The evolution

theories.

By the term of evolution is meant the development of natural and social occurrence. Some negligible and invisible changes occur evolutionary. The evolution theory gives us the explanation of historical development of living things.

In this assay I try to describe the development of the main evolution conceptions from the ancient times to now days. The beginning and development of life have always been a matter of people’s concern and interest. Rather than the theory of evolution, we should speak of several theories of evolution. On the one hand, this plurality has to do with the different explanations advanced for the mechanism of evolution, and on the other, with the various philosophies on which it is based.

Before atheory can be included in the system of science, it must meet all of the following criteria:

1. its ability to explain what has been observed;

2. its ability to predict what has not yet been observed; and

3. its ability to be tested by further experimentation and to be modified as required by the acquisition of new data.

These definitions mean that a scientific theory is not used, as people often use the word theory, to mean a hunch or a guess. A scientific theory is held with a high degree of confidence and is supported by enough evidence to make its abandonment unlikely. As new evidence is found, a theory may be modified but only with compelling evidence, verification and peer review. The business of science is to build theories that explain how the natural world works and can predict how it might work in the future.

Let’s take a look at the most prevailing theories.

After more than two thousand year old history of science development in ancient Greece, Rome, China and India the European countries fall into dark middle ages, a pitch darkness for natural science. People were burnt on fire not only for telling the ideas of life development, but also for reading books of ancient natural scientists and philosophers. Violent implementation of religion makes science a church appendage. The Renaissance appeared a real breakthrough in the sphere of natural science.

The ideas of evolution begin to appear in the works of some philosophers and natural scientists. In 1646-1716 the gradation principle was declared by Leibnitz who divined the existence of intermediary forms between plants and animals. Hereafter, the principle of gradation has been amplified in conception of “the ladder of beings”, which became a picture of ideal continuity of formation for some and confirmation of evolution of living things for others.

Fairly, this theory had the right to exist. But, in my opinion, it is not reliable in now days because of its primitive.

By the 18^th century, scientists have gone through a great deal of work collecting and describing plants and animals throughout the world. But it started to become more and more difficult to orient oneself in the ocean of information that they’d cumulated. A Swedish naturalist Karl Linney has colligated and systemized the data. He laid a foundation of modern systematic.

In order to classify the great amount of plant and animal descriptions a specific systematic unit was needed. Linney thought the genus is the unit. Genus was called a group of persons that shared the same qualities. The genus consists of the variety of kin persons that gives plentiful offspring. For example, a wild raspberry is a specific genus, strawberry is another genus and cranberry is a third genus. All the domestic cats make up an independent genus, tigers do, too and so on. Therefore, all the organic world consists of different genera of plants and animals. All the living nature consists of somewhat like the separate elements, the genera.

It is hard to agree with this theory as well because the modern stage of biology evolution makes it clear that the genus cannot be the only unit of systematic. Because of the religious influence on science at that time can be concluded that Linney was an idealist. He insisted that in nature there are plants and animals species just as many as the God has created at the very beginning of the world. So, I cannot agree to this point.

A French scientist Lamark is known as the first biologist who tried to develop a complete theory of life evolution. He introduced the term of gradation as an internal force of improvement inherent to all living things. By the act of this factor of evolution defines the development of living nature and constant improvement of organization of beings from the simple forms to the most developed ones. According to Lamark, all animal and plant classes are being constantly changed and improved in their organization as a result of influence of external environment and some kind of internal tendency of improvement. All the organisms were allocated by Lamark to 14 different classes and put in the ladder of beings in specific order:

1. protista and polypus;

2. radiant and worms;

3. insects and spiders;

4. crustacea and annulates;

5. shellfish;

6. fish, reptiles, birds and mammals.

This theory is more substantial than the previous ones. For his time period Lamark has very successfully developed the question of species change under influence of natural causes and noted the importance of time and environmental conditions in evolution process, which was accounted as demonstration of a blanket law of natural development. The merit of Lamark is that he was the first one to announce the genealogical classification of animals according to the kinship principle.

Speaking of the Evolution theory it would be wrong to avoid the great work of Darwin. Charles Darvin lived in the time of rapid society development when natural science was on the up-grade. There were many scientific inventions. The epochal work “Origins of species” has been republished seven times during the author’s life. It became known to many scientists from other countries and has been translated into the majority of European languages. The driving forces of evolution, according to Darwin, are heritable change and natural selection. Evolution theory says that all living things are related to one another through common ancestry from earlier forms that differed from the present forms. According to the theory, variability among individuals in a population of sexually reproducing organisms is produced by mutation and genetic recombination. The mutation becomes a base of new words of organisms structures and functions formation, and the heritance anchors them. The resulting genetic variability is subject to natural selection in the environment.

Despite the popularity of that theory, I cannot call it the absolutely right, as well. Darwinism is discredited by the lack of prognoses and unability to forecast new facts. Darwinism turned out to be very appealing to the materially oriented scientific society of 19^th century because this evolution conception alleged to eliminate supernatural ideas of ancestry. It seems to me that the appeal of Darwinism is that it uses pure mechanistic explanations for the evolutionary process allowing the appeal to the term of contingency.

The account of all the system of modern evolutionary biology is a compositive evolution theory, the principal case of which have been established by the works of Chetverikov, Fisher, Holdane, Dubinin and etc. The elementary cell of a compositive evolution theory is a population. The elementary particle of heredity is a gene. The hereditary change of population in a particular way happens under influence of evolutionary factors, such as the mutation process, population waves, isolation and natural selection. The first place in the compositive evolution theory belongs to population, not to ontogenesis. This theory, in my opinion, is the most perfect. It is more integral in theoretical and terminological views. It might be related to the ability of this theory to systemize in itself variety of terms and reflect the full system of evolutionary process.