The vestigal organ appendix is still existent in human beings.

Explanation

i. Sudden development of new tissues or organs is not possible for the purpose of living in changing environment.
ii. The existing organs of an organism undergo gradual changes and may become useless or harmful under certain conditions.
iii. Such structures begin to degenerate, as per teh principle of natural selection.
iv. These organs take thousands of years to disappear. Hence they may appear in different phases of disappearance in different animals.
Hence even though appendix is a vestigial organ, it is still existent in human beings.