# Stronger selection can slow down evolution driven by recombination on a smooth fitness landscape

## TL;DR

This paper reveals that, unlike mutation-driven evolution, stronger natural selection can slow down recombination-driven evolution on smooth fitness landscapes due to opposing effects on genetic variation and recombination.

## Contribution

It demonstrates that in recombination-driven evolution, stronger selection can reduce the rate of evolution, challenging conventional assumptions from mutation-driven models.

## Key findings

- Stronger selection can slow down evolution in recombination-driven models.
- Two opposing effects of selection influence the rate of evolution.
- There exists an optimal selection strength maximizing evolutionary rate.

## Abstract

Stronger selection implies faster evolution---that is, the greater the force, the faster the change. This apparently self-evident proposition, however, is derived under the assumption that genetic variation within a population is primarily supplied by mutation (i.e.\ mutation-driven evolution). Here, we show that this proposition does not actually hold for recombination-driven evolution, i.e.\ evolution in which genetic variation is primarily created by recombination rather than mutation. By numerically investigating population genetics models of recombination, migration and selection, we demonstrate that stronger selection can slow down evolution on a perfectly smooth fitness landscape. Through simple analytical calculation, this apparently counter-intuitive result is shown to stem from two opposing effects of natural selection on the rate of evolution. On the one hand, natural selection tends to increase the rate of evolution by increasing the fixation probability of fitter genotypes. On the other hand, natural selection tends to decrease the rate of evolution by decreasing the chance of recombination between immigrants and resident individuals. As a consequence of these opposing effects, there is a finite selection pressure maximizing the rate of evolution. Hence, stronger selection can imply slower evolution if genetic variation is primarily supplied by recombination.