Nature has thus made two great experiments of the same type, and if one be reasonably careful to avoid arguing from analogy, it is possible to use one case to illuminate the other by furnishing hints as to what mechanisms may be looked for and in what directions inquiry may profitably be pursued.
The sporadic occurrence of gregariousness at widely separated points of the animal field—in man and sheep, in ant and elephant—inclines one to suppose that multicellularity must have arisen also at multiple points, and that the metazoa did not arise from the protozoa by a single line of descent. It {104} suggests also that there is some inherent property in mobile living organisms that makes combination of individuals into larger units a more or less inevitable course of development under certain circumstances and without any gross variation being necessary to initiate it. The complex evolution which multicellularity made possible, and perhaps enforced, can scarcely fail to make one wonder whether the gregarious animal has not entered upon a path which must of necessity lead to increasing complexity and co-ordination, to a more and more stringent intensity of integration or to extinction.
The varying degrees to which the social habit has developed among different animals provide a very interesting branch of study. The class of insects is remarkable in furnishing an almost inexhaustible variety of stages to which the instinct is developed. Of these that reached by the humble bee, with its small, weak families, is a familiar example of a low grade; that of the wasp, with its colonies large and strong, but unable to survive the winter, is another of more developed type; while that of the honey bee represents a very high grade of development in which the instinct seems to have completed its cycle and yielded to the hive the maximum advantages of which it is capable. In the honey bee, then, the social instinct may be said to be complete.
It is necessary to examine somewhat closely into what is denoted by the completeness or otherwise of the social habit in a given species.
To return for a moment to the case of the change from the unicellular to the multicellular, it is obvious that in the new unit, to get the full advantage of the change there must be specialization involving both loss and gain to the individual cell; one loses power of digestion and gains a special sensitiveness to stimulation, another loses locomotion {105} to gain digestion, and so forth in innumerable series as the new unit becomes more complex. Inherent, however, in the new mechanism is the need for co-ordination if the advantages of specialization are to be obtained. The necessity of a nervous system—if progress is to be maintained—early becomes obvious, and it is equally clear that the primary function of the nervous system is to facilitate co-ordination. Thus it would seem that the individual cell incorporated in a larger unit must possess a capacity for specialization, the ability to originate new methods of activity, and a capacity for response—that is, the ability to limit itself to action co-ordinated suitably to the interests of the new unit rather than to those that would have been its own if it had been a free unit in itself. Specialization and co-ordination will be the two necessary conditions for success of the larger unit, and advance in complexity will be possible as long only as these two are unexhausted. Neither, of course, will be of avail without the other. The richest specialization will be of no good if it cannot be controlled to the uses of the whole organism, and the most perfect control of the individual cells will be incapable of ensuring progress if it has no material of original variation to work on.
The analogy is helpful in the consideration of the mechanisms brought into play by the social habit. The community of the honey bee bears a close resemblance to the body of a complex animal. The capacity for actual structural specialization of the individuals in the interests of the hive has been remarkable and has gone far, while at the same time co-ordination has been stringently enforced, so that each individual is actually absorbed into the community, expends all its activities therein, and when excluded from it is almost as helpless as a part of the naked flesh of an animal {106} detached from its body. The hive may, in fact, without any very undue stretch of fantasy, be described as an animal of which all the individual cells have retained the power of locomotion. When one watches the flight of a swarm of bees its unanimity and directness very easily produce the illusion that one is witnessing the migration of a single animal usually sedentary but at times capable of undertaking journeys with a formidable and successful energy. This new animal differs from the other animals of the metazoa which it has outdistanced in the race of evolution, not merely in its immense power, energy, and flexibility, but also in the almost startling fact that it has recovered the gift of immortality which seemed to have been lost with its protozoal ancestors.
The extent to which the hive makes use of the powers of its individuals is the measure of the completeness with which the social habit is developed in it. The worker bee has practically no activities which are not directly devoted to the hive, and yet she goes about her ceaseless tasks in a way that never fails to impress the observer with its exuberant energy and even its appearance of joyfulness. It is thought that the average worker bee works herself to death in about two months. That is a fact which can scarcely fail to arouse, even in the least imaginative, at any rate a moment of profound contemplation.
If we could suppose her to be conscious in the human sense, we must imagine the bee to be possessed by an enthusiasm for the hive more intense than a mother’s devotion to her son, without personal ambitions, or doubts or fears, and if we are to judge by the imperfect experience man has yet had of the same lofty passion, we must think of her consciousness, insignificant spark as it is, as a little fire ablaze with altruistic feeling. Doubtless, such {107} an attribution of emotion to the bee is a quite unjustified fallacy of anthropomorphism. Nevertheless, it is not altogether valueless as a hint of what social unity might effect in an animal of larger mental life. There can be little doubt that the perfection to which the communal life of the bee has attained is dependent on the very smallness of the mental development of which the individuals are capable. Their capacity to assimilate experience is necessarily from their structure, and is known by experience to be, small and their path is marked out so plainly by actual physical modifications that the almost miraculous absorption of the worker in the hive is after all perhaps natural enough. If she were able to assimilate general experience on a larger scale, to react freely and appropriately to stimuli external to the hive, there can be little doubt that the community would show a less concentrated efficiency than it does to-day. The standing miracle of the bee—her sensitiveness to the voice of the hive and her capacity to communicate with her fellows—would undoubtedly be less marvellously perfect if she were not at the same time deaf to all other voices.
When we come to consider animals in which the anatomist can recognize a brain and the psychologist an individual mind, the types of gregariousness we meet with are found to have lost the magnificent intensity of the bee. This decline in intensity seems to be due to the greatly increased variety of reaction of which the individual is capable. The gregarious mammalia are most of them relatively intelligent, they are capable of assimilating experience to a certain extent and have a definite capacity for individual existence. In them the social habit shows comparatively little tendency to a gradual intensification, but is a more static condition. Doubtless, there are other conditions {108} which also limit it. For example, the slowness of multiplication and fixity of structure in the mammalia obviously deprive them of the possibility of undergoing a continuous social integration as the insects have. Be this as it may, we find in them the social habit but little or scarcely at all expressed in physical specialization but shown as a deeply ingrained mental character which profoundly influences their habits and their modes of reaction to bodily and external impressions. Among the mammalia other than man and possibly apes and monkeys, gregariousness is found in two broadly distinguishable types according to the function it subserves. It may be either protective as in the sheep, the deer, the ox, and the horse, or aggressive as in the wolf and allied animals. In both forms it will involve certain common types of capacity, while the distinguishing characteristic of each will be a special kind of reaction to certain stimuli. It is important to understand that these peculiarities are possessed by each individual of the larger unit, and will be displayed by him in a characteristic way whether he is in the company of his fellows or not. It is not necessary to repeat here in any detail the characters of the gregarious mammal. They have been dealt with in an earlier essay, but it is desirable to emphasize here certain features of exceptional importance and some which were but little discussed before.
The quite fundamental characteristic of the social mammal, as of the bee, is sensitiveness to the voice of his fellows. He must have the capacity to react fatally and without hesitation to an impression coming to him from the herd, and he must react in a totally different way to impressions coming to him from without. In the presence of danger his first motion must be, not to fly or to attack as the case may be, but to notify the herd. This characteristic is beautifully demonstrated in the low {109} growl a dog will give at the approach of a stranger. This is obviously in no way part of the dog’s programme of attack upon his enemy—when his object is intimidation he bursts into barking—but his first duty is to put the pack on its guard. Similarly the start of the sheep is a notification and precedes any motion of flight.