Convergent Evolution: Recurrence of Form

Organisms that look remarkably alike are sometimes the result of convergent evolution — although they look similar, they evolved not from an immediate common ancestor with their traits, but within separate lineages that initially lacked them.

Compare the torpedo-shaped body of a fish with the body of a swimming mammal, like a dolphin or a whale. The first mammals were terrestrial and walked on four limbs. As the ancestors of the cetaceans adapted to swimming, their limbs were reduced and their body shape converged on the typical fish shape.

Sometimes convergent evolution modified different body parts to look the same and perform the same function: insect wings were derived from the exoskeleton, while bird wings were derived from forelimbs with an internal skeleton. In other cases, modification of the same basic part occurred independently in separate lineages: the wings of both birds and bats are modified forelimbs, though modified in quite different ways.

The Tree of Life contains many remarkable examples of convergent evolution, which attest to the great power of natural selection to adapt different organisms to similar environments. Such cases are discovered as we study how species are related — finding that similar organisms are actually distantly related and must have evolved their similar traits independently. Sometimes convergent similarities are so striking that they have fooled biologists for decades before being revealed through careful phylogenetic research.