Convergent evolution

Convergent evolution happens when organisms that are not closely related evolve similar features on their own, rather than inheriting them from a common ancestor. The look-alike traits it produces are called analogous structures. They arise because natural selection in similar environments, or for similar ways of life, tends to favor similar solutions to the same problem.

Wings are the textbook case. Insects, birds and bats can all fly, but their wings are built in different ways: a bat wing is skin stretched between long finger bones, a bird wing is a row of feathers along the arm, and an insect wing contains no bone at all. The streamlined bodies of sharks, dolphins and the extinct marine reptiles called ichthyosaurs, and the white winter coats of the arctic fox and the ptarmigan, are other examples. Convergence can also happen in molecules, when unrelated species evolve the same change in a protein.

Telling convergence apart from homology matters when building phylogenetic trees, because traits that evolved independently can make distant groups look related. Comparing underlying structure, embryonic development and DNA usually reveals the difference.