homoplasy

Homoplasy is a term in evolutionary biology describing the similarity of characters in two or more species that does not arise from a common ancestor. In other words, the trait arises independently in different lineages rather than being inherited from a shared ancestor. This contrasts with homology, where similarities reflect descent from a common ancestor.

Homoplasy encompasses several processes. Convergent evolution occurs when unrelated groups face similar environmental challenges and evolve comparable traits. Parallel evolution involves related lineages that diverged a long time ago evolving similar features independently. Evolutionary reversals, or reversals to ancestral states, occur when a derived trait is lost or reverts to an earlier form in some descendants. These processes can produce striking similarities that mask true evolutionary relationships.

Common examples include the streamlined bodies of dolphins (mammals) and ichthyosaurs ( extinct reptiles), which evolved independently to live in aquatic environments. The wings of bats and birds are often cited as a product of convergent evolution toward powered flight, even though their forelimbs are modified in different ways. In plants, the spiny, succulent forms of cacti and some euphorbias illustrate parallel evolution of similar morphologies to cope with arid conditions.

In phylogenetics, homoplasy can complicate the reconstruction of evolutionary trees because similar traits may be misleading about relatedness. Researchers mitigate this by integrating many characters across molecular and morphological data, and by using statistical methods that account for convergent changes. Recognizing homoplasy helps clarify true evolutionary relationships and the processes shaping biodiversity.