Parallel evolution

Definition

Independent evolution of similar traits in separate lineages that share a common ancestor possessing the ancestral state from which the derived similarity arose, typically in response to comparable selective pressures. Distinguished from convergent evolution by the retention of homologous starting points rather than purely analogous outcomes from dissimilar origins.

Etymology

From Greek 'parallelos' (beside one another) + Latin 'evolutio' (unrolling, development)

Example

Cave-dwelling populations of the freshwater amphipod Gammarus minus in separate karst regions of eastern North America have repeatedly evolved reduced eyes and elongated appendages for sensory compensation; phylogenetic analysis confirms these populations arose independently from surface-dwelling ancestors with intact visual systems, demonstrating parallel evolution driven by shared subterranean selective regimes.

Synonyms

• parallelism
• parallel phyletic evolution

Related Terms

• Convergent evolution
• Homoplasy
• anagenesis
• adaptive radiation
• phylogenetic niche conservatism
• replicate radiations

Usage Notes

Specialists debate the threshold for distinguishing parallel from convergent evolution; some restrict 'parallel' to cases involving shared developmental pathways or genetic mechanisms, while others use it for any homologous-origin similarity. The distinction matters for inferring evolutionary predictability and constraint. Contrast with: convergent evolution (analogous traits from non-homologous starting points).