According to natural selection, postulated by the famous biologist Charles Darwin in the year 1859 in his book The Origin of Species, populations evolve over the course of generations through a clearly modulated through a process that is 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 species, since the one with the adaptively viable mutation will reproduce more and spread the trait through its offspring.
Just as there are positive mutations that eventually become 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 will not be able to move properly and will certainly never reproduce. In this way, negative traits are “nipped in the bud,” while positive traits are more likely to become fixed over time (although sometimes they are not, due to a process known as genetic drift).
In all this evolutionary dance, sometimes some structures encoded in the genetic blueprint of the species cease to be useful, although they continue to occur in many species.Although they are still present in many of the specimens of the population, we humans are not spared from this evolutionary dance. Humans are not exempt 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 number of structures and attributes with little or no adaptive value throughout the genetic and evolutionary trajectory of a species.. A vestigial organ or structure is one that has lost its original functionality (present in the ancestors of the population) and therefore lacks a clear purpose today. A vestigial character is one that has ceased to have meaning in an environmental context, i.e., it is a trait that no longer favors the individual’s balance in the mechanisms of selective pressures.
In any case, a vestigial organ need not be bad per se. If the trait shows a clear negative bias, living beings carrying it will die earlier, so natural selection will “hurry” to eliminate it from the population gene pool before it becomes a long-term problem. If the trait is neither bad nor good and its presence does not require a quantifiable or significant investment, it is possible for it to remain for generations without disappearing. This is the case with vestigiality in humans.
Humans have deviated from the typical selective pressures of the environment thousands of years ago and, as a result, many traits that were once essential now have no apparent utility. However, zoologists also operate on the following premise: an apparently vestigial trait can take on other, lesser functions or, alternatively, present a purpose that we have not yet discovered.. For this reason, we must have certain reservations when speaking of vestigiality.
What are the main vestigial organs in humans?
Despite the scientific debate about these structures, there are a number of organs and physiological configurations in our species that do not seem to have a specific use 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, the agenesis of one of the third molars is present in 20-30% of the population, so we move from pathology to the field of evolutionary adaptation.
It has been proven that third molars were a fixed trait in the hominids that preceded us, since the mandibular skeletons of our ancestorsThe 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, as a greater degree of food grinding is necessary with vegetables to compensate for our difficulty in digesting 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, Mexican Indians present absence of the third molar in 100% of the cases.
2. Vermiform appendix
According to scientists, the vermiform appendix (a cylindrical dead-end organ connected to the intestinal cecum) is another clear vestigial structure present in humans. Many mammals have overdeveloped cecums, such as horses, which can contain up to 8 gallons of organic material, which causes it to occupy a large part of the animal’s left abdominal area. In equids, 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 symbiont bacteria.
As in the previous case, the reduction of the appendix over the centuries in humans might be indicative of a transition from a diet with a large herbivore component to one more based on meats, fruits and plant foods rich in hydrogen.and carbohydrate-rich plant foods (such as rice or cereals). As our species has been selecting easily digestible foods, the cecum could have been shrinking due to heritable mutations, which would give rise to this portion of small size and apparently null utility.
3. Vomeronasal organ
Jacobson’s organ, also known as vomeronasal organ, is an auxiliary organ in the sense of smell in some vertebrates, such as snakes and some mammals, located between the nose and the mouth. In those species with which we share taxon, the vomeronasal organ is associated with pumping 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, it is present in up to 60% of corpses during autopsies, but it is argued that its location and designation could be the result 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
Just as you see it: it is stipulated that some structures of the ears could be considered vestigial. In many mammals, the musculature of the area is very strong and versatile, allowing 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 muscles of the ears have been ear muscles are thought to have atrophied to the point atrophied to the point of not possessing any functionality.
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 spine, is a vestige of the tail of our mammalian ancestors. Human embryos present an observable tail during the first weeks of gestation (being more evident in 33-35 weeks), but then it is modified to give rise to the endings of the spine that we know.
Although the coccyx corresponds to the tail in many mammals, in our species it is not entirely useless, since it serves as a muscular insertion point for the tail.. For this reason, it has not disappeared from human physiology to this day.
Although all of the above may seem very clear, it should be pointed out that the vestigiality of these structures is still 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 one in all cases, as it may perform some minor jobs imperceptible to humans with current scientific methods. For example, some believe that the vermiform appendix could serve as a remnant of intestinal microbiota.
In any case, if one thing is clear, it is that these organs are not entirely harmful, otherwise they would have disappeared from the human gene pool hundreds of years ago. Their presence appears to be completely innocuous and, therefore, they are neither positively nor negatively selected.