The selection force weakens with age because ageing evolves and not vice versa

Stefano Giaimo,Arne Traulsen

doi:10.1038/s41467-022-28254-3

Stefano Giaimo, Arne Traulsen

Open Access

https://doi.org/10.1038/s41467-022-28254-3

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Abstract

According to the classic theory of life history evolution, ageing evolves because selection on traits necessarily weakens throughout reproductive life. But this inexorable decline of the selection force with adult age was shown to crucially depend on specific assumptions that are not necessarily fulfilled. Whether ageing still evolves upon their relaxation remains an open problem. Here, we propose a fully dynamical model of life history evolution that does not presuppose any specific pattern the force of selection should follow. The model shows: (i) ageing can stably evolve, but negative ageing cannot; (ii) when ageing is a stable equilibrium, the associated selection force decreases with reproductive age; (iii) non-decreasing selection is either a transient or an unstable phenomenon. Thus, we generalize the classic theory of the evolution of ageing while overturning its logic: the decline of selection with age evolves dynamically, and is not an implicit consequence of certain assumptions.

Highlights

According to the classic theory of life history evolution, ageing evolves because selection on traits necessarily weakens throughout reproductive life
Baudisch put Hamilton’s model[8], recognized as the most mathematically explicit version of the classic theory[1,11,12], under scrutiny. This revealed that a necessary decline in the selection force with age only derives from the restrictive assumptions that, when mutations act at each age separately, they do so via small additive changes in fecundity and small proportional changes in survival[10,13,14]
Reversing the assumptions of the classic theory, small proportional changes in fecundity and small additive changes in survival can lead to increasing selection over some ages (Fig. 1)

Summary

Introduction

According to the classic theory of life history evolution, ageing evolves because selection on traits necessarily weakens throughout reproductive life This inexorable decline of the selection force with adult age was shown to crucially depend on specific assumptions that are not necessarily fulfilled. Baudisch put Hamilton’s model[8], recognized as the most mathematically explicit version of the classic theory[1,11,12], under scrutiny This revealed that a necessary decline in the selection force with age only derives from the restrictive assumptions that, when mutations act at each age separately, they do so via small additive changes in fecundity and small proportional changes in survival[10,13,14]. Baudisch’s work showed that the classic theory implicitly assumed an inexorably declining selection force with age rather than deriving it from general principles To what extent this revelation undermines the validity of the classic theory remains unclear. Our goal is an in-depth exploration of the consequences of possibly non-declining selection with age on life history evolution

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