In evolutionary biology, convergent evolution is the process whereby organisms not closely related (not monophyletic), independently evolve similar traits as a result of having to adapt to similar environments or ecological niches.
It is the opposite of divergent evolution, where related species evolve different traits.
On a molecular level, this can happen due to random mutation unrelated to adaptive changes; see long branch attraction.
In cultural evolution, convergent evolution is the development of similar cultural adaptations to similar environmental conditions by different peoples with different ancestral cultures.
An example of convergent evolution is the similar nature of the flight/wings of insects, birds, pterosaurs, and bats.
All four serve the same function and are similar in structure, but each evolved independently.
Some aspects of the lens of eyes also evolved independently in various animals.
Convergent evolution is similar to, but distinguishable from, the phenomena of evolutionary relay and parallel evolution.
Evolutionary relay refers to independent species acquiring similar characteristics through their evolution in similar ecosystems, but not at the same time (e.g. dorsal fins of extinct ichthyosaurs and sharks).
Parallel evolution occurs when two independent species evolve together at the same time in the same ecospace and acquire similar characteristics (extinct browsing-horses and extinct paleotheres).
Structures that are the result of convergent evolution are called analogous structures or homoplasies; they should be contrasted with homologous structures, which have a common origin.