Paleontology has proven that many past species have completely disappeared.
Progress and regression in nature are opposite concepts. In the first case, the development and spread of species on the planet occurs. Biological regression is an evolutionary movement characterized by a reduction in habitat, a decrease in the number of individuals due to inadequacy. This process is accompanied by a decrease in the number of some group species in connection with the pressure on them of others, as well as the disappearance of the species.
Biological regression is mainly associated with the loss of the ability of organisms to adapt to changing environmental conditions.
This movement is characteristic of parasitic organisms, immobile individuals, and creatures living in caves or underground.
Biological regression can be considered on the example of parasites - flatworms. In the process of reverse development , their sense organs, digestive system, and nervous system are simplified. Along with this, various devices (trailers, suction cups and others) appear, which are necessary for keeping the host in the intestines. For example, a female crustacean leading a parasitic lifestyle completely lost all the signs of arthropods, retaining only the function of laying eggs. The bovine tapeworm parasitizing in the human body is capable of producing about eleven billion eggs, the protection of which is provided by the body of the host. Therefore, these worms are considered the most prolific.
Biological regression is also characteristic of plants. As in living organisms, their reverse development is closely related to parasitism. For example, there is a broomrape plant. It parasitizes on the root system of sunflower, clover, hemp. The broomrape has darkish stems, and its scaly leaves do not contain chlorophyll. They are introduced into the stem of another plant using suction cups and suck out nutrients from the host’s body.
For animals that remain motionless throughout life, the organ of movement functions exclusively during the larval stage. The chord of them is reduced. Such organisms, in particular, include the carriage drive - a representative of a separate type of brachiata. These individuals are not very similar to animals. They live on the seabed and live motionless. Pogonofora has a heart and a brain, however, her stomach and mouth are reduced. Tentacles are the respiratory system. Inside them there are long hairs equipped with blood vessels. Microorganisms gradually accumulate on them. When there are a lot of them (microorganisms), the carriagehorse pulls the hairs inward. Under the influence of special enzymes, the smallest organisms are digested and absorbed into the internal outgrowths. The presence of an embryonic intestine proves the existence of this organ in the ancestors of the pogonophora. But due to the fact that the digestion process is carried out outside the body, the digestive tract organs were reduced.
Regression of animals living underground or in caves can be considered with the example of a protea. This is a representative of the amphibian class, similar to the newt. This animal lives in caves. On the head on both sides he has external gills. Proteus can breathe both in water and on land. In the first case, he uses gills, and in the second - the lungs. Since Proteus lives in deep-sea caves, it has a serpentine shape. His body is transparent, colorless, has no pigments. In adult representatives, the organs of vision are covered with skin, larvae have rudimentary eyes. There are two pairs of underdeveloped extremities on the body of the proteus.
The genetic basis of evolutionary changes leading to a simplification of the organizational level is mutation.
In the development of the organic world there are three directions. Aromorphosis characterizes an increase in the level of organization of organisms. Idiological adaptation is an adaptation to environmental conditions without fundamental changes in the biological structure. General degeneration is a simplification of the level of organization of living things.