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the science that deals with living things. It is broadly divided into zoologyzoology,
branch of biology concerned with the study of animal life. From earliest times animals have been vitally important to man; cave art demonstrates the practical and mystical significance animals held for prehistoric man.
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, the study of animal life, and botanybotany,
science devoted to the study of plants. Botany, microbiology, and zoology together compose the science of biology. Humanity's earliest concern with plants was with their practical uses, i.e., for fuel, clothing, shelter, and, particularly, food and drugs.
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, the study of plant life. Subdivisions of each of these sciences include cytology (the study of cells), histology (the study of tissues), anatomy or morphology, physiology, and embryology (the study of the embryonic development of an individual animal or plant). Also included in biological studies are the sciences of genetics, evolution, paleontology, and taxonomy or systematics, the study of classification. The methods and attitudes of other sciences are brought to the study of biology in such fields as biochemistry (physiological chemistry), biophysics (the physics of life processes), bioclimatology and biogeography (ecology), bioengineering (the design of artificial organs), biometry or biostatistics, bioenergetics, and biomathematics. Evidences of early human observations of nature are seen in prehistoric cave art. Biological concepts began to develop among the early Greeks. The biological works of Aristotle include his observations and classification of his large collections of animals. The invention of the microscope in the 16th cent. gave a great stimulus to biology, broadening and deepening its scope and creating the sciences of microbiology, the study of microscopic forms of life, and microscopy, the microscopic study of living cells. Among the many who contributed to the science are Claude Bernard, Cuvier, Darwin, T. H. Huxley, Lamarck, Linnaeus, Mendel, and Pasteur. See marine biologymarine biology,
study of ocean plants and animals and their ecological relationships. Marine organisms may be classified (according to their mode of life) as nektonic, planktonic, or benthic. Nektonic animals are those that swim and migrate freely, e.g.
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See T. Lenoir, The Strategy of Life (1989); C. A. Villee et al., Biology (3d ed. 1989); N. A. Campbell, Biology (3d ed. 1993).


A natural science concerned with the study of all living organisms. Although living organisms share some unifying themes, such as their origin from the same basic cellular structure and their molecular basis of inheritance, they are diverse in many other aspects. The diversity of life leads to many divisions in biological science involved with studying all aspects of living organisms. The primary divisions of study in biology consist of zoology (animals), botany (plants), and protistology (one-celled organisms), and are aimed at examining such topics as origins, structure, function, reproduction, growth and development, behavior, and evolution of the different organisms. In addition, biologists consider how living organisms interact with each other and the environment on an individual as well as group basis. Therefore, within these divisions are many subdivisions such as molecular and cellular biology, microbiology (the study of microbes such as bacteria and viruses), taxonomy (the classification of organisms into special groups), physiology (the study of function of the organism at any level), immunology (the investigation of the immune system), genetics (the study of inheritance), and ecology and evolution (the study of the interaction of an organism with its environment and how that interaction changes over time).

The study of living organisms is an ongoing process that allows observation of the natural world and the acquisition of new knowledge. Biologists accomplish their studies through a process of inquiry known as the scientific method, which approaches a problem or question in a well-defined orderly sequence of steps so as to reach conclusions. The first step involves making systematic observations, either directly through the sense of sight, smell, taste, sound, or touch, or indirectly through the use of special equipment such as the microscope. Next, questions are asked regarding the observations. Then a hypothesis—a tentative explanation or educated guess—is formulated, and predictions about what will occur are made. At the core of any scientific study is testing of the hypothesis. Tests or experiments are designed so as to help substantiate or refute the basic assumptions set forth in the hypothesis. Therefore, experiments are repeated many times. Once they have been completed, data are collected and organized in the form of graphs or tables and the results are analyzed. Also, statistical tests may be performed to help determine whether the data are significant enough to support or disprove the hypothesis. Finally, conclusions are drawn that provide explanations or insights about the original problem. By employing the scientific method, biologists aim to be objective rather than subjective when interpreting the results of their experiments. Biology is not absolute: it is a science that deals with theories or relative truths. Thus, biological conclusions are always subject to change when new evidence is presented. As living organisms continue to evolve and change, the science of biology also will evolve. See Animal, Botany, Cell biology, Ecology, Genetics, Immunology, Microbiology, Plant, Taxonomy, Zoology



Biology is the group of sciences concerned with living nature. The subjects of biological studies are all the manifestations of life: the structure and functions of living things and their natural communities; their distribution, origin, and development; and their relations with each other and with inanimate nature. The task of biology is to study all the biological laws and to uncover the essence of life and its manifestations in order to comprehend and control them. The term “biology” was suggested independently in 1802 by two scientists—the Frenchman J. B. Lamarck and the German G. R. Treviranus. It is sometimes used in a narrow sense similar to the concepts of ecology and bionomy.

The principal methods of biology are observation, which permits the description of a biological phenomenon; comparison, which makes it possible to find the laws common to different phenomena (for example, of individuals of a single species, different species, or all living things); experimentation, during which the investigator artificially creates a situation that helps to disclose the deeper properties of biological objects; and the historical method, which makes it possible to discern the development of living nature on the basis of data pertaining to the present-day organic world and its past. It is impossible to draw a rigid boundary line between these principal methods of research in modern biology. The once justified division into descriptive and experimental biology has now lost its value.

Biology is closely related to many sciences and to man’s practical activity. It uses chemistry, physics, mathematics, and many technical and earth sciences (geology, geography, geochemistry) to describe and investigate biological processes. Thus, biological disciplines allied to other sciences (biochemistry, biophysics, and so on) and sciences in which biology is a constituent (for example, soil science, which includes the study of the processes that take place in soil under the influence of soil organisms; and oceanology and limnology, which include the study of life in oceans, seas, and fresh water) have arisen.

The second half of the 20th century is often called the century of biology because of biology’s advance to the front lines of natural science and because of the increased importance and relative role of biology among the other sciences, notably as a productive force of society. Biology has vast significance for the development of a systematic materialistic Weltanschauung; for the demonstration of the naturalistic origin of all living creatures and of man, with the highest forms of rational activity peculiar to him; and for the destruction of faith in the supernatural and primordial expediency (theology and teleology). Biology plays an important role in the comprehension of man and his place in nature. In the words of Karl Marx, biology and the theory of evolution that came forth from it provide a naturalistic-historical basis for materialistic views on the development of society. The triumph of the idea of evolution in the 19th century put an end to science’s belief in the divine creation of living things and man (creationism). Biology shows that vital processes are based on phenomena that obey the laws of physics and chemistry. This does not rule out the presence in living nature of unusual biological regularities which, however, have nothing in common with the idea of an incomprehensible “vital force” (vis vitalis). Thus, thanks to the progress of biology, the main supports of the religious Weltanschauung and philosophical idealism are collapsing. Dialectical materialism is the methodological basis of modern biology. Even investigators who are far from affirming materialism in philosophical conceptions confirm by their publications the theoretical knowability of living nature, objectively uncover existing regularities, and verify the soundness of the acquisition of knowledge by experiment or practice—that is, they spontaneously hold materialistic views.

The regularities uncovered by biology are an important component part of modern natural science. They are the basis of medicine, agricultural sciences, forestry, fur breeding, hunting, and fishing. Man’s use of the resources of the organic world is based on principles discovered by biology. The biological data relating to fossil organisms are important in geology. Many biological principles are used in engineering. The utilization of atomic energy and space exploration required the creation and rapid development of radiobiology and space biology. Only on the basis of biological research is it possible to solve one of the most magnificent and urgent tasks facing mankind—the planned reconstruction of the earth’s biosphere in order to create optimum living conditions for the increasing population of the planet.

The system of biological sciences is extraordinarily multileveled; this is determined by the varied manifestations of life, as well as by the many different forms, methods, and purposes of investigating living objects and studying them at different levels of organization. All this makes any organization of biological sciences arbitrary. The study of animals (zoology), plants (botany), and human anatomy and physiology—the basis of medicine—were among the first to develop. Other major divisions distinguished according to the objects studied include microbiology (the science of microorganisms) and hydrobiology (the science of organisms inhabiting a water environment [hydrosphere]). Narrower disciplines grew within biology. For example, there arose mammalology (the study of mammals), ornithology (birds), herpetology (reptiles and amphibians), ichthyology (fish and fishlike organisms), entomology (insects), acarology (ticks), malacology (mollusks), and protozoology (protozoans). Algology (the study of algae), mycology (fungi), lichenology (lichens), bryology (mosses), dendrology (trees and shrubs), and so on arose within botany. The disciplines are sometimes subdivided even further. Animal and plant taxonomy deal with the diversity of organisms and their distribution by groups. Biology can be subdivided into neontology, which studies the present organic world; and paleontology, the science of extinct animals (paleozoology) and plants (paleobotany).

Biological disciplines are also classified according to the properties and manifestations of life studied. The form and structure of organisms are studied by the morphological disciplines; the mode of life of animals and plants and their interrelations with the environment are studied by ecology. The study of the various functions of living things is the field of animal and plant physiology. The patterns of heredity and variability are a subject of research in genetics, and ethology deals with the patterns of animal behavior. The laws governing individual development are studied in embryology or— in the wider modern sense—developmental biology. The theory of evolution is concerned with the laws of historical development. Each of these disciplines is divided into more specialized ones (for example, morphology is divided into functional, comparative, and so on). At the same time different fields are penetrating into and merging with one another to form more complex ones—for example, histo-, cyto-, or embryophysiology, cytogenetics, and evolutionary and ecological genetics. Anatomy studies the structure of organs and their systems macroscopically. The microstructure of tissues is studied by histology, that of cells by cytology, and that of the cell nucleus by karyology. At the same time, histology, cytology, and karyology examine not only the structure of the corresponding formations but also their functions and biochemical properties.

It is possible to distinguish biological disciplines that are associated with the use of particular methods—for example, biochemistry, which studies the main life processes by chemical methods (it is subdivided into animal biochemistry, plant biochemistry, and so on); and biophysics, which uncovers the role of physical phenomena in the life processes (it is also subdivided into several branches). Biochemical and biophysical research are often closely intertwined both with each other (for example, in radiation biochemistry) and with other biological disciplines (in radiobiology). Also of importance is biometry, which is based on the mathematical processing of biological data (in order to uncover relationships that may escape attention when isolated phenomena or processes are described), the planning of experiments, and so on. Theoretical and mathematical biology, by using logical constructions and mathematical methods, make it possible to establish more general biological laws.

Disciplines concerned with the study of living matter at various levels of its organization are molecular biology, which studies vital phenomena at the subcellular, molecular level; cytology and histology, which study the cells and tissues of living organisms; population-species biology (taxonomy, biogeography, and population aspects of genetics and ecology), which is concerned with the study of populations as constituents of a given species; and biogeocenology, which studies the highest structural levels of organization of life on earth up to the biosphere as a whole. Both the theoretical and practical aspects of research are important. It is difficult to draw the boundary line between them because any theoretical research will inevitably (directly or indirectly, at a particular moment or in the future) have practical consequences. Theoretical studies pave the way for discoveries that may revolutionize many fields of practical activity. They ensure the successful development of applied disciplines—for example, industrial microbiology and applied biochemistry, plant protection, plant growing and livestock raising, conservation of nature, and biomedical fields (parasitology, immunology, and so on). The branches of applied biology in turn enrich theory with new facts and present it with problems arising from the needs of society. Among the rapidly growing disciplines of practical importance are bionics (the study of engineering applications of biological phenomena), space biology (the study of the biological effects of space factors and problems involved in space exploration), and astrobiology or exobiology (the study of extraterrestrial life). Several biological disciplines—anthropology, human genetics and ecology, medical genetics, and psychology—are concerned with the study of man as a product and object of biological evolution; they are closely associated with the social sciences.

Several fundamental fields of biology should be particularly noted, for they investigate the laws characteristic of all living things and constitute the basis of modern general biology. These include cytology (the science of the principal structural and functional unit of the organism—the cell), genetics (the science of the phenomena of reproduction and continuity of the morphological and physiological organization of living forms), developmental biology (the science of ontogeny), evolutionary theory (the science of the laws of historical development of the organic world), and also physicochemical biology (biochemistry and biophysics) and physiology, which study functional manifestations, metabolism, and energy in living organisms. It is evident from the above far from complete list of the biological disciplines that the edifice of modern biology is large and complex and that together with the allied sciences which study inanimate nature it is solidly linked to practical areas.

Modern biology is rooted in antiquity. The ancient civilizations in eastern and southern Asia (China, Japan, and India) developed independently and did not exert a direct influence on European science. Modern biology originated in the Mediterranean countries (ancient Egypt and ancient Greece). The first systematic attempts to grasp the phenomena of life were made by the ancient Greeks and later by the Roman natural philosophers and physicians (beginning in the sixth century B.C.). Hippocrates, Aristotle, and Galen made a major contribution to the development of biology. In the Middle Ages, biological knowledge was gathered mainly in the interests of medicine. Plants were studied chiefly for their medicinal properties. Dissection of the human body was prohibited, and the anatomy taught according to Galen was actually the anatomy of animals—chiefly pigs and monkeys. Aristotle was the main philosophical authority of the church, but many of his writings were ignored and sometimes banned. The writings of the ancient naturalists and medieval encyclopedists who wrote about nature spread during the Renaissance. The geographical discoveries made during travels to the Mediterranean countries and then to the shores of Africa and around it (1497), the discovery of North America (1492), and so on increased man’s knowledge of the plant and animal worlds. The creation of botanical gardens in universities and menageries also helped.

The first works on botany were commentaries on the writings of the ancient scientists Theophrastus, Dioscorides, and Pliny the Elder. Original herbals—lists of medicinal plants with brief descriptions and drawings—appeared later on. The plants were divided into trees, shrubs, and grasses. Only the Italian botanist A. Cesalpino attempted (1583) to classify them on the basis of the structure of the seeds, flowers, and fruits. The rudiments of the doctrine of metamorphosis as well as the concepts of genus and species can be seen in Cesalpino’s work. Multivolume compilatory encyclopedias were prepared on zoology: History of Animals by the Swiss naturalist K. Gesner (vols. 1–5, 1551–87) and the series of monographs (13 vols., 1599–1616) by the Italian scientist U. Aldrovandi. There appeared descriptions of “foreign” animals based on observations in nature and on visits to distant countries by the French scientist G. Rondelet, the Italian I. Salviani (on fish and aquatic animals), and especially the French naturalist P. Belon (fish and birds and animals of the Near East). Belon was the first to compare the structure of birds with that of man, depicting the skeletons side by side (1555).

The brilliant successes of anatomy during the Renaissance were due to the incorporation of dissection of the human body into teaching and research. The Flemish scientist A. Vesalius, in his Structure of the Human Body (1543), decided to publish facts showing the discrepancy between actual observations and bookish ones based on Galen’s authority. The rejection of Galen’s statement that there are pores in the heart wall separating the ventricles showed the weakness of Galen’s theory of blood flow and led to the conclusion that there is a lesser circuit of blood circulation in the body. This conclusion was drawn by the Spanish scientist M. Servetus (1593) and the Italian R. Colombo (1559).

The works of the anatomists paved the way for a great discovery of the 17th century—W. Harvey’s theory of blood circulation (1628), a model of physiological research based on quantitative measurements and on the use of the laws of hydraulics in accordance with the newly developing mechanical approach in medicine. The most prominent representatives of iatromechanics were the Italian scientists S. Sanctorius, who tried to verify in himself the quantitative aspect of metabolism in man (1614); and G. Borelli, who endeavored to explain all forms of animal movement (1680), including muscular contraction and digestion, by the laws of mechanics. His explanations encountered insuperable difficulties and came into conflict with iatrochemistry, which explained all life processes on the basis of the theory of enzyme action (fermentation) that was developed in the 16th century by the German physician and chemist P. Paracelsus. This theory also explained the long-assumed spontaneous generation and the generation and development apparently accomplished by the mixing of seminal fluids during fertilization. Even Harvey, who proclaimed “everything from the egg” (1651) as the main principle of animal reproduction, assumed spontaneous generation for the lower animals in which no eggs were found. The experiments of the Italian scientist F. Redi (1668), who showed that “spontaneous generation” of fly larvae in rotting meat is due to the development of the latter from eggs deposited by flies, still did not decide the matter conclusively.

The invention of the microscope (17th century) widened and deepened the opportunities for the study of living things. A galaxy of brilliant microscopists discovered the cellular and fibrous structure of plants (the English scientist R. Hooke, 1665; the Italian M. Malpighi, 1675–79; and the Englishman N. Grew, 1671–82) and the world of microscopic organisms, erythrocytes, and spermatozoa (the Dutch scientist A. van Leeuwenhoek, 1673 and later). They also studied the structure and development of insects (Malpighi, 1669; and the Dutch scientist J. Swammerdam, 1669 and later) and blood flow in the capillaries (Malpighi, 1661), found eggs in fish and follicles in mammalian ovaries that were taken for eggs (the Dane N. Steno, 1667; and the Dutchman R. de Graaf, 1672), and established sexual differences in plants (the Englishman T. Millington, 1676; and the German R. Camerarius, 1694). These discoveries led to the appearance of two erroneous schools in embryology—the ovists and animalculists (spermists), who denied the participation of one of the sexes in fertilization. Both agreed that true development actually does not take place, but rather that a ready miniature embryo of the future organism is enclosed in the egg, according to one, or in the spermatozoid, according to the other. The theory of epigenesis formulated by Aristotle and Harvey was rejected as naive and mechanistic.

The English scientist J. Ray and the French scientist J. de Tournefort tried to systematize plants into artificial systems. Ray, in his History of Plants (1686–1704), described more than 18,000 plants grouped in 19 classes; Tournefort (1700) arranged them in 22 classes. Ray defined the concept of “species” and, using the works of the English scientist F. Willughby, classified vertebrates mainly on the basis of anatomical and physiological features (1693).

Eighteenth century. The Swedish naturalist C. Linnaeus suggested in his System of Nature (1735) a system which was all-embracing for that time, based on the immutability of the primordially created world. He constructed his system of plants, which he called “sexual,” according to the number of stamens and other characteristics of flowers. His classification of animals was more natural and took into account their internal features. Linnaeus distinguished the class of mammals, in which he correctly included whales and man, whom he assigned along with monkeys to the order of primates. Linnaeus’ great contribution was the binomial nomenclature, with dual names (for genus and species) for each plant and animal form. Linnaeus’ artificial system did not satisfy many botanists, who tried to find a “natural” system of plants in accordance with their resemblance to and “relationship” with each other. The French botanist B. de Jussieu carried it out (1759) only in plantings in the royal garden in the Trianon (Versailles), the French scientist M. Adanson tried to devise a natural system of plant families (1763), and the French botanist A. L. de Jussieu completed these attempts in his Plant Genera Arranged in Their Natural Order (1789). The French naturalist G. de Buffon was hostile to all systems, including that of Linnaeus. His Natural History, 36 volumes of which he was able to publish (1749–88), includes descriptions not only of animals and man but also of minerals, as well as a history of the earth’s past. Buffon sought unity in the structure of animals, made guesses about the past animal world, and tried to explain the resemblance between similar forms by their origin from one another. Thus, Buffon’s transformism was limited, but he was compelled to repudiate it under threat of excommunication from the church (1751). Buffon’s ideas regarding the reproduction and development of organisms were of great value in refuting the doctrine of preformation. They marked the return to the theory of two seminal fluids participating in fertilization (1749). Buffon also tried to revive the ancient concept of pangenesis, arguing that seminal fluid contains “organic molecules” representing all the parts of the body. Buffon and another French scientist, P. de Maupertuis (1744), explained the development of the individual by the forces of attraction and repulsion between organic molecules. The Russian academician K. F. Vol’f (1759–68) contributed more to revival of the theory of epigenesis than anyone else. He explained development by some “essential force” which ensures the flow of nutrient juices in embryos. Vol’f ascribed the physical properties of attraction and repulsion to this force by analogy to the force of gravity (1789). Thus, it was not a vitalist concept, but rather a peculiar reaction to “mechanical” medicine. The initial proponent of this view was the German physician and chemist H. Stahl, who contrasted his theory of animism (1708) to the concept of a man-machine controlled by fluids. In ascribing control of the vital processes of the body to the “soul,” he assumed that physiological reactions are related to neuropsychic factors. His teaching on “vital tone” based on the principle of “irritability” (the English scientist F. Glisson, 1672) was elaborated in the teaching of the German physiologist A. von Haller on irritability (1753). After demonstrating experimentally the difference between muscle fiber contractility and the ability of the nerves and brain to conduct irritation, Haller ascribed them to the action of two “forces” inherent in the fibers and tissues proper. Following Haller, the Czech anatomist and physiologist I. Prohaska (1784) admitted the presence of a single “nerve force” that ensures the perception of excitation and its transmission to the motor organs without the participation of the brain. The sensational experiments of the Italian scientist L. Galvani received the same interpretation. Galvani discovered “animal electricity” (1791), which led to the development of electrophysiology (the German physiologist A. Humboldt, 1797; the Italian C. Matteucci, 1840; and the German DuBois-Reymond, 1848).

Much was accomplished in the field of respiratory physiology by the English scientist J. Priestley, who showed (1771–78) in experiments on plants that they release a gas that is flammable and which is essential for animal respiration; and by the Frenchmen A. Lavoisier, P. Laplace, and A. Séguin, who elucidated the property of oxygen in the oxidative processes and its role in respiration and production of animal heat (1787–90). The role of sunlight in the ability of green leaves to release oxygen by using atmospheric carbon dioxide was established by the Dutch physician J. Ingenhousz (1779) and the Swiss scientist J. Senebier (1782) and N. de Saussure (1804). The end of the 18th century was marked by the start of extensive studies on substances released from animals and plants. This work laid the foundation for the organic chemistry of the future (the discovery of urea, cholesterol, organic acids, and so on).

The Russian academician I. Kel’roiter proved the existence of sex in plants and by his work on hybridization showed that both egg cells and pollen (1761 and later) participate in fertilization and development. At the end of the century the Italian L. Spallanzani performed delicate experiments that refuted the possibility of spontaneous generation.

The ideas of the historical development of the organic world became increasingly insistent in the second half of the 18th century. The German philosopher G. W. von Leibniz proclaimed the principle of gradation of living things and predicted the existence of transitional forms between plants and animals. The discovery of freshwater polyps by the Swiss naturalist A. Trembley (1744) was considered evidence of such “zoophytes.” The principle of gradation was elaborated in the idea of a “ladder of creatures” from minerals to man, which was an illustration of ideal continuity in the structure of creatures for some (the Swiss naturalist C. Bonnet) and evidence of the actual transformation of living things for others (the French philosopher J. B. Robinet, 1768; and the Russian writer A. N. Radishchev, 1792–96). In 1749 and 1778, Buffon advanced a bold hypothesis on the earth’s history, which he calculated to be 80,000 to 90,000 years long and divided into seven periods. Plants appeared on the earth only in the last periods; they were followed by animals, and finally by man. Buffon assumed the transformation of some forms into others under the influence of climate, soil, and nutrition. Maupertuis (1750) conjectured that the elimination of forms not adapted to existence played a role in the process.

Nineteenth century. The “ladder of creatures” was given an evolutionary interpretation by the French scientist J. B. de Lamarck, who sketched in his Philosophy of Zoology (vols. 1–2,1809) the pathway of improvement of living things from the lowest to the highest which is based, as he thought, on an internal striving toward progress that is inherent in organisms (the principle of gradation). The environment causes deviations from the “correct” gradation and determines the adaptation of species to the conditions of existence either by direct action (plants and lower animals) or through the exercise and lack of exercise of organs associated with a change in habits (animals with a nervous system). Despite an understanding of the mechanisms of evolution that was undoubtedly progressive for his time (overcoming creationism; the substantiation of the evolution of living things on the basis of natural causes), Lamarck’s theory was a natural-philosophical concept with distinct elements of idealism (the internal striving for progress, the role of the animals’ efforts in changes, invariably expedient and hereditary change in characters under the direct influence of environmental conditions, and so on).

Lamarck’s theory was criticized by many, including the French scientist G. Cuvier, the founder of comparative anatomy and paleontology of animals. To explain the historical succession of living forms and the disappearance of many of them, Cuvier advanced the theory that the catastrophes experienced by the organic world were caused by geological cataclysms (1825). The French biologist A. d’Orbigny (1849), a follower of Cuvier, imparted the final creationistic character to the catastrophe theory. The French naturalist E. Geoffroy Saint-Hilaire tried to substantiate the natural-philosophical doctrine of the “unity of the structural plan” for animals, which he later explained by their common origin. According to his representations, evolutionary changes take place suddenly as a result of direct environmental influences. The changes experienced by animals are particularly sharp in the embryonic period. These ideas were also reflected in the views of the Russian scientist K. F. Rul’e, who deepened them considerably and anticipated their true evolutionary interpretation. Saint-Hilaire’s attempt to substantiate a single structural plan for animals provoked sharp criticism from Cuvier, who advanced in opposition his theory of four types of structure. In a public debate (1830), Cuvier gained the upper hand after long maintaining antievolutionary concepts in France.

Natural philosophy, which originated in the 18th century, had its greatest effect on biology in Germany. German philosophers and naturalists also supported the doctrine of the unity of the structural plan for organisms. For example, J. W. Goethe maintained the existence of the “idea of an organ” and models of the primal plant and the primal animal (1782–1817). L. Oken (Ockenfuss) thought that the structure and development of all living things are based on “bubbles” or infusorians (1805). The principle of parallelism between ontogeny and phylogeny was the most fruitful of the ideas of the German natural philosophers (K. Kielmeyer, 1793; J. Meckel, 1811). This principle later became the point of departure for the formulation of the law of biogenesis.

True scientific confirmation of the idea of development of organisms was found in the embryological studies of the Russian academicians Kh. I. Pander (1817) and K. M. Ber (1827) on embryonic leaflets, in Ber’s substantiation of the principles of comparative embryology (1828–37), and in the creation by the German biologist T. Schwann (1839) of the cell theory applicable to the entire organic world. The theory of the unity of the cell structure of all living things played an enormous role in the development of histology, embryology, and cellular physiology. On the basis of this theory, protozoans were considered unicellular organisms (by the German scientist K. Siebold, 1848); the German A. von Kölliker (1844), the Russian N. A. Varnek (1850), and especially the German R. Remak (1851–55) developed cellular embryology; the German pathologist R. Virchow created “cellular pathology” and proclaimed the principle of “every cell from a cell” (1858); and the German scientists M. Schultze and E. Brücke advanced (1861) the concept of the cell as an “elementary organism” whose main components are protoplasm and a nucleus.

Great success was achieved in the middle of the 19th century in physiological chemistry, mainly because of the works of the German J. von Liebig and the Frenchman J. B. Bous-singault, who established the characteristics of plant nutrition and the difference between it and animal nutrition after formulating the principle of cycle of matter in nature. Liebig divided all the substances making up living things into proteins, fats, and carbohydrates, and he elucidated many of the chemical processes involved in metabolism, including the formation of fats from carbohydrates. The German scientist F. Wöhler was the first to synthesize organic substances— oxalic acid (1824) and urea (1828). However, both he and Liebig assumed the presence of some “vital force” as the cause of vital phenomena. The need for this assumption was shared by such leading physiologists of the time as the German J. Müller and some others. Only the French physiologist C. Bernard and the Germans K. Ludwig, E. DuBois-Reymond, and H. Helmholtz rejected it. Bernard elucidated the role of the secretions of various glands in digestion (1843 and 1847), demonstrated glycogen synthesis in the liver (1848), substantiated the concept of “interior milieu” of the body, and formulated the main principles of experimental physiology and medicine. Ludwig, DuBois-Reymond, and Helmholtz developed the principal physiological methods of studying the nervous system and sensory organs. Their worthy successor in Russia was I. M. Sechenov, who established the inhibition of spinal reflexes by brain centers (1863) and laid the foundation for the materialistic understanding of higher nervous activity (“brain reflexes”).

The studies of the French scientist L. Pasteur (the discovery of the part played by microorganisms in the processes of fermentation, 1857–64), which had major implications for the food industry, agriculture, and so on, made it possible to reject conclusively the doctrine of spontaneous generation of organisms (1860–64). Later he demonstrated the role of microorganisms in infectious diseases of animals and man and worked out methods of controlling rabies and anthrax by vaccinations. The nature of the fermentation processes which provoked disputes between the supporters of the physicochemical (Liebig) and microbiological (Pasteur) explanations was finally revealed by the German scientist E. Buchner, who isolated the enzyme zymase from yeast fungi (1897). This gave rise to a new science—enzymology. The Russian physician N. I. Lunin demonstrated (1881) the presence of vitamins in food products; they were later called vitamins by the Polish scientist C. Funk (1912). The end of the 19th century witnessed the first advances in the chemistry of proteins and nucleic acids (made by the German biochemists F. Miescher, E. Fischer, E. Abderhalden, and others). The observation by the Russian microbiologist S. N. Vinogradskii (1887–91) of bacteria capable of forming organic substances from inorganic ones by chemosynthesis (discovered by Vinogradskii) was of fundamental importance in substantiating the cycle of nitrogen, sulfur, and iron in nature. D. I. Ivanovskii, the founder of virology, discovered a new form of organization of living things—viruses (1892).

The greatest triumph of the 19th century was Darwin’s theory of evolution, set forth in his Origin of Species (1859). He cited a vast number of facts from biogeography, paleontology, comparative anatomy, and embryology to prove the evolution of the organic world. In proposing the theory of natural selection he also uncovered the mechanism of organic evolution and gave a causal analysis of the driving force in the evolutionary process. Darwinism was also of enormous philosophical importance in providing a materialistic solution to the problem of organic expediency. Darwin’s teaching not only finally drove creationism and teleology out of biology but also introduced into biological thought the historical approach to all phenomena of life. It helped to give rise to several new branches of biology—comparative anatomy (the German scientist K. Gegenbaur), evolutionary embryology (the Russian biologists A. O. Kovalevskii and I.I. Mechnikov), and evolutionary paleontology (V. O. Kovalevskii). It was also the basis of the biogenetic law (the German scientists F. Müller and E. Haeckel, 1866 and later) and of several phylogenetic generalizations. The doctrine of evolution greatly stimulated zoogeography and phytogeography (the English scientists P. Sclater and A. Wallace, the Russians N. A. Severtsov and A. N. Beketov, the Germans A. Griesebach and A. Engler, the Dane E. Warming, and many others). T. Huxley in England and E. Haeckel in Germany did much to promote Darwinism. In Russia, K. A. Timiriazev and a galaxy of comparative anatomists, embryologists, and paleontologists (M. A. Menzbir, V. M. Shimkevich, A. N. Severtsov, P. P. Sushkin, M. V. Pavlova, A. A. Borisiak, and others) made a great contribution to the dissemination and elaboration of the theory of evolution.

The doctrine of natural selection quickly gained widespread recognition. However, the inability to elucidate the principles of variability and heredity led to divergent interpretations of evolutionary factors. Various schools of Neo-Darwinism, Neo-Lamarckism, and frankly antievolutionist tendencies arose at the end of the 19th century.

The attempts to uncover the mechanisms of heredity by speculation (the English scientists H. Spencer, 1864; C. Darwin, 1868; and F.Galton, 1875; the German scientists K. von Nägeli, 1884, and A. Weismann, 1883–92; the Dutch scientist H. de Vries, 1889; and many others) were unsuccessful. It was only G. Mendel who succeeded in establishing the general laws of heredity (1865). However, his work went unnoticed, and it was only success in cytology and embryology that led to its rediscovery (1900) and correct evaluation in the 20th century. The first step in this direction was the elucidation of the subtle process of chromosome distribution during cell division, mitosis (the French biologist A. Schneider, 1873; the Russian biologist I. D. Chistiakov, 1874; the Polish biologist E. Strasburger, 1875; the German biologist W. Flemming, 1882; and others). The processes of fertilization, maturation of gametes, and the phenomenon of chromosome reduction were clarified first in animals (the German biologist O. Hertwig, 1875; the Belgian biologist E. van Beneden, 1875–84; the German biologist T. Boveri, 1887–88) and then in plants (the Russians I. N. Gorozhankin, 1880–83; and S. G. Navashin, 1898; and the Frenchman L. Guignard, 1899).

The 1880’s were marked by the great development of experimental embryology, initially called the mechanics of development (the German embryologist W. Roux, 1883 and later). The elucidation of the role of external and internal factors in development and the interrelations of the parts of the embryo quickly led to major theoretical disputes and partly to the revival of vitalism (the German biologist H. Driesch and others).

Twentieth century. The 20th century is characterized by the development of new biological disciplines and an upsurge in research in the “classical” fields, including those based on further specialization or integration of old branches. Genetics, cytology, animal and plant physiology, biochemistry, embryology, evolutionary theory, ecology, theory of the biosphere, microbiology, virology, parasitology, and many other fields have been developing particularly intensely in the 20th century.

The starting point for the development of genetics was Mendelism, which was reinforced by several generalizations, including the mutation theory of the Dutch scientist H. de Vries (1901–03), which despite many errors played an important role in paving the way for the synthesis of genetics and the theory of evolution. The concepts of the gene, genotype, and phenotype were worked out (the Danish scientist W. Johannsen, 1909) and the chromosomal theory of heredity was substantiated (the American scientists T. H. Morgan, A. Sturtevant, H. J. Muller, C. Bridges, and others). The causes of hereditary changes—mutations— became a matter of considerable methodological significance. Evidence that the mutation process is influenced by physical as well as by chemical factors (the Russian scientists G. A. Nadson and G. S. Filippov, 1925; V. V. Sakharov, 1932; and others, especially the Americans H. J. Muller, 1927, and L. Stadler, 1928) conclusively refuted the autogenetic ideas of the geneticists who emphasized the spontaneous origin of mutations and solidly validated the materialistic interpretation of mutagenesis.

The biochemical nature of genes and the matrix principle of their reproduction was first postulated purely theoretically in the idea of “hereditary molecules” (N. K. Kol’tsov, 1927 and later). It was subsequently demonstrated with the help of the phenomena of transduction and transformation in microorganisms that the carriers of genetic information are the strands of deoxyribonucleic acid (DNA) contained in the chromosomes (1944). These discoveries laid the foundation for molecular genetics. The elucidation of the structure of the DNA molecule by the American J. Watson and the Englishman F. Crick (1953) and the development of methods for isolating it from viruses and bacteria led to DNA synthesis in vitro from phage DNA. The synthesized DNA was found to be just as infectious as the original phage DNA (the American scientist A. Kornberg, 1967).

The introduction into biology of the methods of physics, chemistry, mathematics, and so on, as well as the advances made in the study of protein structure, rules for protein synthesis, and transmission and realization of hereditary factors, broadened the scope of research at the molecular level. The sequence in which the amino acids are arranged in more than 200 proteins, their secondary structure, and the way in which polypeptide strands fit into the protein molecule were elucidated. The nucleoprotein structure of chromosomes was demonstrated in giant chromosomes from Drosophila salivary gland cells. Purification of the tobacco mosaic virus made it possible to show the nucleoprotein structure of viruses and phages.

The sciences concerned with the individual development of organisms also made considerable progress. Methods of experimental parthenogenesis and androgenesis were devised. Research was also done on determination of the development of parts and organs of the embryo (the theory of “gradients” [the American scientist C. Child, 1915 and later] and on the theory of “organizers” [theGerman H. Spemann, 1921 and later]), and the foundations of the comparative embryological approach in developmental biology were laid by the Russian D. P. Filatov. Significant progress was made in controlling tissue and organ regeneration and transplantation, which are of great importance in plastic surgery. The immunology of blood groups and the properties and structure of the antibodies produced in response to the invasion of antigens were studied in considerable detail.

Important advances were made in animal physiology and biochemistry: the theory of conditioned reflexes worked out by I. P. Pavlov, the rapid development of neurophysiology, the study of the physiology and biochemistry of muscular contraction, and the isolation and thorough study of the enzymes responsible for the direction and rate of various processes of biosynthesis and their use in synthesizing hormones (insulin and others), vitamins, enzymes (for example, ribonuclease), and other biologically active substances. Progress was made in plant physiology in understanding the chemistry of photosynthesis and studying the pigments participating in it—especially chlorophyll, which was artificially synthesized. Advances were made in the study of plant growth and development—for example, several growth hormones (auxins, gibberellins) were isolated and partially synthesized.

Much of the research, including research by Soviet biologists, had theoretical as well as practical significance—for example, for medicine or agriculture. Such were E. N. Pavlovskii’s teaching on transmissible diseases and natural focality; the outstanding works of V. A. Dogel’, V. N. Beklemishev, and K. I. Skriabin on parasitology; and N. I. Vavilov’s law of homologous series in hereditary mutation and his teaching on the centers of origin of cultivated plants.

The theory of evolution was also significantly elaborated. For example, the synthesis of Darwinism and genetics was achieved in the 1920’s and 1930’s. The discovery of the role in evolution of populations as a mutation process and of the dynamics of abundance and isolation with selection as the directing force led to the formulation of modern evolutionary ideas that reinforce, deepen, and expand Darwinism. These processes were analyzed theoretically by the Russian scientist S. S. Chetverikov (1915, 1926), the American S. Wright (1921–32), and the Englishmen J. B. S. Haldane (1924–32) and R. Fisher (1928–30). The study of natural populations confirmed the correctness of their analysis and uncovered the fundamental nature of microevolution—the processes that occur at the level before speciation. The differentiation of microevolutionary and macroevolutionary levels led to the theory of evolutionary factors (the Soviet biologist I. I. Shmal’gauzen and others), the substantiation of the chief types of evolution and singling out of apomorphoses and idioadaptations as the main types (A. N. Severtsov), and the formulation of ideas on the rates and forms of evolution.

Great success was achieved in studying the living habits of organisms and their relation to the environment—that is, in the ecology of both individuals and populations, as well as of complex communities (biocenoses and ecosystems). The principles of the relationship between environmental conditions and the distribution of organisms in space and time were elucidated, as were the characteristics of the complex structure of populations and biocenoses, factors determining the dynamics of populations, and other fundamental relationships. The concept of tropic levels, food chains, vital forms, ecological niches, biological productivity, and related concepts and ideas were formulated. The achievements of the Soviet scientists V.I. Vernadskii in developing biogeochemistry and the theory of the biosphere (1926) and V. N. Sukachev in creating biogeocenology were outstanding, for they constitute the scientific basis of the relations between man and his habitat—the earth’s biosphere.

Many prominent Soviet biologists contributed to most of the abovementioned and other important trends in modern biology. In addition to those already named, mention should be made of the biochemists A. N. Bakh, V. S. Gulevich, A. R. Kizel’, V. I. Palladin, Ia. O. Parnas, and D. N. Prianishnikov; the physiologists V. M. Bekhterev, N. E. Vvedenskii, L. A. Orbeli, A. F. Samoilov, and A. A. Ukhtomskii; the microbiologists B. L. Isachenko, V. L. Omelianskii, and V. O. Tauson; the botanists V. L. Komarov, S. P. Kostychev, and N. A. Maksimov; the zoologists L. S. Berg, N. M. Knipovich, and V. M. Shimkevich; the histologists, embryologists, and geneticists S. N. Davidenkov, M. M. Zavadovskii, A. A. Zavarzin, S. G. Levig, A. S. Serebrovskii, Iu. A. Filipchenko, N. G. Khlopin; and many others who left behind them major scientific schools.

However, the development of biology in the USSR was not marked only by periods of advances and discoveries. In 1936 and 1939 there were a number of sharp debates on methodological problems of theoretical biology. During these debates, some tenets of genetics and Darwinism and the principles of selection based on them were exposed to sharp, subjectivistic criticism. A group of scientists (T. D. Lysenko and others) defended erroneous, mechanistic views on the nature of heredity, speciation, natural selection, organic expediency, and so on. These views were proclaimed to be the development of the scientific legacy of the prominent Soviet breeder I. V. Michurin, and they were labeled Michurin biology and creative Darwinism. After the 1948 session of the V. I. Lenin All-Union Agricultural Academy, the issue became particularly acute, and research in several fields of general biology came to a complete halt. This created an environment for the spread of unverified facts and hypotheses (the doctrine of the noncellular “living substance,” the intermittent “generation” of species by leaps, the “transformation” of viruses into bacteria, and so on). Discussions on physiology (combined session of the Academy of Sciences and Academy of Medical Sciences of the USSR, 1950) and evolutionary morphology (1953) also had an adverse effect. All of this severely hampered the development of genetics, evolutionary theory, cytology, molecular biology, physiology, evolutionary morphology, taxonomy, and other branches of biology in the USSR. The situation was completely normalized in October 1964, when steps were taken to restore and promote genetics and other disciplines (corresponding institutes were created, the All-Union Society of Geneticists and Breeders was organized, and the training of specialists in these fields was stepped up). This ensured the active participation of Soviet biologists in the rapid growth of world science, in which biology forms the vanguard, during the second half of the 20th century.

Living nature is characterized by a complex, hierarchical coordination of the levels of organization of its structures. The entire organic world together with the surrounding environment forms the biosphere, which consists of biogeocenoses or regions with characteristic natural conditions inhabited by certain complexes (biocenoses) of organisms. Biocenoses are made up of populations—groups of animals or plant organisms of a single species living on the same territory. Populations consist of individuals, and multicellular organisms consist of organs and tissues formed by various cells. Cells, like unicellular organisms, consist of intracellular structures made up of molecules. Each of the above levels exhibits typical patterns resulting from different scales of the phenomena, principles of organization, and peculiar interrelations with the levels lying above and below. Each level of organization of life is studied by the corresponding branches of modern biology.

The physicochemical processes that take place in a living organism are studied at the molecular level by biochemistry, biophysics, molecular biology, molecular genetics, cytochemistry, and many branches of virology and microbiology. Research on living systems at this level has shown them to consist of low- and high-molecular organic compounds rarely found in inanimate nature. The most specific to life are such biopolymers as proteins, nucleic acids, and polysaccharides, as well as lipids (fatlike compounds) and the constituents of their molecules (amino acids, nucleotides, simple carbohydrates, fatty acids, and so on). Synthesis and reproduction, decomposition, and mutual transformations of these compounds in the cell, the associated exchange of matter, energy, and information, and the regulation of these processes are studied at the molecular level. The main pathways of metabolism—the most important characteristic of which is the participation of biological catalysts (protein enzymes), which carry out certain chemical reactions in a highly selective manner—have already been established. The structure of a number of proteins and several nucleic acids, as well as many simple organic compounds, has been investigated. The chemical energy liberated during biological oxidation (glycolysis, respiration) has been shown to be stored in the form of energy-rich (mac-roergic) compounds, chiefly adenosine phosphate acids (ATP and such), and subsequently used in processes requiring the inflow of energy (synthesis and transport of various substances, muscular contraction, and so on). A major achievement of biology was the discovery of the genetic code. The hereditary properties of an organism are “recorded” in molecules of deoxyribonucleic acid (DNA) by four kinds of monomer-nucleotides alternating in a definite sequence. The ability of DNA molecules to double (copy themselves) ensures their replication in the cells and hereditary transmission from parents to offspring. The realization of hereditary information takes place with the participation of molecules of ribonucleic acid (RNA) synthesized on the matrix molecules of DNA. RNA is transported from the chromosomes of the nucleus to special intracellular particles—ribosomes—where protein is synthesized. Thus, the hereditary information coded in DNA regulates through the protein enzymes both the structural proteins and all the main properties of the cells and organism as a whole.

Biological research at the molecular level requires the isolation and study of all kinds of molecules making up the cell and elucidating their relations with each other. To separate macromolecules, use is made of their differences in density and size (ultracentrifugation), charges (electrophoresis), and adsorption properties (chromatography). The relative position of atoms in complex molecules is studied by X-ray diffraction analysis. The ways in which substances are transformed and the rates at which they are synthesized and decomposed are studied by introducing compounds containing radioactive atoms. Another important method is the creation of artificial model systems from isolated cellular components, where the processes at work in the cell can be reproduced in part. (All the biochemical processes in the cell take place not in a homogeneous mixture of substances but in certain cellular structures that separate spatially the various reactions occurring at the same time.)

In investigating cellular structures consisting of specifically chosen and oriented molecules, biology rises to the next level of organization of life—the cellular level. At this level cytology, histology, and their subdivisions (karyology, cytogenetics, cyto- and histochemistry, cytophysiology, and so on), as well as many branches of virology, microbiology, and physiology, study the structure of cells and intracellular components and the relations between cells in different tissues and organs. A cell is the principal independently functioning structural unit of a multicellular organism. Many organisms (bacteria, algae, fungi, and protozoans) consist of a single cell—more precisely, they are acellular. The properties of a cell are determined by its constituents, which perform a variety of functions. In the nucleus are chromosomes that contain DNA and are therefore responsible for preserving hereditary properties and transmitting them to the daughter cells. Energy metabolism in the cell—respiration, ATP synthesis, and so on—takes place chiefly in the mitochondria. The maintenance of the chemical composition of the cell, the active transport of substances into and out of it, the transmission of nervous excitation, the shape of the cell, and the nature of the relations between cells are determined by the structure of the cell membrane. An aggregation of cells of a single type forms a tissue, and the functional combination of several tissues makes up an organ. The structure and functions of tissues and organs are determined mainly by the properties of specialized cells.

Research at the cellular level revealed the main cell constituents, the structure of different cells and tissues, and the changes therein during development. In using the light microscope, which makes it possible to see details on the order of 1 micron, various techniques of fixation, preparation of thin transparent sections, stains, and so on are used to provide a greater contrast range. The localization of various chemical substances and enzymes in the cell is revealed by histochemical color reactions, and the sites of synthesis of macromolecules are shown by autoradiography. The electron microscope makes it possible to distinguish structures as small as 5–10 angstroms—that is, as small as a macromolecules—although they often are hard to describe because of the insufficient contrast range. The functions of intracellular components are studied by isolating them from destroyed (homogenized) cells by precipitation in centrifuges at various speeds of rotation. Cell properties are also investigated under conditions of prolonged culturing outside the organism. Nuclei can be exchanged between cells and cells can be merged (hybridized) by using micromanipulators and microsurgical techniques.

The processes and phenomena that take place in an individual and coordinate the functions of its organs and systems are studied at the level of the integral organism. This level is investigated by physiology (including the physiology of higher nervous activity), endocrinology, immunology, embryology, experimental morphology, and many other branches of biology. Research aimed at uncovering the causal mechanisms of biological organization, differentiation, and integration, and the realization of genetic information in ontogeny, are of particular value in constructing a general theory of ontogeny. The mechanism of functioning of organs and systems, their role in the organism’s life processes, the reciprocal influence of organs, the nervous, endocrine, and humoral regulation of their functions, animal behavior, adaptive changes, and others are also studied at this level. The functions of the various organs are interrelated—the heart with the lungs, some muscles with others, and so on. This integration of the parts of an organism is largely determined by the endocrine glands. For example, the pancreas and adrenals regulate the accumulation of glycogen in the liver and blood sugar level through the hormones insulin and epinephrine. The endocrine glands function together by the feedback principle—that is, one gland (for example, the pituitary) stimulates another (such as the thyroid) at the same time that the latter inhibits the former. This system helps to maintain a constant concentration of hormones and thus regulate all the organs dependent on these glands. A still higher level of integration is ensured by the nervous system with its central divisions, sense organs, and sensory and motor nerves. Information is obtained from all the organs and from the external environment through the nervous system. The information is processed by the central nervous system which regulates the functioning of organs and systems and the behavior of the body.

Among the methods most commonly used at this level are those of electrophysiology, which include the derivation, amplification, and recording of bioelectric potentials. Endocrine regulation is studied mainly by biochemical methods (isolation and purification of hormones, synthesis of their analogues, study of the biosynthesis and mechanisms of action of hormones, and others). Research on higher nervous activity in animals and man includes modeling (involving the use of cybernetic techniques) and experimental analysis of behavior (presentation of problems, formation of conditioned reflexes, and so on).

At the population-species level, the corresponding branches of biology study the elementary unit of the evolutionary process—a population, which is the aggregate of individuals of a single species inhabiting a specific territory and more or less isolated from similar neighboring aggregates. Such a constituent of a species can exist almost indefinitely in time and space by self-reproduction of the individuals that form part of it and can be transformed by preferential reproduction of various groups of genetically different individuals. The composition of a population and forms of its constituent organisms change in the course of several generations—a process that ultimately results in speciation and evolutionary progress. The unity of a population is determined by the potential capacity of all its constituent individuals for interbreeding (panmixia), which is in effect also the capacity for the exchange of genetic material. The sexual reproduction characteristic of most inhabitants of the earth guarantees the common morphological and genetic structure of all the members of a population as well as the possibility of repeatedly increasing genetic variety by combining hereditary elements. The isolation of one population from the others makes it possible for such a “varied unity” to exist in the process of evolution. Even in the case of organisms that reproduce asexually (by vegetative reproduction, parthogenesis, or apomixis), morphological and physiological unity of populations is determined by the commonality of their genetic makeup. However, the concept of species is not strictly applicable to asexual organisms that reproduce vegetatively or by simple division of reproducing organisms. The study of the composition and dynamics of populations is inseparably connected with the molecular, cellular, and organismic approaches. Genetics uses its own methods to study the distribution of hereditary characters in populations. Morphology, physiology, ecology, and other branches of biology investigate populations by their own methods. Thus, a population and species as a whole can serve as objects to be investigated by many different branches of biology.

At the biogeocenotic and biosphere level, the objects of study in biogeocenology, ecology, biogeochemistry, and other branches of biology are the processes that take place in biogeocenoses (often called ecosystems)—the elementary structural and functional units of the biosphere. Every population exists in a definite environment, where it forms part of a multispecies community or biocenosis that occupies a specific habitat or biotope. Photosynthesizing plants and chemosynthesizing bacteria are the primary producers of organic matter in these complexes of living and inert components. Thus, biogeocenoses are the “blocks” in which substance and energy cycles take place. These cycles are caused by the life processes of the organisms and in the aggregate make up the great biosphere cycle. In the structural and energy sense a biogeocenosis is an open, relatively stable system with inputs of substances and energy and outputs that link together the adjacent biogeocenoses. Substances are exchanged between biogeocenoses in gaseous, liquid, and solid phases and, in the words of V. I. Vernadskii, in the peculiar form of living matter (dynamics of plant and animal populations, migrations of organisms, and so on). From the biogeochemical standpoint, the migrations of a substance in the chains of biogeocenoses can be regarded as a series of interconnected processes of scattering and concentration of the substance in organisms, soils, water, and atmosphere.

The study of biological productivity of biogeocenoses (primary, or utilization of the energy of solar radiation by means of photosynthesis; and secondary, or utilization by heterotrophic organisms of the energy stored by autotrophic organisms) acquired considerable practical significance in the second half of the 20th century. The biogeocenotic (biosphere) level of organization must be studied independently because biogeocenoses are the environment in which any vital process on our planet takes place. Comprehensive research is carried out at this level to study the interrelations of the biotic and abiotic components of biogeocenoses and to investigate the migrations of living matter in the biosphere as well as the ways in which the energy cycles occur and the patterns they follow. This broad approach makes it possible to forecast in particular the consequences of man’s economic activity. It is also followed in the International Biological Program, which was devised to coordinate the efforts of biologists in many countries.

The concentration of biological research by levels of organization of living things assumes the interaction of the different branches of biology. This is extremely productive because it enriches the allied biological sciences with new ideas and methods.

Modern biology abounds in important problems whose solution could have a revolutionizing effect on natural science as a whole and on the progress of mankind. These include many aspects of molecular biology and genetics; physiology and biochemistry of muscles, glands, the nervous system, and sense organs (memory, excitation, inhibition, and so on); photo- and chemosynthesis; energetics and productivity of natural communities and of the biosphere as a whole; and fundamental philosophical and methodological problems (form and content, integrity and expediency, progress). Only a few of these matters will be discussed in more detail below.

Structure and functions of macromolecules. Biologically important macromolecules usually have a polymeric structure—that is, they consist of many similar but not identical monomers. For example, proteins are formed from 20 kinds of amino acids, nucleic acids from four kinds of nucleotides, and polysaccharides from monosaccharides. The sequence of monomers in biopolymers is called their primary structure. Establishment of the primary structure is the initial stage in studying the structure of macromolecules. The primary structure of many proteins and several kinds of RNA has already been determined. Methods have been devised for determining the nucleotide sequence in long chains of RNA and especially DNA—the most important task of molecular biology. The chain of biopolymers is usually in the form of a spiral (secondary structure). Protein molecules are constructed in a specific manner (tertiary structure) and are frequently combined in macromolecular complexes (quaternary structure). The way in which the primary structure of proteins determines the secondary and tertiary structures and how the tertiary and quaternary structures of the protein enzymes determine their catalytic activity and specificity of action are still incompletely answered questions. Protein molecules become attached to membranes, where they are combined with lipids and nucleic acids into supermolecular structures, forming intracellular components by “self-assembly.” The methods of X-ray diffraction analysis were used to establish the tertiary structure of some proteins (for example, hemoglobin) and to investigate the functional structure of many enzymes. Further study of the structure of macromolecules and an understanding of how this structure determines their complex and varied functions is one of the key problems of modern biology.

Regulation of cell functions. The characteristic features of the processes that take place in a living system are their coordination with each other and their dependence on regulatory mechanisms that keep the system relatively stable even during changing environmental conditions. The intracellular processes can be regulated by altering the set of enzymatic and structural proteins and the rate at which they are synthesized, by influencing enzymatic activity, and by changing the rate of transport of substances across the cell and other biological membranes. Protein synthesis depends on the synthesis of RNA molecules which transmit information from the appropriate gene (portion of DNA). Thus, the “inclusion” of a gene—the beginning of the synthesis on it of a molecule of RNA—is one of the places where protein synthesis is regulated. As of now, one of the schemes of regulating the uptake of nutrients from a medium (achieved by the inclusion and exclusion of genes that cause the synthesis of the required proteins) is known only for bacteria. The molecular mechanism of inclusion of genes (especially in multicellular organisms) is obscure, and its elucidation is a prime task of molecular biology. It appears that the rate of protein synthesis can also be regulated directly at the site of synthesis—in ribosomes. Another and more efficient regulatory system is based on change in enzymatic activity. This is achieved by the interaction of various substances with the molecule of the enzyme and by reversible modification of its tertiary structure. If an enzyme catalyzes the initial reaction in a chain of chemical conversions and a substance that suppresses its activity is the end product of this chain, a feedback system is established that keeps the concentration of the end product constant. The rate of the chemical processes in a cell may also depend on the rate at which the appropriate substances enter the cell, its nucleus, and mitochondria; or on the rate at which they are excreted. The properties of the biological membranes and enzymes are the determining factors. Many researchers are studying the regulation of intracellular processes because the phenomenon is not clearly understood.

Individual development of organisms. Among organisms that reproduce sexually, the life of each individual starts with a single cell—a fertilized egg—which repeatedly divides to form many other cells. Each cell contains a nucleus with a complete set of chromosomes—that is, it contains genes responsible for the development of all the characters and properties of the organism. However, cells differ in their mode of development. This means that only those genes whose function is essential for the development of a given tissue (organ) operate in each growing cell. The elucidation of the mechanism of “inclusion” of genes in the process of cell differentiation is a basic objective of developmental biology. Some of the factors that determine such inclusion are now known (the heterogeneity of the egg cytoplasm, the influence of some embryonic tissues on others, the action of hormones, and so on). Proteins are synthesized under the control of genes. The properties and characters of a multicellular organism, however, cannot be reduced to the peculiarities of its proteins; they are determined by the differentiation of cells that vary in structure and functions, relations with each other, and formation of different organs and tissues. An important and still unsolved problem is the mechanism of differentiation in the stages from protein synthesis to the appearance of cell properties and their characteristic movements that result in the formation of organs. The proteins of cell membranes may well play a major role in this process. The elaboration of a well-balanced theory of ontogeny, which requires a solution to the problem of integration of differentiating tissues and organs in the integral organism (that is, the realization of heredity), would revolutionize many branches of biology.

Historical development of organisms. More than 100 years have passed since Darwin’s Origin of Species was published, and a vast array of facts has confirmed the fundamental correctness of his theory of evolution. However, many of its important concepts have not yet been worked out. From the evolutionary genetics standpoint, a population can be considered an elementary unit of the evolutionary process, and a stable change in its hereditary characteristics is an elementary evolutionary phenomenon. This approach is useful in identifying the main evolutionary factors (the mutation process, isolation, waves of population, natural selection) and evolutionary material (mutations). It is still not clear whether only these factors act at the macroevolutionary level—that is, “higher than” speciation—or whether other still unknown factors and mechanisms participate in the origin of large groups of organisms (genera, families, orders, and so on). It is possible that all macroevolutionary phenomena can be reduced to change at the intraspecific level. The question of the specific factors of macroevolution cannot be answered until the mechanisms of what appears at times to be the directed development of groups are elucidated. This may depend on the existence of “prohibitions” imposed by the structure and genetic constitution of the organism. For example, the initially nonfundamental change resulting from the acquisition of a spinal cord by the ancestors of the Chordata subsequently determined the various paths of development of major branches of the animal world: first, the origin of an internal skeleton and centralized nervous system, the development of a brain with conditioned reflexes more important than unconditioned ones in vertebrates; and second, the appearance of an external skeleton and development of a different type of nervous system with extremely complex unconditioned reflexes predominant in invertebrates. The study of the “prohibitions” and mechanisms of their appearance and disappearance in the course of evolution is an important task related to the problem of “channeling of development” and discovery of the patterns of evolution of living nature. The concept of “progressive development” or “progress” is now divided into morphological, biological, group, biogeocenotic, and unlimited progress. Thus, the appearance in the earth’s biosphere of man—a creature in whom, in F. Engels’ graphic phrase, “nature reaches an awareness of itself (K. Marx and F. Engels, Soch., 2nd ed., vol. 20, p. 357)—is the result of unlimited progress. The development of sociality in living nature was caused by the appearance not only of human society but of communities of many insects, cephalopod mollusks, and certain mammals. The establishment of the complex relations between the acquisition of adaptations of fundamental character in the course of evolution (those lying on the way of unlimited progress) or of particular adaptations (leading to the flourishing of a group but not freeing it from its connections with its earlier habitat) and the discovery of the laws governing the appearance of the most perfect adaptations in some cases or resulting in the successful survival of comparatively primitive organisms in others are some of the important research objectives for the foreseeable future.

The matter of species and speciation is a peculiar problem. A species is a qualitatively unique stage in the development of living nature—an actually existing aggregate of individuals having in common the possibility of fruitful mating and constituting a genetically “closed” system for individuals of other species. From this standpoint, speciation is the transition from genetically open to genetically closed systems (populations). Many aspects of this process are still obscure, partly because the concept of “species” is not sufficiently definite as applied to different groups of organisms. This inevitably affects systematics and taxonomy—branches of biology concerned with the classification and coordination of species (hence the disputes that flare up from time to time on the “reality” of a system or phylogeny and so on). Theoretical formulations of the concepts of species and speciation are stimulating the continuous search for new approaches and methods to supplement the existing classification methods (for example, biochemical, genetic, and mathematical).

Origin of life. The origin of life is one of the methodologically important problems in biology which is eliminated neither by the unlikely assumption that life was brought to the earth from other worlds nor by the theory of the constant presence of life on this planet throughout its history. The scientific approach here consists in ascertaining the conditions under which life was generated on earth (this happened several billion years ago) and trying to simulate processes that might have occurred under those conditions, reconstructing experimentally the successive stages by which life originated. Thus, data on the physical and chemical state of the atmosphere and earth’s surface at that time provided theoretical and experimental proof that very simple hydrocarbons and more complex organic compounds (amino acids and mononucleotides) could have been synthesized, thereby confirming the theoretical probability of their polymerization into short chains—peptides and oligonucleotides. However, the next stage in the origin of life has not yet been studied. The application of the concept of natural selection to organic structures found on the boundary between living and nonliving things was important for theory. Natural selection can play a constructive role in evolution only when applied to self-reproducing structures capable of storing and repeatedly reproducing the information they contain. These requirements are satisfied only by the nucleic acids (chiefly DNA), in which self-copying can take place only if several conditions are observed (the presence of mononucleotides, a supply of energy, and the presence of enzymes to carry out polymerization and complement the existing polynucleotide, thereby duplicating the information it contains). Nothing is known as yet about the self-copying of other chemical compounds and under different and simpler conditions. The main difficulty faced by theory, therefore, is that enzyme proteins are required for the nucleic acids to double and that nucleic acids are needed to create proteins. After the primary self-copying system appeared, its subsequent evolution was less complex, and this is where the principles discovered by Darwin—the principles that determine the evolution of more complex organisms—begin to operate. Since the mechanism of the origin of life on earth is unknown, it is difficult to assess the probability of life originating under extraterrestrial conditions. In view of the astronomy data on the numerous planetary systems in the universe and the rather high probability of conditions compatible with life arising, many scientists take for granted the multiple origin of life. However, there is another view; namely, that terrestrial life is an extremely rare and virtually unique phenomenon in the visible part of the galaxy surrounding us.

The biosphere and mankind. The rapid growth of the earth’s population raises the question of the limits of biological productivity of the biosphere. Within 100–200 years, if the present methods of agriculture are preserved and the human population grows at the same rate, almost half of the population will not have enough food or water, or even oxygen to breathe. It is for this reason that the necessity has been recognized for the organization within a short period of time (two to three generations) of (1) the strict protection of nature and the restriction within reasonable limits of many industries (above all the wholesale destruction of forests) and (2) the adoption of broad measures aimed at sharply increasing the biological productivity of the earth’s biosphere and intensifying the biological cycles in both natural and cultivated biogeocenoses. A normally functioning biosphere not only provides man with food and very valuable organic raw material but also maintains a balance between the gaseous composition of the atmosphere, solutions of natural waters, and cycles of water on the earth. Thus, the quantitative and qualitative harm done to the working of the biosphere by man both reduces the production of organic matter and disrupts the chemical balance in the atmosphere and natural waters. The future will look different when people become aware of the magnitude of the danger and adopt a reasonable attitude toward their habitat, the earth’s biosphere. The scientific and industrial power of the people is already great enough not only to destroy the biosphere but also to carry out reclamation, hydraulic engineering, and other work on any scale whatever.

The primary biological productivity of the earth is related to the use of solar energy absorbed during photosynthesis and of energy obtained by chemosynthesis by the primary producers. If man increased the average vegetation density (which is technically feasible), he could boost biological productivity by a factor of two to three in terms of the energy input into the biosphere. This can be achieved if, in the course of reclamation and increasing the density of the vegetation, more use were made of species of green plants with high “efficiency” of photosynthesis. In order to introduce useful species into plant communities, it is absolutely necessary to know the conditions that maintain and disrupt the biogeocenotic balance. Otherwise there could be such biological catastrophes as economically dangerous population explosions of some species and precipitous population declines of others. By increasing the efficiency of the biogeochemical work of natural and cultivated biogeocenoses, by placing the hunting of land and sea animals, fishing, lumbering, and other activities on a rational basis, and by growing new groups of microorganisms, plants, and animals from among the vast reserve of wild species, it is possible to increase biological productivity and the biological productivity of the biosphere useful to man by an additional factor of two to three. The breeding of cultivated microorganisms and plants also opens up vast possibilities. In the near future, when breeders will avail themselves of the results of research in the rapidly growing fields of modern molecular genetics and phylogenetics, progress in these fields will be stimulated by the development and use of “experimental” evolution of cultivated plants based on long-range hybridization, creation of poly-ploidic forms, induction of artificial mutations, and so on.

Agricultural technology must also adopt new methods capable of boosting yields sharply (one realistic possibility is to shift from a one-crop to a multiple-crop system). Finally, in the very near future people will have to learn to recover at the end stages of biological cycles the large-molecular organic matter of the sapropelic type rather than the low-value, small-molecular products of the final mineralization of organic residues. All these ways of increasing the productivity of the biosphere lie within the capabilities of science and technology of the foreseeable future and clearly illustrate the magnificent potentialities of the developing human society on the one hand and the importance of biological studies on very different scales and directions for human life on earth on the other. None of the transformations that man must carry out in the biosphere can be achieved without a knowledge of the richness of the main forms and their interactions. This assumes the need for an inventory of the animals, plants, and microorganisms in different regions of the earth, which is still far from complete. In many large groups of organisms, even the qualitative composition of the constituent species is unknown. To make such an inventory requires a revival and sharp intensification of classification field work, field biology (botany, zoology, and microbiology), and biogeography.

An important practical approach is the study of man’s habitat in the broad sense and the organization of efficient ways of managing the economy on that basis. The approach entails the protection of nature and it is followed mainly along biogeocenological lines. Progressive biologists all over the world—zoologists, botanists, geneticists, ecologists, physiologists, biochemists, and so on—are attracted to such research, which is intended to increase the biological productivity of the earth and provide optimum living conditions on our planet for the steadily increasing human population. Their work is coordinated by the International Biological Program.

Man, as a heterotrophic organism, is incapable of directly utilizing the solar energy reaching the earth. He receives the proteins, fats, carbohydrates, and vitamins he needs for nutrition mainly from cultivated plants and domesticated animals, using long “chains” in some cases and short chains in others, from autotrophs (chiefly green plants) to heterotrophs (animals). A knowledge of the laws of genetics and breeding as well as of the physiology of cultivated species helps to improve agricultural technology and zootechny and to develop more productive plant varieties and animal breeds. The level of knowledge in the fields of biogeography and ecology determines the possibility and effectiveness of introducing and adapting useful species and controlling crop pests and parasites of farm animals. Biochemical research permits fuller utilization of organic matter of plant and animal origin. Without the active cooperation of biologists of all specialties with practical agricultural workers, foresters, wildlife biologists, fur breeders, and others, it is impossible to treat such issues as the development of new breeding methods and of the theory of heterosis (which ensures increased productivity of farm animals and plants); the breeding of organisms with predetermined properties; the improvement of biological methods of pest control; and the scientific management of forestry, fur breeding, hunting, fishing, and so on (this requires solving a number of problems—for example, population dynamics and optimum size, place, and time of reduction of a population by hunting or fishing, and so on).

Another exceedingly important practical aspect of biology is the use of its achievements in medicine. Advances and discoveries in biology made possible the present level of medicine. Further progress is also contingent on the growth of biology. Ideas concerning the macroscopic and microscopic structure of the human body and the functions of its organs and cells rely mainly on biological research. Physicians and biologists alike study human histology and physiology, which are the foundation of such medical fields as pathological anatomy and pathological physiology. The theory of the causes and spread of infectious diseases and the principles for controlling them are based on microbiological and virological research. Most of the pathogenic bacteria have probably been identified by now. The ways in which they spread and attack man have been studied. Methods have been devised for controlling them by asepsis, antisepsis, and chemotherapy. Many pathogenic viruses have been isolated and investigated, and the mechanisms of their reproduction are under study. Methods have been devised for controlling many of them.

Ideas concerning the mechanisms of immunity, which is the basis of the organism’s resistance to infection, likewise rest on biological research. The chemical structure of antibodies has been studied, and the mechanisms of their synthesis are now under investigation. The work being done on tissue incompatibility, the main obstacle to organ and tissue transplantation, is of particular significance for medicine. X-irradiation and chemical agents are used to suppress the body’s immune system. It will be possible to overcome tissue incompatibility without endangering life only when the mechanisms of immunity are uncovered. This can only be accomplished by a broad biological approach to the problem. The discovery of antibiotics revolutionized the treatment of infectious diseases, which formerly were the main cause of death. The medical use of substances excreted by microorganisms to combat each other is the greatest biological contribution of the 20th century. Mass production of cheap antibiotics became possible only after highly productive strains of antibiotic-producers were bred by modern genetics methods. The relative significance of old-age diseases— cardiovascular, malignant, and hereditary—has increased as the average human life-span has been extended (largely by medical advances). This has confronted medicine with new problems in the solution of which biology has a major role to play. For example, many vascular diseases are caused by disturbances of fat and cholesterol metabolism that have not yet been completely studied by biochemistry and physiology. Cytologists, embryologists, geneticists, biochemists, immunologists, and virologists are working as a united front to solve the cancer problem. Some progress has already been made in this field (surgery, radiotherapy, and chemotherapy). However, a radical solution to the problems of malignant growth and of tissue and organ regeneration is closely related to the general laws of cell differentiation.

The results of biological research are used not only in agriculture and medicine but also in fields of human endeavor previously remote from biology. A good example of this is the extensive use of microbiology in industry to obtain new and highly efficacious drugs and to work ore deposits using microorganisms.

Human genetics, including medical genetics which studies hereditary diseases, is now an important object of biomedical research. Diseases caused by chromosomal aberrations can now be precisely diagnosed. Genetic analysis can be used to detect harmful mutations, which can be controlled by therapy and medical genetics consultations and recommendations. Reasonable ways of saving mankind from harmful mutations are under active discussion in biological literature. Increasing attention is being paid to the mental health of mankind. The problem cannot be solved without a thorough natural historical and biological analysis of the origin in animals of the highest forms of nervous activity leading to the psyche. The fact that ethology, the science of behavior, has been established as a separate biological discipline is contributing significantly to the solution of this exceedingly important problem—one that has not only theoretical but philosophical and methodological implications.

The connection between biology and agriculture and medicine is responsible both for their development and for the development of biology. The fields of biology that are most promising in terms of practical application are very generously funded by society. In the future the union of biology with agriculture and medicine, for which biology is the scientific foundation, will be strengthened and developed.

The progress of biology in the 20th century and the relatively and absolutely enlarged role of biology among the other sciences and for the existence of mankind as a whole are responsible for the different appearance of biology from what it was even 30 or 40 years ago. The accumulation of knowledge in both the new and classical fields of biology is facilitated by the development and use of new methods and instruments. For example, great progress followed the development of electron microscopy, which made it possible to detect new ultrastructures at different levels of organization of living things. New methods of in vivo studies (cell, tissue, and organ cultures, marking of embryos, use of radioactive isotopes, and so on) and the utilization of physical and chemical devices working at high speeds and partly or completely automated (ultracentrifuges and ultramicrotomes, micromanipulators, electrocardiographs, electroencephalographs, polygraphs, spectrophotometers, mass spectrographs, and many others) are in wide use. The number of biological institutes, biological stations, sanctuaries, and national parks (which also play an important part as “natural laboratories”) is growing. Laboratories have been created in which the effects of any combination of climatic and physicochemical factors can be studied (biotrons, phytotrons). Research organizations now have electronic computers. New branches of industry produce biological instruments. The steadily increasing number of specialized biological institutes and biological faculties of universities are training highly qualified personnel for the various branches of biology. The material and technical development of society can be judged from the level of biological research because biology is becoming a genuine productive force. This guarantees a flourishing biology in the future which will undoubtedly be marked by the discovery of new fundamental laws of living nature. The very existence of man in the earth’s biosphere is closely linked to the progress made in solving the many biological problems. Biology is becoming the scientific, rational basis of relations between man and nature.



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Vvedenie ν molekuliarnuiu biologiiu. Moscow, 1967. (Translated from English.)
Vernadskii, V. I. Biosfera. Moscow, 1967.
Winchester, A. M. Osnovy sovremennoi biologii. Moscow, 1967. (Translated from English.)
Sovremennye problemy evoliutsionnoi teorii. Edited by V. I. Polianskii and Iu. I. Polianskii. Leningrad, 1967.
Teoreticheskaia i matematicheskaia biologiia. Moscow, 1968. (Translated from English.)
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Bertalanffy, L. von. Theoretische Biologie, vols. 1–2. Berlin, 1932–42.
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Biologie générale. Paris, 1966.
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Ramsay, J. A. The Experimental Basis of Modern Biology. Cambridge, 1965.
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(science and technology)
A division of the natural sciences concerned with the study of life and living organisms.


1. the study of living organisms, including their structure, functioning, evolution, distribution, and interrelationships
2. the structure, functioning, etc., of a particular organism or group of organisms
3. the animal and plant life of a particular region
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