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life,although there is no universal agreement as to a definition of life, its biological manifestations are generally considered to be organization, metabolism, growth, irritability, adaptation, and reproduction. Protozoa perform, in a single cell, the same life functions as those carried on by the complex tissues and organs of humans and other highly developed organisms. The attributes of life are inherent in such minute structures as viruses, bacteria, and genes, just as they are in the whale and the giant sequoia. In seeking an understanding of life, scientists have broken down many barriers that once separated the physical sciences from the biological sciences; a result of the growth of biochemistry, biophysics, and other interrelated fields of study has been a better understanding of the composition and functioning of living tissues of all kinds.
Characteristics of Life
Organization is found in the basic living unit, the cellcell,
in biology, the unit of structure and function of which all plants and animals are composed. The cell is the smallest unit in the living organism that is capable of integrating the essential life processes. There are many unicellular organisms, e.g.
..... Click the link for more information. , and in the organized groupings of cells into organs and organisms. Metabolism includes the conversion of nonliving material into cellular components (synthesis) and the decomposition of organic matter (catalysis), producing energy. Growth in living matter is an increase in size of all parts, as distinguished from simple addition of material; it results from a higher rate of synthesis than catalysis. Irritability, or response to stimuli, takes many forms, from the contraction of a unicellular organism when touched to complex reactions involving all the senses of higher animals; in plants response is usually much different than in animals but is nonetheless present. Adaptation, the accommodation of a living organism to its present or to a new environment, is fundamental to the process of evolution and is determined by the individual's heredity. The division of one cell to form two new cells is reproduction; usually the term is applied to the production of a new individual (either asexually, from a single parent organism, or sexually, from two differing parent organisms), although strictly speaking it also describes the production of new cells in the process of growth.
The Basis of Life
Much of the history of biology and of philosophy as related to biology has been marked by a division of thought between vitalistic (or animistic) and mechanistic (or materialistic) concepts. In the most antithetic interpretations of these concepts, the vitalistic school maintains that there is a vital force that distinguishes the living from the nonliving and the mechanistic school holds that there is no essential difference between the animate and inanimate and that all life can be explained by physical and chemical laws. Such diametrically opposed views have actually seldom been held by investigators of either school; elements of both are usually involved. The animistic school, largely predicated on the inexplicability of the basic phenomena of life, has been greatly overshadowed by the accumulating weight of scientific data. As more and more is learned of the minute details of the structure and composition of the substances that make up the cell (to the extent that some have been synthesized chemically), it has become increasingly apparent that living matter is made up of the same (and only those) elements found in inorganic material, except that they are differently organized.
The Origin of Life
Fundamental religious concepts center around special creation and belief in the infusion of life into inanimate substance by God or another superhuman entity. On the other hand, many scientists have hypothesized that during an early geological period there gradually formed in the atmosphere increasingly complex organic substances composed of available inorganic compounds and water, utilizing ultraviolet rays and electrical discharges as energy sources. At a certain stage they formed a diffuse solution of "nutrient broth." Then in some way they were drawn together and developed the capacity for self-renewal and self-reproduction. In 1953, S. L. Miller synthesized several of the most basic amino acids in a glass flask by introducing an electrical discharge into an atmosphere of water vapor and some simple compounds thought to have been present naturally at the time when life first developed on earth. A more recent theory now widely held is that life originated in a volcanic setting more than 3.5 billion years ago, perhaps in hot deep-sea vents, utilizing a biochemistry based largely on sulfur and iron. The theory that life on earth came in a simple form from another planet has had small currency, although the discovery by Melvin Calvin of molecules resembling genetic material in meteors has given it some force.
See M. Calvin, Chemical Evolution (1969); E. Borek, The Sculpture of Life (1973); N. D. Newell, Creation and Evolution (1985); S. W. Fox and K. Dose, Molecular Evolution and the Origins of Life (3d ed. 1990); R. Fortey, Life (1998).
the highest form of matter (by comparison with the physical and chemical), arising in conformity with regular principles and under particular conditions in the course of evolution.
Living objects differ from nonliving objects in the phenomenon of metabolism—an indispensable condition of life—and in the capacity for reproduction, growth, active regulation of composition and functions, various forms of movement, irritability, and adaptability to the environment. However, strictly scientific differentiation of living and non-living matter meets with certain difficulties. Thus, there is to date no unanimous opinion as to whether one may consider viruses to be alive. (Outside the cells of the host’s body, viruses do not possess a single attribute of living things; they lack metabolic processes, they are incapable of reproducing, and so on.) The specific nature of living matter and the life processes may be characterized from the point of view of both material structure and the functions at the basis of all manifestations of life. The most accurate definition of life, which simultaneously embraces both these approaches to the problem, was offered approximately 100 years ago by F. En-gels: “Life is the mode of existence of protein bodies; this mode of existence consists, in essence, in the constant self-renewal of the chemical components of these bodies” (K. Marx and F. Engels, Soch., 2nd ed., vol. 20, p. 82). The term “protein” had not yet been precisely defined, and it was usually applied to protoplasm as a whole. All objects now known that possess the indisputable attributes of life have in their makeup two principal types of biopolymers: proteins and nucleic acids (DNA and RNA). Aware of the incompleteness of his definition, Engels wrote: “Our definition of life is, of course, quite inadequate, inasmuch as it is far from embracing all the phenomena of life; it is, on the contrary, limited to the most general and the most simple among them.… In order to obtain a truly exhaustive concept of life we would have to trace all the forms of its manifestation, from the lowest to the highest” (ibid., p. 84).
C. Darwin, in the final lines of The Origin of Species, writes of the principal laws that, in his opinion, lie at the basis of the emergence of all forms of life: “These laws, taken in the largest sense, being Growth and Reproduction; Inheritance, which is almost implied by reproduction; Variability from the indirect and direct action of the conditions of life, and from use and disuse: a Ratio of Increase so high as to lead to a Struggle for Life, and a consequence to Natural Selection” (Soch., vol. 3, Moscow-Leningrad, 1939, p. 666). Leaving aside the role of use and disuse, which, according to the latest data, are factors in nonhereditary variability, Darwin’s generalization retains its force to this day, and his basic laws of life can be reduced to two even more general laws. These are, first of all, the capacity of living matter to assimilate substances obtained from outside itself—that is, to restructure them, assimilating them into its own structure and, in this way, to reproduce them repeatedly; if the initial structure is by change changed (mutated) it reproduces itself in the new form. (The capacity for abundant self-replication is the basis of cell growth, cell reproduction, body reproduction, and, consequently, the ratio of increase—the basic condition for natural selection—as well as the basis of heredity and hereditary mutability; the Soviet biochemist V. A. Engel’gardt regards the reproduction of one’s own kind as the fundamental property of living matter, which is now interpreted in terms of molecular chemistry.) The other characteristic of life consists in the enormous diversity of properties acquired through the variability of the material structures of living things. Each of these fundamental properties is basically connected to the functions of one of the two biopolymers. The “recording” of hereditary properties, that is, the coding of the characteristics of an organism, which is necessary for reproduction, is accomplished by means of DNA and RNA (although in the process of reproduction itself, protein enzymes continuously participate). Thus, it is not the individual molecule of protein, DNA, or RNA, that is alive, but the system as a whole. The realization of the diverse information about the properties of the organism is accomplished by means of synthesis according to the genetic codes of various proteins (enzymes, structural proteins, and so forth), which, owing to their diversity of form and structure, determine the development of the most varied physical and chemical adaptations of living organisms. It is on this foundation that, in the process of evolution, there have arisen living control systems unsurpassed in their perfection. Thus, life is characterized by highly ordered material structures containing two types of biopolymers (proteins and DNA-RNA) which make up a living system capable as a whole of self-replication on the template principle. A characteristic feature of the chemical composition of the known forms of life is the optical asymmetry of the constituent substances, which are represented in living things by levorotatory or dextrorotatory forms.
Life is possible only under certain physical and chemical conditions (temperature, the presence of water and a number of salts, and so on). However, the cessation of life processes, such as in the desiccation of seeds or the deep freezing of small organisms, does not lead to a loss of viability. If the structure is preserved undamaged, life processes will resume upon a return to normal conditions.
Life qualitatively surpasses other forms of existence of matter in respect to the diversity and complexity of its chemical components and in terms of the dynamics of the transformations that go on in living matter. Living systems are characterized by a much higher level of ordering of the structural and the functional, in space and in time. The structural compactness and energic economy of living matter are results of the highest ordering on the molecular level. One of the important consequences of this compactness is the universal effect of “magnification,” which is characteristic of all living systems. Thus, 5 x 10-15g of DNA contained in the fertilized ovum of a whale contains information for the overwhelming majority of characters of the animal, which weighs 5 x 107g. Consequently, in the presence of the necessary conditions the weight increases by a factor of 1022. “It is precisely in the capacity of living matter to create order out of the chaotic thermal movement of molecules,” writes Engel’gardt, “that the most profound and radical distinction between living matter and nonliving consists. The tendency to regulation, to the creation of order out of chaos, is none other than the counteraction to the increase of entropy” (Kommunist, 1969, no. 3, p. 85). Living systems exchange energy, matter, and information with the environment—that is, they are open systems. At the same time, as distinct from nonliving systems, equalization of energy differences and restructuring in the direction of more probable forms do not occur in living systems; rather, the opposite is observed: differences in energy potential, chemical composition, and so forth are restored, that is, continual work goes on “against equilibrium” (E. Bauer). Erroneous assertions arise on this basis that living systems are not subject to the second law of thermodynamics. However, a local decrease in entropy in living systems is possible only at the expense of an increase in entropy in the environment, so that the process of increasing entropy as a whole continues, which is in accord completely with the requirements of the second law of thermodynamics. According to the figurative expression of the Austrian physicist E. Schrodinger, it is as though living organisms feed on negative entropy (negentropy), drawing it from, and thus increasing the growth of positive entropy in, the environment.
Life on earth, which began no less than 1.5–2 billion years ago, is represented by an enormous number of organisms. Each organism can exist only under the condition of a constant and close bond with the environment, that is, with other organisms and with nonliving nature; in this sense, the bond is a two-way system. Life in all its manifestations has produced the most profound changes in the development of our planet, at least in its outer layers. As they become more perfect in the course of evolution, living organisms spread ever more widely over the planet, participating ever more fully in the redistribution of energy and matter in the earth’s crust and in the air and water that blanket the earth. The emergence and spread of vegetation led to a fundamental modification of the composition of the atmosphere (which initially contained very little free oxygen, consisting mainly of carbon dioxide and, probably, methane and ammonia). Plants, which assimilate carbon from CO2, led to the creation of an atmosphere that contains free oxygen and only traces of CO2. Free oxygen in the atmosphere served not only as an active chemical agent but also as a source of ozone, which obstructs the path of shortwave ultraviolet rays to the surface of earth (the “ozone screen”). At the same time, carbon, which accumulated for ages in the remains of plants, formed huge energy stores in the earth’s crust in the form of beds of organic compounds (coal and peat). The plant cover changed the physical and chemical character of the planet: specifically, there was a change in the coefficient of reflection of various parts of the solar spectrum by land surfaces. The development of life in the oceans led to the development of sedimentary rocks that consist of the skeletons and other remains of marine organisms. These deposits, and their subjection to mechanical pressure and to chemical and physical transformations, altered the surface of the earth’s crust. Active selective absorption of matter by organisms caused a redistribution of matter in the surface layers of the crust. All this testifies to the presence on earth of a special sheath, which the Soviet geochemist V. I. Vernadskii called the biosphere, in which life phenomena evolved and continue to evolve.
In the course of the evolution of living organisms the processes of regulation and adaptation to external conditions improved continuously; this, in free-moving animals, favored the development of a central nervous system. The development of the most perfected form of higher nervous activity in man’s ancestors under the influence of communal labor created the prerequisites for the transition of life to a new, social, level, which is associated with a new form of movement peculiar to man and qualitatively distinct from the biological movement characteristic of other forms of life. After the transition to this level, with the emergence of social consciousness, it becomes possible to predict development and to create new forms of regulation and adaptation capable of ensuring advantages that are impossible in the process of purely biological development.
REFERENCESEngels, F. Dialektika prirody. K. Marx and F. Engels, Soch., 2nd ed., vol. 20.
Engels, F. Anti-Diihring. K. Marx and F. Engels, Soch., 2nd ed., vol. 20.
Lenin, V. I. Materialism i empiriokrititsizm. Poln. sobr. soch., 5th ed., vol. 18.
Vernadskii, V. l.Biosfera, vols. 1–2. Leningrad, 1926.
Bauer, E. S. Teoreticheskaia biologiia. Moscow-Leningrad, 1935.
Schrodinger, E. Chto takoe zhizn’s tochki zreniia fiziki? Moscow, 1947. (Translated from English.)
Shmal’gauzen, I. I. Kiberneticheskie voprosy biologii. Novosibirsk, 1968.
Malinovskii, A. A. “Nekotorye voprosy organizatsii biologicheskikh sistem.” In the collection Organizatsiia i upravlenie. Moscow, 1968.
Engel’gardt, V. “Problema zhizni v sovremennom estestvoznanii.” Kommunist, 1969, no. 3.
Bertalanffy, L. von. Problems of Life. New York [I960].
A. A. MALINOVSKII
an American weekly picture magazine, published from 1936 to 1972 in New York by Time Inc. Life published photo essays on problems of international relations, US domestic and foreign policy, science, literature, and art, as well as entertainment features. One of the magazine’s main purposes was to advocate “the American way of life.” In 1973 financial difficulties brought an end to the magazine’s publication.
An object-oriented, functional, constraint-based language by Hassan Ait-Kacy <email@example.com> et al of MCC, Austin TX, 1987. LIFE integrates ideas from LOGIN and LeFun.
Mailing list: firstname.lastname@example.org.
See also Wild_LIFE.
["Is There a Meaning to LIFE?", H. Ait-Kacy et al, Intl Conf on Logic Prog, 1991].
Conway first devised what he called "The Game of Life" and "ran" it using plates placed on floor tiles in his house. Because of he ran out of floor space and kept stepping on the plates, he later moved to doing it on paper or on a checkerboard, and then moved to running Life as a computer program on a PDP-7. That first implementation of Life as a computer program was written by M. J. T. Guy and S. R. Bourne (the author of Unix's Bourne shell).
Life uses a rectangular grid of binary (live or dead) cells each of which is updated at each step according to the previous state of its eight neighbours as follows: a live cell with less than two, or more than three, live neighbours dies. A dead cell with exactly three neighbours becomes alive. Other cells do not change.
While the rules are fairly simple, the patterns that can arise are of a complexity resembling that of organic systems -- hence the name "Life".
Many hackers pass through a stage of fascination with Life, and hackers at various places contributed heavily to the mathematical analysis of this game (most notably Bill Gosper at MIT, who even implemented Life in TECO!; see Gosperism). When a hacker mentions "life", he is more likely to mean this game than the magazine, the breakfast cereal, the 1950s-era board game or the human state of existence.
["Scientific American" 223, October 1970, p120-123, 224; February 1971 p121-117, Martin Gardner].
["The Garden in The Machine: the Emerging Science of Artificial Life", Claus Emmeche, 1994].
["Winning Ways, For Your Mathematical Plays", Elwyn R. Berlekamp, John Horton Conway and Richard K. Guy, 1982].
["The Recursive Universe: Cosmic Complexity and the Limits of Scientific Knowledge", William Poundstone, 1985].