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Severtsov, Aleksey Nikolaevich

SEVERTSOV, ALEKSEY NIKOLAEVICH

(b. Moscow, Russia, 11 September 1866; d. Moscow, 16 December 1936),

comparative anatomy, evolutionary morphology

Severtsov spent his early childhood in the village of Petrov, Voronezh gubernia, with his father, N. A. Severtsov, a zoologist and explorer, and his mother, S. A. Severtsova. He received his secondary education in a private gymnasium. After his graduation in 1885, Severtsov entered the department of physics and mathematics at Moscow University. Severtsov’s teachers were M. A. Menzbir, I. M. Sechenov, K. A. Timiryazev, and V. V. Markovnikov.

While a student Severtsov, with P. P. Sushkin, entered a department competition on the organization and taxonomy of the Apoda and was awarded a gold medal. In 1895 Severtsov defended his master’s dissertation, “O raxvitii zatylochnoy oblasti nizshikh pozvonochnykh v svyaz: s voprosom o metamerii golovy” (“On the Development of the Occipital area of the Lower Vertebrates in Connection With Metameres of the Head”). For the next three years he worked in the marine biological stations at Banyuls-sur-Mer, Villefranche, and Naples, and in the zoological laboratories at Munich and Kiel. The research done abroad was included in his doctoral dissertation, “Metameria golov elektricheskogo skata” (“Metameres of the Head of the Torpedo Ray”), which he defended in 1898. Severtsov did scientific and administrative work at Dorpat (now Tartu, Estonian S.S.R.), where from 1898 to 1902 he occupied the chair of zoology, then at Kiev (1902–1911), and at Moscow (1911–1930).

In 1930 Severtsov founded at Moscow University a laboratory of evolutionary morphology that later became the Institute of Evolutionary Morphology (now the A. N. Severtsov Institute of Evolutionary Morphology and Animal Ecology). In recognition of his scientific contributions he was elected an academician of the Soviet Academy of Sciences and of the Academy of Sciences of the Ukrainian S.S.R.

Severtsov chose comparative anatomy as his specialty, for he early recognized the necessity of extending morphology and evolutionary theory. Rather than study morphological regularities of evolution however, for a long time he limited himself to problems of comparative anatomy and phylogeny. His classic research on metameres of the vertebrate head (1895) revealed the evolution of the head. Severtsov devoted a number of works to explaining the origin and evolution of the pentadactylic limbs of terrestrial vertebrates arose from the many-rayed fins of fish. In 1926 and 1934 he supplemented this conclusion with the idea that the fins had originated from the lateral folds. Clarifying the course of vertebrate phylogenetic development also was facilitated by Severtsov’s research on the origin of the osseous scales and the evolution of the osseous skull arose from the osseous rhombic scales of the cutaneous cover. Severtsov also investigated the origin of the maxillary apparatus the branchial skeleton, and breathing organs in fish.

Using material obtained through his own work and that of his pupils, Severtsov attempted to restate the evolution of the lower vertebrates in three articles (1916, 1917, 1925). He considered the lower cartilaginous fish, the basic groups of osseous fish, and the ancestors of land vertebrates. Severtsov proposed uniting Ostracodermi with the Cyclostomata in one group of ancient agnathous vertebrates. He tried to re-create the structure of the ancestors of the vertebrates–the primary Acrania and Gnathostomata, ancestors of agnathous and gnathostomatous vertebrates– and to draw a family tree of the lower vertebrates. The first two parts of “Issleddovania ob evolyutsii nizshikh pozvonochnykh” (“Research on the Evolution of the Lower Vertebrates”) were awarded the K. E. Baer Prize in 1919.

In 1910 Severtsov presented a report at the Twelfth Congress of Russian Natural Scientists and Physicians that defined the purposes and methodology of the evolutionary morphology of animals. In it he pointed to the scarcely touched area of research opened after the discovery of the biogenetic law by Haeckel, the principle of change of function by A. Dohrn, the law of substitution by N. Kleinenberg, and the phyletic correlation and certain other regularities of evolution.

Supporting the materialistic view of the evolution of the organic world. Severtsov denied the concepts of vitalism and autogenesis. Without Knowledge of the laws of evolution, he held, it is impossible to understand either the laws of individual development or the laws of life in general. Opposing a dogmatic interpretation of Darwin’s theory, he favored a bold posing of new problems and the introduction of new ideas. Severtsov devoted twenty-five years to the realization of this program. The result was the strict theory of the morphological regularities of evolution, the nucleus of which was the theory of phyloembryogeny and the morphobiological theory of evolution. Having rehabilitated the Darwinist principle of the variability of all ontogenetic stages in the process of evolution, Severtsov investigated modes of phylogenetic transformation of ontogenesis and their influence on the character and tempo of evolution. The theory of phyloembryogeny helped to overcome the limitation of the two opposing points of view: that ontogeny is a function of phylogeny, and vice versa. Severtsov saw the evolution of form and the evolution of ontogeny as mutually interacting processes.

Severtsov first studied the relations of ontogeny and phylogeny. The lively polemic concerning the theory of the gastraea, the theory of embryonic layers, problems of homology, and other phylogenetic questions indicated that the biogenetic law and theory of recapitulation in the form given by Haeckel was unsatisfactory for explaining the correlation of the individual and historical development of organisms. Turning from isolated consideration of the traditional Haeckelian treatment and to give a new basis to the phenomenon of recapitulation in terms of his own theory of phyloembryogeny.

According to the latter, evolutionary changes arise through changes in the first stages of ontogeny (archallaxis), changes in the intermediate stages (deviation), and the addition of new final stages (anabolism). Thus this theory rehabilitated and supplemented the Darwinian principle of variations in all stages of ontogeny during evolution with concrete morphological data.

According to the theory of phyloembryogeny, the biogenetic law is the consequence of evolution by means of anabolism. Archallaxis and deviation limit the completeness of recapitulation. Severtsov showed that Baer’s law, which asserted that the characteristics of small systematic groups appear late in ontogeny while the signs of larger systematic groups appear early, was not a general rule. He related the development of characteristics of animals in a determinate order to anabolic evolution, and viewed Baer’s statement that characteristics of large systematic groups appear in the early stages of ontogeny as the consequence of the anabolic divergent monophyletic evolution.

The theory of phyloembryogeny also can be viewed as a morphological theory of ontogenetic evolution. Severtsov proposed an addition to it in 1934: the hypothesis of ontogenetic evolution of many-celled animals was invoked as an aid in determining the origin and regularity of development of modes of phyloembryogeny. Severtsov considered anabolism the primary method of ontogenetic evolution and the reason for the origin of primary recapitulation. His hypothesis assumed that ontogenetic evolution was completed in the early stages, not only through “piecing” of stages but also by means of archallaxis, deviation, and heterochronism. These secondary modes changed the linear order of stages of ontogeny and caused a reduction in recapitulation. Severtsov also included conogenesis in the regular processes of ontogenetic evolution. showing the irregularity of its opposite, polygenesis.

The study of the relationship of ontogeny and phylogeny on the level of the whole organism, of separate organs, and of tissues showed the universality of the theory of phyloembryogeny. First formulated on the basis of the study of vertebrates, this theory was later recognized in the morphology of vertebrates, the morphology of plants, histology, physiology, and anthropology.

Darawin’s theory presented evolution as a gradual progressive increase in organization, a replacement of lower forms by higher. Darwin gave a basically correct but also highly general solution to the problem of the development of species. His followers—T. H. Huxley, M. Neumayr, Mechnikov, V. O. Kovalevsky—continued the analysis of this problem. Ideas on progress that were alien to Darwinism were widespread, however; the mechanical-Lamarckian theory of ontogeny and autogenetic views. There was no coherent theory showing the basic trends of progress in the organic world from a Darwinian point of view. Severtsov’s morphological theory of evolution filled that lack.

According to Severtsov (1925, 1931), biological progress occurs by means of a general increase in the life activity of the organism (aromorphosis), individual adaption (idioadaption or adaptation in the narrow sense), embryonic adjustment, and morphophysiological regression (for example, the transition to parasitism). In all but the first case the level of organization does not rise (and in the case of morphophysiological regression it is lowered); but, because it is better adapted to the conditions of existence, the group of organisms that is retarded in development gains the opportunity to compete successfully with more highly organized forms. Thus the existence of both highly organized and primitive forms among contemporary fauna is explained.

Using the theory of phyloembryogeny and the studies of the main directions of the evolutionary process, Severtsov closely associated the methods of the phylogenetic transformation of organs (“methods of transition,” according to Darwin) with his hypothesis of correlation. According to this theory, in evolution a few characteristics change at first through heredity; the remaining characteristics and the organism as a whole then change in correlation with these primary changes. His hypothesis served as the basis for the solution of the problem of mutual adaptation (coadaptation) of organs in phylogenesis.

With the appearance of evolutionary morphology, work proceeded on the problem of reduction. Severtsov provided a detailed concept of the courses of reduction, distinguishing the sequential shedding of the final stages of development during the decrease in original formation of the organ (rudimentation) and the reduction of a normally formed organ until it disappears completely (aphanisia).

Severtsov limited his investigations to morphological regularities of evolution and to the routes by which the evolution of form and structure was achieved. Nevertheless, he clearly saw and upheld the tendency to synthesize the data and generalizations achieved by descriptive and experimental biology. Thus he understood and stated that a complete theory of the relation of individual development and evolution cannot be constructed exclusively from morphological material. In his opinion such a theory could be created only by synthesizing the data of evolutionary morphology, genetics, mechanics of development, and ecology. His prognosis was justified: in the 1930’s and 1940’s Severtsov’s student I. I. Shmalgauzen achieved such a synthesis, creating the theory of the organism as a whole in its individual and historical development and the theory of the course and regularities of the evolutionary process.

BIBLIOGRAPHY

I. Original Works. Severtsov’s works have been collected in Sobranie Sochinenii, I. I. Shmalgauzen and E.N. Pavlovsky, eds., 5 vols. (Moscow-Leningrad, 1945–1951). His basic writings are “O razvitii zatylochnoy oblasti nizshikh pozvonochnykh v svyazi s voprosom o metamerii golovy” (“On the Development of Occipital Area of the Lower Vertebrates in Connection With Metamers of the Head”), in Uchenye zapiski Moskovskogo universiteta, Nat.-hist. cl. (1895), no. 2, 1–95; Ocherdi pa istorii razvitia golovy pozvonochnydh (“Sketches in the History of the Development of Vertebrate Head”; Moscow, 1898); “Evolyutsia i embriologia” (“Evolution and Embryology”), in Dnevnik XII Sezda russkikh estestvoispytateley i vrachey (“Daily Journal of the XII Congress of Russian Natural Scientists and Physicians”; Moscow, 1910), 262–275; Etyudy po teorii evolyutsii (“Studies in the Theory of Evolution”l Kiev, 1912); Sovremennye zadachi evolyutsionnoy teorii (“Contemporary Problems in Evolutionary Theory”; Moscow, 1914); “Issledovania ob evolyutsii nizshikh pozvonochnykh” (“Research on the Evolution of the Lower Vertebrates”), in Russkii arkhiv anatomii, gistologii i embriologii, 1 , no. 1 (1916), 1–114; no. 3 (1917), 503–656; and 3 , no. 2 (1924), 279–360-the first two parts are available in French as “Études sur l’évolution des vertébrés inférieures. I. Morphologie du squelette et de la musculature de la tête des Cyclostomes” and “II. Organisation des ancêtres des vertébrés actuels,” in Archives russes d’anatomie, d’histologie et d’embryologie, 1 , no. 1 (1916) and no. 3 (1917); Glavnye napravlenia evolyustsionnogo protsessa (“Main Trends in the Evolutionary Process”; Moscow 1925); Morphologische Gesetzmässigkeiten der Evolution (Jena, 1931); and Morphologicheskie zakonomernosti evolyutsii (“Morphological Regularities in Evolution”; Moscow—Leningrad, 1939).

II. Secondary Literature. See B. S. Matveev and A. N. Druzhinin, “Shinsn i. tvorchestvo A. N. Severtsova” (“Life and Word of Severtsov”), in Pamyati akademika A. N. Severtsova (“Memories of Academician Severtsov”), I (Moscow—Leningrad, 1939); L. B. Severtsova, Aleksey Nikolaevich Severtsoc (Moscow-Leningrad, 1946; 1951); and I. I. Shmalgauzen, Nauchnaya deyatelnost adademika A. N. severtsova kak teoretika evolyutsionista (“Scientific Activity of Severtsov as Evolutionary Theorist”), in Pamyati akademika A. N. Severtsova, I.

E. Mirzoyan

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