Editing Evolvability (section)

==Evolution of evolvability==

While variation yielding high evolvability could be useful in the long term, in the short term most of that variation is likely to be a disadvantage. For example, naively it would seem that increasing the [[mutation rate]] via a mutator allele would increase evolvability. But as an extreme example, if the mutation rate is too high then all individuals will be dead or at least carry a heavy [[genetic load |mutation load]]. Short-term selection for low variation most of the time is likely to be more powerful than long-term selection for evolvability, making it difficult for natural selection to cause the evolution of evolvability. Other forces of selection also affect the generation of variation; for example, mutation and recombination may in part be byproducts of mechanisms to cope with DNA damage.<ref>{{cite journal | vauthors = Michod RE | title = On fitness and adaptedness and their role in evolutionary explanation | journal = Journal of the History of Biology | volume = 19 | issue = 2 | pages = 289–302 | year = 1986 | pmid = 11611993 | doi = 10.1007/bf00138880 | s2cid = 42288730 }}</ref>

When recombination is low, mutator alleles may still sometimes [[genetic hitchhiking |hitchhike]] on the success of adaptive mutations that they cause. In this case, selection can take place at the level of the lineage.<ref>{{cite journal |doi=10.2307/3212376 |author=Eshel I |title=Clone-selection and optimal rates of mutation |journal=Journal of Applied Probability |volume=10 |issue=4 |pages=728–738 |year=1973 |jstor=3212376 |s2cid=123907349 }}</ref> This may explain why mutators are often seen during [[experimental evolution]] of microbes. Mutator alleles can also evolve more easily when they only increase mutation rates in nearby DNA sequences, not across the whole genome: this is known as a contingency locus.

The evolution of evolvability is less controversial if it occurs via the [[evolution of sexual reproduction]], or via the tendency of variation-generating mechanisms to become more active when an organism is stressed. The [[Fungal prions |yeast prion]] [PSI+] may also be an example of the evolution of evolvability through [[evolutionary capacitance]].<ref>{{cite journal | vauthors = Masel J, Bergman A | title = The evolution of the evolvability properties of the yeast prion [PSI+] | journal = Evolution; International Journal of Organic Evolution | volume = 57 | issue = 7 | pages = 1498–512 | date = July 2003 | pmid = 12940355 | doi = 10.1111/j.0014-3820.2003.tb00358.x | s2cid = 30954684 | author1-link = Joanna Masel }}</ref><ref>{{cite journal | vauthors = Lancaster AK, Bardill JP, True HL, Masel J | title = The spontaneous appearance rate of the yeast prion [PSI+] and its implications for the evolution of the evolvability properties of the [PSI+] system | journal = Genetics | volume = 184 | issue = 2 | pages = 393–400 | date = February 2010 | pmid = 19917766 | pmc = 2828720 | doi = 10.1534/genetics.109.110213 }}</ref> An evolutionary capacitor is a switch that turns genetic variation on and off. This is very much like [[Bet-hedging (biology) |bet-hedging]] the risk that a future environment will be similar or different.<ref>{{cite journal | vauthors = King OD, Masel J | title = The evolution of bet-hedging adaptations to rare scenarios | journal = Theoretical Population Biology | volume = 72 | issue = 4 | pages = 560–75 | date = December 2007 | pmid = 17915273 | pmc = 2118055 | doi = 10.1016/j.tpb.2007.08.006 | bibcode = 2007TPBio..72..560K | author2-link = Joanna Masel }}</ref> Theoretical models also predict the evolution of evolvability via modularity.<ref>{{cite journal | vauthors = Draghi J, Wagner GP | title = Evolution of evolvability in a developmental model | journal = Evolution; International Journal of Organic Evolution | volume = 62 | issue = 2 | pages = 301–15 | date = February 2008 | pmid = 18031304 | doi = 10.1111/j.1558-5646.2007.00303.x | s2cid = 11560256 | doi-access =  }}</ref> When the costs of evolvability are sufficiently short-lived, more evolvable lineages may be the most successful in the long-term.<ref>{{cite journal | vauthors = Woods RJ, Barrick JE, Cooper TF, Shrestha U, Kauth MR, Lenski RE | title = Second-order selection for evolvability in a large Escherichia coli population | journal = Science | volume = 331 | issue = 6023 | pages = 1433–6 | date = March 2011 | pmid = 21415350 | pmc = 3176658 | doi = 10.1126/science.1198914 | bibcode = 2011Sci...331.1433W }}</ref> However, the hypothesis that evolvability is an adaptation is often rejected in favor of alternative hypotheses, e.g. minimization of costs.<ref name="Pigliucci 2008" />