Vestigial Organs

Definition of Vestigial Organs

Vestigial organs could be defined as organs or parts of human, plant and animal bodies that do not have any clear function and are considered to be residual parts from their respective ancestors. Vestigial organs are proof that all living organisms have evolved over time and are also helpful in explaining adaptation.

The Key Features of Vestigial Structures:

  • They have no  apparent function and are residual parts from an ancestor

  • These structures can become detrimental but in most cases they are harmless

  • These organs take a long time to be phased out and eliminating them may require major alterations which can have negative effects on the body

The Evolution of Vestigial Organs

These organs are generally homologous to organs that function normally in other species, which is why they can be considered as evidence of evolution. The existence of vestigial traits can be attributed to changes in the environment or behaviour patterns of an organism. If a function of a trait is no longer beneficial for the survival of an organism, the chances of its future offspring inheriting the trait’s normal form would be lower. The transition will take place over many generations and the trait may also be eliminated through genetic drift and other random events. It should be mentioned that gene mutation which can result in a change in protein structures can also give rise to vestigial organs. A good example is the degraded eyes of blind fish and salamanders. Mutation in genes have increased the number of taste buds in their tongue but have made them blind.

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Examples of Vestigial Organs

  • The human appendix and coccyx.

  • In septic weed (Cassia occidentalis) the androecium is vestigial.

  • The teeth of the whale shark. It cannot be used to bite anything and is a filter feeder.

Below we will talk about different types of human, animal and plant vestigial organs.

Vestigial Organs in the Human Body

  • Sinuses: The human face consists of air pockets called sinuses. They are lined by a thin layer of mucosa but they do not have any significant functions. However, an infection can lead to sinusitis.

  • Coccyx: Also known as the tailbone, coccyx forms the last part of the vertebral column. It is the residue of the lost tailbone and is observed during human embryogenesis.

  • Appendix: The appendix is a close-ended finger-like tube connected to the cecum from which it develops in the embryo. It sits in the lower right abdomen and is the storehouse of good bacteria which helps in the digestion of food. In our ancestors, it is believed to assist in the digestion of cellulose.

  • Wisdom Tooth: Wisdom tooth helps in the formation of the third set of molars in our buccal cavity. In prime ancestors, they helped in chewing raw and rough food, but in present, they have no function. They can cause pain infection and are generally extracted.

  • External Ear: The outer rim of our ears is made of underdeveloped muscles which make us incapable of moving our ears. It is a vestigial organ

  • Plica Semilunaris: Also known as the third eyelid is observed in the inside corner of human eyes. It has no role in protecting our eyes from any contaminant. (In animals, it’s known as the nictitating membrane and protects it from foreign particles and also keeps it moist whilst maintaining visibility)

  • Tonsils: Tonsils play a role in protecting the body from harmful microorganisms. However, when they become inflamed and infected, they are removed.

  • The Palmaris Longus muscle: About 16% of the human population does not have this muscle. Scientists think that this muscle helped early humans with their grip. Since we've begun to walk straight, over generations it has lost its purpose because we did not need to hand one to something for a very long while.

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Vestigial Organs in Animals

  • Galapagos Cormorant Wings: Although these birds have wings they can’t use them. 

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  • Female Cockroach Wings:  Female cockroaches have rudimentary wings which they cannot use to fly.

  • Boa Limbs: Boa constrictors have residual pelvic bones and back legs which are not immediately noticeable but can be observed with an X-ray. As snakes are descended from lizards, these are the skeletal remnants of their ancestors.

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  • Plover Toes: The black-bellied plovers in North America have small vestigial hind toes.

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  • Dog’s Dewclaw: The toe found higher up on a dog’s leg and it does not have any function

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Vestigial Organs in Plants

  • Gynoecium: In Shatavari (Asparagus Racemosus) the gynoecium and the staminode are vestigial organs

  • Androecium: In Septic Weed (Cassia occidentalis) the androecium is vestigial and it is called a pistinode.

FAQ (Frequently Asked Questions)

Q: What is a Vestigial Reflex?

A:  A vestigial response in a species can be defined as a reflex that has lost its original function. In humans some examples are

  • Palmar and foot sole grasp reflex: This is generally noticed in new-borns and they automatically want to get hold of anything that is put in front of them. The reflex which disappears after 3-4 months is still observed in modern primates.

  • Goosebumps: It is the pilomotor reflex and its original function was to raise fur to provide additional insulation against cold in our ancestors.

Q: Why are Sinuses Vestigial?

A: Sinuses are a non-vital organ. They are present as four air-filled holes behind the nose and around your eyes. Minor functions of sinuses include helping your voice to resonate and make your head feel light. Sinuses can be surgically removed if necessary. These are some of the reasons that sinuses are considered vestigial.

Q: How do Vestigial Organs Support the Doctrine of Evolution?

A:  Charles Darwin noted vestigial organs in both humans and animals are evidence for evolution. These organs in one species are similar to completely functioning organs in another species. With respect to this fact, biologists have come to a common notion that two different creatures can share a common ancestor. According to organic evolution, modern plants and animals have gradually evolved from simple forms over the course of millions of years. As they evolved, the lost the use of some organs which became vestigial. Thus, the presence of vestigial organs does support the doctrine of evolution.