Question

Which one of the following is not a vestigial structure in Homo sapiens?
A) Third molar
B) Epiglottis
C) Plica semilunaris
D) Pyramidalis muscle

Answer 1

Hint: Evolution is defined as the process of formation of complex organisms via change from simple ancestral types over the course of geological time. It is a constant process that leads to development of an enormous variety of plants and animals that have taken place on this earth at present. Vestigial organs are such organs which used to play a significant role in the evolutionary past but are of rare or no use in the present. 

Complete answer:
Vestigial organs are defined as tissues or cells in a body which are non-functional but they are functional in their ancestral form of the trait. These structures are the result of gene mutation. These mutated genes help to develop the vestigial structures. These structures may develop further if it is beneficial in the population. For example, in humans’ vestigial organs are appendixes and are shrinking in size and disappearing.
Now let us find solution from given options:
Third molar: In our buccal cavity wisdom teeth constitute the third set of molars. They were used in rough chewing in the ancestral times but nowadays they are remote which causes pain and infection.
Epiglottis: epiglottis is defined as the flap-like cartilaginous structure that prevents the entry of food into oesophagus. So, it is functional.
Plica semilunaris: Nictitating membrane is present in few animals which protect eyes from dust and moist. In humans this membrane is replaced by a plica semilunaris and is non-functional.
Pyramidalis muscle: they are small triangular shaped muscles and are present between the anterior surface of rectus abdominis and posterior surface of rectus sheath. But this muscle is non-functional.

Thus, the correct answer is option ‘B’ that is epiglottis.

Note: The structures that occur in an organism that has lost all or most of its original function within the time of evolution are called vestigial organs. In humans, the vestigial organs well known example of these which are still present in our body, like the muscles of the ear (Auricular muscles), wisdom teeth, vermiform appendix, the coccyx, body hair, and also the semilunar fold within the corner of the eye (nictitating membrane).