Pseudorandomness of gene expression: a new evo-devo theory of ageing.

In contrast to the first part of life (development), ageing appears to be under less strict genetic control. The precise timing of events so characteristic of development seems to loosen its grasp, while stochastic and environmental factors seem to become the dominant force. Evolutionary theories put forward a decreasing evolutionary pressure over the course of life as the reason behind this pattern, yet dissenting views on ageing as a genetically programmed process linger. In this paper we address this dissent by presenting insights from an artificial evolutionary-developmental system, ET, and propose a new evo-devo theory of ageing-a theory that sees ageing as a continuation of development in the postreproductive period. In this theory both development and ageing are under genetic control. Nonetheless, while gene expression patterns that drive development are optimised by evolution, patterns that drive ageing are not optimised, because evolutionary pressure decreases with age. For these reasons, during ageing the changes orchestrated by genes are "pseudorandom"- deterministic but erratic-and their effects on an individual's health are more likely to be detrimental than beneficial. As such, they contribute to the continuous deterioration of bodily functions that characterise ageing.