In modern times the essential “normality” of adolescence has been acknowledged. With its pan-cultural and functional perspective, ethology is in a position to elaborate a description of normal human adolescence.Ethologists attempt to elucidate four interrelated aspects of a given behavior: its survival function, evolution, development, and elicitation by internal and external factors. The basic research strategy is two-fold: to identify biologically based, or evolved, behaviors (chiefly by controlling for the effects of experience and seeing if a core of evolved behavior remains); and to discover their functions by isolating the necessary and sufficient ecological conditions for their evolution.Applying this evolutionary analysis to human adolescence, we find that two developments seem to be basic: reproductive maturation and gaining independence from parents. The remainder of the article is an interpretation of various behavioral, morphological, and cultural data in accordance with these two developmental functions.Puberty seems to be timed so as to promote these functions most effectively. Pubertal changes parallel somatic growth and are delayed by poor nutrition, disease, and psychological stress—patterns consistent with functional considerations. The influence of natural selection on the sequencing of pubertal events is also emphasized. The role of pubertal hormones in altering behavior as well as morphology is illustrated.The adolescent gains independence from his parents by means of maturation and sex differentiation. Males become specialized for vigorous exertion, and females for work near the settlement—although considerable overlap in morphological and behavioral tendencies exists between the sexes. Various examples of sex differentiation demonstrate how morphological, behavioral, and cultural factors complement each other.Adolescent initiation rites help channel boys and girls into appropriate adult roles, teach respect for one's culture, and favor the fittest individuals. Hopi rites of passage are described as an example.Reproductive maturation likewise involves adaptive morphological and behavioral changes that are reinforced by cultural mores. Males rely on intimidation more than females, in order to dominate other males and attract females; contrariwise, females employ an endearment strategy more than males do. Many sex differences in human reproductive behavior can be explained with reference to man's parental behavior pattern. These include the male's greater aggressiveness, the preponderance of polygyny over polyandry, and differences in the antecedents of jealousy.Lastly, the need for an ethological understanding of adolescence is underscored as promising to offer a useful perspective on the problems of U.S. youth.