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Table 1 Glossary of terms

From: Repeated evolution and the impact of evolutionary history on adaptation

Term Definition
Convergent evolution The independent evolution of a similar phenotype. In the context of this study, we focus specifically on phenotypic characteristics that achieve a similar adaptive outcome (i.e., are examples of adaptive convergent evolution), but phenotypic convergence can also arise through non-adaptive processes (e.g., see [1] and [3]). Ideally convergent evolution (adaptive or otherwise) is distinct from parallel evolution in that phenotypes have been generated from different genetic processes. However, this distinction cannot be made for most cases of reported convergence because the genetics that underlie characteristics have yet to be investigated. Convergent adaptations should also be distinct from those that are functional redundant, but in some cases it can be difficult to determine whether phenotypic characteristics are in fact similar or different among taxa.
Functional redundancy The evolution of different phenotypes that achieve a similar functional outcome in different taxa. Also referred to as many-to-one form to function mapping. This is distinct from “incomplete” convergence in that divergent phenotypes are believed to be functionally equivalent and potentially adaptive.
Historically contingent All organisms share a common ancestor at some point, but intervening factors such as past selection pressures, genetic drift, random mutation (and mutation order) and other stochastic factors (extrinsic chance events) direct the evolution of lineages along increasingly divergent trajectories as time progresses.
Parallel evolution The independent evolution of similar genetic processes that produce a similar phenotype. As with convergent evolution, our survey focussed on characteristics that were believed to achieve a similar adaptive outcome (i.e., are examples of adaptive parallel evolution), but parallel evolution might also arise from non-adaptive processes. This is distinct from the classical definition still used by many researchers of the independent evolution of similar adaptations among taxa that share a close common ancestor (sensu [48]).
Repeated evolution The independent evolution of a similar functional outcome in different taxa, either through the evolution of similar phenotypes (parallel and convergent evolution) or different phenotypes that achieve the same functional outcome (functional redundancy).