Homoplastie

Homoplastie, also known in English as homoplasy, designates a similarity in biological traits that arises independently in unrelated lineages rather than from a common ancestor. The phenomenon results from convergent evolution, parallel evolution, or evolutionary reversal, and it can involve morphological, physiological, or molecular characteristics.

In convergent evolution, distantly related species evolve comparable adaptations in response to similar environmental pressures; classic examples include the streamlined body shape of dolphins (mammals) and ichthyosaurs (reptiles) or the development of wings in bats, birds, and insects. Parallel evolution describes similar changes occurring in closely related lineages that share a recent common ancestor but diverge in other aspects; for instance, the independent emergence of antifreeze glycoproteins in Antarctic notothenioid fish and Arctic cod. Evolutionary reversal, another form of homoplasy, involves the loss or re‑acquisition of a trait that had previously evolved, such as certain lizards re‑gaining a functional tail after a lineage that had lost it.

Homoplasy poses challenges for phylogenetic reconstruction because shared traits may be mistakenly interpreted as evidence of common ancestry (synapomorphies). Modern systematic studies therefore employ multiple lines of evidence, including DNA sequencing, statistical models of character evolution, and rigorous assessment of trait homology versus homoplasy. Molecular data often reveal hidden homoplastic patterns, as unrelated taxa can acquire identical amino‑acid substitutions under similar selective regimes.

The concept of homoplasy is central to evolutionary biology, ecology, and paleontology, informing discussions of adaptive landscapes, constraint, and the predictability of evolution. Related terms include homology (similarity due to shared ancestry), analogy (functional similarity without shared ancestry), and convergent evolution. Understanding homoplastic patterns helps refine evolutionary trees and clarifies the mechanisms by which similar solutions arise across the tree of life.