Lee, K. A.; Martin, L. B.,. I.; Hasselquist, D.; Ricklefs, R. E.; Wikelski, M.: Contrasting adaptive immune defenses and blood parasite prevalence in closely related Passer sparrows. Oecologia 150 (3), pp. 383 - 392 (2006)
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.