Vestigial organs of the human body: what they are, and 10 examples.

A summary of what vestigial organs are and why we have them.

The human body is not perfect. While we possess great intelligence and can perform quite well in nature, there are many parts of our body that do not seem to have a very clear function.

These structures are known as vestigial organsThese structures are known as vestigial organs, which at some point in evolutionary history must have been useful to us, but nowadays their function has disappeared and they have atrophied.

Next we will deepen in the vestigial organs, how the theory of the evolution explains its existence and which are the most known of the human body.

What are vestigial organs?

The vestigial organs are organic structures that do not appear to serve any important Biological function in the organism that possesses them.. These structures are preserved as an inheritance of the evolutionary process, because at some point in the history of evolution an ancestor of the present species had such a structure, which was useful and functional, but over the years it must have ceased to be important and would eventually atrophy. Thus, vestigial organs can be seen as the "leftovers" of evolution.

These types of organs, which can also be bones, structures in the skin or any other part of the organism, no longer offer any significant function for the organism. In addition, they can cause problems and can be maladaptive, they can be problematic and maladaptive, because they are structures prone to become infected, as would be the case of the appendix.as would be the case of the appendix (appendicitis) or to fracture, as would be the case with the vertebrae that form the coccyx. In the human case, the vestigial organs that we still have are there because evolution has not had time to make them disappear.

How does evolution intervene?

Among many other evidences, 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 remnants of it. The theory of intelligent design, defended by creationists, does not make sense because, if human beings and other species have been created perfectly, what is the need to preserve organs that are useless?

In accordance with Charles Darwin's evolutionary theory, set forth in his book The Origin of Species (1859), all species existing on Earth today come from the same living being, our common ancestor. This ancestor, which must have been very simple, evolved, giving rise to other species that were more complex and 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 extracted 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 it is conserved but progressively atrophies. it progressively atrophies. The latter would be due to the fact that, since there is no evolutionary pressure on this character, the organ in question is not used and develops an increasingly lesser function. This Darwinian idea would explain the existence of vestigial organs.

It must be said that Darwin was not the first to observe the existence of vestigial organs. Darwin was not the first to observe the presence of vestigial organs in animals.. Thousands of years earlier Aristotle would look at the eyes of subterranean living animals, such as moles, which made no sense to have them since they were rarely in contact with sunlight.

But the most remarkable 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 makes it grow stronger little by little, giving it a power proportional to the duration of its use. Thus, an organ that has been little used or is in disuse will eventually weaken. For example, according to Lamarck, the eyes of moles would have been losing functionality with the passing of generations because this species does not need them.

Although Lamarckian theses were quite important in his time, we know today that they are not entirely true. It is not the lack of use that promotes the weakening of an organic structure, but how adapted or functional it is to face the demands of the environment. structure, but rather how adapted or functional it is to cope with the demands of the environment. If the individual has a structure that gives it a disadvantage, it is more likely that it will have more problems to reproduce than those who either do not have it or have the appropriate version.

Since all living beings come from the same 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 old organs that were functional but are no longer functional in the current carrier species. This process is called "involution", and implies that less biological effort is expended to keep the structure active. Thus, it loses its functionality, reduces in size and atrophies.

The vestigial organs of the human body

There are many vestigial organs in the human body, so many that the debate on 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 it is not always possible to 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 we will see below can be considered vestigial organs.

1. Appendix

The vermiform appendix is the best known vestigial organ.. Its fame is due to the fact that, despite being such a small structure, in case of infection it causes appendicitis, a serious disease that if not treated in time by surgically removing the appendix, one can die.

The appendix is attached to the large intestine and has an elongated shape, like a finger-like pouch that projects from the colon to the right side of the abdomen.

The appendix is thought to be what remains of an organ used by our herbivorous ancestors to digest cellulose. This function has been lost in our species because we no longer consume leaves from trees, which are among the foods richest in this substance.

When we switched to a diet with more meat, fruits and legumes, the appendix ceased to be important for our survival, causing it to atrophy more and more as the generations went by, as it no longer had a fundamental importance for our digestion.

Despite this, there are those who believe that it might actually have some function in our digestion.. 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 in charge of maintaining the intestinal flora.

2. Coccyx

The coccyx (or coccyx) is the final part of the spinal column. It is formed by the last four vertebrae that have a small size and lack mobility and, from birth, are fused.

This structure has no functionality, at least apparently. On the other hand, the part anterior to the coccyx, which also lacks mobility, does seem to play an important role in transmitting movement to the pelvis. to the pelvis.

Its evolutionary origins are quite ancient, being found in the most primitive monkeys. It is believed that the coccyx is the result of the progressive loss of the tail, a structure that is common in most vertebrates. Thus, our coccyx would be an involution of the tail.

3. Paranasal sinuses

The paranasal sinuses are hollow cavities located in our skull.. They are like air pockets in our head and, although some say that they could have the function of 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 the home of bacteria or other pathogens that have free access to this structure and remain well isolated. When this happens, the sinuses become infected and sinusitis, a respiratory disease, is produced.

It makes no evolutionary sense to have a structure that, in addition to not having a clear function, is prone to become infected. However, they must have been useful to the animals from which we have inherited them, the sauropsids.. These large reptiles needed these cavities to shape their skulls.

4. Plica semilunaris

The plica semilunaris is a small fold found in the ocular conjunctiva, that is, the membrane surrounding the eye. It is located in the inner corner of the eye Although it facilitates eye movement and helps maintain eye drainage, it is considered a vestigial organ.

Apparently it comes from a structure that served other functions in our ancestors and that has involuted: 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 the eyelids. and clean it without having to close the eyes and lose vision briefly.

5. Posterior auricular muscle

The posterior auricular muscles, which are located behind the ear, are muscles considered vestigial. Most people cannot move them at will and, if they can, their musculature is still very atrophied..

We have inherited these ear muscles from the basal primates, who did need to have a good capacity to move their ears at will in order to be able to locate sounds well.

In the human case, this capacity was lost since 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, they are very 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 are at risk of decay very easily and are not well integrated into our physiognomy. It makes no sense that, after puberty, our wisdom teeth grow, hurting us and, in many cases, need to be removed to maintain good oral hygiene. to maintain good oral hygiene.

These molars are a legacy of our primate ancestors, especially those that consumed roots (rhizophagous). 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, to the point that the human jaw evolved to such an extent that it was not adapted to accommodate 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, it makes no sense for males to possess 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 the change in temperatures and migration to warmer climates, body hair was essential to keep hominids living in cold climates warm, body hair eventually lost its usefulness, making having too much or too little of it an unimportant factor in survival..

While in certain parts such as the arms, legs, back and chest it does not seem to serve a significant function, in other parts it is useful. An example of this is eyebrow hair that prevents dirt 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, i.e. making us have "goose bumps". It is believed that its original function was to make us look bigger in the face of an animal threat, in order to intimidate and scare it.in order to intimidate and frighten it. Sin embargo, al perder vello esta función dejó de tener sentido, y nos ha quedado como un mecanismo vestigial.

Referencias bibliográficas:

• Smith, H.F., Wright, W. (2018) Vestigial organs. Springer Nature Switzerland.
• Müller, G.B. (2002) Vestigial organs and structures. Encyclopedia of Evolution.
• Kabir, A. (2018) Human Vestigial Organs: Hidden Parts in Medical Science. CPQ Medicine
• Audesirk, T., Audesirk, G., & Byers, B. E. (2003). Biología: La vida en la Tierra. Pearson educación.
• Campbell, N. A., & Reece, J. B. (2007). Biología. Ed. Médica Panamericana.
• Conrad, E. C. (1983). True vestigial structures in whales and dolphins. Creation/Evolution, 10, 9-11.
• Dao, A. H., & Netsky, M. G. (1984). Human tails and pseudotails. Human pathology, 15(5), 449-453.
• West-Eberhard, M. J. (2003). Developmental plasticity and evolution. Oxford University Press.