Recurrent evolution

Recurrent evolution is the repeated evolution of a particular character. Most evolution, or changes in allele frequencies from one generation to the next, is the result of drift, or random chance of some alleles getting passed down and others not. Recurrent evolution is when patterns emerge from this stochastic process when looking across populations. These patterns are of particular interest to evolutionary biologists as they can teach people about the underlying forces of evolution.

Recurrent evolution is a broad term, but is usually used to describe recurring regimes of selection within or across lineages. While most commonly used to describe recurring patterns of selection, it can also be used to describe recurring patterns of mutation, for example transitions are more common than transversions. It encompasses both convergent evolution and parallel evolution and can be used to describe the observation of similar repeating changes through directional selection as well as the observation of highly conserved phenotypes or genotypes across lineages through continuous purifying selection over large periods of evolutionary time. The changes can be observed at the phenotype level or the genotype level. At the phenotype level recurrent evolution can be observed across a continuum of levels, which for simplicity can be broken down into molecular phenotype, cellular phenotype, and organismal phenotype. At the genotype level recurrent evolution can only be detected using DNA sequencing data. The same or similar changes in the genomes of different lineages indicates recurrent genomic evolution may have taken place. Recurrent genomic evolution can also occur within a lineage. An example of this would include some types of phase variation that involve highly directed changes at the DNA sequence level. The evolution of different forms of phase variation in separate lineages represent convergent and recurrent evolution toward increased evolvability. In organisms with longer generation times, any potential recurrent genomic evolution within a lineage would be difficult to detect. Recurrent evolution has been studied most extensively at the organismic level but with cheaper and faster sequencing technologies more attention is being paid to recurrent genomic evolution. Recurrent evolution can also be described as recurring or repeated evolution.

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