  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.
