Commonest of all, perhaps, is the jealousy occasioned by the advent of a little brother or sister, who is looked upon as a rival for the parents' affections. Or jealousy may be felt against one of the parents, little boys being frequently jealous of their fathers, and little girls of their mothers. Seemingly, they are unable to tolerate the love their parents feel for each other and would monopolise the affection of the parent of whom they are fonder. Again, there may be jealousy, sometimes of a violent sort, with regard to material possessions. Greatly to the profit of toy-makers, innumerable children have broken their toys to pieces in jealous rage at another child having been allowed to play with them. So, too, there may be jealousy with regard to food. A child will often eat food of which he is not really desirous, rather than see another gain pleasure from it.

As the child grows older, other objects and situations cause in him the unpleasant reaction of jealousy. On this point—the shifting causes of jealousy, through later childhood into adolescence—I cannot do better than quote at some length the findings of Professor M. V. O'Shea, of the University of Wisconsin, as given in his "Social Development and Education," a book of great value to parents and teachers:

"The jealous attitude is manifested most strikingly in children from the fifth year on, in situations where competitors seek to exalt themselves in the eyes of those who have favours to distribute, or where the deeds and virtues of rivals are extolled by outsiders. Let K. begin to describe in the family circle some courageous or faithful deed he has performed, or painful experience he has endured, or duties he has discharged, and C., his natural rival, will at once seek to minimise the importance of the particular act for which praise is sought, so that K. may not be too highly thought of. Then C. will endeavour to attract attention to his own worth by describing more meritorious deeds which he has himself performed. He cannot easily submit to the attempts of his rival to gain the admiration of the company before whom he wishes to exhibit himself. But it is different in situations where K. and C. are united in their interests, in opposition to other groups. Then C. is glad to reinforce the testimony of K. regarding his valorous deeds; and the principle works in just the same way when C. is seeking for favour, and K. is the jealous witness or the faithful comrade.

"It must be impressed that jealousy is an attitude assumed only by individuals in those situations in which they are competing for the same favours. Two children may be intensely jealous in their own homes; but they may abandon this attitude absolutely when they go into the world and compete as a unit with other groups. Normally, the jealousies between members of a family tend to disappear in the measure that their interests broaden, and they form new connections in the world. That is to say, according as persons cease to be keen rivals, they tend either to become indifferent to the successes of one another, or they may even rejoice in the good fortune of each other, and lose no opportunity to celebrate one another's virtues and merits. This latter stage is not reached, however, until rivalry, and so conflict, wholly ceases, and the contestants come to appreciate that their interests are mutual, and each can help himself best by extolling the other. This is frequently seen in adult life, especially in political and professional partnerships....

"As a general principle, the smaller the group of individuals who are in competition with one another, and the narrower the range of their interests, the more intense will be the jealous attitudes developed. As the group increases in membership and their interests and activities become more varied, particular competitors normally come to occupy a less and less important place in any one individual's attention. It is as though the energy which in a restricted situation finds an outlet in one channel, perhaps, is discharged through various channels when the circle of persons and the range of interests to be reacted upon are enlarged. It is probable that most strictly social attitudes become less pronounced, though they are likely to become more habitual, according as the occasions which call them forth are multiplied.

"This principle has an interesting application to the child when he enters school. His new personal environment makes such demands upon his attention and energy, in order that he may take the first steps in adjustment thereto, that the jealous attitudes are not aroused for some time, though they are liable to appear as he begins to feel at home in the new group. The beginner is usually in the learning or adaptive attitude; he is never, at the outset, resentful towards individuals in the group who may secure greater attention than himself from the teacher or his associates. The novice in school seeks, above everything else, to win the favour of those who, for any reason, are prominent in the group. He does not normally oppose his personality to that of any one who stands well with the crowd, or who has the support of tradition in his particular expressions....

"As the child grows to feel at ease in adjustment to the situations presented in the school, he commences to assume attitudes of disapproval, as well as approval, of the expressions of his associates, and even of the teacher. In due course—often by the fourth year in school, possibly earlier—he begins to manifest some feeling of jealousy towards those of his group who attain greater prominence in the work of the school than he does himself. However, according to the observations of the present writer, this feeling is not a dominant one at any period in the elementary school, except in the case of particular children who are displeased at any distinction in recitations or in conduct attained by their classmates.

"In the fourth grade of a certain elementary school of a Western city there are three backward boys who have been in this grade for two years, though they are bright enough in the things of the street. They are in a more or less hostile attitude towards all that goes on in the schoolroom, probably because they cannot succeed in it themselves, and so they would like to escape from it or destroy it. Now, they make it unpleasant, so far as they are able, for all the boys in the grade who apply themselves to their tasks and get 'good marks.' On the playground these dullards 'pick on' the 'bright' boys; and in the school they ridicule them by 'snickering' at them, or 'making faces' at them, and so on, with the result that they deter some boys from doing their best in the schoolroom. These same three ill-adjusted boys will make fun of their mates who come to school 'dressed up in fine togs.' They are themselves attired in plain clothes suited to the rough experience of the street, and they resent the adoption of different styles by any of their associates. Further, they show jealous feeling towards boys who come from 'better' homes than their own, or from more 'aristocratic' parts of the city....

"It will not be necessary here to do more than to mention the chief incitement to jealousy after the beginning of the adolescent upheaval, and lasting well on into middle life. The testimony of autobiographers, as well as the observations of psychologists, indicates that rivalry for sex favours gives rise to most of the jealous attitudes of the adolescent up until full maturity is reached. Often, no doubt, it is the main cause of the jealousies of some people throughout their lives; but, normally, other and more general interests become stronger and more vital as maturity is approached. But, from the age of fifteen or sixteen on to twenty-five, or beyond, the sex needs and interests are supreme, and the individual is sensitive to sex relations above all others. No pain is so keen at this time as that which arises from slight or indifference from persons of the opposite sex, and no experience will stir an individual so deeply as that which threatens to deprive him of the exclusive possession of the affections of the one he loves."

Whatever the cause, I repeat, parents should never delay in combating repeated manifestations of jealousy, in order to make sure of preventing possible acts of extreme violence, subtle distortions of character that may persist through life, and neurotic maladies of gradual or rapid development. To bring home concretely to every parent who happens to read these lines the danger menacing his own jealous child in this last respect, I cannot do better than cite from real life a few instances of nervous trouble directly and demonstrably due to jealousy.