Evolution of the hominidae life history during the first 20 years of life. During evolution, childhood and adolescence have been added as new life-history stages and compared with apes and the presumably early hominidae. The chimpanzee serves as a living representative of the assumed Australopithecus afarensis life history. As childhood emerged and prolonged, infancy has gradually become shorter, and the latest introduced adolescence came at the expense of a shorter juvenility. Detailed accounts of these stages are given in .