While the necessary link between industrialization and a life stage of adolescence is debatable (see Schlegel below) what is clear is that by the twentieth century the term adolescence and the understanding that it represents a life stage that is distinct from both childhood and adulthood was thoroughly embedded in European and North American thinking. Usually linked to the years just after puberty and before marriage, adolescence was not only seen as a unique and distinctive life stage but it was identified as one that posed particular problems and concerns. In 1904 the psychologist G. Stanley Hall published a two-volume set succinctly titled Adolescence that attempted to set forth current theories about this "vast and complex theme" (Hall, p. xix). While Hall's work on adolescence was nothing if not prodigious, his most controversial claim was essentially that "ontogeny recapitulates phylogeny" or, in other words, that the psychic development of each individual mirrors and recreates the evolutionary stages of the species. If this is true, then the behaviors associated with adolescence, which at the time were often referred to as filled with "storm and stress," were rooted in nature and therefore were assumed to be universal. Hall's theories on adolescence, and in particular his concern for describing it as a universal stage of human development, were inspired in part by popular theories of the age concerning both physical and social evolution. Indeed, Hall claims in the concluding chapter of his second volume that "savages" "in most respects are children, or, because of sexual maturity, more properly, adolescents of adult size" (Hall, vol. 2, p. 649).
For several decades before and after the publication of Hall's Adolescence, social theorists were interested in developing ways to incorporate evolution as a conceptual tool for understanding human behavior and cultural difference. Most of their arguments centered on two interconnecting themes: how cultural and social differences could be explained through an evolutionary model; and how much of human behavior could be explained by evolutionary inheritance, or biology. Both of these themes easily qualify as "racist" by twenty-first-century standards, with their emphasis on white, Western civilization (and behaviors) as the apex of social evolution, while "primitive" societies or "races" were held to represent "earlier" stages along the evolutionary trajectory.
By the early decades of the twentieth century, evolutionary theories dominated the social sciences and influenced social policies through ideas such as eugenics. In anthropology, human societies were described as following "natural" laws and many believed that the "history of mankind is the history of nature" (Stocking, 1968, p. 116). A leading theorist of the time, E. B. Tyler, argued both for delineating how different societies could be understood as models of the different stages of a unilinear evolutionary process, and for the concept of the "psychic unity of mankind" (p. 115), which claimed that humans share an evolutionary history and therefore a uniform "nature." Human nature, therefore, was inextricably linked to biology.
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