"Just as good eyesight and longevity are family characteristics, so also color blindness, left-handedness, some slight peculiarity of structure such as an extra finger or toe, or the Hapsburg lip, sense defects such as deafness or blindness, tendencies to certain diseases, especially those of the nervous system,--all these run in families. Certain mental traits likewise are obviously handed down from parents to child, such as strong will, memory for faces, musical imagination, abilities in mathematics or the languages, artistic talent. In these ways and many others children resemble their parents. The same general law holds of likes and dislikes, of temperamental qualities such as quick temper, vivacity, lovableness, moodiness. In all traits, characteristics, features, powers both physical and mental and to some extent moral also, children's original nature, their stock in trade, is determined by their immediate ancestry. 'We inherit our parents' tempers, our parents' conscientiousness, shyness and ability, as we inherit their stature, forearm and span,' says Pearson." The teacher who would really appreciate the feelings and responses of a boy in his class must be aware, therefore, that the boy is not merely one of a dozen type individuals--he is a product of a particular parentage, acting as he does largely because "he was born that way." We shall point out in connection with environmental influences the importance of a teacher's knowing the home condition of his pupils; but it is important here, in passing, to emphasize the point that even though a child were never to live with its parents it could be understood by the teacher acquainted with the peculiar traits of those parents. "Born with a bent" is a proverb of such force that it cannot be ignored. To know the parental heritage of a boy is to anticipate his reaction to stimuli--is to know what approach to make to win him. Because of the fact that in many of our organizations we are concerned with the problem of teaching boys and girls together, the question of the influence of sex is one which we must face. There are those who hold that boys and girls are so fundamentally different by nature that they ought not to be taught coeducationally. Others maintain that they are essentially alike in feeling and intellectuality, and that because of the fact that eventually they are to be mated in the great partnership of life they should be held together as much as possible during the younger years of their lives. Most authorities are agreed that boys and girls differ not so much because they are possessed of different native tendencies, but because they live differently--they follow different lines of activity, and therefore develop different interests. To quote again from Norsworthy and Whitley: