Secular Changes in Size and Maturity: Causes and Effects

Abstract

Secular changes in body size, proportions and composition, in maturation rates during childhood and adolescence, and in adult size have been considered in the preceding chapters. This chapter addresses possible causes and effects of the secular trend evident over about the past 150 years. Before considering the causes and effects of the secular trend, one can inquire as to what may have operated to delay maturation and depress growth before the secular trend became apparent. Backman (1948) estimated the mean age at menarche at about 14 years from ancient through medieval times in Europe, while Amundsen and Diers (1969, 1973a) estimated the mean age at menarche in Classical Greece and Rome and in Europe from the sixth to the fifteenth century at about 12-15 years. These estimated ages are not appreciably different from average ages for some contemporary European populations (12.5-14.0 years; Eveleth & Tanner 1976). Yet, menarche was later in Europe during the nineteenth century; earlier estimates vary between 15.5 and 17.4 years for several European countries (Backman 1948; Tanner 1962). More recent estimates for the earlier data give an average age at menarche of about 16 years in nineteenth-century Norway (Brundtland & Wall0e 1976) and about 15.5 years in nineteenth-century England (Tanner 1966). The apparent discrepancy among the estimates relates to the interpretation of age; for example, does the thirteenth year refer to the thirteenth year of life (12.0-12.99 years) or to the year after the thirteenth birthday (13.0-13.99 years)? Brundtland and Walloe (1976) consider this problem in the early Norwegian data. Since the early-nineteenth century in Europe, there has been a marked decrease not only in age at menarche in girls but also in the age of breaking of the voice in boys (Backman 1948; Daw 1970; Tanner 1966; Taranger, Engstr6m, Lichtenstein, & Svennberg-Redegren 1976).