Although secular trends toward increasing body size are apparent in many human populations, little is known about their occurrence in nonhuman primates. The Cay0 Santiago skeletal collection of Macaca mulatta includes 101 adult animals ( 2 10 years of age) born at different times in the past 3% decades, so that variation in size may be examined relative to birth year. No secular trends in orbital height were observed in this sample, but in both sexes lengths of adult long bones increased significantly over time, while cranial dimensions and length of the second molar in female also showed significant variation with birth year. These changes were consistent with the history of provisioning of the animals and with fluctuations in population size. Low-order correlations were observed between birth year and body proportions, especially the crural index in males, a pattern that has also been observed in human populations. These findings argue that, in addition to biomechanics and heritage, diet may affect allometric relationships and that an inherent plasticity or malleability of the growth process may be characteristic of nonhuman as well as human primates.
Over the past 100 years, secular trends in disease via immunization, broader access to growth and development have been docu-medical care, and particularly, improved numented in many countries around the world. trition (Tanner, 1978;van Wieringen, 1978; Although both positive and negative trends Malina, 1979). However, some studies have have been observed, in industrial countries reported little increase in the growth of chilchildren are consistently growing larger and dren when dietary supplements and modern maturing sooner than their parents and health care are introduced to a population grandparents did Meredith, 1976; Eveleth (Ashcroft et al., 1965;Hagan, 1962). As an and Tanner, 1976;van Wieringen, 1978; alternate explanatory model for secular Roche, 1979). The average height increase in trends, Hulse (1957) suggested that increases Europe and North America has been approx-in size could be due to changes in the breedimately 1 to 2 cm per decade in childhood, ing structure of human populations. Accordsomewhat more per decade in adolescence, ing to this hypothesis, the increased rate of and least per decade in adulthood (cf. Eveleth outmarriage over the past century increased and Tanner, 1976;Meredith, 1976). Compa-the heterozygosity and, through heterosis, rable changes in body weight, cranial Nor-the stature of human populations. Yet, some ita and Ohtsuki, 1973), dental (Garn et al., growth shifts occur in the absence of migra-1968), and other dimensions have occurred, tion, while selection is generally considered although not every body part has been afto operate too slowly to account for observed fected equally (Bowles, 1932; Hunt, 1958; secular trends (Cavalli-Sforza and Bodmer, Himes, 1979). Age at menarche has de-1971;Malina, 1979). creased by about 4 months per decade.
Both nutritional and genetic explanations Recent explanations of these secular trends for secular changes suggest that such trends emphasize improvements in living conditions, including @eater Control Of infectious