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pical example of instinctive behaviour。 Gently lower a recently hatched bird into water： coordinated movements of the limbs follow in rhythmical sequence。 The behaviour is new to the individual though it is no doubt closely related to that of walking； which is no less instinctive。 There is a group of stimuli afforded by the 〃presentation〃 which results from partial immersion： upon this there follows as a complex response an application of the functional activities in swimming； the sequence of adaptive application on the appropriate presentation is determined by racial preparation。 We know； it is true； but little of the physiological details of what takes place in the central nervous system； but in broad outline the nature of the organic mechanism and the manner of its functioning may at least be provisionally conjectured in the present state of physiological knowledge。 Similarly in the case of the pecking of newly…hatched chicks； there is a visual presentation； there is probably a cooperating group of stimuli from the alimentary tract in need of food； there is an adaptive application of the activities in a definite mode of behaviour。 Like data are afforded in a great number of cases of instinctive procedure； sometimes occurring very early in life； not infrequently deferred until the organism is more fully developed； but all of them dependent upon racial preparation。 No doubt there is some range of variation in the behaviour； just such variation as the theory of natural selection demands。 But there can be no question that the higher animals inherit a bodily organisation and a nervous system； the functional working of which gives rise to those inherited modes of behaviour which are termed instinctive。
It is to be noted that the term 〃instinctive〃 is here employed in the adjectival form as a descriptive heading under which may be grouped many and various modes of behaviour due to racial preparation。 We speak of these as inherited； but in strictness what is transmitted through heredity is the complex of anatomical and physiological conditions under which； in appropriate circumstances； the organism so behaves。 So far the term 〃instinctive〃 has a restricted biological connotation in terms of behaviour。 But the connecting link between biological evolution and psychological evolution is to be sought；as Darwin fully realised；in the phenomena of instinct； broadly considered。 The term 〃instinctive〃 has also a psychological connotation。 What is that connotation？
Let us take the case of the swimming duckling or the pecking chick； and fix our attention on the first instinctive performance。 Grant that just as there is； strictly speaking； no inherited behaviour； but only the conditions which render such behaviour under appropriate circumstances possible； so too there is no inherited experience； but only the conditions which render such experience possible； then the cerebral conditions in both cases are the same。 The biological behaviour…complex； including the total stimulation and the total response with the intervening or resultant processes in the sensorium； is accompanied by an experience…complex including the initial stimulation…consciousness and resulting response… consciousness。 In the experience…complex are comprised data which in psychological analysis are grouped under the headings of cognition； affective tone and conation。 But the complex is probably experienced as an unanalysed whole。 If then we use the term 〃instinctive〃 so as to comprise all congenital modes of behaviour which contribute to experience； we are in a position to grasp the view that the net result in consciousness constitutes what we may term the primary tissue of experience。 To the development of this experience each instinctive act contributes。 The nature and manner of organisation of this primary tissue of experience are dependent on inherited biological aptitudes； but they are from the outset onwards subject to secondary development dependent on acquired aptitudes。 Biological values are supplemented by psychological values in terms of satisfaction or the reverse。
In our study of instinct we have to select some particular phase of animal behaviour and isolate it so far as is possible from the life of which it is a part。 But the animal is a going concern； restlessly active in many ways。 Many instinctive performances； as Darwin pointed out （〃Origin of Species〃 （6th edition）； page 206。）； are serial in their nature。 But the whole of active life is a serial and coordinated business。 The particular instinctive performance is only an episode in a life…history； and every mode of behaviour is more or less closely correlated with other modes。 This coordination of behaviour is accompanied by a correlation of the modes of primary experience。 We may classify the instinctive modes of behaviour and their accompanying modes of instinctive experience under as many heads as may be convenient for our purposes of interpretation； and label them instincts of self…preservation； of pugnacity； of acquisition； the reproductive instincts； the parental instincts； and so forth。 An instinct； in this sense of the term （for example the parental instinct）； may be described as a specialised part of the primary tissue of experience differentiated in relation to some definite biological end。 Under such an instinct will fall a large number of particular and often well…defined modes of behaviour； each with its own peculiar mode of experience。
It is no doubt exceedingly difficult as a matter of observation and of inference securely based thereon to distinguish what is primary from what is in part due to secondary acquisitiona fact which Darwin fully appreciated。 Animals are educable in different degrees； but where they are educable they begin to profit by experience from the first。 Only； therefore； on the occasion of the first instinctive act of a given type can the experience gained be weighed as WHOLLY primary； all subsequent performance is liable to be in some degree； sometimes more； sometimes less； modified by the acquired disposition which the initial behaviour engenders。 But the early stages of acquisition are always along the lines predetermined by instinctive differentiation。 It is the task of comparative psychology to distinguish the primary tissue of experience from its secondary and acquired modifications。 We cannot follow up the matter in further detail。 It must here suffice to suggest that this conception of instinct as a primary form of experience lends itself better to natural history treatment than Darwin's conception of an impelling force； and that it is in line with the main trend of Darwin's thought。
In a characteristic work；characteristic in wealth of detail； in closeness and fidelity of observation； in breadth of outlook； in candour and modesty；Darwin dealt with 〃The Expression of the Emotions in Man and Animals〃。 Sir Charles Bell in his 〃Anatomy of Expression〃 had contended that many of man's facial muscles had been specially created for the sole purpose of being instrumental in the expression of his emotions。 Darwin claimed that a natural explanation； consistent with the doctrine of evolution； could in many cases be given and would in other cases be afforded by an extension of the principles he advocated。 〃No doubt；〃 he said （〃Expression of the Emotions〃； page 13。 The passage is here somewhat condensed。）； 〃as long as man and all other animals are viewed as independent creations； an effectual stop is put to our natural desire to investigate as far as possible the causes of Expression。 By this doctrine； anything and everything can be equally well explained。。。With mankind； some expressions。。。can hardly be understood； except on the belief that man once existed in a much lower and animal…like condition。 The community of certain expressions in distinct though allied species。。。is rendered somewhat more intelligible； if we believe in their descent from a common progenitor。 He who admits on general grounds that the structure and habits of all animals have been gradually evolved； will look at the whole subject of Expression in a new and interesting light。〃
Darwin relied on three principles of explanation。 〃The first of these principles is； that movements which are serviceable in gratifying some desire； or in relieving some sensation； if often repeated； become so habitual that they are performed； whether or not of any service； whenever the same desire or sensation is felt； even in a very weak degree。〃 （Ibid。 page 368。） The modes of expression which fall under this head have become instinctive through the hereditary transmission of acquired habit。 〃As far as we can judge； only a few expressive movements are learnt by each individual； that is； were consciously and voluntarily performed during the early years of life for some definite object； or in imitation of others； and then became habitual。 The far greater number of the movements of expression； and all the more important ones； are innate or inherited； and such cannot be said to depend on the will of the individual。 Nevertheless； all those included under our first principle were at first voluntarily performed for a definite object；namely； to escape some danger； to relieve some distress