1. The animal kingdom exhibits a series of mental developments which may be regarded as antecedents to the mental development of man. The mental life of animals shows itself to be in its elements and in the general laws of their combination everywhere the same as that 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. 237). They reach a more advanced stage of development in higher animals only through the increase in the variety of ideas and in the length of time through which the memory-processes extend. From the like structure and development of the sense-organs we must draw the conclusion that the character of the sense-ideas are 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 in the case of the higher organisms in the first stages of their individual development (p. 39).
In contrast whith [sic] this uniformity of psychical elements and their simpler combinations there are great differences in [p. 277] all the processes connected with the development of apperception.
Passive apperception is never absent as the basis for the simple impulsive acts that are found everywhere, but active apperception in the form of voluntary attention to certain impressions and a 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 at most, if at all, only find the first beginnings of intellectual processes in the proper sense of the word, that is activities of imagination and understanding, even in the animals with the highest mental development. Connected with this fact is the other that higher animals have no developed language, though they are able to give expression to their emotions and even their ideas, when these are connected with emotions, through various expressive movements often 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 secondly, certain single functions particularly favored by the special conditions under which the species lives, are more highly developed.
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 for a long time after clumsy in his movements. Yet, 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 [p. 278] in some animals is still 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 that 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 and sexual impulses, is just as much a connate attribute of man as of the animals. The only thing that is characteristic 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 those of men. It is also remarkable that domestication generally tends to do away with the instincts that animals had in their wild state, and to develop new ones that may generally be regarded as modifications of the wild instincts, as, for example, those 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 the former.
The whole psychical life of animals consists almost entirely of the processes that are connected with the predominating instinct.
4. In general, instincts may be regarded as impulsive acts that arise from particular sensations and sense-feelings.