This article presents a current theory of animal (metazoan) evolution,suggesting that it was partly mediated through a biochemical oscillator (cycler), named Life's Timekeeper, and present in all animal cells. The cycler controls cell maintenance and repair,thereby determining how long cells survive (longevity). It originated in the single-celled ancestor of all animals, which had very short cell longevity. Animal evolution progressed by extending cell longevity, and this was mediated by extended cycle time of the oscillator. Multi-celled animals and cell-cell communication systems evolved later. The cycler controls the overall rate of development and aging,these time periods being proportionate to maximum cell longevity. Simple animals have cell rejuvenating abilities hence are potentially long lived, whereas complex animals lost such ability and have limited lifespan determined by the maximum potential longevity of their cells.
Source: phys.org