Editing Evolvability (section)

== Robustness and evolvability ==
{{further|Mutational robustness}}

The relationship between robustness and evolvability depends on whether recombination can be ignored.<ref name="Masel 2010">{{cite journal | vauthors = Masel J, Trotter MV | title = Robustness and evolvability | journal = Trends in Genetics | volume = 26 | issue = 9 | pages = 406–14 | date = September 2010 | pmid = 20598394 | pmc = 3198833 | doi = 10.1016/j.tig.2010.06.002 | author1-link = Joanna Masel }}</ref> Recombination can generally be ignored in asexual populations and for traits affected by single genes.

=== Without recombination ===

[[Mutational robustness|Robustness in the face of mutation]] does not increase evolvability in the first sense. In organisms with a high level of robustness, mutations have smaller phenotypic effects than in organisms with a low level of robustness. Thus, robustness reduces the amount of heritable genetic variation on which selection can act. However, robustness may allow exploration of large regions of [[fitness landscape |genotype space]], increasing evolvability according to the second sense.<ref name="Wagner 2005" /><ref name="Masel 2010" /> Even without genetic diversity, some genotypes have higher evolvability than others, and selection for robustness can increase the "neighborhood richness" of phenotypes that can be accessed from the same starting genotype by mutation. For example, one reason many proteins are less robust to mutation is that they have marginal [[Protein folding|thermodynamic stability]], and most mutations reduce this stability further. Proteins that are more thermostable can tolerate a wider range of mutations and are more evolvable.<ref>{{cite journal | vauthors = Bloom JD, Labthavikul ST, Otey CR, Arnold FH | title = Protein stability promotes evolvability | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 103 | issue = 15 | pages = 5869–74 | date = April 2006 | pmid = 16581913 | pmc = 1458665 | doi = 10.1073/pnas.0510098103 | bibcode = 2006PNAS..103.5869B | doi-access = free }}</ref> For polygenic traits, neighborhood richness contributes more to evolvability than does genetic diversity or "spread" across genotype space.<ref>{{cite journal | vauthors = Rajon E, Masel J | title = Compensatory evolution and the origins of innovations | journal = Genetics | volume = 193 | issue = 4 | pages = 1209–20 | date = April 2013 | pmid = 23335336 | pmc = 3606098 | doi = 10.1534/genetics.112.148627 | author2-link = Joanna Masel }}</ref>

=== With recombination ===
Temporary robustness, or [[canalisation (genetics) |canalisation]], may lead to the accumulation of significant quantities of cryptic genetic variation. In a new environment or genetic background, this variation may be [[evolutionary capacitance |revealed]] and sometimes be adaptive.<ref name="Masel 2010" /><ref name="Whitacre and Bender">{{cite journal | vauthors = Whitacre J, Bender A | title = Degeneracy: a design principle for achieving robustness and evolvability | journal = Journal of Theoretical Biology | volume = 263 | issue = 1 | pages = 143–53 | date = March 2010 | pmid = 19925810 | doi = 10.1016/j.jtbi.2009.11.008 | arxiv = 0907.0510 | bibcode = 2010JThBi.263..143W | s2cid = 11511132 }}</ref>

=== Factors affecting evolvability via robustness ===

Different genetic codes have the potential to change robustness and evolvability by changing the effect of single-base mutational changes.<ref>{{cite journal | vauthors = Firnberg E, Ostermeier M | title = The genetic code constrains yet facilitates Darwinian evolution | journal = Nucleic Acids Research | volume = 41 | issue = 15 | pages = 7420–8 | date = August 2013 | pmid = 23754851 | pmc = 3753648 | doi = 10.1093/nar/gkt536 }}</ref><ref>{{cite journal | vauthors = Pines G, Winkler JD, Pines A, Gill RT | title = Refactoring the Genetic Code for Increased Evolvability | journal = mBio | volume = 8 | issue = 6 | date = November 2017 | pmid = 29138304 | pmc = 5686537 | doi = 10.1128/mBio.01654-17 }}</ref>