Question

Which of the following is not vestigial in man?
(a)Tail vertebrate
(b)Nails
(c)Nictitating membrane
(d)Vermiform appendix

Answer 1

Hint: In the context of evolution, vestigial refers to those traits or organs that have lost all or most of their original function with the process of evolution. In humans, there are many vestigial organs but the keratinous protective organ over fingers and toes is not one of them.

Complete answer:
Nails form a part of the integumentary system and are keratinized hard structures. They are present on the dorsal surface of each finger and toe tip. They serve as protection organs. They are fully developed and fully functional structures in humans. Some examples of vestigial organs are the vermiform appendix and the coccyx.

Additional Information: -The tail vertebrae which consists of the last four coccygeal vertebrae that are fused, represents the remnants of the long useful tail that was present in human ancestors. Despite being attached to the pelvic muscles and ligament, the coccyx is non-functional. This is because the fused, non-moving bones cannot move the muscles.
-Nictitating membrane also known as plica semilunaris is a vestigial third eyelid that represents a fold in the conjunctiva of the human eye. Birds and reptiles have a well-developed third eyelid or nictitating membrane.
-Vermiform appendix is a small cylindrical extension present at the junction of the large and the small intestine. In herbivorous animals and leaf-eating primates, it served as the house of fermenting bacteria that contain the enzymes for the breakdown of cellulose into sugar.
So, the correct answer is, “Nails”.

Note: -There are a lot of other structures that are vestigial in human beings. For example- Pinna of the ear and auricular muscles or the third molar, also known as wisdom teeth.
-These structures are fully functional in lower organisms as they are necessary for them. For example- Auricular muscles are necessary for lower organisms to move their ears in different directions to listen to movements of predators, third molars are necessary for the grinding of food in lower primates and apes.
-This theory of use and disuse of organs forms the basis of the theory of Lamarckism.