General degeneration: the meaning of the term and its brief description

The term general degeneration, proposed by the Russian scientist Severtsov at the turn of the 19th and 20th centuries, refers to the general concepts of evolution and means the loss of certain body structures. But unlike dystrophy, it occurs as a result of the development of the entire species( up to the class and type), and not in a particular individual.

The basic strategies for the development of the living

Throughout the evolution of the living world of the Earth, the unchanging principles were progress or regression. If the taxon( species, family, unit, type) could not successfully adapt to environmental change, then its development led to regress. In the case of the directly opposite situation, progress was observed.

For a better understanding, we need to dwell a little on these two terms.

Progress:

• Increase in the number of individuals of a single group. It can be not only a species or family, but even a class, a type.
• Increase of habitat( range) of representatives of these taxa.
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• Variety of species, families, orders within one superior rank. Most often, the class is meant.

The most vivid representatives of the living world today are viruses, felines, rats, mice, cockroaches. The main reasons for the prosperity of these groups lie in good plasticity - the degree of adaptability to changing habitat conditions. Rats, in general, are considered cosmopolitan animals living on all continents( naturally, including Antarctica).

Regress:

• Reduction in the number of individuals of a particular rank. Most often, speech in our time is about species.
• Decreasing the area of ​​the range.
• Depletion of taxonomic diversity of groups. There are fewer detachments in the class. The family has less and less number of genera and species. And so on.

To date, there are many examples of regression. For the most part, the reason for this is human activity.

Basic ways to achieve progress

Any biological species tends to achieve progress. Not only for prosperity. Without it, survival is impossible. There are three main mechanisms that allow species to follow a progressive path of development.

1. Aromorphosis. Changes that lead to changes in class and type characteristics. As a rule, it is the basis for the emergence of new groups. For example, the appearance of extremities, pulmonary respiration in fish as early as the Paleozoic, gave rise to amphibians and allowed the chordates to develop an anhydrous environment. The appearance of the flower in plants served as an impetus for their further evolution, which led to the creation of angiosperms.
2. Idioadaptation. Changes occurring within small groups and reflecting adaptation to certain conditions. There is no influence on large taxa. For example, narrowly specialized types of beaks of finches in the Galapagos Islands, development of fins, color of zebra and leopard. All these changes are good only for a certain locality. They lead to the appearance of small groups within a whole class, type.
3. General degeneration. Changes affect several bodies and systems. They go along the line of simplification of anatomy. However, all these changes can lead not only to the appearance of species, genera and families, but even classes of living organisms.

General degeneration and its mechanisms

This is important! Under the influence of general degeneration, a complete or partial alteration of the organism takes place in the direction of simplification. What, however, leads to the progress of the biological group. As a result, not only new species can be formed, but also other upstream groups up to the class.

Mechanisms of general degeneration can occur with the participation of one or more organs and systems. All of them occur under the influence of the environment. There are two main mechanisms.

• Simplification to achieve "saving" energy costs. For example, it happened in a group of chainworms( flatworms).Virtually all members of the family are devoid of the digestive system, and the supply of nutrients occurs through the entire surface of the body. The energy to absorb food and its digestion is not wasted.
• Simplification due to the uselessness of certain functions. This mechanism always concerns only one or several separate organs. So, among the moles there is a degeneration of the organs of vision. They just do not need it. The higher monkeys have no tail. To maintain equilibrium, he is no longer needed because of the development of the limbs. Parasitic forms of roundworms, in general, do not have sense organs.

Both these mechanisms can be implemented separately or together. The same roundworms( representatives of roundworms) have, in addition to a complete lack of vision, a poorly developed nervous system.

Despite the seemingly "backward movement", the general degeneration makes it possible for the progress of both species and larger taxa( family, squad and even class).

bivalves, having lost many of the features of the structure ancestors were able to adapt and thrive well in the second half of the Mesozoic and the Cenozoic virtually. Only man was able to actively prevent their wide distribution.

In any case, general degeneration is nothing more than one of the effective ways for the prosperity of some groups. It allows you to occupy such ecological niches, where the existence of other more highly developed( from the point of view of morphology) creatures is impossible. This, first of all, allows to reduce the intensity of competition with other animals and to "increase" their numbers before beginning expansion into other niches and / or increasing the habitat.

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