence of this vague way of regarding the social habit of man has been that no exhaustive investigation of its psychological corollaries has been carried out. When we see the enormous effect in determining conduct that the gregarious inheritance has in the bee, the ant, the {22} horse, or the dog, it is quite plain that if the gregariousness of man had been seriously regarded as a definite fact a great amount of work would have been done in determining precisely what reactive tendencies it had marked out in man’s mind. Unfortunately, the amount of precise work of this kind has been very small.