For video on this topic click on : https://youtu.be/bDhAXYfyOAw
Some organisms have structures or organs that seem to serve no useful function. For example, humans have a tailbone at the end of the spine that is of no apparent use. Some snakes have tiny pelvic bones and limb bones. These functionless parts are called vestigial organs. Vestigial organs are often homologous to organs that are useful in other species. The vestigial tailbone in humans is homologous to the functional tail of other primates. Thus vestigial structures can be viewed as evidence for evolution. Organisms having vestigial structures probably share a common ancestry with organisms in with organisms in which the homologous structure is functional.