Lamarckism(redirected from Lamarckian evolution)
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the first integrated theory of the evolutionary development of living things, the basic ideas of which were propounded by J. B. Lamarck in his Philosophy of Zoology (1809).
At the basis of Lamarckism is the notion of gradation—an internal “striving toward perfection” inherent in all living things. It is the action of this factor that determines the development of living nature—a gradual but undeviating increase in the organization of living beings, from the simplest to the most advanced. The result of gradation is the simultaneous existence in nature of organisms of different degrees of complexity, in effect forming a hierarchical ladder of living things. Gradation can readily be traced in a comparison of representatives of the major taxonomic categories, such as the classes, and in the most important organs. While considering gradation to be a reflection of a basic tendency of natural development, sown by the “supreme creator of all existence,” Lamarck nevertheless attempted also to offer a materialist treatment of the process: in a number of instances, he connected the increasing complexity of organization to the effect of certain “fluids,” such as “thermogen” and electricity, that penetrate the organism from the external environment.
Another factor of evolution, according to Lamarck, is the constant influence of the external environment, which leads to the disruption of regular gradation and brings about the diversity of adaptations to external conditions. Change in the environment is the principal cause of species formation: as long as the environment remains unchanged, species preserve their constancy, but a shift in the environment brings about a species change. Lamarck consciously delimited these factors of evolution, pointing out that “permanent abilities” in an organism correspond to the first of the factors (gradation) and “abilities subject to change under the influence of the surroundings” correspond to the second (environmental change).
The external environment acts directly on plants and lower animals, which lack differentiated nervous systems, and leads to adaptive changes. Animals that do possess a nervous system experience the influence of the environment indirectly, and their evolutionary transformations take a more complex path. Any amount of significant change in external conditions leads to a change in the requirements of the animals living in the given locality. A change in these requirements entails a change in the habits directed toward their satisfaction, and a change in habits leads to the intensified use of certain organs and the nonuse of others. Most often, the functioning organs are strengthened and developed, and the unused organs become weak and disappear. The functional and morphological changes that develop are transmitted to the offspring and become stronger with each generation. Thus, according to Lamarck, function plays a leading role in the evolutionary transformation of organisms: a change in form is a consequence of a change in function.
Lamarck elevated his position on the exercise and nonexercise of organs and on the inheritance of acquired characters to the level of universal laws of evolution. The untenability of both of these “laws” was proved experimentally as early as the beginning of the 19th century, and especially at the beginning of the 20th century, by the advances in genetics.
In his late works (1815 and 1820), Lamarck brought both of his factors of evolution substantially closer to one another, regarding the environment both as a force that disrupts gradation and as a fundamental factor in evolution. Accordingly, he connected the origin of the main branches of the genealogical tree to the influence of concrete life conditions.
Lamarck grounded his theory on the facts that there are varieties that occupy an intermediate position between two species; that there are difficulties in diagnosing closely related species; that there are in nature numerous “doubtful species”; that changes in species occur after the groups are transferred to other ecological and geographic conditions; and that there exist cases of hybridization (especially of an interspecies nature). Lamarck also regarded the discovery of fossil forms, of changes in animals upon domestication, and of changes in plants upon cultivation as important evidence of the transformation of species.
In developing his concepts of evolution, Lamarck came to the conclusion that there are no real boundaries between species. This led to a denial of the very existence of species. The breaks observed in the natural series of organic forms (which makes it possible to classify them) are only apparent disruptions—explained by the incompleteness of our knowledge—in a single, continuous chain of organisms. Nature, in his opinion, represents a continuous series of changing individuals. For the sake of convenience of classification, taxonomies artificially break up that series into separate taxonomic groups.
This sort of notion of the fluidity of species forms stood logically connected to the treatment of development as a process lacking interruptions or jumps (flat evolutionism). The rejection of the natural extinction of species follows: fossil forms, according to Lamarck, do not die out, but, having changed, continue to exist in the aspect of extant species. The existence of the lowest organisms, which would seem to contradict the idea of gradation, is explained by their continual self-generation from nonliving matter. According to Lamarck, evolutionary changes cannot be observed directly in nature only because they occur very slowly, incommensurate with the relative brevity of human life.
Lamarck extended the principle of evolution to the origin of man, although, under the conditions of the prevailing theory of creationism, he was forced to mask his convictions. He believed that man was descended from the apes. He included the transition to an erect posture and the development of speech among the factors involved in the origin of man. Lamarck also took a historical approach to the highest manifestations of life activity—consciousness and the human psyche—connecting their development to the evolution of the nervous system and its highest division, the brain.
Although Lamarck did not give an explanation for organic expediency and did not discover the true cause of evolutionary development, he was the first to proclaim the principle of evolution itself as a general law of life. Hurling a bold challenge at the notions of the immutability of species that prevailed at the time, he was one of the first to make the problem of evolution a subject of special study and research. It is for these reasons that Lamarck earned the high esteem of the classical Marxists.
Lamarckism was never recognized among Lamarck’s contemporaries and, after the death of its creator, the theory seemed consigned to oblivion. A rebirth of the theory, in the form of neo-Lamarckism, occurred during the last third of the 19th century as a reaction to the spread of Darwinism.
REFERENCESMarx, K., and F. Engels. Soch, 2nd ed., vol. 20, pp. 343–626.
Poliakov, I. M. Zk.-B. Lamark i uchenie ob evoliutsii organicheskogo mira. Moscow, 1962.
Packard, A. S. Lamarck, the Founder of Evolution. New York, 1901.
Rostand, J. Aux Sources de la biologie, 4th ed. Paris, 1958.
V. I. NAZAROV