“…telomere shortening (Olovnikov, 1973(Olovnikov, , 1996Rubin, 2002), stem cell senescence (Sharpless & DePinho, 2004), and oxidative damage (Harman, 1981;Finkel & Holbrook, 2000). These variables have been observed to correlate with aging or cellular senescence in some species and cell lines, but the causality is still widely discussed (Hopkin, 2001;Sozou & Kirkwood, 2001;Rubin, 2002;Weinert & Timiras, 2003;Cristofalo et al, 2004;de Magalhaes, 2005). The specific variables observed to correlate with aging are often either species-or individual specific and this has led to a search for more inclusive system-based models of aging (see e.g.…”