Self-propelled flight has only evolved four times throughout history, thanks to insects, birds, bats and the extinct Pterosaurs. But there are a number of creatures alive today that may evolve to become the fifth.
It isn't the same as successful sustained flight, but the biological world is aflutter with animals that have adapted ways of gliding, parachuting or ballooning through the air. Here's our list of nine animals that have found unexpected ways to defy the laws of gravity. (Text: Bryan Nelson)