Basic anatomical structures that are still there in a species despite having lost its primary ancestor role are known as vestigial organs. They are bodily tissues, organs, or cells that are no longer functional in the same way they were in the ancestors. Vestigial organs are evidence of the gradual evolution of all living things and can help to understand adaption.
Vestigial traits, which might be morphological, physiological, or behavioral in nature, are present in all animals. In humans, there are more than 100 vestige anomalies. There are numerous examples of human vestigial, including anatomical ones (such the human tailbone, wisdom teeth, and inside corner of the eye), behavioral forms (like goose bumps and the palmar grasp reflex), and molecular ones (pseudogenes).
Evolution of Vestigial Organs
Vestigial structures frequently resemble those in other species that perform their usual functions. Vestigial structures can therefore be viewed as supporting evidence for evolution, the process through which populations acquire advantageous heritable features over a long period of time. Changes in the organism’s environment and behavior patterns can be blamed for the existence of vestigial features. The chance that future kids will acquire the “normal” form of the trait declines as the trait’s function is no longer advantageous for survival. In some circumstances, the structure starts to harm the organism.
Vestigial organs can also develop as a result of gene mutations that alter the protein structures. Vestigial structures are created as a result of these mutant proteins.
The deteriorated eyes of blind fish and salamanders are an excellent illustration. Although their tongues now have more taste buds than before, they are now blind due to DNA mutations.
Depending on the choice, vestigial organs might range from being useless to advantageous. Some structures degrade over time to avoid the effects of genetic drift or selective pressures because they are less or not useful. Some vestigial structures continue to exist because of developmental constraints, making total elimination of the structure impossible without significant changes to the organism’s developmental pattern, which are likely to have many unfavorable side consequences.
Vestigial Organs in Human Body
Sinuses
Sinuses, small air pockets present in the human face. The human body has four sets of paranasal sinuses: the frontal (located in the forehead), maxillary (located beneath the cheekbones), ethmoid, and sphenoid (behind the nose). Despite possessing a thin mucosal layer covering them, they serve no real purpose. Our earliest ancestors may have had nasal sinuses lined with odor receptors, which would have given them a keener sense of smell and helped them survive.
Other than to make the head light and to warm and moisten the air we breathe, no one knows why humans retain these potentially problematic mucus-lined spaces. Sinusitis, however, can be brought on by an infection.
Wisdom tooth
Wisdom teeth are third molar vestigial organs present in human ancestors which probably was present to grind down the plant-based diet more efficiently. As the diet of human changed, the size of jaw decreased and wisdom tooth started being rudimentary. Only 5% of people in the population have a full set of healthy third molars. They are difficult to reach and far away, which results in pain and infection. Indigenous Mexicans never develop wisdom teeth at all. This variation is related to the PAX9 genetic alterations.
Appendix
The appendix develops in the embryo from a close-ended, finger-like tube attached to the cecum. It is the reservoir of beneficial bacteria that aids in food digestion and is located in the lower right belly. It is thought that it helped our ancestors digest cellulose in the past.
The appendixes of herbivorous animals like rabbits, cows are substantially larger and still functioning. With the change in human diet being more animal based, vermiform appendix is vestigial. An illness known as appendicitis can result if something prevents the appendix from opening. an operation termed an appendectomy to remove the appendix.
Coccyx
All that is left of the tail, which most mammals still rely on for balance and communication, are the fused vertebrae called coccyx. Before they started to walk upright, our predecessors’ hominid species lost the requirement for a tail. According to certain theories, the Coccyx or tail supports the pelvic muscles and smaller organs. There have been numerous instances where the tail has been surgically removed without causing harm to the body.
External Ear
Our ears cannot be moved because the muscles that make up their outer rim are undeveloped. It is a vestigial organ. It is also called as pinna.
Palmaris muscle
In 16% of contemporary humans, this long, slender muscle that goes from the elbow to the wrist is absent. It might have once been crucial for climbing and hanging. According to scientists, this muscle aided early humans in developing their grasp. Over the years, when we started to walk straight, it lost its utility because we didn’t need to hand anybody anything for a very long time. It is removed by surgeons for reconstructive procedures.
Darwin’s point
A bump called Darwin’s point or Darwin’s tubercle can occasionally be seen on the outer ear rim. The structure, which is regarded as a benign ear deformity, is believed to represent the remains of a joint that originally allowed the top of the ear to fold down over the ear canal.
Nictitating membrane or third eye lid
A few animals have a third eyelid called the nictitating membrane, which aids in seeing as well as protecting and maintaining the moisture of the eyes. Pplica semilunaris takes its position in humans.
Other Vestigial Organs
- Galapagos Cormorant birds possess wings, yet they are unable to utilize them. Scientists have hypothesized two explanations for the loss of flight: either the birds have improved their swimming prowess or they no longer need wings since they are not forced to migrate or flee.
- Even though they live in caves, blind fish and salamanders nonetheless have eye structures. Mutations in the genes that produce more taste buds are thought to have damaged their eyes.
- Although female cockroaches have primitive wings, they are unable to fly. The wings are undeveloped and small.
- Snakes are developed from lizards and they lost their feet as they started living and hunting in burrows.
- Some plants have vestigial organs too. Gynoecium and staminode in Shatavari (Asparagus racemosus) are extinct organs. Similarly, the androecium of septic weed (Cassia occidentalis) is rudimentary and is referred to as a palinode.
References
- https://byjus.com/biology/vestigial-organs/
- https://www.vedantu.com/biology/vestigial-organs
- https://link.springer.com/referenceworkentry/10.1007/978-3-319-47829-6_406-1
- https://www.livescience.com/11317-top-10-useless-limbs-vestigial-organs.html
- https://www.geeksforgeeks.org/vestigial-organs/
