One explanation for this pattern is that evolution has acted to create genetic networks that are robust to mutational defects at single genes within the network. Using a combination of mathematical and computational models, Stephen R. Proulx and Patrick C. Phillips investigate the evolution of genetic networks in response to a variety of genetic and environmental perturbations. The models show that natural selection for robustness will only be as strong as the cost of disrupting the network. Because the risk of mutational damage is limited by the mutation rate, these results imply that robustness to mutation will play only a small part in the evolution of genetic networks.
Environmental perturbations, on the other hand, can affect large fractions of a population and are thus more likely to play a significant role in genetic network evolution.
This article will appear in the February 2005 issue of American Naturalist.