m< OU_160737m OSMANIA UNIVERSITY LIBRARY Call No. | / Accession No ' Author Title fvi^oloc '. ^Vck Jh r* U>w have areas of common interest? What other sciences or areas of study might be represented by circles in the above diagram? Where would you draw each? for the individual as a person, as a knowing, thinking, and otherwise reacting organism. Differences in Emphasis among the Sci- ences. The distinction between related sci- ences is usually not a matter of hard and fast differences, with clear lines separating the sciences in question; rather it is one of varying emphasis. Thus, it is not possible to draw a line clearly dividing anthropology from sociology, or to separate sharply soci- ology from psychology or psychology from physiology. In each case, one of these spills over into the other ( or perhaps into several others), and two or more sciences often study the same subject matter. For example, both physiology and psychology are inter- ested in the functioning of the nervous sys- tem, though each from a somewhat different point of view. Psychology, sociology, and anthropology all concern themselves with the relationship of the group and the in- dividual, but again the emphasis differs for each science. Incidentally, we have a similar situation in physics and chemistry, where the emphasis differs but no hard and fast boundaries can be drawn. It is easy to get the idea that this is an unfortunate situation and that the various sciences should straighten out their titles to 14 UNDERSTANDING HUMAN BEHAVIOR certain territories or areas of subject mat- ter. Verbal battles have sometimes been fought over such issues, but fortunately for the welfare of science and society no permanent victories have been won. Areas of overlap in science can be opportunities for cooperation, and two groups of scien- tists, working together, have often attained insights denied to either group working alone. Human behavior is obviously a field that is complex and not so well understood as we should like it to be. No one has a monopoly on information about it or on methods of studying it. It is the concern of many sciences, including psychology. APPLIED PSYCHOLOGY One striking fact about modern psychol- ogy is, as we mentioned earlier, the increas- ing number of psychologists, especially since World War II. A great many more people are now earning a livelihood as psy- chologists than were doing so a few short years ago. This growth is largely due to the expansion of research and professional serv- ices concerned with the applications of psy- chology. Until recently a majority of psychologists were engaged in teaching. Now teaching is still an important field of employment, but positions concerned with research and ap- plying psychology to practical problems are the more numerous. Psychology is now applied in a number of situations, varying from those that deal with children to those that deal with old people, and from those that deal with peo- ple who are in great difficulty to those that deal with people in positions of responsible leadership. Let us look at some of these fields in which psychologists are applying the findings of the science. -Clinical Psychology. The largest single group of professional psychologists are those who work in mental hospitals, mental health clinics, and the like. Clinical psy- chologists, as the term implies, deal with people in difficulty. Some of these persons may have a serious mental illness, while others m^ have encountered more than their share of the problems we all face or may lack the skill that most of us have de- veloped for dealing with such problems. Here it might be wise to make a distinc- tion between a clinical psychologist and a psychiatrist. Ordinarily a clinical psycholo- gist has a Ph.D. in psychology. Having finished a bachelor of arts degree (and pos- sibly a master of arts degree also) in psy- chology or a related field, he goes on to get the doctor'--; degree in psychology. In the course of earning this degree, he usually serves at least one year of internship, which gives practical experience in dealing with persons having psychological difficulties. This is a valuable supplement to classwork. The psychiatrist, on the other hand, al- ways has a medical degree. After complet- ing his premedical training he usually spends four years in medical school, some time as an intern, and then some more as a resident. His area of specialty is the care and treatment of people with emotional and mental illness. Another person who works with mentally disordered individuals, or with persons in difficulty, is the psychiatric social worker. He usually has a master's degree in social work and specializes in getting information about and understanding people who have emotional difficulties. In many clinics and hospitals the team approach is used, the team consisting of a psychiatrist, a clinical psychologist, and a psychiatric social worker. To some extent each member of this team specializes in a particular area, but they combine their training and talents in investigating the problems of a particular patient and, after the diagnosis, in helping him regain his mental health. Many who work in this field feel that the team approach is proving its effectiveness and strengthening our efforts THE STUDY OF HUMAN BEHAVIOR 15 to combat problems in the area of mental health. Counseling Psychology. Another field of professional specialization in psychology is known as counseling psychology. Though counseling and clinical psychology are closely related, they have two fairly distinct roles in the general scheme of psychological services. We use the word "counseling" to refer to the function of psychologists whose prin- cipal job is to deal with people who are in need of help or advice but not primarily with people who have emotional difficulties. A typical example is to be found in the Veterans Administration, where the coun- selor acquaints an individual with voca- tional opportunities and gives him informa- tion designed to better his vocational ad- justments. Since a person's vocation influ- ences so many phases of his life, counseling psychologists often are called upon to deal with other problems which the individual may be facing. Of course, not all counselors are psy- chologists. Other people do counseling teachers, social workers, supervisors, min- isters, lawyers, physicians, and so forth. But psychologists counsel too, and the point that needs to be emphasized is that one branch of psychology is concerned with the theory, as well as the practice and tech- niques, of counseling. A branch of psychology closely related to counseling is to be found in the work of the school psychologist. School psycholgists often do educational and vocational coun- seling, but they also give advice and guid- ance on matters having to do with cur- riculum planning, teacher training, prob- lems of parents, and the like. Psychology in Business and Industry. Psychologists also practice professionally in business and industry. Human-relations problems in business and industry are often as important as any other sort, and the need for effective teamwork is probably nowhere greater than it is in this particular area. Psychologists participate in the affairs of business and industry in at least three ways. In the first place, they have made some real contributions to business management by making it possible to do a better job of selecting, placing, and training employees. Here the first contribution that comes to mind is probably that of psychological tests, but while they have been important, they are not by any means the whole story. In- terviews are also useful, and even observa- tion of behavior over a period of time has proved worthwhile. Furthermore, psycholo- gists have been able to improve methods of training people for their jobs. In the second place, there are psycholo- gists who specialize in counseling with the executives of a business and otherwise help- ing in their development. They are often the persons with whom the executive "talks out" his problems, and they help him gain insight into his own limitations and strengths and to improve his skill as an executive. The emphasis here is primarily on self-improvement, for in these matters as in many others, real development must come from within the individual. ' This process of helping executives and supervisors to grow and develop is some- times carried out with groups rather than with individuals. Through research, psy- chologists have uncovered some of the factors that distinguish successful leaders from those not so successful, and the in- dustrial psychologist often has the opportun- ity to translate these findings into a form and a set of skills that will make them use- ful to the manager. The third area in which psychology has played an increasing role in business and industry is often called human engineering. As the world of work becomes more com- plex and the machines and processes with which we have to deal become more in- volved, the problems of the control of the means of production or transportation be- 16 UNDERSTANDING HUMAN BEHAVIOR EFFICIENCY OF VARIOUS DIALS This experiment * throws some light on the work of the human engineer. The purpose was to determine which of several types of dials would give the most useful readings of an altimeter (instrument for measuring altitude). Each dial was presented to the subjects with twelve different settings. They were printed in a test booklet, with space provided in each case for indicat- ing the correct reading. As far as possible, the printed designs were of the same size, with the same legibility of printing, the same number of grada- tions, etc. The order of presentation of the different dials was also varied systematically to reduce the practice effect. The subjects were 97 United States Air Force cadets and 79 college students without aircrew experience. The accompanying figure presents the various types of dials used and also the results obtained. Dial A was one commonly in use at the time of the experiment, and, as can be seen, it showed up poorly both in errors and time for interpretation. It is interesting to note that at least in some cases the results of this study are quite different from what would be predicted by so-called "common sense." Errors of 1,000 feet or more, per cent Interpretation time, seconds 17.4 J7.5 162 J7.J 10.7 10.7 117 1.8 LEGEND 1 97 AAF pilots I I 79 college students 900 23,000 rr 800 22.900 -^ 700 -; 72,800 [i] 3 ^ | 27.800~ 600 22.700 ~ 1 500 -z 22,600 -^ 400-= 22,500 -^ Errors of 1,000 feet or more, per cent Interpretation time, seconds 14.1 13.0 6.9 ,03 0.4 U 1 9 M.9 (0.4 I 0.0 I 0.0 I 0.0 Speed and accuracy in reading altitude from different types of instruments. (Note that instrument I proved most satisfactory under these conditions.) (W. F. Grether, Instrument Reading: /, The Design of Long-scale Indica- tors for Speed and Accuracy of Quantitative Readings, Journal of Applied Psychology, 33:365, 1949. Courtesy of the publisher.) * W. F. Grether, "Instrument Reading: I. The Design of Long-scale Indicators for Speed and Accuracy of Quantitative Readings/' Journal of Applied Psychology, 1949, 33:363-372. THE STUDY OF HUMAN BEHAVIOR 17 come more difficult. Indeed, in many in- stances, more information can be given to the operator of a machine than he is able to perceive and use. Consider, for example, a large airplane. It has a number of engines, and each engine has a number of instru- ments reporting on its performance. Clearly, more information can be fed into the cock- pit of the plane than any individual could ever assimilate in any reasonable length of time. Indeed, more information can be displayed in the cockpit than a crew of several men are able to assimilate. The problem is to make this information as usable as possible. There is a question, for instance, as to what sort of design an instrument ought to have. Should it be black on white, or white on black? Should it be large or small? Where should it be located? These and many more complex questions are of in- terest to the human engineer. Perhaps nowhere can we find a better il- lustration of the difference between psy- chology and "common sense." The common- sense approach to this problem would be to figure out which of these would seem to be the most serviceable and to use it. The psychologist, on the other hand, uses the experimental approach. He experiments with various kinds of cockpits and instru- ments and controls, and by holding other variables constant, determines not which one looks as though it would work best but rather which one really does work best. There is no doubt of the superiority of the psychologist's approach to this sort of prob- lem. Problems of this sort are to be found in many aspects of the world of work, and the contributions to their solution by psycholo- gists may ultimately touch the lives of all of us. " Psychology and Attitude Measurement. Finally, among the applied fields we have chosen to discuss, there is the field in which the attitudes of individuals or groups are measured. Such attitude measurement has been used extensively in public-opin- ion polling (of which the so-called "Gallup poll" is an example) and in market re- search. We are all familiar in a general way with polling procedures. Questions are carefully designed and studied and, when considered satisfactory, are asked of a great many peo- ple. Their responses are carefully noted, and conclusions are drawn concerning the attitudes of a larger group of people with regard to the matter being studied. This technique may be used to determine the feeling of people toward the several presi- dential hopefuls or toward a new brand of detergent. Complexity of the Field of Psijchology. By now it is apparent that modern psy- chology is not a simple field, with all psy- chologists having the same interests and skills. The various sorts of psychologists have a number of things in common, but they also have their own special interests. The complexity of the field can be seen from a study of the American Psychological Association. This is the scientific and pro- fessional organization of American psychol- ogists. Minimum requirements for associate membership are two years of graduate study in psychology (or one year of grad- uate study plus one year of experience in professional work that is psychological in nature) and employment in a job that is primarily psychological (or continuation of graduate study in psychology). More and more the Ph.D. degree is being required of people who are recognized as psycholo- gists. In 1956 the association had about 15,000 members, in 1957 16,000. At present the association is organized into seventeen divisions, some set up pri- marily on the basis of applied interests and others primarily on the basis of subject matter. These divisions are as follows: UNDERSTANDING HUMAN BEHAVIOR General Psychology The Teaching of Psychology Experimental Psychology Evaluation and Measurement Developmental Psychology Abnormal and Social Psychology The Society for the Psychological Study of Social Issues Esthetics Clinical Psychology Consulting Psychology Industrial and Business Psychology Educational Psychology School Psychologists Counseling Psychology Psychologists in Public Service Military Psychology Maturity and Old Age This list emphasizes the point made earlier that some psychologists are essentially re- search scientists, others arc primarily teach- ers of psychology, and still others are prac- ticing in various fields of applied psychol- ogy. Psychology is thus both a science and an ai t or a profession. WHAT PSYCHOLOGY IS NOT So far we have been talking about what psychology is and how it relates to science in general. Let us look now at some of the popular misconceptions of psychology and see wherein these are in error. Psychology and the Mysterious. Many people imagine that psychology is some- thing magical or mysterious and that some- how psychologists have a superior or al- most superhuman way of looking into the thoughts and feelings of a person. The no- tion is, in other words, that there is a psy- chological method or approach, and that anyone who knows how to use this and uses it successfully has an advantage over anyone who lacks it. Psychology, however, is no more myste- Figure 1.6. Some people seem to think that psychologists have insight into human behavior that is little short of magical or mysterious. Others hold that we learn about human be- havior only from experience and that psycholo- gists really have nothing to contribute to our understanding of this subject. Neither of these extreme positions is correct. THE STUDY OF HUMAN BEHAVIOR rious than medicine or engineering or the other sciences. It is an ordinary, everyday, hard-working science. It has no magic, no mysterious ways, and no dark or hidden routes by which it gets its knowledge. Whatever psychologists have learned, they have learned through observation, through careful reflection upon what they have ob- served, and through the checking of their conclusions with other persons in this and other fields. Psychology is neither magical nor mysterious. Psychology and "Common Sense." Some people go to the opposite extreme and as- sume that psychology is essentially nothing more than common sense. To them, psy- chology is simply what wise people have discovered from their experience, whether they have ever had formal training in the subject or not. It would, of course, be overstating the case to say that psychologists have a mo- nopoly of knowledge of human behavior. We have already acknowledged the role of the other sciences in studying human be- havior, and we tnust further recognize that nonscientific endeavors, such as religion, literature, and the law, also have useful contributions to make to this understanding. We are not maintaining, in other words, that only psychologists understand any- thing about human behavior. The fact nevertheless remains that sci- 1 entific psychology and the "psychology" i of common sense are often rather different. For one thing, there are statements that are accepted by common sense but not accepted by psychology. One example of this is the common notion that those who are insane or seriously mentally ill have "lost their minds." In other words, insane people are considered to be unable to reason adequately or accurately. This com- mon-sense idea of insanity is far from the truth. Although intellectual abilities are sometimes disturbed in mental illness, a great many individuals who are insane are not suffering from lack of ability to reason. If given an intelligence test, they do as well on it as ever. In such cases, the difficulty is not in the intellectual realm at all but rather in the field of emotion. Thus, psychology must insist that insanity cannot be regarded as the "loss of mind." On the other hand, a good many things that are accepted by psychology are not accepted by common sense. An example relates to the phenomenon of color. The common-sense view of color is that the color is in the object which we see. Thus, if we see yellow flowers and blue flowers in a vase on our desk, common sense says the yellowness and the blueness are actually in the flowers themselves. From the stand- point of modern science this view is en- tirely unacceptable. We have every reason at present to believe that the color is not in the object but rather in the pcrceiver. The object reflects to our eyes light waves of a certain length, and the color which we see depends upon the length of the par- ticular light waves. Thus, if long light waves strike our eyes we get a seilsation which we call red, while if short light waves strike our eyes we get a sensation which we call violet. Light waves of intermediate length may lead to blue or green or yellow. But there is no serious reason to believe that the flowers themselves are colored. Color is our response to light waves which they reflect. Thus, it can be seen that psychology, while it sometimes agrees with common sense, is not just common sense. It does not agree with all that common sense holds, and common sense sometimes mistakenly holds to what psychology has shown to be untrue. Psychology and the Pseudo Sciences. People sometimes confuse psychology with a whole group of endeavors which have come to be known as pseudo sciences. (These are called pseudo sciences because the term pseudo means "false/*) Among 20 UNDERSTANDING HUMAN BEHAVIOR these pseudo sciences are phrenology, physi- ognomy, numerology, palmistry, and astrol- ogy- Why do we call them false sciences? In the first place, as will be clear when we examine them in some detail, the claims made by them simply do not fit with the other established facts about the nature of the world and of man. In the second place, they are untrue to, or inconsistent with, the spirit of science and the scientific method. In other words, they do not stick close to the facts but rather rely on essences for their explanations. They do not depend pri- marily on observation but rather on a priori reasoning and predetermined conclusions and prejudices. Instead of being objective they select evidence supporting their posi- tions, while overlooking, neglecting, or even denying the facts that do not fit their pre- conceptions. Let us look more closely at some of these endeavors. Phrenology goes back about 150 to 175 years. A celebrated anatomist by the name of Gall got the idea that he could re- late the contours of the brain to the mental life of the individual. He further believed that the contour of the skull reflects ac- curately the contour of the brain. He went on to map out the brain area, finding thirty-nine "propensities" and "faculties," as he called them, each with its own local- ized area. Thus, he concluded that the in- tellectual faculties are mainly concentrated in the forehead and that emotional factors are located toward the back part of the head. Gall believed that the size of an area was a measure of the strength of the par- ticular faculty, and hence he advocated careful mapping of these areas. We now know that Gall's suppositions were without foundation, although different parts of the brain and even of the cerebrum do have different functions. There is no reason to believe that we actually have the faculties which he designated (or any fac- ulties, for that matter) or that they were located as he thought they were. Further- more, the contours of the brain cannot be inferred from the shape of the skull, nor is the size of a brain area correlated with the strength of a faculty. All Gall's major assumptions are false. Hence, phrenology is a pseudo science. Much the same remarks can be made about physiognomy. This pseudo science did not restrict itself to the shape of the skull but considered facial features and the shape of the body as a whole. For ex- ample, one physiognomist held that a per- son with a misshapen or a deformed body is also likelv fo have a personality similarly warped. More specifically, it has been held by some physiognomists that a square jaw means determination, a high forehead means intelligence (a view which they might share with the phrenologists), and so forth. Now, the truth is that the claims of physiognomy, like those of phrenology, do not stand up when carefully investigated. There is no serious reason to believe that any of the teachings of physiognomy cor- respond to the facts. Likewise, numerology attempts to de- termine the character of the individual (and sometimes his future) from the combina- tions of numbers connected with his name or other things in his life. Palmistry at- tempts to predict his character and his fu- ture from the lines on the palm. And finally, astrology makes predictions about him from the stars under which he was born. The claims made by these endeavors are false almost without exception. There is no trustworthy evidence that the numbers really influence a person's life or that the life line on a palm has anything to do with how long he will live. Likewise, the stars under which he was born have no real in- fluence on his personality. Psychologists have had a great deal to do with showing through experiment and other careful study how these claims have no basis in fact. They involve a priori reasoning and "essences." THE STUDY OF HUMAN BEHAVIOR 21 It is easy to understand that psychologists do not like to be classed with these pseudo sciences. This is partly because the con- clusions of the pseudo sciences are false, but it is even more because they violate the fundamental spirit of science in their ways of investigation and their methods of arriving at conclusions. SUMMARY All of us have an interest in human be- havior. Part of this interest comes from the fact that we need to understand, predict, and control the actions of other people. Part of it comes from our need for self- understanding and self-control. Psychology is the scientific study of the behavior of living organisms, with especial attention given to human behavior. It is to be distinguished from anthropology and sociology in that they focus their attention largely on the group, while psychology studies primarily the individual. It is to be distinguished from physiology in that physi- ology emphasizes the various systems of the body and how they interact and also how the organism adjusts to its physical en- vironment, whereas psychology studies the individual as a person, as a thinking, re- membering, imagining, feeling, and react- ing individual. Actually all these sciences overlap in sub- ject matter. No hard and fast lines can be drawn to separate psychology from any of the others, but there are differences in de- gree and in emphasis. This makes it pos- sible for scientists from several areas to concentrate on the same problem. When we say that a certain endeavor is a science, we refer primarily not to a set of facts or a body of knowledge but to a set of attitudes and values and, in particular, to certain methods for acquiring knowledge. A science proceeds from observations, care- fully checked, recorded, and confirmed. It insists on objectivity, on drawing conclu- sions on the basis of what is observed and not on the basis of what the scientist wants to find or believe. It stays as close to the actual observations as practicable, though it is admitted that observations never in- terpret themselves and the scientist has to go at least somewhat beyond them to inter- pret them. Finally, though a scientist may be interested in information that can be used, another important motive is a desire to know simply for the sake of knowing. Scientists customarily use two kinds of observation: (1) the experiment, which in- volves control of all the relevant conditions except the independent variable, which is allowed to change or forced to change; and (2) naturalistic observation, which is the observing of events as they occur. If it were practicable, scientists would use ex- periments in all their observations, because they permit better control of variables, but since this is often impossible, they must make use of naturalistic observation. Psychology is both a science and a profes- sion. As a science, it is interested in under- standing more and more about the be- havior of the organism. As a profession, it is concerned with applications of this knowl- edge to the prediction and control of be- havior. It is easy to believe that psychology is magical or mysterious, or, on the other hand, that it is nothing more than ordinary common sense. Likewise, psychology is sometimes associated with pseudo sciences like phrenology. All these are false concep- tions, as psychologists have been able to demonstrate. 22 UNDERSTANDING HUMAN BEHAVIOR QUESTIONS 1. What is a science? In what ways does it differ from nonscientific endeavors? 2. What do we mean by saying that a scientist often wants to know for the sake of knowing? 3. What is an experiment? How does it differ from other types of observation? 4. Compare and contrast (a) "armchair" the- orizing and experiment; (/;) "armchair" the- orizing and naturalistic observation. 5. What is the law of parsimony, and what is its importance? 6. Just what is psychology? Name several problems that are distinctively psychological in character. 7. In what applied areas are psychologists found today? Describe the principal work of each area. 8. What is anthropology? On what kinds of problems would both psychologists and an- thropologists work? 9. What is sociology? On what kinds of prob- lems would both psychologists and sociologists work? 10. What is physiology? On what kinds of problems would both psychologists and physi- ologists work? 11. In the experiment on remembering favor- able and unfavorable material, what was the independent variable? What was the depend- ent one? What other variables did the experi- menters attempt to control? 12. Do the > iine for the experiment on the efficiency of * ions dials, 13. What aiguments can you give to prove that psychology is not just "common sense"? 14. How would you demonstrate the inaccu- racy of the claims of phrenology? What are the chief differences between psychology and phrenology? (Consider both conclusions and methods of arriving at conclusions.) SUGGESTED READINGS Britt, Steuart Henderson: Social Psychology of Modern Life, rev. ed., Rinehart, New York, 1949, chap. 2. (An interesting and informative treatment of the scientific method in psychology.) Brown, C. W., and E. E. Ghiselli: Scientific Method in Psychology, McGraw-Hill, New York, 1955. (Application of the scientific method to many psychological problems.) Chapanis, A., W. R. Garner, and C. T. Morgan: Applied Experimental Psychology, Wiley, New York, 1949. (A discussion of the scientific design of equipment for human use.) Daniel, R. S., and C. M. Louttit: Professional Problems in Psychology, Prentice-Hall, Englc- wood Cliffs, N.J., 1953. (The nature and growth of the profession of psychology.) Gray, J. Stanley: Psychology Applied 1o Hu- man Affairs, 2d ed., McGraw-Hill, New York, 1954. (Application of psychology to contempo- rary problems.) Marcuse, F. L.: Areas of Psychology, Harper, New York, 1954. (An introduction to the various fields or branches of psychology.) Ogg, Elizabeth: "Psychologists in Action," Public Affairs Pamphlet 229, 1955. (A survey of the activities of the profes- sional psychologist. ) Watson, Robert I.: Psychology as a Profession, Studies in Psychology series, Random House, New York, 1954. (Applications of psychology to the prob- lems of today; the nature of the profession of psychologist.) THE STUDY OF HUMAN BEHAVIOR 2 HEREDITY AND ENVIRONMENT In order to study behavior more efficiently, the psychologist often separates the biologi- cal and cultural factors. In his separation of these factors, he does not mean to imply that some characteristics are biologically in- herited and that others are acquired by liv- ing in a certain society. Rather, our traits and characteristics are the products of the interaction of our heredity and our environ- . ment. In this chapter we shall discover why the emphasis is to be put on the word "interac- tion." We shall see what the facts are that make it incorrect to think that any trait of a living creature is entirely hereditary or com- pletely environmental. On the contrary, it is more correct to say that all traits and characteristics are both hereditary and en- vironmental. HEREDITY VERSUS ENVIRONMENT During the nineteenth century biology emerged and took its place among the sci- ences. By the end of the century, both the facts and theories of biology were having considerable impact on the thinking of sci- entists about human nature. Of particular importance was Darwin's theory of evolu- tion, which stressed the survival of those in- herited characteristics through which ani- mals adapted to their environments. The Darwinian emphasis on heredity led biolo- gists, physicians, and even people generally to consider heredity as the most important factor in determining human traits and char- acteristics. By the close of the nineteenth century, too much emphasis (as we see it now) had been placed on man's heredity as the molder of his character and per- sonality. 24 In time, opinion began to shift away from this view. Many scientists, especially the sociologists, came to feel that too much emphasis had been placed on heredity. Gradually, during the early decades of the twentieth century, a case was made for en- vironment as the more influential factor in growth and development. By the time of World War I, many sociologists were ex- pressing the belief that heredity is relatively unimportant in the elaboration of character and personality. They admitted, however, that for some physical traits, such as eye color and shape of face, heredity had some importance. As so often is the case, the full swing of the pendulum put too much emphasis on environment, just as heredity had been ac- corded too much importance by biologists and physicians. Caught in the middle were several groups to whom the issue was of some practical significance. The educators were one such group. They did not know whether to go along with the emphasis of physicians and biologists on heredity, or whether to join those sociologists who stressed environment. To seek a resolution of the problem, one group of educators set up a study committee. 1 The purpose of the committee was to determine which is more important heredity or environment. At least they wanted to find out which traits and characteristics of the human being are accounted for by heredity and which are accounted for by environment. When the committee got into the prob- lem, assembling and organizing the relevant scientific facts, it became apparent to them, as it had to some biologists and some soci- ologists, that it is impossible to separate the influences of heredity from those of environ- ment. Rather, the two always go along to- gether. 1 Intelligence: Its Nature and Nurture, Thirty- ninth Yearbook of the National Society for the Study of Education, 1940. Figure 2.1. Julian Huxley, the noted biologist, is the grandson of the distinguished nineteenth century biologist Thomas Huxley. His brother is Aldous Huxley, noted critic and novelist. Does this illustri- ous family tend to show the greater significance of heredity in the production of genius? Can a case be made here for the interaction of heredity and en- vironment? (International News Photos.) HEREDITARY AND ENVIRONMENTAL INFLUENCES ON TRAITS Today we know that all traits the social, the psychological, and the physicalare a product of the interaction and the interrela- tion of heredity and environment. Certainly, no trait can develop without some inherit- ance, nor, on the other hand, can any trait or characteristic develop unless the proper environment is provided. It is obvious that the hereditary factors present in the egg of a chicken cannot produce a human being. It should also be obvious that, if the right environment is not provided, these same factors cannot be made to produce a chicken. It is correct to think of every organism HEREDITY AND ENVIRONMENT 25 and also of each part of every organism as a joint function of three factors: .heredity, environment, and time. Each of these fac- tors is indispensable. If there is no heredity, all the time and environment in the world cannot produce a living organism. On the other hand, if there is no place (environ- ment) in which to grow and develop, no amount of time and heredity can bring forth a living organism. Likewise, in addi- tion to the other two factors, a life span (time) is necessary for the very existence of every living plant and animal. In order to clarify our thinking, let us set up a concise expression for the interac- tion of these factors. P = /(H,E,T) P is the individual person who is some function ( / ) or product of the three factors heredity (H), environment (E), and time (T). This is a way of saying that all three factors are essential and must work to- gether for an organism to survive and de- velop. Note in the formula that if any one of the three (H, or E, or T) is reduced to zero (is nonexistent), the result is zero, which means that there will be no person. Also, we can think of P as the whole person or as any part of the person, i.e., any trait or characteristic. In order to understand some of the im- portant implications of this formula, we must now see what is technically meant by the terms heredity and environment. HEREDITY A human body is composed of many small cells, each of which has a nucleus. Within each nucleus are a number of small rodlike or threadlike objects named chromosomes. Particularly important for our discussion is the fact that in these chromosomes are some tiny submicroscopic particles called genes. These genes are the unit carriers of heredity. They are the units that largely direct the growth and development of the human being, Biologists have good reason to believe that the genes are giant organic molecules, which somehow act as the blue- prints for the building of the organism. Under their influence and given the proper environment, a fertilized egg (one cell) can divide and grow into a human being composed of billions of cells. Furthermore, these billions of cells are formed into tissues and organs which have definite places and functions in the life of the organism. How the minute genes manage to do what they do is still one of nature's closely guarded secrets. In any case, what we mean by the word "hereditary" is gene-directed. Let us consider now the role of the genes in human heredity. For a human being to be conceived, an egg from the mother must be fertilized by a sperm cell from the father. Once the egg has been fertilized, a brand-new individual is begun. From the mother comes half the number of genes needed and from the father the other half. Hence, both mother and father contribute an equal amount of heredity to the new individual. If these genes are to direct the growth of this new individual, a specific, proper environment must be present. In the case of the human being, the proper place is the mother's uterus. If the fertilized egg is left in a normal uterus for seven to nine months, an infant more or less ready to take its place in the outside environment will develop. Were we to remove the egg from the uterus at the time of conception and place it in a test tube, it would soon die. Even our common sense tells us that a test tube is not the proper place for an egg to develop. So we see that we must have both the necessary genes and also the proper environment for the development of a new individual. Chromosomes. As a rule, each of the bil- lions of cells in the human body has a nu- cleus containing 48 chromosomes. In each chromosome are something like 1,000 genes. 26 UNDERSTANDING HUMAN BEHAVIOR Actually, it is better to speak of the 48 chromosomes as 24 pairs, because they are found in pairs and also because there are a few cells in the body that contain 24 chromosomes ( one from each pair ) instead of the full 48.- These cells, which prove to be the exceptions to the rule of 48, are the egg cells in the female and the sperm cells in the male. But nature has provided well. When the sperm cell fertilizes the egg cell, its 24 chromosomes pair up with the egg's 24 and form the 48 needed by the new in- dividual. Thus, nature gains variety by letting two different lines of heredity con- tribute equally to the new offspring. The baby will be somewhat like both its mother and father and yet not exactly like either of them. Reductive cell division. How does it come about that the egg and sperm each contain only 24 chromosomes rather than the typi- cal 48? In the female ovaries, where eggs are produced, and in the male tcstcs, where sperm cells are made, mother cells with 48 chromosomes each divide into daughter cells that have only 24. This process is called reductive cell division. During this division the 48 chromosomes of the mother cell line up in 24 pairs. One member of each pair goes to each daughter cell. However, for each individual pair it is a matter of pure chance as to which member of the pair goes to which of the two daughter cells. Because of this random process, millions of different combinations of chromosomes are possible. It is unlikely that any two eggs produced by the same woman would have exactly the same 24 chromosomes. With the exception of one pair, each chromosome in a pair carries genes which match the genes on the other member of the pair. That is to say, each member of a given pair has genes controlling the growth 2 For many years, biologists have* set the num- ber of chromosomes at 48. A very recent count, however, has found 46 (23 pairs). With cither number, genetic theory and principles are the same. Every cell in our body has 48 chromosomes (or 24 pairs) (A pair of chromosomes showing genes; each chromosome has about 1,000 genes) except the egg cell and the sperm cell, each of which has only 24 (1 from each pair) and development of the same specific set of features and characteristics as the other member of the pair. Biologists have sorted out these 24 pairs and designated them by the first 24 letters of the alphabet, A through X. Thus, either member of any woman's A pair can match up with either member of any man's A pair and the developing child that receives this new A pair (along with the other pairs) will be assured of those human features that are transmitted by the A pair. The one exception to the simple match- ing of pairs occurs in the twenty-fourth pair. Where both of the A's, B's, C's, etc., are the same in shape and size, the two mem- bers of the last pair may be different. Biolo- gists note this fact by labeling this pair HEREDITY AND ENVIRONMENT 27 (8 chromosomes 48 chromosomes 48 chromosomes 24 chromosomes ORDINARY CELL DIVISION REDUCTIVE CELL DIVISION XX when the two members are alike and XY when they are different. The X chromo- some is a full-sized chromosome, but the Y is dwarfed. This pair of chromosomes is important because the sex of the offspring depends on it. If a child receives an X from its mother and an X from its father so that it has a matched XX pair, the child is a girl. If it receives an X from the mother and a Y from the father, it is a boy. Every woman and girl has two X's, and every man and boy has an X and a Y. We see, then, that we al- ways receive an X from our mother and either an X or a Y from our father. Hence, any complaints about our sex should be made to our father, not our mother. Ordinary cell division. One egg and one sperm cell unite to begin one new human being. This fertilized egg divides by what is called ordinary cell division into two cells. Each of these cells has its own nucleus with 48 chromosomes. Moreover, these cells, usu- ally stick together. The process of cell di- vision continues, and with each new divi- sion the number of cells is doubled. Be- fore long, billions of cells have been pro- duced. Under the direction of the genes and in the ideal environment of the uterus, these cells form a human infant. Twins. Most of the time the fertilization of one egg by one sperm cell produces one offspring. Once in a while, however, the first two cells into which the fertilized egg divides do not stick together. Instead, each of these two cells then multiplies independ- ently and produces an infant. These two in- fants are identical twins. The important point is that they come from one egg and one sperm cell and are, therefore, two in- dividuals with exactly the same heredity (genes). Identical twins (triplets, etc.) are, in fact, the only cases known where two (or more) people have identical heredity. Since they are identical in heredity, they are always of the same sex. We shall see 28 UNDERSTANDING HUMAN BEHAVIOR later that these facts are valuable to the psychologist who is trying to study experi- mentally the influences of heredity and en- vironment. Occasionally two eggs instead of one are ready at the same time for fertilization within the mother. In this case two different sperm cells may fertilize these two eggs and two infants result. These twins are called fraternal twins and may be two boys or two girls or a boy and a girl. Moreover, these twins are not of the same heredity. They arc no more related than any other two brothers and sisters born at different times. The relatedness of relatives. On the aver- age, brothers and sisters are related to each other in heredity about as much as they arc to cither parent; that is, on the average, siblings (all the children of the same par- ents) have 24 chromosomes in common. Some siblings have more than 24 in com- mon, and some less than 24. Since kinship depends upon the possession of common chromosomes, some siblings are more (or less) related than others. One of the ex- tremes in relationship is, of course, the case of identical twins ( all 4(8 chromosomes in common). The other extreme, which probably never occurs (but is theoretically possible ) , is the case of a brother and a sis- ter who have no chromosomes in common. Biologically speaking, these two siblings would not be akin to each other at all. This remarkable state of affairs might arise if, by chance, 24 of the mother's chromosomes went to the boy and a different set en- tirely went to the girl and if the father's chromosomes were similarly divided. In the usual case, however, the girl receives one or more of the chromosomes that also went to the boy. Consequently, our best bet is what our common sense tells us, that broth- ers and sisters are related. Or to emphasize the point in another way, we may say that there is no known case of siblings who are not related, even though it is possible ge- netically for them not to be related. We have presented these extremes simply to set the limits of kinship. We may now say that, biologically speaking, we are related to only those people who share with us at least one chromosome. We have also ^oen that we receive 24 chromosomes from our mother and 24 from our father. Thus, we are always related half and half to our two parents there are no exceptions. Our par- ents, of course, received their chromosomes from their parents, which means that our chromosomes came to us (through our par- ents) from our four grandparents. On the average, then, we received 12 from each of our gr a rd parents. However, because which chrj-riosomes are passed on is a matter of chance, some of us received more than 12 from a particular grandparent (e.g., our mother's father) and some received fewer. Thus we may be more or less re- lated to a particular grandparent, just as we are to our siblings. Moreover, as in the case of siblings, it is theoretically possible for us to have received as many as 24 or as few as none from any one of our grandpar- ents. Again it is not very likely that we possess no kinship at all to one of our grand- parents, and even less likely that we are un- related to two of them. The likelihood of no kinship increases as we trace our lineage back through more and more generations. From each of our 8 great-grandparents we receive, on the average, 6 chromosomes. This far back, the possibility of our not being related to one of them is not so remote. From our great-great-grandparents we receive on the average 3 from each. From the next genera- tion back, we average only 1% from each. And from our ancestors six generations back, we are given on the average only % chromosome from each. Since a chromo- some is usually transmitted all in one piece, we have at last come to a generation of ancestors in which some of the individuals are definitely not akin to us. These facts make highly questionable our attempt to trace our family trees back very far. Many HEREDITY AND ENVIRONMENT 29 great grandparents grandparents m X^.^Trw i parents an individual Figure 2.2. On the average, how many chromosomes does a person receive from each generation of his ancestors? In this drawing the chromosomes are represented as ovals and may he traced hack for three generations. A count will show that the typical individual represented received 24 from each of his parents, 12 from each grandparent, and 6 from each great-grandparent. people who glory in a supposed kinship with some historic personage are only fool- ing themselves. The possibility that they have a chromosome in common with that person is too remote to consider seriously. Dominant and Recessive Genes. Genetics is the name biologists give to the special study of heredity. As the name indicates, genetics is the science that deals with the genes. The first laws of heredity were for- mulated about a hundred years ago by an Austrian monk, Gregor Johann Mendel 3 3 V. Grant, "The Development of a Theory of Heredity," American Scientist, 44(2):158-179. ( 1822-1884). He learned about inheritance by growing and crossing several varieties of garden peas. His work was neglected until about 1900, when his laws were re- discovered and the science of genetics be- gan to flourish. One of the most important findings of genetics is that some gens are dominant and_spmg_are recessive^ To illustrate the meaning of these terms, let us first take a classical example from Mendel's work with the color of pea flowers. Some of these flowers are white and some are red. If the flower contains only the genes for red, it UNDERSTANDING HUMAN BEHAVIOR is called pure red. If it has only genes for white, it is called pure white. If it contains j genes for both red and white, it is called a 'hybrid. In Figure 2.4 we see that the crossing (mating) of a pure red flower and a pure white produces offspring that are all red in color and that are designated as hybrid red. In Figure 2.5 we observe that, if two of these hybrid reds are crossed, the result, on the average, is three red and one white off- spring out of every four. Further, by subse- quent breeding experiments, we can show that one of these reds is pure red like its red grandparent and the one white flower is pure white like the other grandparent. The other two reds, however, are hybrids like their parents. The foregoing illustrations show that, though the hybrid red looks like the pure red, it breeds differently. It must carry a gene for white because, when cross-bred, it has white offspring. Because the gene for white is not expressed when paired with the gene for red, it is called "recessive." The fact that the hybrid is red indicates that the gene for red dominates the gene for white. For that reason, it is called "domi- Figure 2.3. What is peculiar about the heredity of this individual? By counting the chromosomes, drawn as ovals, we discover that this individual received 24 from each parent, just as ice all do. However, from his paternal grandmother he received 15 and from his paternal grandfather only 9, making up the 24 from his father. Even more unusual, he received 24 chromosomes from his ma- ternal grandfather and none at all from his maternal grandmother. Thus, he is not genetically related to his own mothers mother! Such an occurrence as this is very unlikely, but it does illustrate one remote possibility in heredity. grandparents parents an individual HEREDITY AND ENVIRONMENT 31 PARENTS pure red pure white OFFSPRING Figure 2.4. If we cross a pure red sweet pea with a pure white sweet pea, we obtain a hy- brid red offspring. This hybrid looks exactly like the pure red parent but differs in that it carries the recessive genes for whiteness as well as the dominant genes for redness. Since we cannot tell by looking at a flower whether or not it is a pure red or hybrid red, how can we determine this fact? hybrid reds Figure 2.5. When two hybrids are crossed, we obtain what is known as the ft Mendelian ratio" What is this ratio? Will it hold every time four offspring are produced? Why was the discovery of this ratio im- portant for the science of genetics? (For further discussion of this ratio, see Figure 2.6.) hybrid red hybrid red pure red hybrid red hybrid red pure white UNDERSTANDING HUMAN BEHAVIOR nant." A dominant gene is one that, when paired with a recessive gene, dominates; i.e., its character shows up in the offspring. It dominates but does not eliminate the recessive gene. Whenever in later genera- tions two recessive genes come together, the recessive characteristic again appears. If we let R stand for the dominant red gene in our pea and w for the recessive white, we have in Figure 2.6 a picture of hew the genes pair off. Figure 2.6 is a combination of the facts of Figures 2.4 and .5. In this figure one R and one iv have been enclosed in parentheses simply to al- low us to follow them more easily from generation to generation. This same rule of dominants and reces- sives holds for human genes as well as for those of the pea plant. Human character- istics, however, are seldom determined by a single pair of genes. Rather, we must think in terms of complex groups of genes pairing with each other. This is the reason that sim- ple human examples are hard to find. It would be convenient, for example, if we could say simply that brown eyes arc con- FIRST CROSS - (as seen in Fig. 2.4) R(R) pure red w(w) pure white All offspring are hybrid reds being either Rw, R(w), (R)w, or (R)(w). If we take any two of these hybrid reds and cross them, we get the following: SECOND CROSS - (as seen in Fig. 2.5) >- Rw hybrid red (R) hybrid red (w) R(R) pure red (R)w hybrid red w(R) hybrid red w(w) pure white trolled by a single dominant gene and blue eyes by a single recessive one. Such a state- ment would allow us to follow Figures 2.4, 2.5, and 2.6, changing only "pure red flower" to "pure brown eyes" and "pure white flower" to "pure blue eyes." Unhappily, such a statement is not true. Although brown eyes are usually dominant and blue eyes usually recessive, eye color in the human being is so complex that we need further genetic laws to handle them. Some of these laws exist, but we must leave their study to the course in genetics. It is sufficient for us in this introduction to genetics u see that human heredity fol- lows define e patterns and laws. Further- more, these principles hold generally for all living organisms, plants and animals alike. The So-called "Purely" Hereditary Traits. In the last section we seemed to ignore the part environment plays in the determina- tion of the characteristics of redness and whiteness in pea plants or brownness and blueness in human eyes. Actually we merely considered environment to be held constant. This is not to say, however, that environ- ment is unimportant. If E and T in the formula P = /(//,E,T) are held constant between two individuals, they nevertheless influence the growth and development of both individuals. However, any difference between these two people will be attrib- Figure 2.6. A first cross between a pure red and a pure white pea plant. All offspring of this cross are hybrid reds. A second cross between two of these hybrids shows the Mendelian ratio of 1-2-1; i.e., one pure dominant, two hybrids, and one pure recessive. With only a few sec- ond-cross offspring this ratio may show chance variations. However, with large numbers of offspring the ratio holds. This ratio was dis- covered by Grcgor Mendel. (The parentheses are used simply to identify one of the R's and one of the w's. ) HEREDITY AND ENVIRONMENT utablc to H which has varied (i.e., H is different for each of them). In identical twins we have it the other way around; H and T are constant (they have exactly the same genes and age), while only E can vary and be different for each of them. In the example of the pea plants we are assuming that all the plants are grown in the same soil, with the same climate, etc. Also we are comparing them after the same lapse of time in each case. In a later section, we give a number of examples that show how changes in environment can affect traits ordinarily called "hereditary." For the time being we shall simply reaffirm that all traits and characteristics are both hereditary and environmental. ENVIRONMENT Each of us realizes that he lives in an environment. Whenever the word is men- tioned, we probably think of the house we live in, of the school we attend, of all the objects we own, of the grass and the trees in our yard, and even of the air we breathe. All these elements, and many more, are a part of our external, physical environment. But it would be a great mistake if we were to limit our use of the word to only this sort of environment. The most useful way for us to define the word "environment" is to say that it-in - eludes aJL the_ conditions in ^he _ world that influence injiny way ouTjbghavior, fflowtH, development, or life processs=-except the genes (and even genes can be considered to provide environment for other genes). According to this broad definition, not only are there a multitude of factors in our en- vironment at any one time, but there are also a great number of other factors that are potentially capable of influencing us. However, our actual environment consists in only those factors in the world around us which do exert their influence. In order to examine more closely the composition of our environment, let us divide it into three parts: the external, physical environment; the internal environment; and the social en- vironment. The External, Physical Environment. We have already listed a few of the elements that make up our external, physical en- vironmenthouses, trees, air, etc. It would take a list almost without end to exhaust everything that could possibly become a part of this environment. We get around this difficulty by using the general term ex- ternal stimuli. Since we take up the topic of stimuli in a later chapter, it is enough to say here that a stimulus is anything which is able to stimulate or excite the receptors in any one of the several sense organs ( eye, ear, skin, etc.). It is through our sense or- gans that the external world ordinarily in- fluences us... To some extent our every action is de- termined by what we see, hear, or feel.. Life is a continual and continuous responding to stimulation. We change and mold and shape our external environment at the same time that it molds and shapes and changes us. Moreover, certain external factors must be in the environment if genes are to exert their influence on human characteristics. For example, in Europe during World War II some children could not find enough food and were permanently stunted in growth. Although a boy might have inher- ited the genes that with the right environ- ment (a better diet) would have allowed him to be 6 feet tall, under wartime con- ditions he might stop growing at a height of barely 5 feet. The Internal Environment. We have men- tioned food as a part of our external en- vironment. We see food, taste it, and re- spond to it by eating it. Once it is in our stomachs and intestines, it is in between our external and internal environments. We say "in between" because until it is digested and absorbed into our blood stream it is not properly spoken of as internal environment, 34 UNDERSTANDING HUMAN BEHAVIOR If it were not for the fact that it is inside our digestive tract, it would be best to con- sider it as an external stimulus, Once food and water are in the blood stream (and in the lymph fluids), they affect every cell in the body and are defin- itely part of the internal environment. The same thing can be said for the vitamins we eat and the hormones produced by the glands. This aspect of our internal environ- ment is treated more fully in Chapter 9* If we accept the concept of inter-- 1 en- vironment, we must be prepared to admit that it is nearly impossible to tell where our environment leaves off and we begin. Or to put it another way, we must say that we cannot draw a sharp line between ourselves and our environment. The Social Environment. Psychologists generally recognize our social environment to be extremely important in shaping our individual behavior and personality. In using the word "social" we mean to include all the other human beings who in any way influence us. Some people influence us by direct, daily contact our families, our friends, our school and business acquaint- ances, etc. Other people have as much or more influence through indirect contact- over radio and television, in books and other publications, and in many other ways. Especially in personality is each of us a result of the interaction of our genes and our social environment. Because of this in- teraction, each of us is unique. Even in the cases of individuals who have some genes in common or similar social environments, Figure 2.7. Which aspects of this scene can be considered as the external environment of these students? What things are actually stimu- lating them at the moment and what are po- tential stimuli? Can you describe the social en- vironment as it is depicted here? (Standard Oil Company, New Jersey.) the interaction produces wide variations in personality. Siblings, who have both simi- lar social environment and some genes in common, also show this wide variation. Even where heredity is the same (identical twins), and the social environment is al- lowed to vary, personalities show remark- able differences. The reason we ordinarily think of identi- cal twins as having inherited the same per- sonality is that they most often have very nearly the same social environment as well as the same genes_. However, on close anal- ysis such identical twins show consistent individual J inferences in personality (note the case of twin T and twin C on page 36). In the rare instances where identical twins have been separated at birth and reared in extremely different social environments, their adult personalities have been quite different (note the case of Mabel and Mary on page 37). In the next section we shall examine several more examples of inter- action, some of which show the effect on the total personality and some the effect on one or two characteristics. HEREDITY AND ENVIRONMENT 35 These babies are identical twins, 38 weeks old. Since they have exactly the same heredity and have been reared together, they are about as much alike as two human beings can be. It is not surprising that they are responding quite similarly in the test situation. However, one infant is reaching with its right hand and the other with its left. The reason is that they are "mirror-image" twins the left side of one twin is identical with the right side of the other one. (Courtesy of Dr. Arnold Gesell.) IDENTICAL TWINS REARED TOGETHER- TWIN T AND TWIN C Because they have exactly the same heredity, identical twins reared to- gether can be expected to show great similarity in nearly all respects. On the other hand, since there are at least small differences in their environment, we can also expect to see some individual differences between them. Such similarities and differences are shown in the study of twin T and twin C.* These identical twin girls were studied for fourteen years by the Yale Clinic of Child Development. From time to time in this study the method of co-twin control was used. Twin T would be given training in such activities as stair climbing, manual coordination, block building, and vocabulary, while twin C was left untrained as a control. At first in each task twin T would tend to excel, but as C reached the proper level of maturation, she soon equaled T's performance. As would be expected, these twins were very much alike in physical growth and appearance, in intelligence, and in many other characteristics. However, closer study showed a number of persistent and durable dif- ferences. T was quicker, C more deliberate. In drawing a picture T preferred to use straight lines and angles, while C preferred curved lines. T appeared a little brighter, C was a bit better in a social situation. T was more prompt in attention, while C was more alert. Although these differences were slight, they added up to a distinctive per- sonality for each of the two girls. Certainly they were not so unlike as most people, but each had her unique personality. Of interest is the fact that some of their differences showed up in infancy. This fact points up the importance of the, prenatal environment in the development of temperament. Other of the differences showed up later. We should remember that interaction of heredity and environment pro- duced everything about these twins, including both their differences and their similarities. However, since their heredity was identical, we must con- * A. Getell and H. Thompson, "Learning and Growth in Identical Infant Twins: An Ex- perimental Study by the Method of Co-twin Control/' Genetic Psycho/ogy Monograph, 6:1- 124, 1929. UNDERSTANDING HUMAN BEHAVIOR elude the environmental variations accounted for the differences they pos- sessed. Certainly such differences exist, for since two people cannot occupy the same identical space at the same time, they must have at least slightly different environments. In the mother's uterus, for example, if one twin is on the left side the other must be on the right side. Also, in growing up even twins will receive, at least occasionally, different treatment. Very important in the case of twin T and twin C were the co-twin control observations. The training that twin T received constituted environmental stimulation which twin C did not have. We can conclude from this study that even identical twins reared together can be expected Jo show^mall differences in addition to a great amount of Mabel and Mary * were identical twin's e pa rated early in life. Mabel lived in the country and participated in all the rural activities, including hard farm chores. She was permitted to finish only eight grades in the small IDENTICAL TWINS , . , . __ __. . . . REARED APART country school near her home. Mary grew up in a medium-sized city, where MABEL AND MARY ner ma ' n interest was the study of music. She attended three years of high school in this city and then finished her fourth year in a large-city school. After graduation she became a music teacher. Both girls had the advantage of living in relatively prosperous homes. At the age of twenty-nine Mabel and Mary were studied by a psychologist. In intelligence they were separated by 17 IQ points on the Stanford-Binet Test (see Chapter 17 for information about this test). Mary was rated as high average in intelligence and Mabel was low average. In personality Mabel, who was still a farm woman, was slow and phlegmatic, and yet was con- sidered an aggressive leader in her community. Mary was excitable, nearly neurotic. In manner Mabel was almost masculine, while the music teacher Mary was quite ladylike. This difference in manner showed up in their walk- Mabel had a firm, manlike stride, Mary a very feminine step. Even in physical appearance these twins differed. Mabel had hard muscles and weighed 138 pounds. Mary's muscles were soft and not well developed, and she weighed 110 pounds. Over-all, they were unlike in behavior and appeared to be as strikingly dissimilar in personality as the psychological tests had indicated. They did not seem to be identical twins at all, although undoubtedly there was a fam- ily resemblance. Mabel and Mary illustrate how widely two persons, even with heredity constant between them, can vary in personality and appearance if reared r separately. We have already seen in the study of twin T and twin C how identical Heredity and rather small variations in environment can produce small but real differences in personality. In these studies we again see proof that ajperson is a result of the inter- action of both heredjty_and environment. These twins wer^ ajike because ol identical heredity, yet dissimilar because of environmental different ~ * H. H. Newman, Multiple Human Births, Doubleday, New York, 1940. HEREDITY AND ENVIRONMENT 37 INTERACTION OP HEREDITY AND ENVIRONMENT Most of us have learned somewhere in our education that eye color is inherited. This is true, but it is also true that eye color is partly determined by environmenta statement which may at first seem a little surprising, since we are likely to think that "inherited" means "completely inherited." How can environment in any way affect the development of eye color? When a human individual is conceived, he has the proper genes present to deter- mine the production of eyes, eye color, hair, face, limbs, and all the other features of a human being. We must remember, how- ever, that he also had present the proper environment, his mother's uterus, in which to develop. If he had not had that proper environment, a number of features might have turned out differently. We know this from experiments in lower animals. Fruit-fly Experiments. It has been said that geneticists know more about the hered- ity of the fruit fly, Drosophila, than they do about any other living organism. Why this preoccupation with the fruit fly? The reason lies in the facts that Drosophila has in its salivary glands giant chromosomes, which are easy to study, and that it can be bred rapidly under laboratory conditions. In one experiment it was shown that fruit flies whose heredity did not contain a gene for yellow body color could be caused to have yellow bodies by an environmental change. This was done by including a chemical, silver nitrate, in the food on which the larvae fed. These flies were not different in appearance from flies that have the gene for yellowness. However, when these flies which had been fed silver nitrate were bred, their offspring were not yellow but were, as they should be by the laws of genetics, the dark-brown color of their grandparents and other ancestors. Of course, these dark-brown offspring had not had their environment changed by the ad- dition of silver nitrate to the food they ate. Bearing directly on our interest in envi- ronmental influences on eye color are a number of other experiments with Dro- sophila. Some of these experiments show that even such relatively simple environ- mental factors as changes in temperature during the incubation of the eggs can affect the adult fly's eye color. In one experiment fruit flies with genes that normally produce rust-colored eyes were made to have red eyes by adding a certain chemical, kynu- renine, to the fruit flies* environment dur- ing eye development. Since the interaction of genes and environment in Drosophila is not basically different from that in human beings, we must conclude that similar changes could be effected in human eye- color development. It is within the realm of possibility that chemical changes in a human mother's uterus could cause an eye color to develop that would not have been predictable from a knowledge of the child's heredity. Al- though actual human examples pertaining to eye color are not available, we do have examples that illustrate the importance of prenatal environment in the development of other so-called "hereditary" character- istics. Let us consider two of them. Human Examples of Interaction. One example of interaction in human develop- ment is sometimes seen in German measles in the pregnant woman. German measles, of course, is a rather mild disease so far as most adults are concerned. It is also a mild disease so far as the pregnant woman her- self is concerned, but it can be injurious to the unborn child. As the mother's body fights the disease, toxic substances are built up in her blood stream. These substances reach the developing embryo. If the em- bryo is at the stage when the eyes are de- veloping, there may be a defect in the structure of the eyes. If it is at the stage when the ears are developing, the ears may be defective. Thus, the child may be born UNDERSTANDING HUMAN BEHAVIOR blind, or deaf, or with any of a number of other defects. A proper environment is therefore just as important as the genes in the development of such organs as eyes and ears. Furthermore, if a child blinded in this way grows up, marries, and has chil- dren, they will have normal sight; for the toxic environment has affected only the developing organs, not the genes that partly direct their development. Another somewhat similar example is so- called Mongolian feeble-mindedness. This is a type of feeble-mindedness in which the child has peculiar-appearing eyes, a long pointed tongue, and certain other distinc- tive physical characteristics. The misfor- tune of being feeble-minded, or at least dull in intellect, is, of course, the most im- portant part of the defective condition. Ij has been discovered only recently that cer- tain toxic substances builtii^inlhe mother's blood stream at about the_eighth week of pregnancy may be the cause of this mal- forming of various organs and parts of the body, resulting in Mongolian feeble-mind- edness. 4 Both these examples illustrate the fact that the human being can have its environ- ment changed in its early days of life just as the fruit fly can in the laboratory. Most important, they show that such environ- mental changes result in serious conse- quences. Both structurally and functionally the organism is different from what it would have been had not the environment been altered. Thus, we see that heredity and environ- ment are inseparable. It is a hopeless task to try to separate the various human traits and characteristics into those which are hereditary and those which are environ- mental. The only correct statement is thatf 4 This hypothesis about the cause of Mongolian feeble-mindedness has not yet been conclusively proved. However, it does illustrate the fact that scientists are searching for causes based on the interaction of heredity and environment. Figure 2.3. This unfortunate child is an ex- ample of Mongolian feeble-mindedness. At the present time it is thought that chemical changes in his mothers uterus denied him a normal pre- natal environment. (From Dr. Theodore H. Ingalls, "Mongolism" Scientific American, February, 1952, pp. 60-62, by courtesy of the author and publisher.) all traits and all characteristics are pro- duced by the joint action, interaction, and interrelation of both heredity and environ- ment. To say that one is more important than the other is like saying that either the ball or the bat is more important in playing baseball. Without both a bat and a ball a baseball game is impossible. It may seem, at this point, that only ex- treme changes in environment or very ab- normal conditions will in any way affect the action of the genes. It may seem further that in an ordinary or normal situation en- vironment is a neutral factor and that genes alone direct growth and development. The facts are, however, that environment is just as important in normal development as in abnormal (see the two twin studies). HEREDITY AND ENVIRONMENT 39 MATURATION May people confuse the terms "hered- ity" and "maturation." The two words do not, however, mean the same. We have seen that heredity is the direction given by the genes to growth and development. Matura- tion is the completion of growth and devel- opment within the organism. Every organ and every system within the body must mature over a period of time before it is ready to function. Most organs are capable of functioning at birth, but some of the organs and systems are farther along than others. The heart, for example, is already capable of pumping blood, and the digestive system can handle milk. The nervous system is functioning at its lower levels, but many years must pass before the higher levels of the brain are completely developed and fully functioning. In the process of maturation we see the interaction of heredity and environment over the course of time. For example, a girl's ovaries are not mature enough to pro- duce fully