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.
5. Coccyx the Tailbone
The coccyx, commonly referred to as the tailbone, is the final segment of the ape vertebral column. Comprises three to five separate or fused vertebrae (the coccygeal vertebrae) below the sacrum. In humans and other tailless primates (e.g. great apes) the coccyx is the remnant of a vestigial tail, but still not entirely useless; it is an important attachment for various muscles, tendons and ligaments — which makes it necessary for physicians and patients to pay special attention to these attachments when considering surgical removal of the coccyx. Additionally, it is also part of the weight-bearing tripod structure which act as a support for a sitting person. Nevertheless coccyx, or tailbone, is the remnant of a lost tail. All mammals have a tail at one point in their development; in humans, it is present for a period of 4 weeks, during stages 14 to 22 of human embryogenesis. This tail is most prominent in human embryos 31–35 days old. The tailbone, located at the end of the spine, has lost its original function in assisting balance and mobility, though it still serves some secondary functions, such as being an attachment point for muscles, which explains why it has not degraded further.
4. Wisdom Teeth
Wisdom teeth are the four third molars, present in the upper and lower jaws. Wisdom teeth usually appear between the ages of 17 and 25. Most adults have four wisdom teeth, but it is possible to have more, in which case they are called supernumerary teeth. Wisdom teeth commonly affect other teeth as they develop, becoming impacted or “;coming in sideways”;. They are often extracted when this occurs. About 35% of the population does not develop wisdom teeth at all. Wisdom teeth are vestigial third molars that human ancestors used to help in grinding down plant tissue. The common postulation is that the skulls of human ancestors had larger jaws with more teeth, which were possibly used to help chew down foliage to compensate for a lack of ability to efficiently digest the cellulose that makes up a plant cell wall. As human diets changed, smaller jaws were selected by evolution, yet the third molars, or “;wisdom teeth,”; still commonly develop in human mouths.Currently, wisdom teeth have become useless and even harmful to the extent where surgical procedures are often done to remove them.
3. Outer Ear
The ears of a Macaque monkey, and most other monkeys, have far more developed muscles than those of humans and therefore have the capability to move their ears to better hear potential threats. Humans and other primates such as the chimpanzee however have ear muscles that are minimally developed and non-functional, yet still large enough to be identifiable. A muscle attached to the ear that cannot move the ear, for whatever reason, can no longer be said to have any biological function. In humans there is variability in these muscles, such that some people are able to move their ears in various directions, and it has been said that it may be possible for others to gain such movement by repeated trials. In such primates the inability to move the ear is compensated mainly by the ability to turn the head on a horizontal plane, an ability which is not common to most monkeys—a function once provided by one structure is now replaced by another. The outer structure of the ear also shows some vestigial features, such as the node or point on the helix of the ear known as Darwin’;s tubercle which is found in around 10% of the population. Darwin’;s point, or tubercle, is a minor malformation found in a substantial minority of people and takes the form of a cartilaginous node or bump on the rim of their outer ear, which is thought to be the vestige of a joint that allowed the top part of the ancestral ear to swivel or flop down over the opening to the ear.
2. Male Nipples
Men’;s nipples, cited as vestigial structures, are in a sense vestigial and are analogous to vestigial structures such as the remnants of useless pelvic bones in whales but are not truly vestigial because they are not remnants of functional male nipples in ancestral species. They occur because nipple precursors are grown early in the development of the human embryo, before sexual differentiation. Later in life these structures become more fully developed in women. The presence of nipples in male mammals is a genetic architectural by-product of nipples in females. So, why do men have nipples? Because females do.
1. Palmar Grasp Reflex
Not a structure but a vestigial behavior, the palmar grasp reflex appears at birth and persists until five or six months of age. When an object is placed in the infant’;s hand and strokes their palm, the fingers will close and they will grasp it. The grip is strong but unpredictable; though it may be able to support the child’;s weight, they may also release their grip suddenly and without warning. The reverse motion can be induced by stroking the back or side of the hand. The palmar grasp reflex is supported to be a vestigial behavior in human infants. When placing a finger or object to the palm of an infant, it will securely grasp it. This grasp is found to be rather strong. Some infants—37% according to a 1932 study—are able to support their own weight from a rod, although there is no way they can cling to their mother. The grasp is also evident in the feet too. When a baby is sitting down, its prehensile feet assume a curled-in posture, much like what is observed in an adult chimp.An ancestral primate would have had sufficient body hair to which an infant could cling unlike modern humans, thus allowing its mother to escape from danger, such as climbing up a tree in the presence of a predator without having to occupy her hands holding her baby.
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