The Attempt to Classify Human Instincts. — No one as yet has succeeded in making even a helpful classification of instincts. It is far more difficult to make such a classification in the human realm than in the animal. Fairly serviceable classifications in the animal world are food-getting, home-building activities, attack and defense, migration, etc. In man there may be rudi- ments of many of these activities, but long before the organism is in a situation to exercise such integrations, habit has overlaid everything. Such a classification as the above has been attempted for the human being, but without much success. Another attempt at a classification is seen in the splitting up of hereditary instinc- tive action into positive reaction tendencies and negative reaction tendencies. We give a separate discussion of some observations on this point on page 248. Several efforts have been made to enumerate the human instincts. The most noteworthy example of this is to be found in Thorndike. In a serviceable way he de- scribes the reaction and then defines the stimulus or situation to which the reaction is made. We present this enumeration on page 254. The difficulty with this method of procedure is due to the fact that we have not the genetic data at present to make Jl either the enumeration accurate or the definition of the stimulus at all complete. Only long and careful study by the genetic method will yield a scientific classification. We shall show in a later paragraph some of the preliminary results which have been obtained by a genetic study of instincts.
Some of the Problems in Instinct. — A point which should be emphasized here is that in order to make a profitable study in the field of instincts we should come to it. with a definite problem be- fore us. It is believed that when the human infant has been gone over more thoroughly from the standpoint of special interests, rational lines of cleavage in instinct will appear. Instincts should be studied from the vocational, social, pedagogical and psy- HEREDITARY MODES OF RESPONSE: INSTINCT 235 ehiatric points of view. We might emphasize here just a few of the definite problems which interest the behaviorist: (1) Is hand- edness congenital or merely social? If congenital, will any seri- ous consequences result if left-handedness is changed to right- handedness? (2) Are there important variations in instinctive equipment? May these variations be made use of in the later development of the child? It is believable, at least, that the posi- tive reactions of the child may from earliest infancy point toward definite vocational interests. His negative or indifferent reac- tions may be just as important factors. A good deal of popular material has been collected upon this, but little of scientific value has appeared. (3) It is just possible that we may succeed in working out the life history of groups of instinctive activities in such a way that an index may be obtained of the child 's normality of development at certain ages, since certain instincts appear haltingly at first, ripen or develop, and then disappear. We know very little about the types and level of behavior the child should show at six months, at a year, and at two years, etc. The Binet scale does not help us. (4) We should know enough about the normal development and functioning of instinct to be able to detect instinct distortions. We should know, for example, at what point to break or socialize instinct by habit. We mention here nursing, continence of urine and faeces, etc. (5) Sex differ- ences in instinct — is there a differentiation of activity between the male and the female child, or is the differentiation wholly social (such differentiation, of course, begins almost at birth). This is involved in (2) above. Some material has been collected upon this point, but not under wholly trustworthy conditions of investigation.
What at present deters us from making the more circum- scribed studies is the fact that we have really no orientation as yet in the field. The first need is for a rough survey of a useful kind. Such a survey should be made upon more than one child and under a better controlled situation than is to be found in the ordinary home and school conditions. In the general section below on the genetic study of instincts we summarize some of the types of instincts which have been studied under reasonably con- 236 PSYCHOLOGY • trolled conditions. This study must be looked upon merely as the beginning of the general survey suggested above.
THE GENETIC STUDY OF INSTINCTS Early Sensory Responses. — A large number of observations have been collected in our laboratory upon the early sensory re- sponses of infants. If the infant's breathing and hand move- ment are being recorded during sensory stimulation, evidences of sensitivity can be obtained. From birth the infant responds to loud noises, to the tearing of paper and to the scraping of one object upon another (Fig. 55, A). The responses have been partially considered under the emotion of fear — the catching of the breath, spasmodic movements of arms and legs and the closing of the hand are the responses to be observed. Sensitivity to tuning forks and other musical instruments is not marked. Unless placed very close to the ear or made very loud, no re- sponse can be obtained. Similar undifferentiated responses have been obtained by stimulating with different olfactory substances, such as oil of peppermint, asafoetida, butyric acid and ammonia (Fig. 55, C). Most of the responses were obtained from sub- stances which stimulate the fifth nerve, which is a tactual nerve. No very sure results have been obtained from the milder per- fumes. Pinching, sticking with a pin, warm and cold objects, twisting and turning of a joint (contact and kingesthetic), all will produce changes in respiration and in the rate, amplitude and form of the movement curve obtained from the hands. Vision so far has been tested only with respect to the infant's ability to fixate a white light (page 243). This occurs at birth. Color sensitivity has not been tested. It can be determined, but only with difficulty.
The First Thirty Days of Childhood—Infants often sneeze immediately upon being taken from the mother. Hiccoughing may begin after the first few hours. Yawning has been noted five minutes after birth. Crying is also one of the earliest re- sponses. The birth cry occurs at the moment the respiratory centers are stimulated after birth. In some cases it is necessary to stimulate the infant with hot and cold plunges in order to start HEREDITARY MODES OF RESPONSE: INSTINCT 237 C FIG. 55. — Showing wrist and arm movements under stimulation. A shows the arm reaction when auditory stimulus is given. The first stimulation was tearing paper. The second was the word "Boo" said loudly. B is a graphic record of the left and right wrist and arm movements during "free" activity. C is the reaction of the right and left wrist and arm movements to two faint ammonia stimulations. (Infant less than one day of age.1) 238 PSYCHOLOGY breathing. The cry often conies an. instant after the infant touches the water. The mechanisms involved in the erection of the penis, voiding of urine and defecation are functional at birth or very shortly thereafter. Tears apparently are shed within the first few hours after birth. Children, however, often fail to shed tears until several days after birth. Some dates are as follows: 8 showed dampness in corners of eyes after crying on the 13th day; L on the 15th, crying with a copious flow of tears on the 34th day. Smiles are rare at an early age. Under observation some first dates are as follows: 8, 4 days; 0 'K, 1 days; K, 8 days; C smiled repeatedly on the 28th day. Tickling under the chin and stroking other parts of the body will occasionally bring out a smile. Children at an early age can turn the head when placed face down on a pillow. C, 30 minutes old, rotated her head in such a way as to leave her mouth and nose free. Several other infants did equally well at 1% hours of age. Raising the head may occur at any time after birth. These head movements appear most clearly if the infant is supported by placing the open hand under the stomach and supporting its back with the other hand. In observed cases subjects ranging from 2 to 15 days could support their heads for times varying from one to six seconds. Hand movements.* Spreading of the fingers and closing of the hands occur at any time after birth. Repeated movements of many kinds are made with legs, feet and toes. It is often asserted that babies can cling with their toes, but this has not been observed. Kicking with the legs and slashing with the arms are almost con- tinuous during active moments from a few minutes after birth. Turning over: Subject T at 7 days turned repeatedly from face to back when not impeded by clothing. Stretching: Begins very early in life and varies from a mere raising of the arm to a com- plete stretching of the legs and toes, arching of the back and ab- domen, etc. (Summarized from Mrs. Blanton's study).
Some Instincts Singled Out for Study.—(1) Nursing. If either cheek or the chin is touched lightly with the finger, an infant shortly after birth will move the head in such a way as to bring the mouth in contact with the finger. In deep sleep it apparently disappears. After feeding it is also very hard to elicit.
HEREDITARY MODES OF RESPONSE: INSTINCT 239 During hunger it is very easy to elicit, the infant often moving with such surprising quickness that it catches the finger in its mouth. Again, if one taps lightly above or below the corner of the mouth of a sleeping baby the lips are pursed into a nursing position; occasionally the tongue will protrude and complete suck- FIG. 56. — Showing some infant reflexes. A, defensive reflex with left foot to slight pinch on inner surface of right knee. B, stimulation for Babinski. The blunt end of a match is rubbed across the sole of the foot. The result is shown in C. The great toe shows extension, whereas the small toes show "fanning" or flexion. (This is a very variable reflex so far as the pattern is concerned.) D shows the grasping reflex (infant 12 days old.)
ing movements will appear. Children a few hours after birth seem to be able to get the fingers and hands into the mouth. The sucking instinct as a whole seems to be well coordinated by the end of the first half-hour. The series of reflexes as a whole is made up of tongue, lip and cheek movements, swallowing being the final link in the chain of activities. Although the evidence is not complete as yet, failure in the ability to swallow is suggestive PSYCHOLOGY STRENGTH OF GRASPING REFLEX WT. IN GRMS.
BODY WEIGHTS •— — WEIGHT SUSTAINED WITH RIGHT HAND I6~I8 AGE IN WT. IN 'GRMS (6) NUMBER OF OBSERVATIONS BODY WEIGHTS — — WEIGHT SUSTAINED WITH LEFT HAND , AGE IN (6) NUMBER OF OBSERVATIONS FIG. 57.— Showing the strength oi the grasping reflex for the first 21 days. The curves show that the strength of the right and left hand is approximately equal.
HEREDITARY MODES OF RESPONSE: INSTINCT 241 of retardation. Children born of defective parents seem to have difficulty with swallowing.
(2) Grasping reflex. Records of tests on approximately one hundred babies in Baltimore ranging in age from birth to 150 days show that the grasping reflex is present in practically all normal cases. There have been.only three or four exceptions found. The method of testing the babies is shown in Fig. 56, D. Not all babies will support the full weight. Most of them, how- ever, will support the full body weight for a longer or a shorter time and with either hand. The results for the first twenty days of infancy are shown in Fig. 57. Our records from the twentieth day are not yet complete, but generous samplings show that the reflex is present in more or less perfect form up to about the 120th day or longer. It seems to give way about the time the eye- hand coordination is formed. This habit is discussed on page 275. In abnormal cases, rickets, mal-nutrition generally, oversupply of fat, illness, etc., the reflex is apparently lacking. In one baby born without a cerebrum the reflex was practically perfect up to the day of its death at 18 days.
(3) Right- and left -handedness. This method opens up the problem of testing whether handedness is- an instinct or a socially acquired habit. Those babies which will support their full weight on any given day will cling for a longer or a shorter time with either the right or the left hand. A wide series of records has been kept and a large number of babies has been followed through day by day, but the application of statistical method shows that there is not any steady predominance in either right or left hand in the length of suspension. The problem of handedness has also been attacked in another way. The baby is laid flat on its back; its hands are attached by means of a linen thread to two pivoted writing levers in practically frictionless bearings. No matter whether the infant moves its hand down or up, to the right or to the left, or to any intermediate position, a vertical tracing is recorded upon a smoked drum. Fig. 55, B, shows such a trac- ing. It was hoped by this method to obtain a constantly greater or less amount of activity with either the one or the other hand in a given period of time. In making the test both the random 16 242 PSYCHOLOGY 16 242 PSYCHOLOGY activity (intra-organically aroused) and activity extra-organi- cally aroused by midline contact stimulation were recorded. The method has not as yet yielded any very decisive results. Although the child is stripped it is almost impossible to keep it lying in such a way that the one or the other hand is not given more or less freedom. Still another method for determining handedness has been tried, namely, the anthropometric one of measuring the diameter of the right and left biceps, the length of the left and right forearms from the elbow to the second joint of the middle fingers. The preliminary report of this method shows that the right bicep is larger and the length of the right forearm is slightly greater than the left. These results probably cannot be trusted. We are thus left without conclusions as to the problem of handedness. In early infancy there is certainly no preferen- tial use. The early habit coordinations, too, seem to form about as readily with the left as with the right hand, and yet we know that so far as adult activity is concerned, about 96 per cent, of individuals are right-handed.
. (4) Defense movements. Early defense movements have been rather thoroughly tried out in a large number of infants, but by a very crude method. The nose is lightly pinched and the length of time it takes the child to touch the experimenter's fingers is recorded. A few sample records are given: B. 4 days. Hands went up at once, and pushed at experi- menter 's fingers in three seconds.
H. 12 days. Movement started rapidly. Struck experi- menter's fingers in three seconds.
BE. 3 days. Right hand struck experimenter's fingers in 18 seconds on the first trial, 2 seconds on the second trial.
T. 8 days. Struck experimenter's fingers with the right hand in 3 seconds and with the left in 4 seconds. On the next trial, struck first with the left hand in 5 seconds, with the right in 6.
Another interesting defense movement may be noted as fol- lows: If the baby lies on its ba,ck with legs extended and the inner surface of one knee is lightly pinched, the opposite foot is brought up almost with the regularity seen in the reflex frog. (Fig. 56, A, shows the reflex.)
HEREDITARY MODES OF RESPONSE: INSTINCT 243 T. 8 days. Left knee pinched. Right heel struck experi- menter's fingers in 3/5 second. Right knee pinched. Left heel struck experimenter's fingers in 20 seconds. Several abortive attempts were made.
M. Less than one day. Pinched left knee. Right foot struck in 35 seconds. Pinched right knee. Left foot struck in 48 seconds.
//. 5 days. Pinched left knee. Right foot failed to reach ex- perimenter's fingers. When right knee was pinched, the left foot struck in 10 se'conds.
These are only samples of a very large number of records. The records as a whole run closely similar to these samples. It will be noticed that we have here an interesting opportunity to study rapidity of habit formations in even the one-day-old infant. Such experiments have not yet been conducted. The pinching is never made severe enough to produce any mark and there is not the slightest injury or danger in making the experiment. In fact, it may be made to serve as a very useful exercise at the hands of a considerate experimenter.
(5) Absence of swimming movement. Some speculation has been entered into as to whether the new-born infant would show coordinated swimming movements (see recapitulation theory, page 266). Some definite experiments have been carried out a few minutes after birth. A small galvanized iron tank was filled with water to a height of about ten inches and maintained at the body temperature in readiness for the test. After breathing1 was established, the infant was lowered slowly into the water and sup- ported on the back by the experimenter 's hands. Violent expres- sion of fear — a cry, checking of breathing followed by deeper inspiration and rapid, entirely uncoordinated slashing of hands and feet were all that could be observed. In making the test the greatest care was used not to let the baby 's head sink so low as to allow water to enter the nose or mouth. The infant's behavior is in marked contrast to that observed in certain other young1 mam- mals, some of which swim moderately well the first time they are placed in the water.
(6) Orientation to Light. — The following experiment was 244 PSYCHOLOGY made on approximately 20 children at varying ages from birth to several days of age: the child was laid flat on its back and its head held horizontally by means of two cotton-wool pads. Immediately above the head was fastened a perimeter, the radius of which was one-half meter. A small carriage bearing a light could be made to travel from one portion of the perimeter to another. The position of the light immediately above the baby's eyes was called the zero position. From that position the light could be carried to any desired number of degrees to the right or to the left. The tests were, of course', carried out in the dark room. The light was just bright enough for the dark-adapted observers' eyes to note whether or not orientation occurred. Two observers had to agree that it had occurred. A few sample records only are offered. The times given represent the interval from the moment the light was exposed until orientation occurred: Infant 5, 14% hours old: 10 degrees to the left, 15 seconds; 10 degrees to the right, 10 seconds; 15 degrees to the right, 12 seconds; 15 degrees to the left, 6 seconds; 25 degrees to the left, failed in two trials; 25 degrees to the right, failed.
In the last two cases, of course, the extent of the eye movement demanded is so great that it was not expected that the child could attain it.
Infant C, 17 hours old: 10 degrees to the right, 15 seconds; 10 degrees to the left, 13 seconds; 20 degrees to the left, cried and closed eyes in two trials; 20 degrees to the left, 30 seconds (after a slight rest in the light); 10 degrees to the left, 5 seconds; 20 degrees to the right, 12 seconds; the right eye turned perfectly, but the left did not seem to follow synchronously.
Similar tests were carried out with perimeter swung so that the object would appear in the upper and lower meridians. Natu- rally the infants do not make these movements so well.
HEREDITARY MODES OF RESPONSE: INSTINCT 245 Definite orientation was not found in every trial, but in a group' of. twenty or more infants selected at random, one infant 17 hours of age, and one other that never could be kept awake long- enough to make the tests failed to give positive results. In many cases the infants would go so fast asleep that the tests on any given day would have to be abandoned.
We thus see that the child at birth has at least a well de- veloped mechanism for turning- the eyes toward the lighted half of the -visual field. That true fixation occurs is not maintained. That 'we are dealing here with a native mechanism is probable, since the infants had had little opportunity in their darkened room to form visual habits. The true fixation of people's faces and definite objects in. a well-lighted room occurs at a much later date; at just what date has not been determined upon any large number of children.
(7) Blinking. — Blinking, which may be considered a part of the general avoiding movements, and which in older children and adults is followed by the backward throw of the head and preparatory movements for stepping backward, is not present at birth. A number of children have been consistently tested for the purpose of determining its incidence. Some random examples are given here: 8. 174 days, perfect.
W. 72 days, absent.
Y. 47 days, absent.
B. 55 days, absent.
r. 75 days, slightly present.
B. 83 days, present on half of the tests.
F. 124 days, present.
Lee, one of the youngsters most carefully tested, blinked twice on the 87th day; would not blink on the 127th day; on the 129th day blinked on the first two stimulations, but failed on the next four. On the 136th day, blinked at every stimulation, eight times. Thus, in her case, blinking was not firmly established until the 136th day.
The earliest the reflex has been noted is at 55 days. It seems to vary as a rule between 75 and 120 days, although this has not been very accurately determined. There seems to be, too, a de- veloping or ripening period.
(8) The BabinsUi Reflex. — The Babinski has been tried out 246 PSYCHOLOGY I several hundred times, but at present we are not prepared to give any detailed report of the life history of this reflex. At birth and for some months thereafter if the sole of the foot of the infant is stroked with the blunt end of a match (Fig. 56 B), the great toe shows extension, whereas the small toes "fan" or else show flexion as in the adult. The total result is shown in Fig. 56, C. The reflex is connected by physicians with lack of medul- lation in the pyramidal tract. It is assumed that as soon as medullation is complete in the tract the reflex disappears. As a whole the pattern of the reflex is a very variable one.
(9) Crawling. — Whether crawling is a genuine pattern in- stinct is, we should say, somewhat doubtful. Our results again are not as yet secure. If an infant from birth is put down upon a thin mat fastened tightly to a table top, it will at the end of ten minutes have slightly changed its position. Very shortly after birth a regression of as much as four inches has been no- ticed. Long before anything like the coordinated movements of legs and arms that are so necessary in the complete set of crawl- ing movements occur, slashing movements of legs or arms or of both will throw the infant's trunk to the right or to the left. Systematic tests were begun upon L at 87 days of age. The method in general was as follows: A single cotton blanket was stretched tightly to a table top. A small piece of wood was then pushed up against the feet. In a minute or two she had pushed this away as far as the toes would reach. This position was then marked. A piece of candy was put in front of her face. On the 87th day, "climbing" movements with the legs were fairly well coordinated. The right leg would struggle forward and then the left; then one or both would be kicked out. The hand and arm movement showed no coordination. No advance was shown up to the 115th day. Definite progress was noted on that day in the use of the arms. There was some slight use of the elbows. The fore part of the body was considerably raised. From the 87th day on, the head was well raised for the first two or three min- utes. It would gradually sink down. On the 115th day, she made a forward progress of two inches in nine minutes. Circus, mo- HEREDITARY MODES OF RESPONSE: INSTINCT 247 tions were present, and the body would be rocked from side to side. This rocking movement seemed to net the gain rather than the progressive movements of the legs and arms. On this date for the first time, she grasped the blanket ahead of her and apparently pulled herself slightly forward. Even on the 220th day crawling was not much further advanced, although she had been tested every week from the 87th day. At that time the experiment had to be discontinued. (The mother reports that one week after the above date this baby began to crawl, and during that week she learned to pull herself up by holding on to objects.) Subject N at the end of 163 days had made little more progress. T, a fine, well-developed baby, at 182 days had not learned to crawl, although on that date she had learned to stand alone, supporting herself on the bars of the crib after her mother had helped her up. F, another well-developed baby, up to 131 days had not made the slightest effort to crawl. When placed upon the mat he would usually lie still with head resting on the table and with the left cheek down. Feet and arms were sprawled out. M, the son of one of the instructors, was watched very carefully for the first ten months of his life. On the 280th day, the infant took hold of a side of its bassinet and raised itself to its feet for the first time. This he practiced incessantly for a week, standing for as long a time as he could, then sitting down to rest and then repeating the process. This general method of reach- ing out for an object, pulling himself up to it if it were fixed, standing up, sitting down, reaching out again, gave him a method of locomotion, but he did not crawl in the ordinary sense. When placed on the floor in the crawling position on the 284th day, he began to twist and turn, to sit up and roll over, and to go through any movement which would produce locomotion except crawling. Crawling in this child was never an instinctive process. Two other children of my colleagues never crawled in the ordi- nary sense of that term. M had a system, all her own. Loco- motion was effected practically by the use of her left arm, which she very speedily learned to use without making circus move- ments. This endured up to the walking period at 380 days. J adopted a most curious and unusual method of locomotion. He 248 PSYCHOLOGY would sit up, put his hands forward on the floor and slightly raise and slide his body along. He would come to a rest and again reach out his hands and repeat the process. He became very adept in this, moving at no mean speed. His success prob- ably delayed his walking, which did not take place until he was 510 days of age. Even after learning to walk, when he was in a hurry he would resort to the more primitive method of loco- motion. While we do not affirm that crawling may not have a definite time of appearance and that it is not a definite instinc- tive pattern in some cases, we are prepared to affirm that it is not anything like as prevalent an instinct as1 is commonly sup- posed. Walking has not yet been brought under observation in our laboratory.
(10) Positive and Negative Reaction Tendencies*. — The method of making tests on this very important subject is to estab- lish first the eye-hand coordination. This is done usually by means of a stick of old-fashioned red striped peppermint candy. When this was established perfectly, the infant was offered a series of objects to which it had not reacted before. Some test cases are given: L completed eye-hand coordination at about the 129th day. She reached for stop watch, dark ink eraser (136 days), pipette with red bulb and for candle (150 days). The re- action to the candle was most pronounced. She held out both hands for it and reached out as far from her mother's lap as was possible. She was tested with a round metal ball and reached for it immediately. Attention has already been called to the fact that this child reacted positively to small animals. On the 169th day, she was tested for the presence of the washing or wiping reac- tion (so-called instinct of cleanliness). We first rolled up a ball of library paste, making it just as sticky as possible. After it had been warmed in the experimenter's hands it was offered to her on a piece of paper. She took hold of the edge of the paper with both hands, but did not roll the paste down to her hand.