How to distinguish rudiments from atavisms. Rudimentary organs and atavisms in humans
Vitruvian Man, Leonardo da Vinci
The presence of vestigial organs is known to be one of the proofs of Darwin's theory of evolution. What are these organs?
Rudimentary organs are called organs that have lost their significance in the course of evolutionary development. They are laid down in the prenatal state and persist for life, in contrast to the so-called provisional (temporary) organs, which only embryos have. Rudiments differ from atavisms in that the former are extremely rare (continuous hairline in humans, additional pairs of mammary glands, tail development, etc.), the latter are present in almost all representatives of the species. We'll talk about them - the rudimentary organs of a person.
In general, the question of what is the role of rudiments in the life of this or that organism and what, in fact, should be considered as such, is still quite difficult for physiologists. One thing is clear: vestigial organs help to trace the path of phylogenesis. Rudiments show the relationship between modern and extinct organisms. And these organs, among other things, are evidence of the action natural selection, which removes an unnecessary feature. What human organs can be considered rudiments?
Diagram of the human coccyx
it lower section spine, which consists of three or five fused vertebrae. It is nothing more than our rudimentary tail. Despite its rudimentary nature, the coccyx is quite important body(as well as other rudiments, which, although they have lost most their functionality, still remain very useful for our body).
The anterior coccyx is necessary for the attachment of muscles and ligaments that are involved in the functioning of organs genitourinary system and distal departments large intestine (coccygeal, iliococcygeal and pubic-coccygeal muscles are attached to them, which form the muscle that lifts anus, as well as the anal-coccygeal ligament). In addition, part of the muscle bundles of the gluteus maximus muscle, which is responsible for hip extension, is attached to the coccyx. And we also need the coccyx in order to properly distribute physical activity on the pelvis
X-ray of wisdom teeth not growing properly
Wisdom teeth
These are the eighth teeth in the dentition, commonly referred to as the figure eight. As you know, the “eights” got their name due to the fact that they erupt much later than the rest of the teeth - on average, at the age of 18 to 25 years (some people do not erupt at all). Wisdom teeth are considered rudiments: at one time our ancestors needed them, but after the diet of Homo sapiens changed significantly (consumption of hard and hard food decreased, people began to eat food that had undergone heat treatment), and the volume of the brain has increased (as a result of which nature “had” to reduce the jaws of Homo sapiens) - wisdom teeth resolutely “refuse” to fit into our dentition.
These "hooligans" among the teeth now and then strive to grow at random, because of which they pretty much interfere with other teeth and general oral hygiene: due to the incorrect arrangement of the "eights" between them and adjacent teeth food gets stuck every now and then. And it’s not so easy for a toothbrush to get to the wisdom teeth, so they are often affected by caries, which leads to the removal of a diseased tooth. However, when correct location wisdom teeth, for example, they can serve as a support for bridges.
Remote appendix
Appendix
On average, the length of the appendage of the caecum in humans is about 10 cm, the width is only 1 cm. Nevertheless, it can cause us a lot of trouble, and in the Middle Ages, “intestinal disease” was a death sentence. The appendix helped our ancestors digest roughage and, of course, played a very important role in the functioning of the whole organism. But even today this body is not at all so useless. serious digestive function it, however, has not been performing for a long time, but it performs protective, secretory and hormonal functions.
Diagram of the muscles of the human head, ear muscles are visible above the auricles
ear muscles
They are the muscles of the head that surround the auricle. Ear muscles (more precisely, what is left of them) is a classic example of vestigial organs. This is understandable, because people who can move their ears are quite rare - much rarer than people who would not have a coccyx, appendix, etc. rudiments. The functions that the ear muscles performed in our ancestors are quite understandable: of course, they helped move the ears in order to better hear the approaching predator, rival, relatives or prey.
Scheme of the muscles of the human body
Pyramidal abdominal muscle
It belongs to the anterior group of muscles of the abdominal region, however, in comparison with the rectus muscle, it is very small in size, and appearance looks like a small triangle muscle tissue. The pyramidal muscle of the abdomen is a rudiment. It matters only in marsupials. Many people don't have it at all. For those who are the happy owner of this muscle, it stretches the so-called white line belly.
epicanthus - skin fold upper eyelid
epicanthus
This rudiment is characteristic only for Mongoloid race(or, for example, for African Bushmen - most ancient people on the planet, whose descendants, in fact, we all are) and is a skin fold of the upper eyelid, which we see with the eastern section of the eyes. By the way, it is thanks to this fold that the effect of “narrow” Mongoloid eyes is created.
The exact cause of epicanthus is not known. But most researchers are inclined to the version that the skin fold on upper eyelid arose as a result natural conditions human habitation - for example, in conditions of severe cold or, on the contrary, deserts and hot sun, when the epicanthus is designed to protect the eyes.
Scheme of the human larynx, at number 5 are the Morganian ventricles of the larynx
Morgan's ventricles of the larynx
This organ is a sac-like depression located between the true and false vocal folds on the right and left sides of the larynx. They are important for creating the so-called common resonator chamber, that is, a resonant voice. Apparently, blinking ventricles were needed by our ancestors in order to create a series of certain sounds and protect the larynx.
Some others can be attributed to rudimentary organs, in addition, representatives of certain races may have their own rudiments that are not characteristic of other races. For example, steatopygia in the aforementioned Bushmen and related Hottentots is the deposition of a large amount of fat on the buttocks. In this case, fat reserves play the same function as the humps of camels.
Comparison with animals is unpleasant for most of us. I'm not talking about diminutive nicknames like "pussy" and "bunny". I'm talking about completely innocent designations livestock and dogs, taking into account their gender, which have long been firmly entrenched in our speech as curses. Meanwhile, whether we like it or not, we are all a little animals. And a locksmith with nine classes of education, and a scientific professor - we all live, guided by ancient instincts embedded in us. Evidence of this is rudiments and atavisms. For those who nevertheless listened to this topic at school, let me remind you: atavisms are something that animals have, but, ideally, should not be found in people. However, sometimes, very, very rarely, it occurs. For example, the tail. Or webbing between fingers. And even the third breast in women. Unlike atavisms, each of us has rudiments. The most famous is the appendix. As well as the coccyx, the third eyelid, the ability to get goosebumps, and even body hair. In fact, we don’t really need all these details of the body today. But nature is not inclined to waste her time in creating useless things. Rudiments and atavisms must have a logical explanation. I wonder why in the distant past, we had all of the above attributes and why some of them have remained with us today? Are you interested too? Then read on!
wag your tail
It is almost impossible to see a tailed person today. And all thanks to the skill of surgeons - they learned to remove unnecessary processes deftly and without a trace. But there were times when people, whom nature endowed with a tail, had no choice but to wear them all their lives on the lower half of the back - where most have the coccyx.
tailed facts
In the 13th century, Marco Polo wrote that the inhabitants of Sumatra, one and all, had tails like a dog. In 1890, the scientist Paul d'Enjoy caught a member of the Indochinese Moi tribe who had a tail 25 cm long. The researcher assured that all Moi have tails, but from generation to generation the tails are getting shorter as a result of crossing with tailless neighboring tribes.
In 1848, a boy was born in Germany with a tail 10 cm long. When the boy cried, shouted, got angry, the tail moved, that is, he reacted to emotions in the same way as animals do. And in 1889, a 12-year-old boy from Thailand was described in the journal Scientific American, who had a soft tail 30 cm long.
In 1930, Dr. Velázquez of San Pedro informed the public that while swimming in the sea near San Truilo in Honduras, he saw on the beach "a Caribbean woman who threw off her clothes, revealing a tail no less than 20 centimeters long, from which one could judge that it is shortened.
The presence of a tail is considered an anomaly. And meanwhile, up to a certain point absolutely each of us possessed it. We just don't remember it. Each human fetus in the first half of pregnancy (at the end
1st and early 2nd month) has a tail. Then, if the development of the fetus goes well, the tail becomes smaller and smaller until it disappears completely. But sometimes there is a failure, and then tailed babies are born.
EXTRA DETAILS?
According to statistics, in the United States alone, 300-400 people die every year from an untimely excised appendix. Meanwhile, any surgeon will say that this operation is from the category of banal ordinary ones. In addition, it does not entail any harm to health. The appendix is not a kidney, cut out and forgotten. But if so, why is it present in our body at all? Scientists say that this outgrowth of the caecum is nothing but the legacy of our herbivorous ancestors. In animals, this sac (caecum) is much larger than in humans, and serves to facilitate the digestion of food, rich in fiber. For example, in a koala, the length of the appendix is from 1 to 2 meters! The human appendix is quite small - from 2 to 20 centimeters and is not involved in the breakdown of food. But it has a nasty habit of becoming inflamed, causing appendicitis - an inflammation of the appendix. And here, as in the case of the tail, surgeons again come to the rescue. However, there are other scientists - those who question the fact that the appendix is a rudiment in humans. They argue that people who had it removed in childhood are physically and mentally less developed than people who have it. However, this theory has not been confirmed at least, official.
WISDOM FACTOR
Those who know how painfully long and unpleasant wisdom teeth erupt will understand my indignation: why did nature leave these details if we don’t need them at all? Not only do these teeth announce their appearance when a person has long been out of childhood, they also have a disgusting habit of growing incorrectly, interfering with their "non-rudimentary" counterparts, which is why these "wise" teeth have to be removed. The same procedure, I tell you! We inherited wisdom teeth from our ancestors when the skull was shaped in a slightly different way, the jaw was much larger, and the food at that time was much tougher than what we eat today. Then the wisdom teeth served their intended purpose - they chewed. Now their presence pleases only dentists - one third of people turn to doctors with a request to remove them.
AND EARS MOVES
As a child, I was very jealous of the neighbor's boy - he knew how to move his ears! His skill did not bring any practical benefit, but how impressive it looked. But no matter how hard I tried, I could not move my ears even a millimeter. Then I did not know yet that the skill of the neighbor's boy was an atavism, which he got as a result of a small genetic mutation from distant ancestors. In ancient times, the ability to move your ears could save lives: a moving ear better captures the source of a sound - for example, a saber-toothed tiger crouching or an enemy lurking behind a tree. Animals use this ability to this day: have you noticed how the ears of a dog rise, how a prickly horse spins with its ears, how a cat listens to barely audible sounds? And to us, people, evolution denied this skill, believing that the number of dangers has already noticeably decreased. And only selected individuals have not lost the ability to set in motion their auricles.
Between pundits studying the evolution of man, the dispute has not yet been completed - whether to consider atavisms and rudiments as proof of the "animal" nature of man. And I'm thinking: even if this is so, what's offensive? After all, the animal came from the word "belly", in old Slavonic - life. And this means that every living being endowed with life is a little animal. And you, dear reader, too.
Artists and thinkers of the Renaissance, following the ancient Greeks, admired the expressive forms human body, accuracy and coordination of his movements. Admiration, even reverence sounds in the words of Leonardo da Vinci: “Consider these beautiful muscles, and if it seems to you that there are a lot of them, try, subtract, if not enough, add, but enough, praise the First builder of such a marvelous machine.” In the XVI-XVIII centuries. many researchers continued to believe that the study of nature and man is reading a book created by the Creator. It is unlikely that any of them would dare to talk about the imperfection of creation.
Is there really nothing superfluous in our body? This question was answered only in early XIX c., when data were accumulated on the structure of not only humans, but also other creatures. Comparative anatomy, which by that time had become an independent discipline, helped to understand that a person is arranged according to the same plan as vertebrate animals. (True, the project according to which God or nature created the world allowed, according to many scientists, countless variations.) Anatomists could not fail to notice that the same parts of the body - bones, muscles, internal organs at different organisms vary in size and shape. Sometimes some "details" are completely absent, sometimes they are very small and relatively poorly developed compared to similar parts in other species. Underdeveloped organs, which seemed useless, began to be called rudimentary or rudiments(from lat. rudimentum - "rudiment", "fundamental"). Apparently, this term was first used in the 80s. 18th century French naturalist Georges Louis Buffon.
Rudiments were found not only in animals, but also in humans. For example, in the inner corner of the eye there is a barely noticeable fold called the lunate. This is the remainder of the third century - nictitating membrane well developed in reptiles and birds. It serves to lubricate eyeball oily secretion secreted by a special gland. In humans, a similar function is performed by the upper and lower eyelids, so that the crescentic fold turned out to be superfluous and reduced (from lat. reductio - "return") - decreased.
Some bones, muscles, internal organs and their individual parts also turned out to be superfluous. For example, the bones of the coccyx are the remnants of the caudal vertebrae, which have grown together, decreased in size and simplified. Crow-shaped, or coracoid (from Greek"Korakoides" - "like a crow"), the bone is needed by amphibians, reptiles and birds to attach the front limbs. Mammals did without it, and in them small remnants of this bone have grown together with the shoulder blade. Mammals also lost their cervical ribs - they left a perforated transverse process of the cervical vertebrae.
A classic example of a vestigial human mouse is the ear muscles. They are well developed in many mammals and are needed to direct the auricles to the sound source. Another vestigial human muscle is the pyramidal muscle of the abdomen. And the notochord - the elastic axis, thanks to which chordate animals arose (man also belongs to their type), in people it turned into a gelatinous mass inside the intervertebral discs.
Scientists found more and more "extra organs" in humans, and the assumption of the perfection of the "crown of creation" ceased to seem unshakable. The rudiments did not remain a particular, interesting only to anatomists, but served for broad scientific generalizations. So, Charles Darwin used them as one of the proofs of the origin of man from animals. He explained the presence of rudiments by the fact that in the course of evolution some organs have decreased and almost disappeared as unnecessary. It follows from this that a person was not created once and for all perfect and unchanged, but the rudiments are only the remnants of unnecessary parts of the body that have not yet had time to disappear. The evolutionary doctrine allowed us to take a fresh look at known facts and clarify which organs in a person should be considered rudiments.
In 1902, the German anatomist Robert Wiedersheim (1848-1923) published a book in which he listed at least 107 rudimentary human organs that were not suitable for performing any function or were greatly simplified, capable of not fully functioning. Among the former are body hair, which cannot protect a person from the cold; appendix of the caecum (appendix), unable to digest coarse vegetable food; as well as the coccyx, lunate fold, remnants of the chord, etc. The list of the second includes the epiphysis - gland internal secretion. Apparently, the epiphysis is a rudiment of the parietal eye, which was in the most ancient vertebrates. Having lost its main function (vision), it acquired a new one - the production of hormones. It is believed that the most famous rudiment - the appendix is an organ of the immune system.
In addition to rudiments, scientists distinguish atavisms(from lat. atavi - "ancestors") - signs lost by man in the course of evolution and found as a rare exception. Textbook examples - thick hair on the body, tail, extra nipples. There is also a concept provisional authorities(from lat. provisor - “taking care of something in advance”): they are only in the human embryo, and then disappear; their functions are performed by other parts of the body.
The focus of modern biological science is the study of the human genome and other living beings. Data on the origin of the rudiments will probably help to find out which genes are turned on or, conversely, blocked during the development and reduction of certain organs.
In this article we will consider atavisms and rudiments: we will give their definitions and characteristics, we will give examples. It should be understood that these are not synonyms. After reading this article, you will find out what is the difference between such concepts as atavisms and rudiments.
What are rudiments?
Rudiments are not body parts that have turned out to be completely unnecessary. They have only lost, at least partially, their original purpose. Organs considered as rudiments play a certain role in the functioning of the body. Try, for example, to take away the wings of an ostrich... Without them, will this animal be worse or better? The answer is obvious: although its wings are less functional than those of other birds, the ostrich needs them. Wings, for example, allow him to maintain balance when moving.
Kakapo parrot wings
The kakapo parrot is found in New Zealand. He, like an ostrich, does not know how to fly at all. However, he has small wings, the muscles on which are atrophied, as well as an underdeveloped keel. This animal is nocturnal. He runs on the ground and loves to climb trees. Nevertheless, he still does something from the life of birds. Parrot climbing on great height, performs occasional jumps, simply using its wings for gliding. However, this jump ends most often unsuccessfully. "Bird" often flops on the ground. The parrot is not adapted to climb trees. However, this is his main occupation. But it is fully adapted for flight, since the body of this bird is identical in design to other parrots (with the exception of certain aspects). But kakapo can't fly at all. However, he tries, which sometimes ends sadly.
Are Rudiments Necessary?
Thus, rudiments can be useful, but they are always the remnants of something that was much more effective in the past. In this parrot, the wings are vestigial, as they have lost the ability (partially) to perform their former functions. Same story with the ostrich. He is no longer able to fly, but he still has wings (as well as hollow bones of the skeleton, which are typical for full-fledged birds).
Man is no exception here. We also have atavisms and rudiments. Examples of the latter are the appendix, which is certainly a useful organ. However, in our ancestors, its importance was more significant - it played a more important role in the digestion of food. Therefore, the appendix is a rudiment. But sometimes it is somewhat more difficult to determine what role rudiments and atavisms play in a person. For example, answering the question why we need molars today is no longer so simple. It is known that the pain and trouble delivered by them sometimes force us to turn to the surgeon.
The value of the appendix in the human body
One of the most famous human vestiges is perhaps the appendix. The concept of appendicitis (inflammation of this appendix). In surgical practice, interestingly, appendicitis surgery is one of the most frequent. The disease is often fraught with serious complications in the form of an abscess (an abscess of the abdominal cavity is formed) and peritonitis (covering abdominal cavity tissue is inflamed).
However, the appendix carries useful features. It maintains microbiological balance in the intestines, promotes adequate digestion, and also supports local immunity, since it contains a large number of lymphoid tissue.
What are atavisms?
One of the most important proofs of evolutionary theory are atavisms. They are quite common and today are well studied. Atavisms are signs that appear in a particular individual and do not correspond to the species common in this moment. These are traces that have been preserved due to the fact that they were once natural for an individual that was at a lower stage of evolution. She improved over time her external and functional qualities, gradually getting rid of extra signs. But traces of an individual of the old model have been preserved in the genetic code, and therefore atavisms sometimes arise. They are present from birth in an individual and cannot be formed during life. This is often hereditary.
From what ancestors can rudiments and atavisms appear?
The presence of rudiments and atavisms proves the existence of evolution. And now you will be convinced of it. Mammals, as well as birds, are without exception the ancestors of reptiles. In turn, reptiles were the ancestors of amphibians, amphibians - fish, etc. It can be argued that atavisms can appear only from our ancestors. However, parallel branches will not be able to influence each other in any way. For example, a person can have atavisms from mammals (wool, nipples, tail) and even reptiles (the so-called "snake heart"). As you probably already guessed, we also have rudiments only from mammals, amphibians, reptiles and fish. And atavisms and rudiments from parallel evolutionary branches (in our case - birds) are impossible. Also, birds will never show signs of mammals, but may show signs of reptiles. Thus, the presence of rudiments and atavisms in animals (as in humans) is not an accident, but a natural event predicted by evolutionary theory.
Atavisms in humans
Examples of atavisms in human body the following can be given.
1. An elongated coccyx, or caudal process. It appears as a result of the fact that, according to Darwin, man has common roots with an ape that possessed a tail.
2. Thick hairline. In humans, the abundance of hair on the face and body betrays signs of our ancestors. These features allowed them to exist in different climatic conditions. Such a cover began to decrease over time, but in some cases it was reformed into an atavism. This atavism is expressed in excess hair on the face (beard in women) and on the body (long thick hair).
3. There is an additional pair of nipples. The fact that man descended from a mammal is evidenced by the presence of three pairs of nipples on the body. These organs are often not functional, but there are cases when, along with the main ones, extra mammary glands also work.
Why do atavisms appear far from everyone?
Even if completely lost outward manifestation trait, the genome can still retain for a long time fragments of genetic "programs" that provided development in ancestors this feature. One of the main and, perhaps, the most delicate of the principles of regulation of the work of genes in the body is post-transcriptional control. That is, everything that the gene responsible for the development of this or that atavism has "acquired" is "cleaned up" in developing cell embryo. Thus, an unnecessary feature is not generated. However, under special circumstances (extreme effects on the embryo, mutations), these gene programs can still work. It is then that we encounter anomalies that can sometimes be deadly (for example, in the case of oval window, an unclosed atrial foramen).
The fate of the rudiments
The rudiments, genetic essence of their own, are practically "unsuppressable". Therefore, they are found in most individuals (for example, in humans - coccygeal vertebrae, molars, etc.). It is important to note that these signs usually do not cause significant harm to the individual. Perhaps they are even a potential basis for development in the future. useful feature. It can be assumed that they will be removed by evolution from genetic code quite soon. Or even not removed at all.
Thus, there is big difference between such concepts as "atavism" and "rudiment". The difference lies in the fact that rudiments appear in almost all individuals, while atavisms - only in some.
Charles Darwin's opinion
What does Charles Darwin think about this? The founder of evolutionary theory believed that atavisms and rudiments are the most important sign that people, like other creatures, evolved into other species over time. Supporters of this idea were so carried away by the search for non-working organs that about 200 of them were found in the human body. Their theories are based on this moment have been refuted. Of course, no one denies the existence of rudiments and atavisms, but here is their meaning - point of contention. It has been proven that most of these organs have a functional purpose. However, this does not exclude that genetic predisposition, due to which atavisms and rudiments are formed (their examples are not limited to those presented in this article) is inherent in every organism.
Rudiments(undeveloped organs and parts of the body) - manifestations of the evolution of nature, for example, they include the wings of a non-flying bird or the eyes of a deep-sea fish. The existence of such excesses in the body is not justified, but is steadily passed down from generation to generation. This article discusses the basic rudiments of man, and how they arose.
Coccyx
The most famous rudiment of a person who remained from ancient ancestors is coccyx(coccyx) - a triangular bone formed by the fusion of 4-5 vertebrae. Once it formed a tail - a balance organ that also serves to transmit social signals. As man became an upright creature, all these functions were transferred to the forelimbs and the need for a tail disappeared.
However, on early stages development, the human embryo has this rudiment (caudal process), which is often preserved. Approximately one in fifty thousand babies is born with a tail, which can be easily removed without consequences for the body.
Appendix
appendix of the caecum or appendix(appendix vermiformis) has long ceased to play any role in the human body and has become a rudiment. Presumably, it served for the long-term digestion of solid food - for example, cereals. The second theory is that the appendix acted as a reservoir for digestive bacteria where they thrived.
The adult appendix is between 2 and 20 centimeters long, but in most cases, its length is about ten centimeters. Inflammation of the appendix (appendicitis) is a very common disease, accounting for 89 percent of all surgical operations abdominal cavity.
Wisdom tooth
Third molars ( wisdom teeth) got their name for the reason that they erupt much later than all other teeth, at the age when a person becomes “wiser” - 16-30 years. The main function of wisdom teeth is chewing, they serve to grind food.
However, in every third person on Earth, they grow incorrectly - they do not have enough space on the jaw arch, as a result of which they either begin to sprout to the sides or injure their neighbors. In such cases, wisdom teeth have to be removed.
Synthesis of vitamin C
Vitamin C deficiency ( ascorbic acid) in the body can lead to scurvy disease with subsequent lethal outcome. However, a person cannot synthesize vitamin C in his body, unlike most primates and other mammals.
Scientists have long assumed that a person had an organ responsible for the production of ascorbic acid, but confirmation of this was discovered only in 1994. Then this human rudiment was found - a pseudogene responsible for the production of vitamin C, similar to that of Guinean pigs. But modern man this feature is disabled at the genetic level.
Vomeronasal organ (VNO)
Loss of functionality VNO can be considered one of the great evolutionary losses of man. This department olfactory system(also known as Jacobson's organ or vomer) is responsible for the recognition of pheromones.
AT social behavior animal pheromones play a dominant role. With their help, females attract males, and the gentlemen themselves mark the territory under their control. Most emotions are accompanied by the release of pheromones - fear, anger, peace, passion. A person, on the other hand, relies more on the verbal and visual components of social communication, so the role of pheromone recognition has become a vestige.
Goosebumps or goosebumps
Goosebumps(cutis anserina) occur when the pilomotor reflex is triggered. The main motives for this reflex are cold and danger. Wherein spinal cord stimulates peripheral nerve endings that lift the hairline.
So, in case of cold, raised hair allows you to keep more warm air inside the cover. If there is a danger, an increase in hairline gives the animal a more massive appearance. In humans, the pilomotor reflex remains a vestige, since the dense hairline was lost in the course of evolution.
male nipples
One of the earliest scientific theories suggested that axes for men are a sign of the ability to breastfeeding which has been lost in the course of evolution. However, later studies showed that none of the males of our ancestors had such a bodily function.
Currently, it is generally accepted that the nipples are formed at that stage of embryo development, when its sex is not determined. And only later, when the fetus begins to independently produce hormones, it is possible to determine who will be born - a boy or a girl. therefore, the nipples in men remain as a vestige.
