Hudson remarks that it seems strange that animals so well prepared to defend themselves should possess this “safeguard.” When caught or run down by dogs, the fox fights savagely at first, but after a time its efforts stop, it relaxes, and it drops to the ground. The animal appears dead, and Hudson states that the dogs are “constantly taken in by it.” He has seen the gauchos try the most barbarous tricks on a captive fox in this condition, and, despite the mutilations to which it was subjected, it did not wince. If, however, the observer draws a little away from the animal, “a slight opening of the eye may be detected, and finally, when left to himself, he does not recover and start up like an animal that has been stunned, but cautiously raises his head at first and only gets up when his foes are at a safe distance.” Hudson, coming once suddenly upon a young fox, saw it swoon at his approach, and although it was lashed with a whip it did not move.

The common partridge of the pampas of La Plata (Hothura maculosa) shows this death-feigning instinct in a very marked degree. “When captured, after a few violent struggles to escape, it drops its head, gasps two or three times, and to all appearance dies.” But if it is released it is off in an instant. The animal is excessively timid, and if frightened, may actually die simply from terror. If they are chased, and can find no thicket or burrow into which to escape, “they actually drop down dead on the plain. Probably when they feign death in their captor’s hand they are in reality very near to death.”

In this latter instance it must appear very improbable that we are dealing with an instinct that has been built up by slow degrees on account of the benefit accruing at each stage to the individual. In fact, it appears that the instinct is in this case of really no use at all to the animal, for there can scarcely be any question of an escape by this action. Yet so far as we can judge it is the same instinct shown by other animals, and it is not logical to account for its origin in one case on the grounds of its usefulness, when we cannot apply the explanation in the other cases. If this be admitted, we have another illustration of the importance of keeping apart the origin of an instinct or of a structure and the fact of its usefulness or non-usefulness to the organism. Thus under certain conditions this death-feigning instinct might really be of use to the animal, while under other conditions and in other animals it may be of no advantage at all, and in still other conditions it may be a positive injury to its possessor. Perhaps we need not go outside of our own experience to find a parallel case, for the state of fright into which imminent danger may throw an individual may deprive him for the moment of the proper use of those very mental qualities of which he stands in this crisis in greatest need.

The peculiar behavior of cattle caused by the smell of blood is another case of an instinct whose usefulness to its possessors is far from apparent. It is known that cattle and horses and several wild animals become violently excited by the smell of blood. Hudson gives a vivid account of a scene witnessed by himself, the animals congregating, “and moving around in a dense mass, bellowing continually.” Those animals that forced their way into the centre of the mass where the blood was “pawed the earth and dug it up with their horns, and trampled each other down in their frantic excitement.”

This action leads us to a consideration of the behavior of animals toward companions in distress. “Herbivorous animals at such times will trample and gore the distressed one to death. In the case of wolves and other savage-tempered carnivorous species the distressed fellow is frequently torn to pieces and devoured on the spot.” If any one will be bold enough to claim in this case that this habit has been acquired because of advantage to the pack, i.e. if it be imagined that the pack gains more by feeding on a weak member than by letting him take his chances of recovery, it may be pointed out in reply that cattle also destroy their weak or injured, but do not devour them, and the same statement holds for birds, where the same instinct has often been observed. Romanes has suggested that the instinct of destroying the weak or injured members is of use because such members are a source of danger to the rest of the herd; but Hudson points out that it is not so much the weak and sickly members of the herd that are attacked in this way, as those that are injured, and concludes, “the instinct is not only useless, but actually detrimental.” He suggests that these “wild abnormal movements of social animals” are a sort of aberration, so “that in turning against a distressed fellow they oppose themselves to the law of being.” Yet whether we gain anything by calling this action aberrant or abnormal, the important fact remains that it is a definite response under certain external conditions, and is shown by all the individuals of the species.

The preceding illustrations of reactions that go to make up the so-called instincts of animals may be separated into those that are essential to the life of the individual or of the race, those that are of some apparent use, although not absolutely essential, and a few of no use at all, and fewer still that appear to be even injurious. If the latter reactions take place only rarely, as appears often to be the case, they are not sufficiently harmful to cause the destruction of the race. The evidence points to the conclusion, I believe, that the origin of these tropisms and instincts cannot be accounted for on the ground of their benefit to the individual or to the race; and it does not seem reasonable to make up one explanation for the origin of those that are essential, and another for those that are of little use or even of no use at all.

From what has been already said more than once, while discussing each particular case, the simplest course appears to be in all instances to look upon these instincts as having appeared independently of the use to which they may be put, and not as having been built up by selection of the individual variations that happen to give an organism some advantage over its fellows in a life and death struggle. It appears reasonable to deal with the origin of tropisms and instincts in general in the same way as in dealing with structures; for, after all, the tropism is only the outcome of some material or structural basis in the organism.

No attempt has been made here to interpret the more complex reactions of the nervous system, for until we can get some insight into the meaning of the simpler processes, we are on safer ground in dealing with these first.