Origin of Life
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Origin of Life
one of the central problems of natural science.
Theologians and idealists (finalists, holists, organicists) assert that life is the creative act of a spiritual source and “higher intelligence,” god. Materialists, on the other hand, believe that life is material in origin and arose naturally as a result of the general laws of nature. Mechanistic materialism, the prevailing view in natural science at the turn of the 20th century, attempted to understand life by comparing the organism to a machine. This theory was inadequate in rationally resolving the problem of the origin of life. Only dialectical materialism, as discussed in F. Engels’ Dialectics of Nature, explained life’s beginning.
During the first two decades of the 20th century, there were two prevailing concepts on the origin of life on earth. According to one, life was brought to the earth from without, and according to the other, life was the result of the chance formation of a single organic molecule, whose structure contained the entire plan for the subsequent development of life. Both concepts excluded the possibility of a scientific approach to solving the problem of life’s origin. They were mere cunning tricks of the mind that evaded the resolution of the problem.
The first attempt at a systematic explanation of the origin of life was A. I. Oparin’s The Origin of Life (1924), which contained the first formulation of the origin of life on earth based on natural science. Oparin believed that life emerged as a result of the prolonged evolution of matter. By correlating the facts established by natural science, he traced the natural history and subsequent evolution of organic compounds, simple structures, energy processes, and biochemical functions that could have been present on the earth during the period of the emergence and establishment of life. As J. Bernal remarked (1967), this theory is the basis of almost all the modern concepts on the origin of life.
On the basis of facts accumulated over the past 50 years, the emergence of life on earth must be considered a natural process of the evolution of carbonaceous compounds. Radio astronomical studies, revealing the presence of carbonaceous compounds in the interstellar medium, and the study of cometary spectra and the chemical composition of meteorites have shown that organic substances originated not only before the appearance of life (which earlier had been categorically denied) but even before the formation of our planet. Consequently, organic matter of abiogenetic origin was already present at the time of the earth’s formation. Chemical and paleontological investigations of the oldest Precambrian deposits and especially the numerous experiments reproducing the conditions on the earth’s primeval surface have made it possible to understand how, under those conditions, the formation of increasingly more complex organic substances occurred, including polypeptides and polynucleotides. The abiogenesis of the simplest hydrocarbons—the first step in the development of organic matter—is thus indisputable.
The greatest contribution to the development of the theory of the origin of life was made by Oparin and the American scientist H. Urey, who theorized that the initial atmosphere of the earth had reductional properties and that at a certain stage of its development it must have contained, along with gaseous hydrogen and water vapor, carbonaceous compounds (in the form of methane [CH4] and cyanogen [CN]) and nitrogen (in the form of ammonia [NH3]). With time, the composition of the atmosphere gradually changed. Its oxygen content increased as a result of the development of primitive anaerobic forms of life, and the atmosphere began acquiring oxidative properties. Scientists have established that the earth formed more than 4.5 billion years ago and that the first signs of life appeared 2 to 3 billion years ago. The period of time when no life existed on the earth is called the period of chemical evolution. During this period, various chemical transformations occurred resulting in the formation of complex organic substances. These substances became the components of the phase-individuated systems of organic substances (probionts) and later the components of the simplest living cells (protocells). The creation of protocells marked the beginning of biological evolution. Theories that the chemical evolution of matter led to the origin of life have been confirmed by experiments, in which the most important organic compounds were abiogenetically synthesized in systems that simulated the chemical composition of the primeval atmosphere of the earth. These experiments are one of the basic proofs of the theory of the origin of life advanced by Soviet scientists.
In 1953, S. Miller, an American scientist, conducted studies on abiogenetic synthesis; he synthesized a series of amino acids by passing an electrical discharge through a gaseous mixture presumed to have the same composition as the primeval atmosphere of the earth. In 1956 the Soviet scientists A. G. Pasynskii and T. E. Pavlovskaia demonstrated that it is possible to form amino acids by the ultraviolet irradiation of a gaseous mixture of formaldehyde and ammonium salts. In 1960, J. Oro, a Spanish scientist, abiogenetically synthesized the components of nucleic acids—purines, pyrimidines, ribose, and deoxyri-bose. American scientists abiogenetically synthesized adenosine triphosphate (ATP), which is the basic source of energy in living organisms (C. Ponnamperuma, 1970). Amino acids, polypeptides, and protein-like substances were also abiogenetically synthesized (S. Fox, 1969). These experiments proved that the abiogenetic formation of organic compounds in the universe could have occurred as a result of heat energy, ionizing and ultraviolet radiation, and electrical discharges. A primary source of these forms of energy are the thermonuclear processes that occur within stars.
Extensive geological investigations show that in the early geosynclinal period of the orogenic cycle of the earth’s surface, the waters that permeated the ground continually transported dissolved substances from their places of formation to their places of accumulation and concentration. On the same sub-vital territories, increasingly more complex substances were synthesizing at the same time that the decomposition and subsequent new synthesis of other organic substances was also occurring. Such processes could have led to the repeated development of probionts. This concept completely excludes the hypothesis that life originated by chance and is especially significant in understanding the transition from chemical to biological evolution. This transition must certainly have been the result of the emergence of polymolecular, phase-individuated, and open systems capable of interacting with the external environment, that is, of growing and developing by using the environment’s matter and energy, thus avoiding an increase in entropy.
Simulated experiments with phase-individuated systems (probionts) were conducted primarily by Oparin and his colleagues, who separated coacervate drops from the aqueous solutions of various organic polymers. It was shown that phase-individuated systems are able to absorb various energy-rich substances from the surrounding solution and, as a result, grow in size and mass. The rate of the process is determined by the chemical and spatial organization characteristic of each individual drop, so that two types of drops in the same solution behave differently. Some drops grow rapidly, while others grow slowly and may even decompose. These simulated experiments have shown that a primitive selection of drops is possible, depending on their interaction with the external environment.
Beginning in 1964, Fox and his colleagues investigated microspheres—spherical formations that arise when there is solution and subsequent condensation of protein-like substances abiogenetically obtained by them. It has been shown that in the process of synthesizing these substances from amino acids, guanine and fatty acids are formed. Microspheres are thus of interest in studying one of the ways that cells appeared. A possible way that the phase-individuated systems of organic substances emerged could have been the spontaneous formation of surface films and elementary membranes (R. Goldacre, Great Britain, 1963).
The concept that the chemical evolution of matter resulted in the emergence of life remains indisputable, regardless of which formation theory is considered most probable. Polymolecular systems were formed and later subjected to adaptation and evolution. The proposition that the initial formation of living systems was dependent on the emergence of internally organized and efficiently structured molecular protein substances and nucleic acids in the primeval hydrosphere of the earth is still very popular. The formation of primitive organisms was presumably the result of the joining of molecules. Still unclear is the question of the independent formation of the molecules of proteins and nucleic acids, which not only had definite intramolecular structures but were also adapted to performing the functions of integral living systems.
The emergence and perfection of the adaptability of the intramolecular structure of proteins and nucleic acids to their organic functions could only have occurred by the natural selection of integral evolving systems—probionts—and the living systems that developed from them. Probionts were converted into systems of a higher order—living organisms—as a result of prolonged evolution and natural selection. The appearance of nucleic acids as the bearers of genetic information and of enzymes as biochemical catalysts could not have led to the emergence of life without a system that would ensure the transmission of genetic information and the constant synthesis of enzymes. Precisely for this reason it is impossible to imagine that a single nucleic-acid or nucleoprotein (virus) molecule was the beginning of life. The development of the genetic code meant that parents would transmit genetic information to offspring, which has become one of the basic characteristics of organisms.
What happened on the earth could certainly have also occurred in other parts of the universe. This is the basis for the conviction that life exists on other planets. However, authentic signs of life have not yet been discovered either in outer space or on the planets closest to us in our solar system.
REFERENCESEngels, F. “Dialektika prirody.” In K.. Marx and F. Engels, Sock, 2nd ed., vol. 20.
Oparin, A. I. Proiskhozhdenie zhizni. Moscow. 1924.
Oparin, A. 1. Vozniknovenie i nachal’noe razvitie zhizni. [Moscow, 1966.)
Oparin, A. I. “Filosofskii i estestvennoistoricheskii aspekt problemy proiskhozhdeniia zhizni.” Izv. AN SSSR: Ser. biologicheskaia, 1970, no. 5.
Oparin, A. I. “Istoriia vozniknoveniia i razvitiia teorii proiskhozhdeniia zhizni.” Izv. AN SSSR: Ser. biologicheskaia, 1972, no. 6.
Bernal, J. Vozniknovenie zhizni. Moscow, 1969. (Translated from English.)
Rutten, M. G. Proiskhozhdenie zhizni (estestvennym putem). Moscow, 1973. (Translated from English.)
Calvin, M. Chemical Evolution. Oxford, 1969.
A. I. OPARIN AND G. A. DEBORIN