Evolution of Senescence by Damage Accumulation That Accelerates With Age Throughout an Organism's Lifespan.

Abstract

In recent years, senescence is increasingly understood as a process of damage accumulation that accelerates with age throughout an organism's lifespan. That understanding has rarely been introduced to senescence evolution theory. In classic models, including Mutation accumulation and Antagonistic pleiotropy, the intensity of selection over genes is determined by the timing of their effect on mortality. They conclude senescence evolution occurs because of weak selection on late-acting genes. Here we explore, consistent with recent evidence, an alternative model: where genes affect mortality throughout an organism's lifespan, and the shape of this effect determines selection. We expanded Hamilton's classic model of senescence evolution using these notions. Our model takes into account evolutionary dynamics between external mortality risk, potential mortality risk from internal damage, reproduction start age, and reproduction rate. The analysis of the model suggests biological limitations on reducing the potential mortality risk from internal damage can lead to a positive feedback loop in senescence evolution where genes that slow senescence can increase selection for further senescence retardation. Our model sheds light on several phenomena, not fully explained by classic theory, including Peto's paradox, Strehler-Mildvan correlation, and negligible senescence.