Convergent evolution is an evolutionary process in which organisms not closely related independently acquire some characteristic or characteristics in common. This usually reflects similar responses to similar environmental conditions.
An example of convergent evolution is the similar nature of the wings of insects, birds, and bats. All three serve the same function and are similar in structure, but each evolved independently. Eyes also evolved independently in various animals.
Another example is the aerial rootlets found in English ivy (Hedera helix) and wintercreeper (Euonymus fortunei) (and other vines). These rootlets are not derived from a common ancestor, but developed independently as an effective way to cling to whatever support the vine is climbing on.
Another example is the streamlined, fish-like shape of the extinct ichthyosaurs and the shape of extant dolphins and small whales. Except for the tail fins, cetaceans greatly resemble fish in outline, but are instead descended from four-legged land mammals. Their closest land relative today is thought to be the hippopotamus. Their modern shape is due to their water-based life cycle, as is the shape of the fish.
Insect mimicry is also an example of convergent evolution: an example is when when an edible (palatable) butterfly develops a color pattern similar to a relatively unrelated and inedible (unpalatable) butterfly, and by so doing escapes being eaten. This phenomenon, where a harmless species evolves to resemble a harmful species, is known as Batesian mimicry.