Vestigiality describes those similar characters of organisms that have seemingly lost all or most of their original function in a species through evolution. A structure or organ or even a function is vestigial if it has diminished in size or usefulness in the course of evolution . Vestigial structures are markers of evolutionary descent. These may take various forms such as anatomical structures, behaviors and biochemical pathways. Some of these disappear early in embryonic development, but others are retained in adulthood. The idea that we are carrying around useless relics of our evolutionary past has long fascinated scientists and laypeople alike. Although some researches show nothing is rudimentary at all but having them is not a necessity.
10. Vermiform Appendix
The vermiform appendix is a vestige of the cecum , an organ that would have been used to digest cellulose by humans’ herbivorous ancestors. One potential ancestral purpose put forth by Charles Darwin was that the appendix was used for digesting leaves as primates. It may be a vestigial organ, evolutionary baggage, of ancient humans that has degraded down to nearly nothing over the course of evolution. Evidence can be seen in herbivorous animals such as the koala. The cecum of the koala is very long, enabling it to host bacteria specific for cellulose breakdown. Human ancestors may have also relied upon this system and lived on a diet rich in foliage. As people began to eat more easily digested foods, they became less reliant on cellulose-rich plants for energy. The cecum became less necessary for digestion and mutations that previously had been deleterious were no longer selected against. These alleles became more frequent and the cecum continued to shrink. After thousands of years, the once-necessary cecum has degraded to what we see today, with the appendix. Analogous organs in other animals similar to humans continue to perform that function, whereas other meat-eating animals may have similarly diminished appendices. In line with the possibility of vestigial organs developing new functions, some research suggests that the appendix may guard against the loss of symbiotic bacteria that aid in digestion. An alternative explanation would be the possibility that natural selection selects for larger appendices because smaller and thinner appendices would be more susceptible to inflammation and disease.
9. Goose Bumps
Goose bumps , also called chicken skin or the medical term cutis anserina , are the bumps on a person’s skin at the base of body hairs which may involuntarily develop when a person is cold or experiences strong emotions such as fear, awe, admiration or sexual arousal. The reflex of producing goose bumps is known as piloerection and the vestigial structures involved are the piloerector muscles. It occurs not only in humans but also in many other mammals; a prominent example are porcupines which raise their quills when threatened, or sea otters when they encounter sharks or other predators. Goose bumps do not appear on the face. As a response to cold: in animals covered with fur or hair, the erect hairs trap air to create a layer of insulation. Goose bumps can also be a response to anger or fear: the erect hairs make the animal appear larger, in order to intimidate enemies. This can be observed in the intimidation displays of chimpanzees, in stressed mice and rats, and in frightened cats. In humans, it can even extend to piloerection as a reaction to hearing nails scratch on a chalkboard, listening to awe-inspiring music, or feeling or remembering strong and positive emotions (e.g., after winning a sports event). Some people have learned to will goose bumps at any time they please. Piloerection as a response to cold or emotion is vestigial in humans. As we retain only very little body hair, the reflex now provides no known benefit. Humans also bear some vestigial behaviors and reflexes. The formation of goose bumps in humans under stress is a vestigial reflex; its function in human ancestors was to raise the body’s hair, making the ancestor appear larger and scaring off predators. Raising the hair is also used to trap an extra layer of air, keeping an animal warm. Due to the diminished amount of hair in humans, the reflex formation of goosebumps when cold is now vestigial.
A number of muscles in the human body are thought to be vestigial, either by virtue of being greatly reduced in size compared to homologous muscles in other species, by having become principally tendonous or by being highly variable in their frequency within or between populations. The Occipitalis Minor is a muscle in the back of the head which normally joins to the muscles of the ear. This muscle is very sporadic in frequency—always present in Malays, in 56% of blacks, 50% of Japanese, 36% of Europeans, and is nonexistent in the Khoikhoi people of southwestern Africa and in Melanesians. In many non-human mammals the upper lip and sinus area is associated with whiskers or vibrissae which serve a sensory function. In humans these whiskers do not exist but there are still sporadic cases where elements of the associated vibrissal capsular muscles or Sinus hair muscles can be found. Similarly the palmaris longus muscle of forearm, the pyramidalis muscle of abdomen and plantaris of the leg are considered useless or vestigial.
7. Vomeronasal Organ
Rodents and other mammals secrete chemical signals called pheromones that carry information about their gender or reproductive state, and influence the behaviour of others. Pheromones are detected by a specialised sensory system, the vomeronasal organ (VNO) , which consists of a pair of structures that nestle in the nasal lining or the roof of the mouth. Although most adult humans have something resembling a VNO in their nose, neuroscientists have no hesitation in dismissing it as a remnant. If you look at the anatomy of the structure, you don’t see any cells that look like the sensory cells in other mammalian VNOs. You don’t see any nerve fibres connecting the organ to the brain. Genetic evidence suggest that the human VNO is non-functional. Virtually all the genes that encode its cell-surface receptors – the molecules that bind incoming chemical signals, triggering an electrical response in the cell – are pseudogenes, and inactive. So what about the puzzling evidence that humans respond to some pheromones? Larry Katz and a team at Duke University, North Carolina, have found that as well as the VNO, the main olfactory system in mice also responds to pheromones. If that is the case in humans too then it is possible that we may still secrete pheromones to influence the behaviour of others without using a VNO to detect them.
6. Nictitating Membrane The Third Eyelid
The nictitating membrane is a transparent or translucent third eyelid present in some animals that can be drawn across the eye for protection and to moisten the eye while also maintaining visibility. Various reptiles, birds, and sharks have a full nictitating membrane, whereas in many mammals including humans, there is a small vestigial remnant of the membrane present in the inner corner of the eye having no known function. Some mammals, such as camels, polar bears, seals, and aardvarks, also have a full nictitating membrane. It is often called a third eyelid or haw and may be referred to as the plica semilunaris in scientific terminology.