[X. THE SIGNIFICANCE OF INDIVIDUAL DIFFERENCES FOR THE TEACHER]
It has been indicated here and there throughout the previous chapters that, despite the fact that there are certain laws governing the various mental traits and processes, still there is variation in the working of those laws. It was pointed out that people differ in kind of memory or imagination in which they excel, in their ability to appreciate, in the speed with which they form habits, and so on. In other words, that boys and girls are not exact duplicates of each other, but that they always differ from each other. Now a knowledge of these differences, their amounts, interrelations, and causes are very necessary for the planning of a school system or for the planning of the education of a particular child. What we plan and how we plan educational undertakings must always be influenced by our opinion as to inborn traits, sex differences, specialization of mental traits, speed of development, the respective power of nature and of nurture. The various plans of promotion and grouping of children found in different cities are in operation because of certain beliefs concerning differences in general mental ability. Coeducation is urged or deplored largely on the ground of belief in the differing abilities of the sexes.
Exact knowledge of just what differences do exist between people and the causes of these differences is important for two reasons. First, in order that the most efficient measures may be taken for the education of the individual, and second, in order that the race as a whole may be made better. Education can only become efficient and economical when we know which differences between people and which achievements of a given person are due to training, and which are due more largely to original equipment or maturity. It is a waste of time on the one hand for education to concern itself with trying to make all children good spellers--if spelling is a natural gift; and on the other hand, it is lack of efficiency for schools to be largely neglecting the moral development of the children, if morality is dependent primarily on education. Exact knowledge, not opinions, along all these lines is necessary if progress is to be made.
The principal causes for individual differences are sex, remote ancestry, near ancestry, maturity, and training. The question to be answered in the discussion of each of these causes is how important a factor is it in the production of differences and just what differences is it responsible for. That men differ from women has always been an accepted fact, but exact knowledge of how much and how they differ has, until recent years, been lacking. Recently quantitative measurement has been made by a number of investigators. In making these investigations two serious difficulties have to be met. First, that the tests measure only the differences brought about by differences in sex, and not by any other cause, such as family or training. This difficulty has been met by taking people of all ages, from all sorts of families, with all kinds of training, the constant factor being the difference in sex. The second difficulty is that of finding groups in which the selection agencies have been the same and equally operative. It would be obviously unfair to compare college men and women, and expect to get a fair result as to sex differences, because college women are a more highly selected group intellectually than the college men. It is the conventional and social demands that are primarily responsible for sending boys to college, while the intellectual impulse is responsible to a greater extent for sending girls. Examination of children in the elementary schools, then, gives a fairer result than of the older men and women. The general results of all the studies made point to the fact that the differences between the sexes are small. Sex is the cause of only a small fraction of the differences between individuals. The total difference of men from men and women from women is almost as great as the difference between men and women, for the distribution curve of woman's ability in any trait overlaps the men's curve to at least half its range. In detail the exact measurements of intellectual abilities show a slight superiority of the women in receptivity and memory, and a slight superiority of the men in control of movement and in thought about concrete mechanical situations. In interests which cannot be so definitely measured, women seem to be more interested in people and men in things. In instinctive equipment women excel in the nursing impulse and men in the fighting impulse. In physical equipment men are stronger and bigger than women. They excel in muscular tests in ability to "spurt," whereas women do better in endurance tests. The male sex seems on the whole to be slightly more variable than the female, i.e., its curve of distribution is somewhat flatter and extends both lower and higher than does that of the female; or, stated another way, men furnish more than their proportion of idiots and of geniuses.
Slight though these differences are, they are not to be disregarded, for sometimes the resulting habits are important. For instance, girls should be better spellers than boys. Boys should excel in physics and chemistry. Women should have more tact than men, whereas men should be more impartial in their judgments. With the same intellectual equipment as women, men should be found more often in positions of prominence because of the strength of the fighting instinct. The geniuses of the world, the leaders in any field, as well as the idiots, should more often be men than women. That these differences do exist, observation as well as experiment prove, but that they are entirely due to essential innate differences in sex is still open to question. Differences in treatment of the sexes in ideals and in training for generation after generation may account for some of the differences noted.
What these differences mean from the standpoint of practice is still another question. Difference in equipment need not mean difference in treatment, nor need identity of equipment necessarily mean identity of training. The kind of education given will have to be determined not only by the nature of the individual, but also by the ideals held for and the efficiency demanded from each sex.
Another cause of the differences existing between individuals is difference in race inheritance. In causing differences in physical traits this factor is prominent. The American Indians have physical traits in common which differentiate them from other races; the same thing is true of the Negroes and the Mongolians. It has always been taken for granted that the same kind of difference between the races existed in mental traits. To measure the mental differences caused by race is an extremely difficult problem. Training, environment, tradition, are such potent factors in confusing the issue. The difficulty is to measure inborn traits, not achievement. Hence the results from actual measurement are very few and are confined to the sensory and sensorimotor traits. Woodworth, in summing up the results of these tests, says, "On the whole, the keenness of the senses seems to be about on a par in the various races of mankind.... If the results could be taken at their face value, they would indicate differences in intelligence between races, giving such groups as the Pygmy and Negrito a low station as compared with most of mankind. The fairness of the test is not, however, beyond question."[14] The generality of this conclusion concerning the differences in intelligence reveals the lack of data. No tests of the higher intellectual processes, such as the ability to analyze, to associate in terms of elements, to formulate new principles, and the like, have, been given. Some anthropologists are skeptical of the existence of any great differences, while others believe that though there is much overlapping, still differences of considerable magnitude do exist. At present we do not know how much of the differences existing between individuals is due to differences in remote ancestry.
Maturity as a cause of differences between individuals gives quite as unsatisfactory results as remote ancestry. Every thoughtful student of children must realize that inner growth, apart from training, has something to do with the changes which take place in a child; that he differs from year to year because of a difference in maturity. This same cause, then, must account to some extent for the differences between individuals of different ages. But just how great a part it plays, what per cent of the difference it accounts for, and what particular traits it affects much or little, no one knows. We say in general that nine-year-old children are more suggestible than six-year-old, and than fourteen-year-old; that the point of view of the fifteen-year-old is different from that of the eleven-year-old; that the power of sense discrimination gradually increases up to about sixteen, and so on. That these facts are true, no one can question, but how far they are due to mere change in maturity and how far to training or to the increase in power of some particular capacity, such as understanding directions, or power of forced attention, is unknown. The studies which have been undertaken along this line have failed in two particulars: first, to distribute the actual changes found from year to year among the three possible causes, maturity, general powers of comprehension and the like, and training; second, to measure the same individuals from year to year. This last error is very common in studies of human nature. It is taken for granted that to examine ten year olds and then eleven year olds and then twelve year olds will give what ten year olds will become in one and two years' time respectively. To test a group of grammar grade children and then a group of high school and then a group of college students will not show the changes in maturity from grammar school to college. The method is quite wrong, for it tests only the ten year olds that stay in school long enough to become twelve year olds; it measures only the very small per cent of the grammar school children who get to college. In other words, it is measuring a more highly selected group and accepting the result obtained from them as true of the entire group. Because of these two serious errors in the investigations our knowledge of the influence of maturity as a cause of individual differences is no better than opinion. Two facts, however, such studies do make clear. First, the supposition that "the increases in ability due to a given amount of progress toward maturity are closely alike for all children save the so-called 'abnormally-precocious' or 'retarded' is false. The same fraction of the total inner development, from zero to adult ability, will produce very unequal results in different children. Inner growth acts differently according to the original nature that is growing. The notion that maturity is the main factor in the differences found amongst school children, so that grading and methods of teaching should be fitted closely to 'stage of growth,' is also false. It is by no means very hard to find seven year olds who can do intellectual work in which one in twenty seventeen year olds would fail."[15]
The question as to how far immediate heredity is a cause of differences found between individuals, can only be answered by measuring how much more alike members of the same family are in a given trait than people picked at random, and then making allowance for similarity in their training. The greater the likenesses between members of the same family, and the greater the differences between members of different families, despite similarities in training, the more can individual differences be traced to differences in ancestry as a controlling cause. The answer to this question has been obtained along four different lines: First, likenesses in physical traits; second, likenesses in particular abilities; third, likenesses in achievement along intellectual and moral lines; fourth, greater likenesses between twins, than ordinary siblings. In physical traits, such as eye color, hair color, cephalic index, height, family resemblance is very strong (the coefficient of correlation being about .5), and here training can certainly have had no effect. In particular abilities, such as ability in spelling, the stage reached by an individual is due primarily to his inheritance, the ability being but little influenced by the differences in home or school training that commonly exist. In general achievement, Galton's results show that eminence runs in families, that one has more than three hundred times the chance of being eminent if one has a brother, father, or son eminent, than the individual picked at random. Wood's investigation in royal families points to the same influence of ancestry in determining achievement. The studies of the Edwards family on one hand and the so-called Kallikak family on the other, point to the same conclusion. Twins are found to be twice as much alike in the traits tested as other brothers and sisters. Though the difficulty of discounting the effect of training in all these studies has been great, yet in every case the investigators have taken pains to do so. The fact that the investigations along such different lines all bear out the same conclusion, namely, that intellectual differences are largely due to differences in family inheritance, weighs heavily in favor of its being a correct one.