Oelze, V. M.; Fuller, B. T.; Richards, M. P.; Fruth, B.; Surbeck, M.; Hublin, J.-J.; Hohmann, G.: Exploring the contribution and significance of animal protein in the diet of bonobos by stable isotope ratio analysis of hair. Proceedings of the National Academy of Sciences of the United States of America 108 (24), pp. 9792 - 9797 (2011)
Scientists studying a rare population of tool-using chimpanzees have found that aging can have a profound impact on their abilities—but not all chimps decline equally.