Vestigial Organs: What They Are and Why They Were Useful

According to natural selection, postulated by the famous biologist Charles Darwin in 1859 in his book The Origin of Species, populations evolve over generations through a process clearly modulated by environmental pressures. When a trait is heritable and beneficial to its bearer, it is expected to spread in future generations of the population. species, since the one with the adaptively viable mutation will reproduce more and extend the trait through its offspring.

Just as there are positive mutations that end up being fixed in the population, others are neutral and others are deleterious. For example, if an animal is born with one less limb, it will die faster than the rest because it cannot move properly and will surely never reproduce. In this way, the negative traits are “nipped in the bud”, while the positive ones have more likely to be fixed over time (although sometimes it is not, due to a process known as Genetic drift).

In all this evolutionary dance, sometimes some structures encoded in the genetic imprint of the species are no longer useful.

, although they continue to appear in many of the specimens of the population. Humans are not spared from this rule and, therefore, we also have some vestigial organs that will surprise you. Do not miss it.

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What is a vestigial organ?

Vestigiality is defined as the retention of a series of structures and attributes with little or no adaptive value throughout the genetic and evolutionary path of a species. An organ or vestigial structure is one that has lost its original functionality (present in the ancestors of the population) and that, therefore, currently lacks a clear purpose. The vestigial character is one that has ceased to make sense in an environmental context, that is, that it is a trait that no longer favors the balance of the individual in the pressure mechanisms selective.

In any case, a vestigial organ does not have to be bad per se. If the character shows a clear negative bias, the living beings that carry it will die sooner, so the selection natural "will rush" to remove it from the population gene pool before it poses a long-term problem. term. If the character is neither bad nor good and its presence does not require a quantifiable or significant investment, it may remain for generations without disappearing. This is the case of vestigiality in humans.

Humans have deviated from the typical selective pressures of the environment thousands of years ago, and thus many traits that were once essential are now of no apparent use. However, zoologists also operate on the following premise: an apparently vestigial trait can take on other minor functions or, failing that, present a purpose that we have not yet discovered. Therefore, one must have certain reservations when talking about vestigiality.

What are the main vestigial organs in humans?

Despite the scientific debate that these structures provoke, there are a series of organs and physiological configurations in our species that do not seem to have a concrete utility today. Here are the most common ones.

1. Wisdom teeth

Dental agenesis is defined as the absence of teeth due to isolated or syndromic genetic alterations. In our species, agenesis of one of the third molars is present in 20-30% of the population, so we move from pathology to the terrain of evolutionary adaptation.

It has been proven that third molars were a fixed feature in the hominids that preceded us, since the mandibular skeletons of our ancestors have a longer mandibular size with space for more teeth. It is stipulated that this was due to a diet much more inclined to the consumption of plants and fruits, since a greater degree of Grinding of food is necessary with vegetables to compensate for our difficulty in digesting the cellulose.

The absence of third molars has been associated with mutations in the PAX9 gene, which are heritable. For this reason, the percentage of dental agenesis is very different among the age population analyzed: for example, indigenous Mexicans present absence of the third molar in 100% of the cases.

2. Vermiform appendix

According to scientists, the vermiform appendix (a cylindrical organ with no outlet connected to the intestinal cecum) is another clear vestigial structure present in humans. Many mammals have hyperdeveloped blind men, such as horses, which can enclose up to 8 gallons of organic material, occupying much of the left abdominal area of ​​the animal. In equines, this structure serves to store water and electrolytes, as well as to promote the digestion of cellulose and other plant compounds with the help of symbiotic bacteria.

As in the previous case, the reduction of the appendix over the centuries in humans could be an indication of a transition from a diet with a large herbivore component to one more based on meat, fruits and plant foods rich in carbohydrates (such as rice or cereals). As our species has been selecting easily digestible foods, the cecum could have been dwindling due to heritable mutations, which would give rise to this portion of small size and apparently useful null.

3. Vomeronasal organ

The Jacobson's organ, also known as the vomeronasal organ, is an auxiliary organ in the sense of the smell in some vertebrates, such as snakes and some mammals, located between the nose and the mouth. In those species with which we share a taxon, the vomeronasal organ is associated with a pump to attract pheromones and other compounds related to chemical communication.

In humans, the existence of a vomeronasal organ is still under debate. According to several studies, this occurs in up to 60% of the corpses during autopsies, but it is argued that its location and designation could be the product of an anatomical error. In any case, it seems that there is no connection between this structure and the human brain, so if it exists in our anatomy, it is stipulated that it would be vestigial.

4. Musculature of the ears

As you see it: it is stipulated that some structures of the ears could be considered vestigial. In many mammals, the musculature in the area is very strong and versatile, which allows the animal to position its pinna in the direction of the sound to better perceive it. Since most humans do not possess this ability, it is believed that some of the ear muscles have atrophied to the point of not having any functionality.

5. Coccyx

Along with the wisdom teeth, the coccyx is the vestigial structure par excellence. This bone, formed by the union of the lower vertebrae of the spinal column, is a remnant of the tail of our mammalian ancestors. Human embryos have an observable tail during the first weeks of gestation (being more evident in 33-35), but is later modified to give rise to the endings of the column that we know.

Although the coccyx corresponds to the tail of many mammals, in our species it is not entirely useless, since it serves as a point of muscular insertion. For this reason, it has not disappeared from human physiology today.

Final annotations

Although all the above seems very clear, it should be noted that the vestigiality of these structures still remains under scrutiny to this day. The fact that the function of an organ has not been discovered does not mean that it does not have it in all cases, it can do some minor work imperceptible to humans with scientific methods current. For example, some believe that the vermiform appendix could serve as a remnant of the gut microbiota.

In any case, if one thing is clear, it is that these organs are not entirely harmful, since otherwise they would have disappeared from the human gene pool hundreds of years ago. Their presence appears to be completely harmless and therefore they are neither positively nor negatively selected.