Homoplasy

Definition

The independent evolutionary origin of a similar trait in separate lineages, producing superficial resemblance that does not reflect common ancestry. Homoplasy confounds phylogenetic inference because shared features may arise through convergence, parallel evolution, or evolutionary reversal rather than descent from a common ancestor with that trait.

Etymology

Greek homos (same) + plasis (formation)

Example

Winglessness in fleas (Siphonaptera) and some parasitic lice (Phthiraptera) represents homoplasy: both groups lost wings independently as adaptations to ectoparasitic life, rather than inheriting winglessness from a common ancestor.

Synonyms

• convergent trait
• analogous trait

Related Terms

• Homology
• analogy
• Convergent evolution
• Parallel evolution
• synapomorphy
• autapomorphy
• Parsimony
• phylogenetic signal

Usage Notes

Distinguished from homology by its lack of common ancestry; distinguished from simple analogy by its specific phylogenetic context. Homoplasy is detected through outgroup comparison and phylogenetic analysis—traits that optimize poorly onto a tree or require multiple evolutionary origins suggest homoplastic origins. Common sources include similar selection pressures (convergence), shared developmental pathways (parallelism), or reversion to ancestral states.