Vestigial structure or organ describes characters of organisms that have seemingly lost all or most of their original function in a species through evolution – basically useless. 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.
Human vestigiality is related to human evolution, and includes a variety of characters occurring in the human species. Vestigial organs are sometimes pressed into a secondary use when their original function has been lost. Many of these are also vestigial in other primates and related animals.
Here is a list of the top 10 body parts that are completely useless in the human body of our times.
The most common explanation for the appendix’s existence in humans is that it’s a vestigial structure which has lost its original function. The vermiform appendage — in which some recent medical writers have vainly endeavoured to find a utility — is the shrunken remainder of a large and normal intestine of a remote ancestor. This interpretation would stand even if it were found to have a certain use in the human body.
One potential ancestral purpose put forth by Charles Darwin was that the appendix was used for digesting cellulose - leaves (herbs) – as primates. When the human diet consisted of mostly plants, the appendix was extremely important.
2. Wisdom teeth
Are those teeth that are located in the back of the mouth being called so because they develop at an older stage in human life – having absolutely no resemblance to “wisdom” whatsoever. These teeth were once very helpful, especially when humans had a diet that consisted of a lot of tough meat. Wisdom teeth, at this time, allowed humans to properly chew their food. They 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.
3. Male nipples
In the male, nipples are not considered functional with regard to breastfeeding, although male lactation is possible. This doesn’t need much further explanation.
Adenoids (or pharyngeal tonsils) are a mass of lymphoid tissue situated at the very back of the nose, in the roof of the nasopharynx, where the nose blends into the mouth. These tissues are part of the immune system and trap bacteria that can cause viruses. However, they only provide defense against bacteria that is inhaled. As you grow, your adenoids shrink down a lot, which makes them useless. They are only helpful till you are a 3 years old child.
This structure or tailbone (a remnant of a lost tail) is still considered vestigial (useless body part). The coccyx is usually formed of four rudimentary vertebrae (sometimes five or three). However it is still not entirely useless, as 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.
The anterior side of the coccyx serves for the attachment of a group of muscles important for many functions of the pelvic floor.
In any case, the coccyx is generally much more important in those mammals with tails.
6. Arrector Pili
Are small muscles which attach to the hair follicles in mammals. Contraction of these muscles causes the hairs to stand on end – known colloquially as goose bumps. The contraction of the muscle is involuntary – stresses such as cold, fear etc. may stimulate the sympathetic nervous system and thus cause contraction, but the muscle is not under conscious control.
Its principal function in the majority of mammals is to provide insulation: air becomes trapped between the erect hairs, helping the animal retain heat. Erection of the porcupine’s long, thick hairs causes the animal to become more intimidating, scaring predators (like erecting the feathers of some birds). However, effectiveness of the muscles’ action in humans is questioned, as humans have relatively little body hair to allow for thermal insulation (so it really wouldn’t count).
7. Plica semilunaris
It is a remnant of the nictitating membrane (a semi-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)
8. Auricular muscles (Ear)
The muscles connected to the ears of a human do not develop enough to have the same mobility allowed to many animals, thus non-functional. It is yet still large enough to be easily identifiable. A muscle that cannot move the ear, for whatever reason, can no longer be said to have any biological function. This serves as evidence of homology between related species. 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 – yet still with no use.
9. Plantaris muscle (Leg)
Plantaris is a vestigial structure and one of the superficial muscles of the posterior crural compartment of the leg. It is composed of a thin muscle belly and a long thin tendon. It’s approximately 2-4 inches long and is absent in 7 – 10% of the human population. The plantaris is considered an unimportant muscle, it mainly and barely acts with gastrocnemius.
This muscle is mainly used by surgeons for tendon grafts needed in other areas of the body. Although the plantaris has very little importance, there are injuries that can occur. It can be damaged in an Achilles tendon rupture. Tennis leg is a commonly known injury. It is a result of eccentric loading placed on the ankle while the knee is extended, and occurs while running or jumping.
10. Junk (noncoding) DNA
There are also vestigial molecular structures in humans, which are no longer in use but may indicate common ancestry with other species. One example of this is L-gulonolactone oxidase, a gene that is functional in most other mammals and produces an enzyme that synthesizes vitamin C. In humans, a mutation disabled the gene and made it unable to produce the enzyme. However, the remains of the gene are still present in the human genome as a vestigial genetic sequence called a pseudogene.
Some people consider Tonsils and Sinuses as also being useless body parts, which is wrong. They actually have an important role in the human body.
- Decreasing the relative weight of the front of the skull, and especially the bones of the face.
- Increasing and/or giving different resonance of the voice.
- Providing a buffer against blows to the face.
- Insulating sensitive structures like dental roots and eyes from rapid temperature fluctuations in the nasal cavity.
- Humidifying and heating of inhaled air because of slow air turnover in this region.
- They are consisted of immuno-competent tissues that represent a defense mechanism of first line against ingested or inhaled foreign pathogens.
- Swollen tonsils are an alert, showing that bacteria/viruses are present in the body and especially in the respiratory system. This often happens in the case of ‘common cold’ or laryngitis.