The existence of atavisms and vestigial structures was one of the lines of evidence for evolution Darwin advanced in his Origin of Species, and to this day remains one of the most misunderstood arguments for evolution. Special creationists still think that vestigial means useless, but as Darwin pointed out:
"[a]n organ serving for two purposes, may become rudimentary or utterly aborted for one, even the more important purpose, and remain perfectly efficient for the other....an organ may become rudimentary for its proper purpose, and be used for a distinct object." [1]
In other words, a structure is vestigial if it has lost its original function, irrespective of whether it has secondarily acquired a new function. Examples of vestigial structures include the inner wings of flightless beetles that are atrophied and unable to perform their original function of flight, and the human coccyx, which no longer functions as a tail, but has secondarily acquired new function. The presence or absence of function is not relevant as to whether the structure is vestigial.
This short video shows a number of vestigial structures in the human body, and shows how they provide evidence for common descent - they are features inherited from a remote ancestor which are present, but no longer have the same function that they do in related species with whom we share common ancestry.
Reference
1. Darwin C. " On the Origin of Species by Means of Natural Selection" (1859: John Murray: London.)
This short video shows a number of vestigial structures in the human body, and shows how they provide evidence for common descent - they are features inherited from a remote ancestor which are present, but no longer have the same function that they do in related species with whom we share common ancestry.
Reference
1. Darwin C. " On the Origin of Species by Means of Natural Selection" (1859: John Murray: London.)
