There are over 300 hypotheses of aging, but none of them has enough predictive power to explain most experiments and observations on this process. On the basis of a critical analysis of the most relevant data on aging, especially on the factors that influences its rhythm, we present a new hypothesis, as well as the way the hypothesis' predictions explain some of the phylogenetic implications of the aging process. The hypothesis starts from a new, biochemical view on evolution and the behavior of living matter. According to this view, life is a fabric of chemical reactions that sustain each other. Reactants and energy support are needed for these reactions to take place in a cell. Given this, aging stems from a leftward shift of the global equilibrium of some biochemical reactions involved in cell differentiation and repair, which take place at a high level during the organism's growth period. In time, for species with evident aging, some reactions lose their specificity, which affects cell division and differentiation. This, in turn, influences cell energy metabolism. Cell and tissue degeneration appears when, while some specific reactions are absent, non-specific reactions such as those of cell proliferation receive additional energy support. This hypothesis explains phylogenetic differences related to lifespan and longevity, and body-size differences between species and within the same species.