460 



NA TURE 



[September 5, 1901 



cells accustomed to act with these sensory cells send out mes- 

 sages to particular muscles. If the message is responded to, if 

 the foot comes up and the offending particle is brushed away, 

 the stimulus and the effort cease. If the stimulus still goes on, 

 other cells which supply accessory muscles are called into play. 

 If this effort to remove the offending matter is vain, and the 

 irritation still goes on, the stimulus is passed on to other cells, 

 which have in an emergency previously been in the habit of 

 assisting ; the stimulus thus travels to the opposite side of the 

 spinal cord, and the other leg now comes up to the point required. 



It is the effect of drill, of practice, in the forgotten past. I 

 am aware that in making this statement I am assuming the in- 

 heritance of acquired powers — an assumption directly in oppo- 

 sition to the views of Weismann, who maintains that no powers 

 acquired during the lifetime of the individual are transmitted to 

 the progeny. 



The development of the reflexes and instincts which we shall 

 refer to will be seen to be of such importance to the maintenance 

 of the life of the individual or to the procreation of its race; 

 that the slow and gradual formation of nervous connections can 

 probably be explained by the Weismann theory ; but for our 

 purposes to-night the assumption of the inheritance of acquired 

 powers enormously increases the ease with which we can under- 

 stand their development. 



The idea of this paper is therefore that, as in the individual, 

 constant habit causes in time such a free connection between 

 nerve cells as to facilitate the passage from cell to cell of a 

 particular stimulus until the action follows the stimulus auto- 

 matically, so in the race a particular response to a particular 

 stimulus has been repeated so often that the connection has 

 become congenitally perfect, has become in fact what we know 

 as a reflex. And, further, that the frequent repetition of particular 

 actions under similar stimuli have so influenced the intelligent 

 actions of the animal, that they also have become engrafted upon 

 the nerve system, and recur under the influence of similar 

 stimuli in an automatic manner ; the result of these reactions of 

 the intelligence to a particular stimulus being what we know as 

 instincts. 



The great advantage of a reflex is the certainty and usually 

 the rapidity with which it acts. The response to the stimulus 

 does not have to travel round through the brain. It takes a 

 short cut. With imperfect reflexes the animal is at the mercy 

 of its surroundings. 



Nature does not pass imperfect work. The eye reflexes, for 

 instance, have been developed by constant practice. If through 

 their failure an animal were partially blinded, some self-constituted 

 P'aclory Inspector in Nature's workshop would soon get on the 

 blind side of that animal, and there would be no chance of its 

 perpetuating its failings. If the cough reflex failed, some septic 

 fly would quickly start a fatal pneumonia. 



Assuming that all reflexes have been developed by practice, it 

 follows that our own are not merely aids to the diagnosis of 

 disease at the hands of the physician, but are now, or have been, 

 of use in some period of our history. 



A year or two ago, in the British Medical Journal, there was 

 a very interesting description of the strength of the reflex grip of 

 the newly-born infant, this being suflicient to maintain the 

 weight of the child for some minutes while hanging from a slick. 

 This the writer attributed to the necessities of a time before 

 perambulators, when a child had to hang on for bare life to its 

 mother's hair or clothes. The inward-turned feet of the newly- 

 born child and the plantar reflex point to a time when the feet 

 were used for climbing and for grasping. 



Many of the superficial reflexes were probably developed to 

 get rid of flies and other irritants which must constantly have 

 troubled the naked body. The reflex action exhibited by the 

 decapitated body, described at the commencement of this paper, 

 was attributed by the observer to an attempt at self-defence. I 

 think it was more probably an attempt at scratching, an act 

 which was probably habitual in our hairy ancestors, as it is now 

 in our poor relations at the Zoo — a movement, in fact, strictly 

 analogous to the movement of the frog's foot incited by the 

 irritation of the acid. To assume that there was an intention 

 of defence in the action imports into the movement an element 

 of consciousness for which in the absence of the brain we have 

 no warrant ; and this brings us to the question of instincts, which 

 have been defined as reflex actions into which an element of 

 consciousness has been imported. 



I will endeavour to trace an ascending scale of instincts show- 



NO. 1662, VOL. 64] 



ing their dependence on reflex excitation. A newly-born 

 infant has to be placed to the breast ; it then seizes the nipple 

 with its lips and sucks. There is little difference between the 

 reflex action incited by the contact of the maternal nipple with 

 the infant's mouth and the cough or sneeze reflex ; both are 

 complicated actions of many groups of muscles. In the one 

 case, spasmodic ; in the other, rhythmical. The young of the 

 rabbit, born blind and helpless, nuzzles about till it finds a 

 nipple, and then takes its hold. The lamb, calf, or fawn, 

 guided by sight and smell, seeks its mother's teat. In each of 

 these cases a stimulus is required, either of touch, sight, or 

 smell. Without the stimulus the experiment fails. 



Fawns are peculiarly precocious. From the first they show 

 a tendency to couch and hide on the approach of danger. The 

 following is an extraordinary instance of combination of 

 maternal and infant instinct :— 



" I have had frequent opportunities," says the " Naturalist in 

 La Plata," " of observing the young from one to three days old 

 of the Cemns cainpestris, the common deer of the Pampas, 

 and the perfection of its instincts at that tender age seems very 

 wonderful in a ruminant. When the doe with fawn is ap- 

 proached by a horseman, even when accompanied by dogs, she 

 stands perfectly motionless, gazing fixedly at the enemy, the 

 fawn motionless by her side ; and suddenly, as if at a precon- 

 certed signal, the fawn rushes away from her at its utmost speed, 

 and going to a distance of 600 to 1000 yards, conceals itself in a 

 hollow in the ground or among the long grass, lying down very 

 close with neck stretched out horizontally, and will thus remain 

 until sought by the dam. When very young it will allow itself 

 to be taken, making no further effort to escape. After the fawn 

 has run away, the doe still maintains her statuesque attitude, as 

 if to await the onset ; and when, and only when, the dogs are 

 close upon her, she also rushes away, but invariably in a direction 

 as nearly opposite to the fawn as possible. At first she runs 

 slowly with a limping gait, and frequently pausing as if to entice 

 her enemy on, like a partridge, duck, or plover when driven 

 from its young ; but as the dogs begin to press her more closely 

 her speed increases, becoming greater the further she succeeds 

 in leading them from the starting point." 



In considering this case we have to remember that the deer is, 

 as a rule, a woodland animal, and that its fawn, while feeble, 

 crouches under cover, of which there is plenty within immediate 

 reach ; but the deer of the Pampas lives on rolling prairies 

 where the only cover is the isolated tufts of Pampas grass. 

 While, therefore, the instinct to crouch is suflicient for the fawns 

 of most deer, crouching in the immediate neighbourhood of the 

 surprise would be useless in the open ground of the Pampas ; 

 and this artful combination of tactics has doubtless been de- 

 veloped by practice. 



In birds we get even more marked differences in connate 

 powers and instincts, from the naked young of the sparrow, which 

 is nearly as helpless as the human baby, to the newly-hatched 

 chicken, which is a regular little man-about-town .at once. The 

 habits of the latter have been closely studied. Hatched out in 

 an incubator, and deprived of all maternal instruction and ex- 

 ample, he quickly begins to peck at all small objects, with a pre- 

 ference for moving ones, and from the first shows an almost perfect 

 power of estimating distance and direction, which is very mar- 

 vellous when we consider the great number of muscles which have 

 to be co-ordinated in the act. 



The late Mr. Douglas Spalding placed beyond question the 

 view that all the supposed examples of instincts may be nothing 

 more than cases of rapid learning, imitation, or instruction, but 

 also proved that a young bird comes into the world with an 

 amount and a nicety of ancestral knowledge that is highly 

 astonishing. Thus speaking of chickens which he liberated from 

 the egg and hooded before their eyes had been able to perform 

 any act of vision, he says that on removing the hood, after a 

 period varying from one to three days, " almost invariably they 

 seemed a little stunned by the light, remained motionless for 

 several minutes, and continued for some time less active than 

 before they were unhooded. Their behaviour was, however, 

 in every case conclusive against the theory that the perceptions 

 of distance and direction by the eye are the result of experience 

 or of associations formed in the history of each individual life. 

 Often, at the end of two minutes, they followed with their eyes 

 the movements of crawling insects, turning their heads with all 

 the precision of an old fowl. In from two to fifteen minutes 

 they pecked at some speck or insect, showing not merely an 

 instinctive perception of distance, but an original ability to judge 



