We have derived the equation of lifespan including the regulation system of aging such as a switching, timing, and memory. Indeed, in our model, two important parameters (
t0 and z) are contained (Shoyama et al., Mech. Ageing Dev. 128 (2007) 529-537). The one represents the onset of demographic aging. We have proved that another is proportional to the reciprocal of physiological decline rate. However, the biological meaning of the former parameter remains unclear. Thus, to address this issue, we approach from understanding the regulation mechanism at the molecular level. In this work, we used the long-lived
daf-2 mutant strain. Interestingly, when we quantitatively analyzed the survival curve of this mutant using the equation of lifespan, it was composed of two distinct components. The first component was close to that of
daf-16 or wild-type. This specific feature has to become a crucial key to perform our aim. On the other hand, we observed a periodic fluctuation in metabolism energy and body size after maturation. The heterogeneity revealed in biodemographic data seems to be concerned with this finding. Thus, to investigate how the onset of biodemographic aging is determined, we quantitatively analyze the survival curves obtained by varing the timing of
daf-16-RNAi feeding, using the equation of lifespan.