February 3. 1898] 



NATURE 



329 



organs. The former gives the well-defined consciousness of 

 activity ; the latter the relatively ill defined feelings which are 

 classed as emotional. But so swift is the backstroke from the 

 Ixxly to the brain that, ere the instinctive behaviour is complete, 

 messages from the limbs— and, under the appropriate circum- 

 stances, from the heart — that is to say, of both instinctive and 

 emotional origin — begin to be operative in consciousness, and 

 the final stages of a given performance may be guided in the 

 light of the experience gained during its earlier stages. 



The exact manner in which consciousness exercises its guiding 

 influence, is a matter of speculation. Perhaps the most probable 

 hypothesis is that the cerebral hemispheres are an adjunct to the 

 rest of the central nervous system, and exercise thereon by some 

 such mechanism as the pyramidal tract in the human subject, a 

 controlling influence. Given an hereditary ground-plan of auto- 

 matic and instinctive responses the cerebral hemispheres may, 

 by checking here and enforcing there, limit or extend the be- 

 haviour in definite ways. In any case, from the psychological 

 point of view, their action is dependent on three fundamental 

 properties : first, the retention of modifications of their struc- 

 ture ; secondly, differential results according as these modifica- 

 tions have pleasurable or painful accompaniments in conscious- 

 ness ; and thirdly, the building of the conscious data, through 

 association, into a system of experience. The controlling in- 

 fluence of this experience is the essential feature of active intelli- 

 gence. Or, expressed in the almost obsolete terminology of the 

 older psychology, intelligence is the faculty through which past 

 experience is brought to bear on present behaviour. 



Prof. Stout, whose careful work in analytical psychology is 

 well known, has done me the service of criticising, in a private 

 communication, my use of the phrase " past experience," 

 urging that present experience is not less important in determin- 

 ing behaviour than that which is past and which can only be 

 operative through its revival in memory. The criticism is valid 

 in so far as it shows that I have not been sufficiently careful to 

 define what I mean by past experience. But T certainly had in 

 mind, though I did not clearly indicate, the inclusion of what 

 Mr. Stout regards as present experience. My conception of 

 " present," as I have elsewhere described it, is that short but 

 appreciable period of time, occupying only some small fraction 

 of a second, which is comprised in the fleeting moment of con- 

 sciousness. All anterior to this, if it were but a second ago, I 

 regard as past — past, that is to say, in origin, though still 

 operative in the limited field of the present moment. When we 

 are reading a paragraph and near its close, the net result of all 

 that we have read in the earlier sentences, is present to influence 

 the course of our thought. But the very words — "all that we 

 have read" — by which we describe this familiar fact, imply that 

 the guiding experience originated in a manner which demands 

 the use of the past tense. Still I am none the less grateful to 

 Mr. Stout for indicating what to many may have seemed a 

 serious omission in my interpretation. Suffice it to say that if 

 we include under the phrase "present experience" the occur- 

 rences of five minutes, or even of five seconds ago (all of which 

 I regard as past), I most fully agree that present experience (in 

 this sense) exercises a most important guiding influence. 



We have distinguished four classes of messages affecting con- 

 sciousness in the central office of the sensorium : first, stimuli 

 of the special senses ; secondly, internal cravings ; thirdly, 

 motor sensations due to bodily activity ; and fourthly, emotional 

 states. These are combined in subtle synthesis during the 

 growth of experience, and are associated together in varied 

 ways. Into the manner in which experience grows we cannot 

 enter here. It will be sufficient to indicate very briefly the 

 effects of this growth on the behaviour of animals in the earlier 

 stages of their life. This may be considered from a narrower 

 or f»om a broader standpoint. In the narrower view we watch 

 how, within the field of a widening synthesis, the particular 

 associations are formed. We see how, within experience, the 

 taste and appearance of certain caterpillars or grubs become so 

 associated that for the future the larva is left untouched. Or 

 we see how the terrible pounce of the cat has become so 

 associated with her appearance as thenceforth to render her an 

 object of fear to enlightened sparrows. But of the physiological 

 mechanism of association we know little. 



There is a familiar game in which a marble is rolled down an 

 inclined board at the bottom of which are numbered compart- 

 ments. The lower part of the board is beset with a series of 

 vertical pins so arranged that the marble rebounding from one 

 to another pursues a devious course before it reaches its destina- 



NO. T475. VOL. 57] 



tion. But if we tie threads from pin to pin we may thus direct 

 the course of the marble along definite lines. Now the brain 

 may be roughly likened to a set of such pins, and the marble to 

 an incoming nerve current. The congenital structure is such that a 

 number of hereditary threads connect the pins in definite ways, 

 and direct the discharge into appropriate channels. But a vast 

 number of other threads are acquired in the course of individual 

 experience. These are the links of association which direct the 

 marble in new ways. Observation of behaviour can only give 

 us information that new directing threads have been introduced. 

 The psychology of association can only indicate which pins have 

 been connected by linking threads. Even such researches as 

 those of Flechsig can at present do no more than supplement the 

 psychological conclusion by general anatomical evidence. Of 

 the details of brain modification by the formation of association 

 fibres we are still profoundly ignorant. 



Nor when we turn from the narrower to the wider point of 

 view are we in better case. We are forced to content ourselves 

 with those generalities which are the makeshift of imperfect 

 knowledge. Still, even such generalities are of use in showing 

 the direction in which more exact information is to be sought. 

 And we can, perhaps, best express the net result of acquired 

 modification of brain-structure by saying that every item of ex- 

 perience makes the animal a new being with new reactive 

 tendencies. The sparrows, which yesterday were unaffected by 

 the stealthy approach of the cat, garrulously scatter to-day 

 because they are not the same simple-minded sparrows that they 

 were. The chick comes into the world possessed of certain in- 

 stinctive tendencies — with certain hereditary directing threads. 

 But at the touch of experience its needs are modified or further 

 defined. New connecting threads are woven in the brain. On 

 the congenital basis has been built an acquired disposition. The 

 chick is other than it was, and reacts to old stimuli with new 

 modes of behaviour. 



In its early days the developing animal is reading the para- 

 graph of life. Every sentence mastered is built into the tissue 

 of experience, and leaves its impress on the plastic, yet retentive 

 brain. By dint of repetition, the results of acquisition become 

 more and more firmly ingrained. Habits are generated ; and 

 habit becomes second nature. The organism which to begin 

 with was a creature of congenital impulse and reaction becomes 

 more and more a creature of acquired habits. It is a new being, 

 but one with needs not less imperious than those with which it 

 was congenitally endowed. 



All of this is trite and familiar enough. But it will serve its 

 purpose if it help us to realise how large a share acquired 

 characters take in the development of behaviour in the higher 

 animals, and how fundamentally important is the plasticity of 

 brain-tissue, and its retentiveness of the modifications which are 

 impressed on its yielding substance. 



Such being the relations of intelligence and instinct in the 

 individual, what are their relations in the evolution of the race ? 

 Granting that instinctive responses are definite through heredity, 

 how has this definiteness been brought about ? Has it been 

 through natural selection ? Or are the acquired modifications 

 of one generation transmitted through heredity to the next ? Is 

 instinct inherited habit? Darwin, who wrote before the trans- 

 mission of acquired characters was seriously questioned, admitted 

 both. And Romanes, to whose ever-kindly sympathy I am 

 deeply indebted, still adhered to this view in spite of modern 

 criticism. There is not much in my own observational work 

 which has any decisive bearing on the question. But there are 

 one or two points which are perhaps worthy of consideratiorr. 

 The part played by acquisition in the field of behaviour is the 

 establishment of definite relations between particular groups of 

 stimuli and adaptive responses. If this be so, and if acquired 

 modifications of brain-structure be transmitted, we might 

 reasonably expect that the sight of a dog would have a similar 

 effect on young pheasants to that which it has on their parents. 

 But this does not appear to be the case. Again, one might 

 reasonably expect that the sight of water would evoke a drink- 

 ing response in recently hatched birds, just as the sight or scent 

 of a Yucca flower excites a definite response in the Yucca moth. 

 But here, too, this is not so. Thirsty chicks and ducklings 

 seem to be uninfluenced by the sight of water in a shallow tin. 

 They may even run through the liquid and remain unaffected 

 by its presence. But if they chance to peck at a grain at the 

 bottom of the tin, or a bubble on the water, as soon as the beak 

 touches the liquid, this stimulus at once evokes a drinking 

 response again and again repeated. Why does the touch of 



