Vestigial does not mean "functionless." Even if the tail bone does have a function, that doesn't refute it's status as a vestigial trait nor does it refute the evidence for common descent that the tail bone provides. The tail bone of humans is regarded as being vestigial because it, along with the tail bones of all other apes, directly corresponds to the tails of monkeys, which use their tails as organs of balance. Given as how both humans, and all other apes no longer need tails to maintain their balance, scientists are totally justified in saying that the tail bone is vestigial. Being the at