ADOLESCENCE (Latin, adolescere, to grow up) is the period of -life between the ad vent of puberty and maturity. Puberty, or the period when an individual first becomes capable of begetting or of bearing children, occurs approximately in the 12th or 13th year for girls and the 14th year for boys, • though in individual cases its advent may be as early as the 10th or as late as the 21st year. These alterations of structure and function in the body which fit it for the processes of reproduc tion are the primary aspect of the period of adolescence on its physical side and the remain ing phenomena, both physical and mental, which make the period so striking and so significant for psychology and education, can be shown to be related more or less directly to this funda mental process of preparing the body for its role in the perpetuation of the race.
Physical Changes.— Thus, on the physical side, measurements of the body and its capaci ties show during adolescence, and particularly in the four or five years from puberty onward, distinct acceleration in the rate of growth, and this acceleration begins earlier and ends earlier in boys than in girls, just as the onset of pu berty itself is earlier in girls. The consequence of this sex difference in the appearance of ado lescence is that for a time, approximately from the age of 12 to the age of 141/2, girls are actu ally taller and heavier than boys of the same age, while in other respects, as for example in strength and in breathing capacity, the girls come near to, though they do not exceed, the capacity of boys during these years. These bodily changes at adolescence are prominent in every aspect of physical development; the bones not only lengthen and thicken but alter their shapes and their structure. The facial expression changes during this period and the shift in the shape of chest and pelvis, particu larly in girls, is marked. There is quite excep tional growth of muscles. There are decided changes in the volume and capacity of the heart.
The alteration in the dimensions of the larynx and its vocal cords is responsible for the char acteristic mutation of the voice in boys. The brain, while not increasing appreciably in weight, certainly undergoes rather marked alterations in its connective systems, if we may judge from the corresponding alterations in instinctive ten dencies, impulses,. feelings and emotions and the obviously greater maturity of thought.
While all these physical changes are to be noted in adolescent boys and girls, it remains true that there is considerable unevenness in their appearance when we consider the indi vidual rather than the group. It is agreed that one of the characteristics of the period is this increase in variability; there is more difference between individual and individual during ado lescence than during the first 12 years of life, and this is true of all the aspects of develop ment, both physical and mental.
Mental Characteristics.— On the mental side adolescence is characterized by analogous and equally striking alterations. The central phenomenon is the correlate of the physical changes of puberty, namely, the emergence and rapid development of sex feelings and impulses, in the widest sense of these terms. Thus, con comitant with the ripening of the sex instinct, appear such psychological manifestations as %showing off,) jealously, heightened conscious ness of social relations, deeper and richer appre ciation of beauty in all its forms, a wider range of ambitions and ideals, an enlarged mental horizon, new and more vital appreciation of moral and religious relations, a lessening of home ties with a corresponding augmentation of interest in the world's life outside the famil iar circles of the earlier years. Mere maturity would account for a portion of these manifes tations, yet psychologists detect the undercur rent of sex in all of them, so that they are to be regarded as primarily due to the irradiation or of the sex impulse.