Question

Which is not a vestigial organ in man?
A. Nictitating membrane
B. Tail vertebrae
C. Vermiform appendix
D. Nails

Answer 1

The vestigial organs are useless body parts in humans which are non functional due to evolutionary changes.

Complete Answer:
- The vestigial organs were functional in our ancestors but due to evolutionary changes it is now not an essential part of the body.
- The nictitating membrane is also called as third eyelid. The small fold of tissue inside the eye corner is plica semilunaris which is remnant of nictitating membrane. Plica semilunaris is known to have some lacrimal drainage function and helps in eye movement. These move horizontally across the eyeball, unlike upper or lower eyelids which move vertically across the eyeball.Therefore the position of this vestigial remnant in the human eye.

- The modern man is more developed than their ancestors. Humans don't live in wildlife anymore so they don't have to climb trees. Unlike other mammals that use tails for their balance, humans have adapted to better conditions and can walk with legs and therefore they do not need a tail. Due to natural selection, gradually the use of the tail reduced which led to non functional organs. The tail bone was useless and it converted into fused vertebrae called coccyx.

- Vermiform appendix is a narrow tube that joins the colon at the end. In the ancient era, the ancestors were herbivorous, the appendix played a role in digesting tough plant based food. But now the dietary supplements of humans have changed the role of appendix and became useless.

- The nails have keratin protein. These are tough external structures that can be used to climb trees as they give a good grip on trees and it is one of defence mechanisms for humans.

Therefore, the correct answer is option D. Nails.

Additional information: Calabar angwantibo the only species of primate is known to have a functioning nictitating membrane.They are found in reptiles, birds and amphibians. Nictitating membrane in such organisms helps to keep their eyes moist and offer protection for maintaining visibility even if the eyes are open. Researchers from Duke University Medical Centre found that appendix nights have a role in storing beneficial bacteria.

Note: Natural selection has made a lot of evolutionary changes that resulted in non functionality of some body parts.