The advantage the new unit obtains by aggressive gregariousness is chiefly its immense accession of strength as a hunting and fighting organism. Protective gregariousness confers on the flock or herd advantages perhaps less obvious but certainly not less important. A very valuable gain is the increased efficiency of vigilance which is possible. Such efficiency depends on the available number of actual watchers and the exquisite sensitiveness of the herd and all its members to the signals of such sentries. No one can have watched a herd of sheep for long without being impressed with the delicacy with which a supposed danger is detected, transmitted throughout the herd, and met {111} by an appropriate movement. Another advantage enjoyed by the new unit is a practical solution of the difficulties incident upon the emotion of fear. Fear is essentially an enfeebling passion, yet in the sheep and such animals it is necessarily developed to a high degree in the interests of safety. The danger of this specialization is neutralized by the implication of so large a part of the individual’s personality in the herd and outside of himself. Alarm becomes a passion, as it were, of the herd rather than of the individual, and the appropriate response by the individual is to an impulse received from the herd and not directly from the actual object of alarm. It seems to be in this way that the paralysing emotion of fear is held back from the individual, while its effect can reach him only as the active and formidable passion of panic. The gregarious herbivora are in fact timid but not fearful animals. All the various mechanisms in which the social habit shows itself apparently have as their general function a maximal sensitiveness to danger of the herd as a whole, combined with maintaining with as little interruption as possible an atmosphere of calm within the herd, so that the individual members can occupy themselves in the serious business of grazing. It must be doubted whether a truly herbivorous animal of a solitary habit could ever flourish when we remember how incessant must be his industry in feeding if he is to be properly nourished, and how much such an occupation will be interfered with by the constant alarms he must be subject to if he is to escape the attacks of carnivorous enemies. The evidence suggests that protective gregariousness is a more elaborate manifestation of the social habit than the aggressive form. It is clear that the security of the higher herbivora, such as the ox and especially the horse and their allies, is considerable in relation to the carnivora. One may {112} permissibly perhaps indulge the speculation that in the absence of man the horse possibly might have developed a greater complexity of organization than it has actually been able to attain; that the facts should seem to contain this hint is a curious testimony to the wonderful constructive imagination of Swift.