“Vestigial organs are the organs that have no apparent function and are considered to be the residual parts from the past ancestors.”
What are Vestigial Organs?
Vestigial organs 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 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.
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 organs 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
Examples of Vestigial Organs
Following are a few examples of vestigial organs:
Human cheekbones hold the maxillary sinuses. The 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.
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’.
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 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.
Nictitating membrane is the third eyelid found in a few animals that protect and keep the eyes moist and also helps in vision. In humans, it is replaced by plica semilunaris.
The tonsils remain as vestigial organs in the human body. They act as the first line of defence and protect the body from harmful microorganisms that are either inhaled or ingested by the body.
Other Vestigial Organs
Few other vestigial organs are mentioned below:
- The snakes are believed to have descended from the lizards. Their legs grew smaller and smaller until a small bump was left at the back of some of the largest snakes like pythons.
- Blind fish and salamanders still possess eye structures but live in caves. It is believed that mutations in genes that increase the taste buds degraded their eyes.
- Cockroaches have wings. The wings that are present on the females do not facilitate flying.
- The Galapagos cormorants have wings which are non-functional. These birds are believed to have turned into flightless birds abut 2 million years ago.
- The whale shark is a filter feeder. It consists of rows of teeth that cannot bite anything.
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Related Links: Gene Mutation