Evolutionary theory is partly based on mutation, a process which creates genetic variants, and selection, a process which favors or disfavors some of these variants. The intensity of selection may vary over time, e.g., may be higher during a famine, but do organisms always adapt at a constant rate, or is it possible that their ability to evolve, their "evolvability" is itself subject to natural selection?
Two authors from Rice University have recently written an article where they propose just that, citing many results which are explained by the assumptions of selectable evolvability. It now appears that the rate of genetic change should not be considered constant, but may rather fluctuate depending on selection pressure: as organisms find themselves in new or changed environments, they do not change only because of selection, but also because the propensity to mutate itself is encouraged. This is particularly clear when organisms undergo many successive episodes of changed environmental conditions.
Proc Natl Acad Sci U S A. 2004 Aug 10;101(32):11531-6.
Evolvability is a selectable trait.
Earl DJ, Deem MW.
Concomitant with the evolution of biological diversity must have been the evolution of mechanisms that facilitate evolution, because of the essentially infinite complexity of protein sequence space. We describe how evolvability can be an object of Darwinian selection, emphasizing the collective nature of the process. We quantify our theory with computer simulations of protein evolution. These simulations demonstrate that rapid or dramatic environmental change leads to selection for greater evolvability. The selective pressure for large-scale genetic moves such as DNA exchange becomes increasingly strong as the environmental conditions become more uncertain. Our results demonstrate that evolvability is a selectable trait and allow for the explanation of a large body of experimental results.