The human body is not perfect. While we have great intelligence and can perform quite well in nature, many parts of our organism do not seem to have an obvious role.
These structures are known as vestigial organs, which must have been useful to us at some point in the history of evolution, but today, their function has disappeared, and they have been atrophying.
Next, we will delve into the vestigial organs and how the theory of evolution explains their existence and the human body’s best known.
What are vestigial organs?
Vestigial organs are organic structures that do not appear to fulfil any important biological function in the organism that possesses them. These structures are preserved as an inheritance of the evolutionary process. At some point in the history of evolution, an ancestor of the current species had that structure, useful and functional. Still, over the years, it must have become important and would end up atrophying. Thus, vestigial organs can be seen as the “leftovers” of evolution.
This type of organ, which can also be bones, structures in the skin or any other part of the body, no longer offers any significant body function. They can also cause problems and be unadapted because they are structures prone to infection, such as appendix (appendicitis) or fracturing, as would be the case with the vertebrae that make up the tailbone. In the human case, the vestigial organs that we still preserve have them because evolution has not had time to make them disappear.
How does evolution intervene?
Among many other tests, vestigial organs in animals are the most irrefutable proof that evolution exists. Natural selection is the force behind the process since they are the remnants of it. The theory of intelligent design, defended by creationist sectors, does not make sense. If humans and other species have been created perfectly, what is the need to preserve useless organs?
According to Charles Darwin’s evolutionary theory, set out in his book The Origin of Species (1859), all species that exist today on Earth come from the same living being, our common ancestor. This ancestor, which had to be very simple, evolved, giving rise to other species more complex and better adapted to the environment’s needs. As a result of the different adaptations, we can see the diversity of species found today.
It is extracted from this theory that if a characteristic is not adaptive in nature, it may disappear because the individuals who possess it do not get to reproduce because they have a disadvantage, or are preserved but progressively atrophying. The latter is because, in the case of no evolutionary pressure on this character, the organ in question is not used and is developing a devouring function. This Darwinist idea 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 earlier Aristotle would look at the eyes of animals of underground life, such as moles, which made no sense for them to have them since they were rarely in contact with sunlight. What’s the point of having eyes in a place where you can’t see them?
But the most noteworthy antecedent to Darwin is Jean-Baptiste Lamarck. This French naturalist considered that a fundamental principle governed evolution: the frequent and sustained use of an organ makes it gradually strengthened, giving it a power proportional to its use duration. Thus, the organ that has been little used or is deprecated will eventually weaken. For example, according to Lamarck, moles’ eyes would have been losing functionality over generations because this species does not need them.
Although the Lamarckian thesis was quite important today, we know 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 meet the environment’s demands. If the individual has a structure that disadvantages him, he will most likely have more trouble reproducing than those who either do not have it or have the right version.
Since all living things come from an apparent ancestor, it is quite easy to find vestigial structures shared by an immense number of species. As we have mentioned, vestigial organs are only ancient organs that were functional, but species are no longer functional in the current carrier. This process is called “involution” and implies that less biological efforts are put in place to keep that structure active. This loses its functionality, shrinks in size and atrophy.
The vestigial organs of the human body
There are many vestigial organs in the human body, so many that the debate about how many are exactly still open. It is estimated that it could be 86, but there have also been classifications in which more than 180 vestigial organs have been spoken of.
This is because you cannot always be sure that an organ has completely lost its functionality, as it may be reminiscent of its ancestral function. However, the scientific community agrees that the 10 structures we will see below can be considered vestigial organs.
The vermiform appendix is the most well-known vestigial organ. Its fame is because, despite being such a small structure, appendicitis occurs if infected, a serious disease that is surgically extracting the appendix can die if not treated in time.
The appendix is attached to the large intestine and has an elongated shape, such as a kind of finger-shaped pojain projected from the colon to the abdomen’s right side.
It is thought that the appendix is what remains of an organ used by our herbivorous ancestors to digest cellulose. This function has lost it in our species because we no longer consume leaves from trees, from the richest foods in this substance.
As we moved on to a diet with more meat, fruits and legumes, the appendix became irrelevant to our survival, making as generations passed increasingly atrophying as it was not of fundamental importance to our digestion.
Despite this, some believe that it could really have some function. It has been said that it could be involved in the immune response, at least indirectly. It has also been hypothesized that it could be responsible for maintaining the intestinal flora.
The coxis (or coccyx) is the final part of the spine. It consists of the last four vertebrae that are small in size and lack mobility and, from birth, are fused.
This structure has no functionality, at least apparently. By contrast, the anterior part of the tailings, which also does not have mobility, plays an important role in transmitting movement to the pelvis.
Its evolutionary origins are quite ancient, being found in the most primitive monkeys. Coxis is thought to be the result of progressively losing the tail, a structure that is common in most vertebrates. Thus, our tail coxis would be an involution of the tail.
The sinuses are hollow cavities found in our skull. They are like air pockets in our heads and, although some say that they could have as a function that of resonance chamber or to release weight from the skull, the truth is that they appear to be vestigial structures that, above, give serious problems.
The paranasal breasts can develop into the home of bacteria or other pathogens with a freeway to access this structure and become well isolated. When this happens, the breasts become infected, and sinusitis occurs a respiratory disease.
There is no evolutionary point in having a structure that, in addition to not exercising a clear function, is prone to infection. However, they should have been useful to the animals from whom we have inherited them, the sauropsids. These large reptiles needed these cavities to shape their skull.
The semilunar stem is a small crease found in the eye conjunctiva, the membrane that surrounds the eye. It is located in the eye’s inner corner and looks like reddish tissue protruding between the eyelids. Although it facilitates eye movement and helps maintain eye drainage, they are considered vestigial organs.
It appears to come from a structure that fulfilled other functions in our ancestors and has involved: the third eyelid or nictitating membrane. This membrane is common in birds and reptiles, consisting of a translucent eyelid that lubricates the eye and cleans it without closing the eyes and losing vision briefly.
Rear atrial muscle
The posterior atrial muscles, which are located behind the ear, are muscles considered vestigial. Most people cannot move them at will and, in the event of power, their muscles are still very atrophy.
These ear muscles have been inherited from the basal primates, who did need to have a good ability to move the ears at will to locate the sounds well.
In the human case, this capacity was lost since our species’ auditory ward has evolved well enough to detect the origin of the sounds without having to move them.
Phalanxes of the small toe
The phalanges of the small toe are tiny bones and lacking mobility. Compared to the other toes’ phalanxes, they are highly involuted, so they are considered vestigial bones. Their origins lie in our primate ancestors, who could move the small toe more freely.
Wisdom teeth are considered vestigial organs since they do not fulfil any important function. Also, they risk having cavities very easily and are not well integrated into our physiognomy. It makes no sense that, from puberty, our wisdom teeth grow, hurting us and, in many cases, needing to be removed to maintain good oral hygiene.
These teeth are a legacy of our primate ancestors, especially those who consumed roots (rizóphages). These animals needed much larger, stronger teeth to chew the hard roots, which were fundamental food in their diet.
Due to the changes in nutrition that occurred at some point in our evolutionary history the first hominids were needing 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 the wisdom teeth.
The nipple is an essential structure for females since it breastfeeds their young and feeds them when they are too small to consume solid foods. This is the only biological purpose of the nipple, so it makes no sense for males to possess them. Thus, the male nipple is a vestigial organ.
A few million years ago, body hair was essential to keep hominids living in cold climates warm. With changing temperatures and migrating to warmer climates, body hair lost its usefulness, making owning a lot or owning little not an important factor in surviving.
While in certain parts such as the arms, legs, back and chest it doesn’t seem to perform a significant function, it’s useful elsewhere. An example of this is eyebrow hair that prevents sudo from entering the eyes, while facial hair is considered a secondary sexual character for reproductive purposes to attract females.
The erector pili is a muscle group near the hair follicle responsible for lifting hair in situations of danger or fear, that is, for making us have “goose skin”. It is believed that his primary function was to make us look bigger in the face of an animal threat, to intimidate and frighten him. However, when we lost hair, this function ceased to make sense, and we have been left as a vestigial mechanism.
- 7 Vestigial Features of the Human Body
- 5 Useless Body Parts
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- Vestigial organs (scienceoxford.com)
- West-Eberhard, M. J. (2003). Developmental plasticity and evolution. Oxford University Press.