Convergent Evolution

Convergent evolution is the independent evolution of similar traits in organisms that are not closely related, because they face similar challenges. The similar features are called analogous, in contrast to homologous traits that come from a shared ancestor.

Wings evolved separately in insects, pterosaurs, birds and bats. Camera-type eyes with a lens appear in vertebrates and in cephalopods such as the common octopus, but are built differently. Echolocation arose in toothed whales such as the bottlenose dolphin and in bats. The extinct thylacine, a marsupial, looked remarkably like the placental gray wolf, and the northern marsupial mole resembles the unrelated golden moles of Africa.

The pattern also appears at the molecular level. C4 photosynthesis has evolved more than sixty times in plants, and the antifreeze proteins of Arctic and Antarctic fish arose independently. Resistance to toxins in unrelated animals has often involved changes at the same position in the same protein. Such cases suggest that natural selection can repeatedly find the same solutions.

Convergence is evidence for the power of selection and for constraints on form, and it is a trap for classification, since similar looks can hide different ancestry. Biologists use DNA to separate shared ancestry from convergence, as in building the tree of life. The study of repeated outcomes is central to evolutionary biology.

• Natural Selection — the process that drives it
• Thylacine — a marsupial that resembled a wolf
• C4 Carbon Fixation — a trait that evolved many times