Selection shadow has been the conventional theory of evolution of ageing for decades. I argue that selection shadow is merely a phenomenon by which deleterious mutation will be inevitably passed on if they manifest only after mating. However, to explain prevalence of ageing, the authors of the conventional theory erroneously equated passing on and persistence by interpreting selection shadow as if “selection pressure is decreased after mating” and for the same reason assumed that ageing is deleterious1,2. In their conventional framework, although ageing is assumed to be deleterious, it is immune to natural selection, due to happening after mating i.e. being in the selection shadow. In reality selection pressure still remains after mating in form of the need to feed offspring and so also in form of inter- and intraspecies competition and predation avoidance etc. I show that the conventional selection shadow theory is therefore inconsistent, since shadowed counteracting “positive” mutations will inevitably pass with “negative” mutations, resulting in individuals that do not age. And so, since ageing is assumed to be deleterious in this conventional framework, inevitable non-ageing individuals will outcompete ageing ones in intra- and interspecies competition for similar ecological niches. This way the inconsistency of the conventional theory of selection shadow predicts that non-ageing organisms will prevail, which is not what we observe. Recently, some articles incline towards adaptive theory of ageing i.e. ageing as an advantageous mechanism. However, the ground of such inclination has mostly been reduced competition for food and space between parents and offsprings3,4. I show that ageing allows for increased reproduction rate, while maintaining optimal population size. As a result of promoted reproduction rate, rate of introduced germline mutations is increased, which means faster adaptation. Faster adapting ageing individuals outcompete non-ageing slower adapting individuals that occupy similar ecological niches, inter and intraspecies. Therefore, since ageing is obviously advantageous, this means that all experimental evidence that supported selection shadow theory of ageing5–9, also support the proposed adaptive theory of faster adaptation, the difference is interpretation: investigated pleiotropic muta-tions are not antagonistic after all, and mutation accumulation actually accumulates positive germline ageing mutations. Based on genome analysis10 of the longest living mammal – bowhead whale, I also propose that mutations in DNA repair proteins are a mechanism to tune ageing by natural selection when optimal population size is changed by long lasting shifts in ecosystem, such as new food source. I suggest that DNA repair complexes are purposely of lowered fidelity to allow for somatic mutations to accumulate and so to increase deathrate by ageing leading to faster adaptation.
Adaptive ageing theory of faster adaptation and inconsistency of the conventional selection shadow evolutionary theory of ageing.