Vestigial Structure

This is a picture of a penguin. Penguin "wings" are considered a vestigial structure. A vestigial structure is a structure, or organ, that has seemed to have lost all, or most, of its functions over time through the process of evolution. They provide clues to the evolutionary history of species, because they are the remnants of structures seen in ancestral species. The wings of flightless birds, such as penguins, are vestigial structures since the evolutionary function of the wing structure was to fly. Penguins use their wings to swim; not for flight.