Editing Natural selection (section)

===By effect on a trait===

Selection has different effects on traits. [[Stabilizing selection]] acts to hold a trait at a stable optimum, and in the simplest case all deviations from this optimum are selectively disadvantageous. [[Directional selection]] favours extreme values of a trait. The uncommon [[disruptive selection]] also acts during transition periods when the current mode is sub-optimal, but alters the trait in more than one direction. In particular, if the trait is quantitative and [[univariate]] then both higher and lower trait levels are favoured. Disruptive selection can be a precursor to [[speciation]].<ref name=Michigan/>