Evidence from comparative anatomy and morphology - vestigial organ

 

In a large number of animal species, there are several organs that are not developed completely or found in rudimentary form. These incomplete developed body organs are called vestigial organs. These organs are useless and present as non functional organs.

Evolution provides the answer to this question that when these are non functional then why are these organs present in the body?

During the evolution various body organs were developed under changed climatic conditions and some organs lost their utility and not developed completely. The organ that lost their utility did not disappear in the next generation. These are appearing but gradually they lost their structure because these are non functional. These organs were present their ancestor of animals.

For example - Terrestrial habits of man evolved from arboreal monkeys or tree dwelling monkeys through the semi arboreal ape. Therefore monkeys have a functional tail that provides balance of body during the tree dwelling whereas it is present as a vestigial organ in humans.

Snakes lost their limbs during evolution because they adapted themselves for creeping and did not use their limbs during creeping. The fore limb disappeared completely but their hind limb with pelvic girdle are still present in some species of snake like python and Boa as vestigial organs. This proves that evolution of snakes occurs from the limb bearing reptile.

In aquatic mammals like seal and whale forelimb are modified into flippers but hind limbs have been lost and their pelvic girdle are present as vestigial organs.

Whales also lost the function of collecting the sound wave in air and ear pinna are present as vestigial organs.

Adaptation for fast running cursorial animals like horse deer has resulted in the excessive development of third digit in their limb and other digit in their limb lost their utility and first and fifth digit lost completely but second and fourth digit are present as vestigial organs. 

Some species like Salamanders live in deep caves and some fish live in deep ocean in absence of light therefore their eyes lose their utility  hence present as vestigial organs.

In Human there are several vestigial organ. Some of organ have been describe here.

Plica semilunaris is a small red color folded at the inner angle of the eyes. Muscle of ear pinna, vertebrae tail, vermiform appendix and wisdom tooth are vestigial organ.