Helfer, G.; Fidler, A.; Vallone, D.; Foulkes, N. S.; Brandstätter, R.: Molecular analysis of clock gene expression in the avian brain. Chronobiology International 23 (1-2), pp. 113 - 127 (2009)
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.