1Department of Human Evolutionary Biology, Harvard University, 2Freelance Nature Photographer, Harvard University, 3Department of Biological Sciences, Wellesley College, 4Department of Anthropology, University of New Mexico
Friday 5:15-5:30, Ballroom B
Understanding dental development in chimpanzees, our closest living relatives, is of fundamental importance for reconstructing the evolution of human development. Most early hominin species are believed to show rapid ape-like patterns of development, implying that a prolonged modern human childhood evolved quite recently. Yet chimpanzee developmental standards are uncertain because they have never been based on living wild individuals. Furthermore, although it is well established that molar tooth eruption (movement into the mouth) is broadly correlated with the scheduling of growth and reproduction across primates, its precise relation to solid food consumption or nursing behavior is unknown. To address these concerns we conducted a photographic study of subadult chimpanzees in Kanyawara, Kibale National Park, Uganda. Five healthy infants erupted their lower first molars (M1s) by or before 3.3 years of age, nearly identical to captive chimpanzee mean ages (~3.2 years, n= 53). Kanyawara chimpanzees showed adult patterns of solid food consumption by the time M1 reached functional occlusion, spent a greater amount of time on the nipple while M1 was erupting than in the preceding year, and continued to suckle during the following year. Estimates of M1 eruption age in australopiths are remarkably similar to the Kanyawara chimpanzees, and recent reconstructions of their life histories should be reconsidered in light of these findings. First molar emergence in early fossil hominins may be more informative about feeding behavior than about weaning age or maternal reproductive status.
Funding provided by the Leakey Foundation, Harvard University, Wenner Gren Hunt Fellowship, and National Science Foundation grants 0849380 and 1126470.