Gregariousness seems frequently to be regarded as a somewhat superficial character, scarcely deserving, as it were, the name of an instinct, advantageous it is true, but not of fundamental importance or likely to be deeply ingrained in the inheritance of the species. This attitude may be due to the fact that among mammals at any rate the appearance of gregariousness has not been accompanied by any very gross physical changes which are obviously associated with it.[C] [C] Among gregarious insects there are of course physical changes arising out of and closely dependent on the social organization. To whatever it may be due, this method of regarding the social habit is, in the opinion of the present writer, not justified by the facts, and prevents the attainment of conclusions of considerable fruitfulness. A study of bees and ants shows at once how {20} fundamental the importance of gregariousness may become. The individual in such communities is completely incapable, often physically, of existing apart from the community, and this fact at once gives rise to the suspicion that even in communities less closely knit than those of the ant and the bee, the individual may in fact be more dependent on communal life than appears at first sight. Another very striking piece of general evidence of the significance of gregariousness as no mere late acquirement is the remarkable coincidence of its occurrence with that of exceptional grades of intelligence or the possibility of very complex reactions to environment. It can scarcely be regarded as an unmeaning accident that the dog, the horse, the ape, the elephant, and man are all social animals. The instances of the bee and the ant are perhaps the most amazing. Here the advantages of gregariousness seem actually to outweigh the most prodigious differences of structure, and we find a condition which is often thought of as a mere habit, capable of enabling the insect nervous system to compete in the complexity of its power of adaptation with that of the higher vertebrates. If it be granted that gregariousness is a phenomenon of profound biological significance and one likely therefore to be responsible for an important group of instinctive impulses, the next step in our argument is the discussion of the question as to whether man is to be regarded as gregarious in the full sense of the word, whether, that is to say, the social habit may be expected to furnish him with a mass of instinctive impulse as mysteriously potent as the impulses of self-preservation, nutrition, and sex. Can we look to the social instinct for an explanation of some of the “_a priori_ syntheses of the most perfect sort needing no proof but their own evidence,” which are not explained by the three {21} primitive categories of instinct, and remain stumbling-blocks in the way of generalizing the conduct of man?