Extinction of Species

(of plants, animals, microorganisms), a phenomenon that occurs during the process of development of living nature during the earth’s geological history. Extinction of organic forms takes place as a result of natural selection in the presence of essential changes in the external environment in those instances when organisms do not have time to adapt to these changes or when even insignificant changes in the conditions of existence lead to a hindrance of the species’ propagation. Thus, extinction is an important part of the evolution of living nature.

The history of the organic world shows that an enormous number of forms have become extinct. G. Cuvier and his followers tried to explain extinction by the theory of catastrophes. Refuting this theory, J. B. Lamarck asserted that all species that had disappeared had not become extinct but had been regenerated into new ones. In the beginning of the 19th century, the Italian paleontologist G. Brocchi mistakenly supposed that species, like individuals, have a definite life expectancy and die upon reaching a known “age.” Other hypotheses attempted to explain extinction by a change of some single factor in the environment—for example, a general cooling or warming of the climate or a strengthening or weakening of solar radiation.

Only Darwinism explains extinction in accordance with the facts of the history of the organic world. C. Darwin showed that the extinction of organic forms is caused by changes in the surrounding environment, during which not only changes of the abiotic factors of the external environment (those pertaining to the inorganic world) have enormous significance, but so do biotic factors (interspecies relations). A rapid change of environment can be a direct cause of the extinction of species occupying a limited land or water territory. Forms and groups of forms that are widely distributed (such as those living simultaneously in all the oceans or on a majority of the earth’s continents) do not become extinct everywhere. The final extinction of certain species is often prolonged, so that they can be preserved in limited regions because of local favorable conditions (usually biotic). The existence of relict forms is connected with this process. V. O. Kovalevskii developed and extended the Darwinian concept of extinction on the basis of paleontological facts by showing that one of the most important conditions for extinction is inadaptive evolution.

In connection with swift technical progress and the continual growth of population, one of the most important biotic factors that directly or indirectly condition the extinction of many species is the activity of man.