Analogy (biology)

An analogy is a trait or an organ that appears similar in two unrelated organisms. The cladistic term for the same phenomenon is Homoplasy, from Greek for same form. Biological anologies are often the result of convergent evolution.

Analogies in taxonomy
The classical example of an analogy is the ability to fly in birds and bats. Both groups can move by powered flight, but flight has evolved independently in the two groups. The ability to fly does not make birds and bats close relatives. The opposite of analogy is homology, where the ability or organ in question has been inherited from a common ancestor. The British anatomist Richard Owen was the first scientist to recognise the fundamental difference between analogies and homologies, and named them.

Similar problems - similar solutions
Analogous traits will often arise due to convergence, where different species live in similar ways and/or similar environment, and thus face the same environmental factors. Both herrings and dolphins are streamlined. Both are active predators in a high drag environment, but the herring is a bony fish, the dolphin a mammal. In the Mesozoic, similarly streamlined ichthyosaurs navigated the worlds oceans, yet another example of a group evolving a similar shape due to the same environmental factors. A similar phenomenon is earless seals and eared seals. It was long debated whether the two groups are a single marine group, or represent two separate episodes of carnivorans turning to a marine environment.