Question

What are vestigial organs? Give an example.

Answer 1

VESTIGIAL ORGANS

Explanation:

• Vestigial organs are organs of the body which are smaller and simpler than those in related species. They have lost, or almost lost their original feature.

• Vestigiality is evidence for evolution, since they only make sense if evolution has occurred.[1] They were one of the puzzles of pre-Darwinian natural history. The puzzle vanished once biologists realised they once were working adaptations, in the ancestors of present-day animals.

• They occur in animals (and plants) which have changed their style of life from their ancestors. Thus snakes lost their legs as their system of movement changed. But one type of snake – the boas – have vestigial rear legs and pelvis. The human vermiform appendix is another example. That was much larger, and stored microbes which produced cellulase to break down plant cell walls. Leaves are the main diet of apes, but they are not a main part of man's diet. Cellulose cannot be digested by our species.

• An unused organ usually degenerates, and becomes smaller or vanishes altogether. Thus amphibia living in dark caves lose their sight and their body colour.Mutations pile up. All structures need energy for their development, maintenance, and weight. This, and the risk of disease in the part (e.g., infection, cancer), provide some selection for the removal of parts which no longer help an organism's fitness.

• The human appendix had selection against it because of deaths from appendicitis. Appendicitis was untreatable until modern times. The selection pressure was probably weak, because most cases occur after the age of peak fertility.

• Occasionally, selection turns vestigial organs to a new function. Thus the mammalian ear ossicles were once bones in the jaw of early proto-mammals, the Therapsida. The halteres of flies is a perfect example. The word exaptation was coined for this phenomenon.
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Answer 2

Organs which had function in our bodies earlier but are now useless. Eg, pinna