Summary: “Balancing robustness and evolvability” (Lenski et al. 2006)
This is a summary of Lenski, Barrick and Ofria (2006). The following are direct quotes of the original article. My comments are given as footnotes, highlighting and italics.
- Organisms must have a balance between robustness and evolvability, that is, between resisting and allowing change in their own internal states.
- A genome may be robust because it encodes proofreading and repair systems1 that reduce replication errors or because it is organized such that many mutations have little effect2 on its phenotype.
- We will focus on genomic robustness to mutations.
- Two mechanisms that could make a genome more robust are genetic redundancy, so that many otherwise deleterious mutations are masked, and proofreading during replication, so that fewer mutations occur.
- Evolution at low mutation rates favors populations that achieve high fitness peaks, even if they are surrounded by steep cliffs, because mutations that push progeny off those cliffs are rare.
- At high mutation rates, most offspring carry mutations, and selection favors populations that find lower fitness peaks surrounded by less precipitous mutational chasms.
- Environmental change is a pervasive feature of nature, and those physiological mechanisms that allow organisms to adjust to changing environments, such as by regulating gene expression, will also compensate for the effects of many mutations.
- Proofreading and repair must inhibit evolvability because they reduce the production of new beneficial mutations.
- Are robustness and evolvability inversely correlated more generally? Robustness and evolvability might again be positively, rather than negatively, correlated.
- Redundancy can also promote adaptation by allowing duplicated genes to evolve distinct functions3
- Evolving populations can also become robust by finding regions of genotypic space that are flat because they contain a high proportion of neutral mutations.
- Deleterious mutations may lead to genetic neighborhoods that are more promising.
- One could ask how robustness and evolvability change depending on whether evolution occurs in constant or variable environments (Meyers, Ancel, and Lachmann 2005).
The original paper was published in PLoS Biology under a CC-BY license.
Lenski, Richard E., Jeffrey E. Barrick, and Charles Ofria. 2006. “Balancing robustness and evolvability.” PLoS Biology 4 (12): e428. doi:10.1371/journal.pbio.0040428.
Meyers, Lauren Ancel, Fredric D Ancel, and Michael Lachmann. 2005. “Evolution of genetic potential.” Edited by Eddie Holmes. PLoS Computational Biology 1 (3). Public Library of Science: 236–43. doi:10.1371/journal.pcbi.0010032.
Low mutation rate (U)↩
Small mutation effect (s)↩
The amplification model↩