Vestigial organs: characteristics and 6 examples

A Vestigial organ Is an organ that was once useful in the evolutionary past of an animal, but which becomes useless or very close to useless. The list of vestigial organs in humans has been reduced from 180 in 1890 to 0 in 1999.

It can also be considered a vestigial organ to any part of an organism that has diminished in size during its evolution because the function that served has diminished in importance or became totally unnecessary.

Vestigial organs

Classic definition

The most common definition of a vestigial organ throughout the last century was similar to the following:

" Living creatures, including man, are virtual museums of structures that have no useful function but represent remains of organs that once had some use. A vestigial organ is defined as one that has lost its function in the course of evolution, and is usually very small in size" .

Dorland's Dictionary defines the term vestigial as"vestige, vestige or relic,"and defines the term as"the remnant of a structure that functioned in an earlier stage of a species." Churchill's Dictionary defines vestigial as an organ that has no"obvious function"and points out that the word vestigial derives from the Latin vestigium, which means trace or trace.

A standard biology dictionary defines the word vestigial as follows:

" An organ without function and generally reduced in size, but that has some similarities with the fully functional organs found in related organisms. Examples include the wings of birds that can not fly, snake tip girdles, appendages and ear muscles of humans, and scale leaves of parasitic flowering plants. It is believed that the presence of vestigial organs indicates that the organism's ancestors had fully functioning organs."

Asimov provides two examples of a vestigial organ: (1) the tiny bones posterior to the sacrum, called coccyx (which Asimov claims were for a tail); And (2) the small muscles around the ears (which Asimov claims are 'muscles that are supposed to move the ears'). As we will see, these conclusions are not based on empirical evidence but on evolutionary assumptions.

In the past, evolutionists claimed that there were approximately 180 vestigial organs in humans, including the appendix, tonsils, and thymus. Now we know that:

  • The appendix is ​​part of the immune system, strategically located at the entrance of the ileum, with its normally high bacterial content.
  • The tonsils have a similar function at the entrance of the pharynx.
  • The thymus is part of the immune system, related to T cells. HIV attacks T cells, making them ineffective and for this reason is always fatal.

The number of organs that were once believed to be functional in the evolutionary past of humans, but do not work today has been steadily reduced as the fields of anatomy and physiology have progressed.

The idea of ​​vestigial organs in human beings is also discussed in popular books on science and medicine, whose authors often admit that common examples are no longer considered valid. Tonsillectomy has been the most frequently performed piece of surgery.

The doctors once thought that the tonsils were simply useless evolutionary leftovers and pulled them out thinking that it could not hurt. There is considerable evidence today that there are more problems in the upper respiratory tract after tonsil removal than when the tonsils were present.

Definition of revisionists

The creationists' assertion that there are no vestigial organs in humans generally refers to the most common definition that has been used during the last century, not to the problematic definition, more recently used by evolutionists in an attempt to Save the idea. Vestigial organs are those that have 'reduced function' compared to their use in some vague, indefinite past.

According to the revisionists' definition, a vestigial structure is:

"Any part of an organism that has declined in size during its evolution because the function it served declined in importance or became totally unnecessary." Examples: The human appendix and the wings of the ostrich.

Another source defines a vestigial structure as"any organ that during the course of evolution has been reduced in function and usually in size". This revisionist definition of"reduced in size and function"is not justified for several reasons.

For example, how much reduction is required before the 'vestigial' label is appropriate? Is 30% a sufficiently large reduction, or will a reduction of 1% suffice? In addition, there are so many examples of"reduced size"(and sometimes function) that the"vestigial"label loses meaning.

For example, an analysis of the skull morphology of our supposed evolutionary ancestors would lead us to the conclusion that our jaw is vestigial, compared to that of our presumed ancestors, as it is alleged by evolutionists to be comparatively less in beings (And also has a reduced function, at least in relation to its resistance and ability to chew food). In fact, as a result of our smaller jaw, some of our teeth (eg, teeth of judgment) are said to be vestigial.

This definition of vestige would also require the conclusion that, because the outer nostrils (the nostrils) are smaller in modern humans (compared to hypothetical simian-like ancestors), they should also be labeled as vestigial. Many people have trouble breathing partly because their nostrils are too small, as is obvious from the widespread use of nasal bridge expansion units and nasal sprays.

This is also illustrated by the frequency of rhinoplasty surgery, especially surgery to repair a deviated septum. No evolutionist has claimed that our jaws or nostrils are vestigial, however, according to the revisionists' definition, they would clearly be vestigial structures.

On the other hand, since the human jaw, eyes, eyebrows, forehead ridges, forelegs, nose, ears, eyes and even mouth could be labeled vestigial, the term obviously loses meaning when Defines this way.

The illustrations of textbooks of our presumed ancestors consistently show them with thick skulls and large prominent crests of forehead that serve to protect their eyes. Therefore, our skulls and front bridge would be vestigial.

Why natural selection would cause these structures to diminish in size in modern humans is never discussed (especially since the selection would seem to do the opposite). Evolutionists even use the lack of forehead ridges in humans as an example of poor design.

For example, Colby concluded that the"human skull is too thin to provide adequate protection to the giant brain and the absence of ridges of the forehead leaves eyes poorly protected." Also, on average, muscle mass, organ function and strength have declined in modern humans, no doubt because of the lack of use due to life in modern society.

According to the revisionists' definition, aging only produces vestigial organs in practically all human beings. If the definition of a vestigial organ is less developed in a modern animal (compared to an ancestor) due to mutations of loss, adaptation, etc., all the organs in modern humans that were more developed in our supposed ancestors would be vestigial.

This means that if macroevolution was true and if humans evolved from inferior animals, it could be argued that virtually all structures in modern humans are vestigial because vestigial organs are defined as those which are somewhat less useful today than in past.

A rare exception would be the human brain, and even the brain could be claimed as vestigial size if we accept Neanderthals as our ancestors. Neanderthals, on average, had a larger brain than modern humans: about 1,500 cc compared to 1,300 cc for humans today.

Probably the best example of this definition of vestigial structures is the ability of some bacteria to digest the most common organic compound in the soil, cellulose. Cellulose is the main component of plants (grass, leaves, wood and bark of the trees are mainly cellulose). The only reason many animals (including cows, horses, sheep, and termites) feed on grass and wood is because they have a symbiotic relationship with certain bacteria that are able to digest cellulose.

However, evolutionists postulate that higher organisms lost the ability to digest cellulose. Thus, most modern animals have a vestigial system of cellulose metabolism. If humans possessed this ability, starvation and increased malnutrition would be a thing of the past.

Famine and malnutrition have been major problems throughout history, and even today it is estimated that 60 percent of the world's population is malnourished. Evolution, it seems, should select the ability to metabolize cellulose, and would certainly select against those forms of life that lost this ability.

The revisionists' definition of vestige also requires that the evolutionary history of an animal be known, when, in fact, the evolutionary history of most living beings is often largely speculative. In addition, the vestige judgment is based on evaluations of modern examples of monkeys, rabbits, other animals and humans. These judgments can not be based on our present evolutionary ancestors for several reasons.

Although many fossil bone fragments have been found, no well-preserved mammals (or mammalian organs) have been found that are estimated in 1,000,000 or even 50,000 years. Therefore, only modern examples can usually be used to compare them. The example of Asimov:

" In certain animals that eat plants, the blind is a great storage place where food can be broken down by bacteria so that the animal can digest them and absorb them more easily. The appendix in man and apes (which happens in almost no other animal) is what remains of that great blind man. It indicates that the close ancestors of man and apes fed on plants. The appendage, then, is the useless remainder of an organ, once useful; It is a vestige, from the Latin 'vestigium' (footprint). Just as a trace is a sign that a man once passed by, so a trace is a sign that a useful organ once passed by ".

The example often given to support this conclusion is the modern human appendix, which is judged vestigial when compared to an animal having a larger appendix (like the modern rabbit). However, modern humans and modern rabbits, modern humans and our royal ancestors, are something to be compared, something that can only be estimated by examining the extant fossil remains of our ancestors (most of which are fragments of Bone distortions).

Much can be learned about an animal from fragments of bone, but little can be determined about organs, organ tissues, cellular structures and most other key biological aspects of life because there are no examples in the fossil record. The only criterion for making judgments about the evolution of the organ is the examination of modern animals (such as the rabbit).

However, the definition of another revisionist suggests that any"organ or structure lacking a function related to the survival of the animal"should be labeled vestigial. In fact, all organisms have a large number of structures that fit this definition.

Such structures can not be explained by natural selection for the simple reason that they do not confer any known survival advantage. Examples are everywhere, and in humans include the ability to create music, song and dance. Even in the plant world there are many examples of structures that can not be explained by natural selection. Some plants with modern flowers (like dandelions) are self-pollinating and therefore have no need for flowers. According to the definition of"lack of function for survival", they would be vestigial.

conclusion

Evolutionists have never explained how and why so many structures could exist in humans (such as the complex structures that allow music, singing, and dance) that do not confirm any survival advantage yet delight millions. Only creation can explain this observation. The clear conclusion is that the concept of evolutionary vestigial organs is useless, or largely speculative.

Vestigiality

There has been speculation about the nature of seemingly useless physical features in living beings for thousands of years. However, it was not until the late eighteenth and early nineteenth centuries that the idea of ​​vestigiality penetrated the public imagination through the writings of a pair of French naturalists and Darwinists, Étienne Geoffroy Saint-Hilaire and Jean-Baptiste Lamarck.

Darwin would naturally redefine the field of human biology about half a century after his work"On the Origin of Species,"but this time with his second book,"The Decline of Man"of 1871, where he listed several of The structures we know today as vestigial for the first time, including the appendix, the tailbone and the teeth of judgment.

Examples of vestigiality

By adjusting to the evolutionist idea of ​​vestigiality we can give these examples existing in human beings:

1- Goose skin or piloerection

Goosebumps are activated reflexively by a series of stimuli, including fear, pleasure, wonder, nostalgia, and cold. The mechanism causing the reaction, piloerection, causes the tiny muscles at the base of each body hair to contract, causing a small shock.

The reflex played a crucial role in the fight or flight response of our human evolutionary ancestors, who were covered with body hair: Straight hairs could make primitive man appear larger before his predators, so that goose bumps could Perhaps avoid the threat.

Although piloerection remains a useful defense for many animals (think of an annoying porcupine or a cornered cat), humans, having long lost most of our body hair, retain it almost exclusively as an emotional response.

2- Unintended or discarded DNA

This term refers to portions of our human genome for which no functional role has been discovered. Although controversial, many scientists believe that much of our DNA exists simply as remains of some purpose that served for a long time.

Among the DNA sequences in our body, a good portion of them have traces of genetic fragments called pseudogenes and transposons, indicating a defect in the strand that could have been caused by a virus or some other mutation incurred in the course of our evolution.

Like any vestigial structure, we keep parts of this genetic material because it's really not causing any problems: Century after century, scrapped DNA is doubled and transmitted, even when it no longer has any use.

Plica semilunaris

This small fold of skin in the corner of the eye is a vestige of the nictitating membrane, essentially a third eyelid. This third eyelid is still present in birds, reptiles, and fish, as a fully functional structure, is translucent and its function is to help protect and clean the cornea.

At one point primitive humans stopped using that third eyelid but retained a small piece along with their associated (also vestigial) muscles. The semilunaris is one of a handful of vestigialities that are more pronounced or prevalent in certain ethnic groups, in this case, Africans and indigenous Australians.

4- Muscles

As we have evolved, having to rely less on our physical ability, a number of muscles throughout the body have lost usefulness. This category of vestigiality is strongly determined by ethnic origin.

The lower occipital, for example, is a thin muscle, with bands at the base of the skull that works to move the scalp. All Malays are born with it, half of all Japanese, and a third of Europeans, but never present in the Melanesians.

The occipital joins the auricular muscles, which once allowed us to move our ears to better listen to predators, but now have no function. Other vestigial muscles include palmaris longus, the tendon that tightens the lower wrist when the hand is tightened; The pyramidalis in the abdomen, which 20 percent of all humans no longer have and planting in the leg, still slightly helps in knee flexion, but whose contribution is so trivial that it is best known as a tendon Surgeons often remove to graft in other areas of the body compromised by injuries.

5- Smell

Let's call our vestigial smell. Although we obviously still use it every day, its role and role in humans is greatly reduced from what it once was. Animals with the keenest sense of smell are still dependent on it to track food, to avoid predators, or for mating purposes.

Since we now have grocery stores, there are no natural enemies, and smell is more a feature of convenience at this point (although there is evidence that pheromones may play a role in human interaction). However, smell can still help in survival, for example, by alerting to a toxicity that is invisible, such as a gas leak.

6- Reflection palmar prensil

It is the ability of newborns to grasp anything. This ability was used by our ancestors' newborns when we were still covered in hair, to cling to their mother's shelter and was also a useful skill in case the mother had to avoid a danger, the baby clung to the mother That he could have both hands free to escape, perhaps climbing a tree.

The reflex is also active on the feet, which is noticeable in the way the baby's feet curl when seated. Both reflexes usually disappear around six months.

References

  1. Kampwirth, K. (2013). Surprising Examples of Human Vestigiality. Website: http://mentalfloss.com/article/50302/6-surprising-examples-human-vestigiality. 18-1-2017
  2. Valenti, P. (2016). Vestigial Organs. Website: http://www.amnh.org/exhibitions/darwin/evolution-today/how-do-we-know-living-things-are-related/vestigial-organs/. 18-1-2017.
  3. Wieder-Sheim, R. (2013). Remains of the past in Homo Sapiens. Website: http://deloposiblesesabedemasiado.blogspot.com/2013/04/restos-del-pasado.html. 18-1-2017.
  4. Live Science Staff. (2012). 5 Useless Body Parts. Website: http://www.livescience.com/21513-vestigial-organs.html. 18-1-2017.
  5. Bergman, J. (2016). Do any vestigial organs exist in humans? Website: http://creation.com/do-any-vestigial-organs-exist-in-humans. 18-1-2017.
  6. Miller, B. (2005). Vestigial Organs. Website: http://www.livescience.com/11317-top-10-useless-limbs-vestigial-organs.html. 18-1-2017.

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