Atavisms and rudiments, examples of which will be considered in our article, are irrefutable proofs of the evolutionary theory of the development of living organisms. What do these concepts mean and what is the significance of their discovery for modern science?
Evidence of evolution
Evolution is the irreversible process of the development of all living things from simple to complex. This means that over time, organisms replaced each other. Each subsequent generation possessed more progressive structural features, which led to their adaptation to new living conditions. And this means that organisms belonging to different systematic units must have similar features.
For example, the forelimbs of birds and pinnipeds are composed of the same sections. This is the shoulder, forearm and hand. But since the birds are adapted to flight, this limb turns into wings in them, and in aquatic inhabitants it changes into fins. Such organs are called homologous.
Another proof of the theory of evolution is analogies. So, both insects and bats have wings. But in the former they are derivatives of epithelial tissue, and in the latter they represent a skin fold between the front and rear limbs. These organs have a different origin, but have common features of structure and functioning. This phenomenon has arisen due to a divergence of signs, or divergence.
Atavisms and rudiments, examples of which are studied by comparative anatomy, are also direct evidence of the relationship of all living things with each other.
What is rudiment?
Some organs are said to be "rudimentarily developed." This means - not enough for the full implementation of the intended functions. And indeed, rudiments are called organs that in the process of evolution have lost their original meaning. On the one hand, they are developed to a certain extent, and on the other, they are at the stage of extinction. Typical examples of vestiges are changes in the shape of the auricle and the degree of development of the muscles that surround it. Every minute our ancestors needed to listen to the approach of danger or long-awaited prey. Therefore, the shape of the shell was sharper, and the muscles provided its movement. The ability to move the ears of a modern person is unlikely to be useful in everyday life. Therefore, individuals with such skills can be found very rarely.
Examples of rudiments in humans and animals
Underdeveloped organs inherent in ancestors are found in animals quite often. Examples of rudiments are the presence of a tailbone in a person, which is the remainder of the caudal spine, as well as the wisdom teeth needed to chew on rough and unprocessed food. At this stage, we practically do not use these parts of the body. The appendix is a rudiment that humans have allegedly inherited from herbivores. This part of the digestive system secrete enzymes and is involved in the processes of cleavage, but compared with the ancestors is significantly shortened. For comparison: in humans, its average length is about 10 cm, and in a sheep or camel - a few meters.
The list of human rudiments continues the third eyelid. In reptiles, this structure moisturizes and purifies the outer shell of the eye. In humans, it is motionless, has a small size, and the upper eyelid performs the above functions. A rudiment is also a scar in the upper palate of a person - these are the rudiments of the next row of teeth, which a person does not need.
The rudiments of animals are the hind limbs of the whales hidden inside the body, and the hummer of the dipteran insect, which is a modified pair of wings. But in snakes, the limbs are not developed at all, because thanks to the features of their musculoskeletal system, the need for them is completely absent.
Rudiments: photo of plants
Plants also have rudimentary organs. For example, wheatgrass weed has a well-developed rhizome, which is an underground shoot with elongated internodes. On it, small scales, which are rudimentary leaves, are clearly visible. Since under the ground it will not be able to fulfill its main function - the implementation of photosynthesis, then their development is not necessary. The rudiment is also the rudimentary pestle in the form of a tubercle in the stamen flower of cucumbers.
What are atavisms?
Atavisms are another proof of evolution. We can say that this concept is the opposite of rudiments. Atavisms are called the manifestation in individual individuals of signs characteristic of their distant ancestors. Their presence also indicates a certain degree of kinship among several generations. In the early stages of embryo development, there is both a tail and gill sacs. If embryogenesis occurs correctly, these structures stop their development. In violation of the development process, individuals with the unusual structural features may appear. Therefore, a tailed boy and an amphibian are not just a fantasy.
Human atavisms
In addition to the appearance of the tail, typical atavisms in humans are excessive body hair. Sometimes it significantly exceeds the norm. There are cases when hair covered the entire human body, except for the palms and feet. The appearance of additional mammary glands on the body is considered to be atavism, and this can occur both in women and in men. This trait is inherited from mammals in which many children were born. At the same time, there was a need to feed all of them at the same time. A person does not have such a need.
The second row of teeth is also a trait inherent in our distant ancestors. For example, a shark has several rows. This is necessary for predators to effectively capture and hold prey. There is an opinion that microcephaly can be considered atavism. This is a genetic disease that manifests itself in a decrease in the size of the brain and skull. In this case, all other body proportions remain normal. This entails mental retardation.
Man displays some signs of animals in the form of reflexes. For example, hiccups are a typical feature of ancient amphibians. This reaction was necessary for them to pass water through the respiratory system. A grasping reflex, which is especially strongly developed in children, is a manifestation of this in mammals. They clutched at their parents' wool so as not to get lost.
Atavisms of animals and plants
Examples of ancestral traits in animals are the appearance of hair or hind limbs in cetaceans. This is evidence of the origin of these animals from extinct ungulate mammals. Atavism is also the development of extra fingers in modern horses, moving limbs in snakes and legless lizards. In primroses, an increase in the number of stamens is sometimes observed to 10. That is how many ancestors of modern plants had. Although modern species have only 5 stamens.
Causes of Evolutionary Change
As you can see, rudiments and atavisms appear in many species of plants and animals. This indicates a certain degree of kinship between representatives of different systematic units within the same kingdom. Evolutionary changes always occur in the direction of their complexity, as a result of which living organisms are able to better adapt to certain living conditions.
Having examined examples of rudiments and atavisms, we became convinced of the commonality of the organic world system and the consistency of the theory of evolution.