Ontogenetic plasticity in nonhuman primates: I. Secular trends in the Cayo Santiago macaques.

Although secular trends toward increasing body size are apparent in many human populations, little is known about their occurrence in nonhuman primates. The Cayo Santiago skeletal collection of Macaca mulatta includes 101 adult animals (greater than or equal to 10 years of age) born at different times in the past 3 1/2 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.