the wider, freer, and more varied life of the higher animals the plastic survives and the stereotyped succumbs.

Imperfect as is our present knowledge of the manner in which the nervous connections implied in psychological associations are established, there can be no question that they are acquired in the course of individual life; they are modifications of nervous structure due to a special mode of use under the conditions of experience. Here, then, in the case of the nervous system, as in that of the bodily organs before mentioned, two factors determine the limits of efficiency -heredity and use. And these two, again, co-operate in such a way that we may say, either that due use-here represented by adequate experience-is the essential condition of the effective development of the hereditary potentialities, or that heredity serves to condition their effective development through use and experience. And just as the heart and lungs must inherit the power of standing abnormal strain if the animal is to avoid elimination in times of unwonted exertion, so must the nervous system inherit some reserve power of dealing effectively with unwonted circumstances by intelligent accommodation, if the animal is not to fall a victim to such circumstances. In other words, at times of heightened competition those animals which can draw on a reserve fund of intelligent accommodation will survive, while the stupid blunderers will be eliminated. We may term this reserve fund of intelligent accommodation, this inherited ability to meet specially difficult circumstances as they arise, innate capacity. From the nature of the case it must be indefinite, for it must carry with it the ability to meet unforeseen combinations of the environing forces by new combinations of the results of experience. Its distinguishing mark is plasticity, in contradistinction to the stereotyped fixity of typical instinct. And accompanying its evolution there is probably, as we have seen, a dissolution of its antithesis, instinct. Thus may we account for the fact that man, with his great store of innate capacity, has so small a number of stereotyped instincts.

But the dissolution of instincts is not complete. Residua are left in the inherited mental constitution. And these we term congenital tendencies and propensities. They differ from the typical instincts in the fact that the definiteness of response has been lost. They dictate a general trend of action, but the particular application in behaviour is due to intelligent accommodation. They are commonly spoken of as instinctive; and their mode of origin justifies the use of the adjective in association with the term "propensities." But it must be remembered that the behaviour to which they lead is not, as such, wholly instinctive; it is a joint product of instinct and intelligence, the general trend being due to the instinctive propensity, while the mode of application is guided by intelligence.

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There is, however, another way in which analogous propensities may be ingrained in the mental constitution. It is a well-known and familiar fact that the frequent repetition of intelligent accommodation in certain definite lines begets habits, which so far simulate instincts as to be commonly described in popular speech as instinctive. Professor Wundt indeed places them in the category of "acquired instincts"— a usage which we regard as unsatisfactory, seeing that it tends to mask the distinction between the congenital and acquired factors in behaviour, and seeing that we have the well-defined term habits" for acts rendered to a large extent automatic through repetition. Lamarckian thinkers regard habit as the mother of instinct, assuming that the acquired automatism of one generation may be transmitted to become congenital in the succeeding generation. This conclusion we provisionally reject regarding the basal assumption as at present unproven. But though we cannot accept the view that habit is the mother of instinct, we regard it as not improbable that habit may be the nurse of congenital propensities. Remembering that similar habits are acquired by animals of the same species throughout a series of succeeding generations, and assuming that congenital variations are constantly occurring in many directions, it seems probable that some of these variations will

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be coincident in direction with the acquired habits. Thus would arise a congenital propensity to perform the habitual acts; and should they be of sufficient importance in the conduct of life to be subject to the action of natural selection, those animals in which such propensities were congenital would survive, whereas those in which no such propensities existed would be eliminated. It is unnecessary, however, to elaborate this conception further, since it is in line with that already discussed in considering the influence of intelligence in fostering a diversion of instinct under changing circumstances.

Sufficient has now been said to illustrate some of the ways in which instinct and intelligence interact in the evolution of behaviour. Such interaction is further exemplified in the social life of animals, which will be dealt with in the next chapter.

THE characteristic feature of social behaviour is that it is in large degree determined by the behaviour of other members of the social community. In all animals which mate there is a temporary or more lasting influence on each other of the individuals which unite to procreate their kind; and in those which foster their young there is a social relation of parents and offspring. Some of these mutual relationships will be discussed, in their emotional aspects, in the next chapter. Here we will consider the more general factors which serve to determine the course of social evolution.

Among these is commonly reckoned imitation. M. Tarde says, La société c'est l'imitation." But this word, like so many others which are employed alike in popular speech and in more or less technical discussions, carries a somewhat wide range of meaning, and is by some writers used in a broader, by others in a narrower sense. Thus Professor Mark Baldwin * says, "that all organic adaptation in a changing environment is a phenomenon of biological or organic imitation," under which category will fall, therefore, the organic behaviour of the protozoa and of plants. On the other hand, Professor E. L. Thorndike, though he admits in the lower animals "certain pseudo-imitative or semi-imitative phenomena," has been led by experiments, to be presently noticed, to the conclusion that

* "Mental Development in the Child and the Race-Methods and Processes," p. 278.

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animals as high in the scale of life as cats and dogs cannot form new associations under the influence of imitation. "It seems sure," he says,* "from these experiments, that the animals were unable to form an association leading to an act from having seen another animal, or animals, perform the act in a certain situation." In face of such apparently diverse usage it is necessary to show within what limits and with what qualifications the word may profitably here be used to indicate a factor in social evolution.

Professor Mark Baldwin's use of the term "imitation" can only be understood in its relation to an hypothesis of organic and mental evolution, which he develops with no little skill and brilliancy. † He regards the processes of life as issuing in a great twofold adaptation, due to expansions and contractions, —the former representing waxing, the latter waning vitality ; and he holds that all special adaptations are secured by the new hold upon beneficial stimulations reached by the expansive outreaching movements. "Among the variations in organic forms,” he says, “it is easy to see that some of them might react in such a way as to keep in contact with the stimulus, to lay hold of it, and so keep on reacting to it again and again— just as our rhythmic action in breathing keeps the organism in vital contact with the oxygen of the air. These organisms will get all the benefit or damage of the repetition or persistence of the stimulus, or of their own reactions, again and again; and it is self-evident that the beneficial stimulations are the ones which should be maintained in this way, and that the organisms which did this would live. The organisms which reacted in such a way as to retain the damaging stimulations, on the other hand, by this same process, would aid nature in killing themselves. If this be true, only those organisms would survive which had the variation of retaining useful stimulations in what I have called, in speaking of imitation elsewhere, a ‘circular way' of reacting. . . . So, when we come to consider phylogeny

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* "Animal Intelligence:" monograph supplement to Psychological Review, 1898, p. 61.

† Op. cit., pp. 263, 172, 201, 132, and 248 (note).