Michiels, N. K.; Beukeboom, L. W.; Pongratz, N.; Zeitlinger, J.: Parthenogenetic flatworms have more symbionts than their coexisting, sexual conspecifics, but does this support the Red Queen? Journal of Evolutionary Biology 14 (1), pp. 110 - 119 (2001)
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.