1. The animal kingdom exhibits a series of mental developments which may be regarded as antecedents to the mental development of man, for the mental life of animals shows itself to be throughout, in its elements and in the general laws governing the combination of these elements, the same as the mental life of man.

Even the lowest animals (protozoa and coelenterata) manifest vital phenomena that allow us to infer ideational and volitional processes. They seize their food, to all appearances spontaneously; they flee from pursuing enemies, etc. There are also to be found in the lowest stages of animal life traces of associations and reproductions and especially processes of sensible cognition and recognition (p. 267). In the higher animals these functions reach a more advanced stage of development only through the increase in the length of time through which the memory processes extend. Furthermore, from the fact that structure and development of the sense organs is similar in man and animals, we must draw the conclusion that the character of the sense ideas is in general the same, the only difference being that in the lowest forms of life the sensory functions are limited to the general sense of touch, just as they are in the case of the higher organisms in the first stages of their individual development (p. 51).

In contrast with this uniformity of psychical elements and their simpler combinations, there are great differences in all the processes connected with the development of apperception. Passive apperception is never absent as the basis of the simple impulsive acts which are found everywhere, but active apperception in the form of voluntary attention to certain impressions and choice between different motives, probably never exists except in the higher animals. Even here it is limited to the ideas and associations aroused by immediate sensible impressions, so that we can find even in animals with the highest mental development certainly nothing more than the first beginnings of intellectual processes in the proper sense of the word, that is, activities of imagination and understanding. Indeed, it may be questioned whether even these first beginnings are here present. Connected with this fact is the fact that higher animals have no developed language, though they are able to give expression to their emotions and even their ideas, when these ideas are connected with emotions, through various expressive movements which are frequently related to those of man.

2. Though the development of animals is in general far behind that of man, in spite of the qualitative likeness of the fundamental psychical processes, still, in two ways it is often superior. First, animals reach psychical maturity much more rapidly, and second, certain single functions particularly favoured by the special conditions under which the species lives, are often more highly developed than the corresponding function in man. The fact of more rapid maturity is shown by the early age at which many animals (some immediately after birth) are able to receive relatively clear sense impressions and to execute purposive movements. To be sure, there are very great differences among higher animals in this respect. For example, the chick just out of the shell begins to pick up grain, while the pup is blind at birth, and is for a long time after birth clumsy in his movements. The development of the child seems to be the slowest and the most dependent on help and care from others.

3. The special one-sided development of single functions in some animals is even more striking. These functions show themselves in certain impulsive acts regularly connected with the satisfaction of certain needs, either of alimentation, reproduction, or protection, and in the development of the sense perceptions and associations which form the motives for such acts. Such specially developed impulses are called instincts. The assumption that instincts belong only to animal and not to human consciousness is, of course, entirely unpsychological, and contradictory to experience. The disposition to manifest the general animal impulses, namely, the alimentive impulses and sexual impulses, is just as much a connate attribute of man as of the animals. The only thing that is characteristic of animals is the special highly developed form of the purposive acts by which many animals reach the ends aimed at. Different animals, however, are very different in this respect. There are numerous lower and higher animals whose acts resulting from connate instincts show as few striking characteristics as do those of men. It is also noteworthy that domestication generally tends to do away with the instincts which animals had in their wild state, and to develop new ones which may generally be regarded as modifications of the wild instincts. This is seen, for example, in the instincts of certain hunting dogs, especially those of bird-dogs and pointers. The relatively high development of certain special instincts in animals as compared with men, is simply a manifestation of the general unsymmetrical development of animals. The whole psychical life of animals consists almost entirely of the processes which are connected with the predominating instinct.

4. In general, instincts may be regarded as impulsive acts which arise from particular sensations and feelings. The physiological sources of the sensations chiefly concerned in instincts' are the alimentary and genital organs. All animal instincts may, accordingly, be reduced to alimentive and sexual instincts, though in connection with the latter, especially in their more complex forms, there are always auxiliary protective and social impulses which may be regarded, from the character of their origin, as special modifications of the sexual impulse. Among these auxiliary forms must be classified the impulses of many animals to build houses and nests, as is the case with beavers, birds, and numerous insects (for example, spiders, wasps, bees, ants), and also the instinct of animal marriage found chiefly among birds and appearing both in the monogamic and polygamic forms. Finally, the so-called "animal states", as those of the bees, of ants, and of termites, belong under this head. They are in reality not states, but sexual communities, in which the social impulse which unites the individuals, as well as the common protective impulse, are modifications of the reproduction impulse.

In the case of all instincts the particular concrete impulsive acts arise from certain sense stimuli, partly external, partly internal. The acts themselves are to be classed as impulsive acts, or simple volitions, since they are preceded and accompanied by particular sensations and feelings which serve as simple motives. The complex, connate character of these acts can be explained only from general inherited attributes of the nervous system, as a result of which connate reflex mechanisms are immediately, without practice on the part of the individual, set in action by certain stimuli. The purposive character of these mechanisms must also be regarded as a product of general psycho-physical development. As further evidence of this we have the fact that instincts show not only various modifications in different individuals, but they also show a certain degree of higher development through individual practice. In this way, the bird gradually learns to build its nest better; bees accommodate themselves to changing needs, instead of sending out new colonies they enlarge the hive if they have the necessary room. Even abnormal habits may be acquired by a single community of bees or ants; bees, for example, may learn to rob a neighboring hive instead of gathering the honey from the flowers, or ants may acquire the remarkable habit of making the members of another species slaves, or of domesticating plant-lice for the sake of their honey. The rise, growth, and transmission of these habits, as we can trace them, show clearly the way in which all complicated instincts may arise. An instinct never appears alone, but there are always simpler forms of the same instinct in related classes and species. Thus the hole that the wall-wasp bores in the wall in which to lay her eggs, is a primitive pattern of the ingenious hive of the honey-bee. Between these two extremes there is, as the natural transition stage, the hive of the ordinary wasp made of a few hexagonal cells constructed of cemented sticks and leaves.

We may, accordingly, explain the complex instincts as developed forms of originally simple impulses which have gradually differentiated more and more in the course of numberless generations, through the gradual accumulation of habits which have been acquired by individuals and then transmitted. Every single habitual act is to be regarded as a stage in this psychical development. The gradual passage of a habit into a connate disposition is to be explained as a psycho-physical process of practice through which complex volitional acts gradually pass into automatic movements following immediately and reflexly the appropriate impression.

5. If we try to answer the general question of the genetic relation of man to the animals on the ground of a comparison of their psychical attributes, it must be admitted, in view of the likeness of psychical elements and of their simplest and most general forms of combination, that it is possible that human consciousness has developed from a lower form of animal consciousness. This assumption is also rendered stronger by the fact that the animal kingdom presents a whole series of different stages of psychical development and that every human individual passes through an analogous development. The doctrine of psychical development thus confirms in general the results of the theory of physical evolution. We must not, however, overlook the fact that between the psychical attributes of man and those of the animals, as expressed in the intellectual and affective processes resulting from apperceptive combinations, there are differences much broader than the differences in their physical characteristics. Then too, the great stability of the psychical condition of animals, which condition undergoes little change even in domestication, renders it exceedingly improbable that any of the present animal forms will develop in their psychical attributes, much beyond the limits that they have already reached.

5a. The attempts to define the relation of man and animals from a psychological point of view vary between two extremes. One of these is the predominating view of the old psychology that the higher "faculties of mind", especially "reason", are entirely wanting in animals, or that, as descartes held, animals are mere reflex mechanisms without mind. The other is the wide-spread opinion of representatives of special animal psychology, that animals are essentially equal to man in all respects, in ability to consider, to judge, to draw conclusions, in moral feelings, etc. With the rejection of faculty-psychology the first of these views becomes untenable. The second rests on the tendency prevalent in popular psychology to interpret all objective phenomena in terms of human thought, especially in terms of logical reflection. The closer analysis of so-called manifestations of intelligence among animals shows, however, that they are in all cases fully explicable as simple sensible recognitions and associations, and that they lack the characteristics belonging to concepts proper and to logical operations. But associative processes pass without a break into apperceptive, and the beginnings of the latter, that is, simple acts of active attention and choice, appear without any doubt in the case of higher animals, so that the difference is after all more one of the degree and complexity of the psychical processes than a difference in kind.

Animal instincts presented a great difficulty to the older forms of psychology, such as the faculty theory and the intellectualistic theories (§ 2). There the attempt to deduce these instincts from the conditions given in each individual case led to an improbably high estimate of the psychical ability of the animal, especially when the instinct was more complex. As a result, the conclusion was often accepted that instincts are incomprehensible, or, what amounts to the same thing, due to connate ideas. This "enigma of the instincts" ceases to be an enigma when we come to look upon instincts, as we have done above, as special forms of impulsive action, and consider them as analogous to the simple impulsive acts of men and animals, for which we have a psychological explanation. This is especially true when we follow the reduction of what were originally complicated acts, to impulsive or reflex movements in the phenomena of habit. Such reduction can be easily observed in the case of man, as for example in the habituation to complex movements in learning to play the piano (comp. p. 221 sq.). It is often argued against this theory of instinct that it is impossible to prove empirically the transmission of acquired individual variations which we have assumed; that, for example, there are no certain observations in proof of the transmission of mutilations, as was formerly so frequently asserted. Many biologists accept the view that all the properties of the organism arise through the selection resulting from the survival of the individual best adapted to natural conditions; that all such properties of the individual are accordingly deducible from "natural selection", and that in this way alone changes can be produced in the germ and transmitted to descendants. Though it is admitted that an attribute acquired by a single individual, generally has no effect on the descendents, still, there is no apparent reason why habitual acts, which are indeed indirectly due to outer natural conditions, but depend primarily on the inner psycho-physical attributes of the organism, may not, just as well as the direct influences of natural selection, cause changes in the nature of the germ, at least, when the acts in question are repeated through many generations. Further evidence in favor of the view we have been defending is to be found in the fact that in some cases whole families inherit peculiar expressive movements or technical ability in some line. This does not exclude in any case the cooperation of natural influences, but is in full agreement with the facts of observation which show that these influences act in two ways: first, directly in the changes which natural selection brings about in the organism while the organism remains passive, and second, indirectly in the psycho-physical reactions which are caused by the outer influences, and which then in turn give rise to changes in the organism. If we deny the latter fact, we not only lose an important means of accounting for the purposive character of organisms, but further, and more especially, we render impossible a psychological explanation of the gradual development of volition and its retrogradation into purposive reflexes which processes we see going on in a large number of connate expressive movements (§ 20, 1).

References. Schneider, Der tierische Wille, 1880. Romanes, Mental Evolution in Animal. Espinas, Die tierischen Gesellschaften, 1889. Lubbock, Ants, Bees and Wasps. Wasmann, Instinkt und Intelligenz im Tierreich, 1897, and Die psychischen Fähigkeiten der Ameisen, Zoologica, vol. 26, 1899. Bethe, Pflüger's Archiv f. Physiol., vol. 70 (the author seeks to reduce the instinctive acts of ants and bees to pure mechanical reflexes). Groos, (Engl. trans. by Baldwin) The Play of Animals. Wundt, Lectures, lectures 23, 24, 27 and 28.