Editing Evolvability (section)

==Modularity==
If every mutation affected every trait, then a mutation that was an improvement for one trait would be a disadvantage for other traits. This means that almost no mutations would be beneficial overall. But if [[pleiotropy]] is restricted to within functional [[modularity |modules]], then mutations affect only one trait at a time, and adaptation is much less constrained. In a modular gene network, for example, a gene that induces a limited set of other genes that control a specific trait under selection may evolve more readily than one that also induces other gene pathways controlling traits not under selection.<ref name="Olson-Manning et al. 2012">{{cite journal | vauthors = Olson-Manning CF, Wagner MR, Mitchell-Olds T | title = Adaptive evolution: evaluating empirical support for theoretical predictions | journal = Nature Reviews Genetics | volume = 13 | issue = 12 | pages = 867–77 | date = December 2012 | pmid = 23154809 | pmc = 3748133 | doi = 10.1038/nrg3322 }}<!-- |access-date=November 23, 2012--></ref> Individual genes also exhibit modularity. A mutation in one cis-regulatory element of a gene's promoter region may allow the expression of the gene to be altered only in specific tissues, developmental stages, or environmental conditions rather than changing gene activity in the entire organism simultaneously.<ref name="Olson-Manning et al. 2012" />