Vestigial organs are organs of the entity which are smaller and less complex. These structures are organs, tissues or cells in a body which are no more functional the way they were in their ancestral form of the trait. It is an authentication of evolution and hence, were helpful in explaining adaptation. Such a structure can arise due to gene mutation which causes a change in the proteins. These mutated proteins result in the formation of vestigial structures. In the population, the occurrence of such structures may, however, increase if it is beneficial enough. For instance, snakes have evolved to slither as they no longer have legs excluding some snakes who still possess rear legs(the Boas).
In humans, the appendix is a good example of a vestigial organ. This non-functioning organ eventually degenerates, shrinking in size disappearing ultimately. All structures require nourishment to develop, grow and to be able to perform their functions. When all these requisites are not provided, the region develops a risk of infection or tends to become cancerous. These criteria contribute to the removal of such structures which only worsen the health of the individual. The Human appendix causing appendicitis in the past has proven to be fatal. In some cases, the selection causes these structures to transform to a new function(ear ossicles in mammals) which is referred to as exaptation. During evolution, some genetically determined structures are retained but have lost their ancestral function which is mentioned as Vestigiality.
Examining vestigiality should be governed by drawing similarities with their counterparts with respect to their homologous features. The exposure of this occurs through various processes of evolution, one of which is the loss of function of a feature that is not subjected to positive selection pressures in accordance with its surroundings. Vestigial structures vary from being pointless to favourable based on the selection. Some structures due to less or no utility, degenerate over a period of time to avoid consequences of genetic drift or selective pressures.
See Also: Evidence Of Evolution
Some Vestigial Organs
Following are a few examples of vestigial organs:
Human cheekbones hold the maxillary sinuses. Face consists of pockets of air called sinuses. They are lined by a thin layer of mucosa. It has no significant use but infection can lead to sinusitis.
- The Appendix
It is one of the most commonly known vestigial organs. This finger-like tube closed at one end arises from the vermiform process. In prime ancestors, the appendix is believed to have brought about the digestion of cellulose. Today, scientists predict that the appendix may play a role in digestion by bacteria.
It forms the last part of the vertebral column, the residue of the lost tail and is often termed as the tailbone. It is observed during human embryogenesis. This formed as the centrepiece of the ‘theory of recapitulation’.
- Wisdom Tooth
Forms the third set of molars in our buccal cavity. They may have been significant in the past(chewing rough and raw food) but in modern times, as they are inaccessible and remote, it causes pain and infection.
- The Ear
The Helix(outer rim of the ear) is known to be a vestigial structure. Underdeveloped muscles in the ear make us incapable to bring about the movement of ears. Darwin’s tubercle is a vestigial feature present on the juncture of the upper part of the ear. Register at BYJU’S to know more about Vestigial organs and their impact on the body.
Related Links: Mutation – A Genetic Change