Vestigial Organs Of The Human Body: What They Are And 10 Examples
The human body contains several vestigial organs—structures that once had important functions in our ancestors but have since lost their primary purpose due to evolution. While some vestigial organs have completely lost their function, others may still serve minor roles in the body.
This article explores the definition of vestigial organs, their significance in evolution, and 10 examples of vestigial structures in the human body.
Vestigial organs are remnants of evolutionary history. These structures were once fully functional in ancestral species but have since become redundant or nonessential due to changes in lifestyle, environment, and natural selection.
Some key characteristics of vestigial organs include:
Reduced or limited functionality compared to their ancestral state.
No longer necessary for survival in modern humans.
Evolutionary evidence linking them to past species.
Although these structures may seem useless, many have adapted to perform minor functions or exist without causing harm.
The Role of Vestigial Organs in Evolution
Vestigial structures support the theory of evolution by demonstrating how organisms change over time. They show that:
Humans share common ancestors with other species.
Some traits become unnecessary as species adapt to new environments.
Evolution does not remove structures immediately but instead gradually reduces their function.
Among many other pieces of evidence, the presence of vestigial organs in animals is the most irrefutable proof that evolution exists and that natural selection is the force behind the process, since they are the remains of this one. The theory of intelligent design, defended by creationist sectors, does not make sense because, if human beings and other species have been created perfectly, what need is there to preserve organs that are useless?
According to Charles Darwin’s evolutionary theory, set forth in his book The origin of species (1859), all the species that exist today on Earth come from the same living being, our common ancestor. This ancestor, which should have been very simple, evolved, giving rise to other more complex species better adapted to the needs of the environment. As a result of the different adaptations we can see the diversity of species that can be found today.
From this theory it is concluded that if a characteristic is not adaptive in nature, it can either disappear, because the individuals that possess it do not reproduce because they have a disadvantage, or they are conserved but, progressively is atrophying The latter would be due to the fact that, as there is no evolutionary pressure on this character, the organ in question is not used and develops an increasingly smaller function. This Darwinian idea would be what would explain the existence of vestigial organs.
It should be said that Darwin was not the first to observe the presence of vestigial organs in animals. Thousands of years before, Aristotle would notice the eyes of animals that live underground, such as moles, which made no sense for them to have them since they were rarely in contact with sunlight. What is the point of having eyes in a place where it can not be seen?
But the most notable antecedent to Darwin is Jean-Baptiste Lamarck. This French naturalist considered that evolution was governed by a very basic principle: the frequent and sustained use of an organ causes it to strengthen little by little, giving it a power proportional to the duration of its use. Thus, the organ that has been used little or is in disuse will end up weakening. For example, according to Lamarck, the eyes of moles would have lost functionality over the generations because this species does not need them.
Although Lamarckian theses were quite important in their time, today we know that they are not entirely true. It is not the lack of use that promotes the weakening of a structure organic, but how adapted or functional it is to face the demands of the environment. If the individual has a structure that gives them a disadvantage, they will most likely have more trouble reproducing than those who either do not have it or have the appropriate version.
Since all living beings come from a certain ancestor, it is quite easy to find vestigial structures shared by an immense number of species. Vestigial organs, as we have mentioned, are nothing more than ancient organs that were functional but are no longer functional in the current carrier species. This process is called “involution,” and it implies that less biological effort is spent to keep that structure active. Thus it loses its functionality, reduces in size and atrophies.
10 Examples of Vestigial Organs in Humans
In the human body there are many vestigial organs, so many that the debate about exactly how many there are is still open. It is estimated that there could be 86, but there have also been classifications in which more than 180 vestigial organs have been mentioned.
This is because one cannot always be sure that an organ has completely lost its functionality, since reminiscences of its ancestral function may remain. In any case, the scientific community agrees that the 10 structures that we will see below can be considered vestigial organs.
1. Appendix
The appendix is a small, tube-like organ attached to the large intestine. In herbivorous ancestors, it played a role in digesting cellulose from plants. Today, it serves no essential digestive function, though some research suggests it may help store beneficial gut bacteria.
The vermiform appendix is the best known vestigial organ. Its fame is due to the fact that, despite being such a small structure, if it becomes infected, appendicitis occurs, a serious disease that, if not treated in time by surgically removing the appendix, can lead to death.
The appendix is attached to the large intestine and has an elongated shape, like a kind of finger-shaped bag that projects from the colon to the right side of the abdomen.
The appendix is thought to be what remains of an organ that our herbivorous ancestors used to digest cellulose. This function has been lost in our species because we no longer consume tree leaves, which are some of the foods richest in this substance.
By switching to a diet with more meat, fruits and legumes, the appendix ended up no longer being important for our survival, causing it to become increasingly atrophied as the generations passed as it was no longer of fundamental importance for our digestion.
Despite this, there are those who think that it could really have some function. It has been said that it could be involved in the immune response, at least indirectly, and it has also been hypothesized that it could be responsible for maintaining the intestinal flora.
2. Coccyx
The coccyx is a remnant of the tail found in our primate ancestors. While it no longer serves a purpose for balance or movement, it provides attachment points for pelvic muscles and ligaments.
The coccyx (or Tailbone) is the final part of the spine. It is formed by the last four vertebrae, which are small in size and lack mobility and, from birth, are fused.
This structure has no functionality, at least apparently. Instead, the anterior part of the coccyx, which is also not mobile, does seem to play a certain important role in transmitting movement to the pelvis.
Its evolutionary origins are quite ancient, being found in the most primitive monkeys. The tailbone is believed to be the result of progressively losing the tail, a structure that is common in most vertebrates. Thus, our tailbone would be an involution of the tail.
3. Paranasal sinuses
The paranasal sinuses are hollow cavities found in our skull. They are like air bags in our head and, although there are those who say that their function could be as a resonance chamber or to release weight from the skull, the truth is that they seem to be vestigial structures that, on top of that, cause serious problems.
The paranasal sinuses can become home to bacteria or other pathogens that have a free way to access this structure and remain well isolated. When this happens, the sinuses become infected and sinusitis, a respiratory disease, occurs.
It makes no evolutionary sense to have a structure that, in addition to not performing a clear function, is prone to infection. However, yes, they must have been useful for the animals from whom we inherited them, the sauropsids. These large reptiles needed these cavities to shape their skull.
4. Plica semilunaris
The plica semilunaris is a small fold found in the ocular conjunctiva, that is, the membrane that surrounds the eye. It is located in the inner corner of the eye and it looks like a reddish tissue that protrudes between the eyelids. Although it facilitates eye movement and helps maintain eye drainage, they are considered vestigial organs.
Apparently it comes from a structure that fulfilled other functions in our ancestors and that has evolved: the third eyelid or nictitating membrane. This membrane is common in birds and reptiles, consisting of a translucent eyelid that serves to lubricate the eye and clean it without having to close your eyes and briefly lose vision.
5. Posterior auricular muscle
The posterior auricular muscles, which are located behind the ear, are considered vestigial muscles. Most people cannot move them at will and, if they can, their muscles are still very atrophied.
We have inherited these ear muscles from basal primates, who did need to have a good ability to move their ears at will and thus be able to locate sounds well.
In the human case, this ability was lost given that the auditory pavilion of our species has evolved well enough to detect the origin of sounds without having to move them.
6. Phalanges of the little toe
The phalanges of the little toe are very small bones and lack mobility. Compared to the phalanges of the other toes, these are highly involuted, which is why they are considered vestigial bones. Its origins are found in our primate ancestors, who did have the ability to move the little toe more freely.
7. Wisdom teeth
Wisdom teeth are teeth that are considered vestigial organs, since they do not fulfill any important function and, in addition, they run the risk of having cavities very easily and are not well integrated into our physiognomy. It makes no sense that, starting with puberty, our wisdom teeth grow, causing pain and, in many cases, making it necessary to remove them to maintain good oral hygiene.
These molars are a legacy from our primate ancestors, especially those that consumed roots (rhizophages). These animals needed much larger and stronger teeth to be able to chew the hard roots, which were a fundamental food in their diet.
Due to the nutritional changes that occurred at some point in our evolutionary history, the first hominids needed other types of teeth to be able to eat meat, fruits and legumes, reaching the point that the human jaw evolved to such an extent that it was not adapted to house wisdom teeth.
8. Male nipple
The nipple is an essential structure for females, since it is used to breastfeed their young and feed them when they are too small to consume solid food. This is the only biological purpose of the nipple, therefore, It doesn’t make sense for males to own them. Thus, the male nipple is a vestigial organ.
9. Body hair
A few million years ago body hair was essential to keep hominids living in cold climates warm. With changing temperatures and migration to warmer climates, body hair ended up losing its usefulness, making having too much or too little not an important factor for survival.
Although in certain parts such as the arms, legs, back and chest it does not seem to fulfill a significant function, in other parts it is useful. An example of this is eyebrow hair that prevents sweat from entering the eyes, while facial hair is considered a secondary sexual characteristic with the reproductive purpose of attracting females.
10. Erector pili
The erector pili is a muscle group near the hair follicle that is responsible for raising the hair in situations of danger or fear, that is, making us have “goosebumps.” It is believed that its original function was to make us appear larger in the face of an animal threat, in order to intimidate and scare him. However, when we lost hair, this function stopped making sense, and it has remained a vestigial mechanism.
Vestigial organs provide a fascinating glimpse into human evolution, revealing how our bodies have adapted over time.
FAQs About Vestigial Organs in the Human Body
What is the most well-known vestigial organ?
The appendix is one of the most famous vestigial organs, as it no longer serves a major role in digestion but was once important for digesting plant matter in our ancestors.
Do vestigial organs have any function?
Some vestigial organs, like the appendix and coccyx, still serve minor roles in the body. However, they are not essential for survival.
Why do humans still have vestigial organs?
Vestigial structures remain because evolution is a gradual process. As long as they do not harm survival or reproduction, there is no strong evolutionary pressure to eliminate them completely.
Do other animals have vestigial organs?
Yes. Whales have vestigial leg bones, snakes have remnants of hind limbs, and flightless birds like ostriches have vestigial wings.
Can vestigial organs disappear completely?
Over millions of years, vestigial organs can shrink or disappear if they serve no function. Some scientists predict that wisdom teeth and the appendix may eventually disappear from the human species.
