On the causal connection in lifespan correlations and the possible existence of a 'number of life' at molecular level.

Multiple physiological traits correlates with lifespan, being unclear both the causal connection among them and with the process of ageing. In this paper, we show that six traits (such as metabolic rate, mass, heart rate, etc) acting at the system level, are all related to lifespan thru the existence of an approximately constant number of respiration cycles in a lifespan ([Formula: see text]), therefore, we find that those relationships are not independently related to ageing. In addition, we study if the approximately constant [Formula: see text] is possibly linked with the end-of-lifespan somatic mutation burden, another number recently found to be approximately constant (Cagan, Nature 604:517-524, 2022). We find that the dataset of mammals studied is consistent with a direct proportionality between the somatic mutation rate and the respiration frequency, being a tentative link between both invariant numbers.