Academician V.I. Vernadsky also adhered to the panspermia hypothesis. In his opinion, life in the Universe is spreading with the help light quanta. As for Earth, life could have occurred when a meteorite being a particle of other planet that disintegrated as a result of some kind of disaster hit our planet. The fragments of such a planet with bacteria or other microorganisms could go beyond the planet and get to Earth.
Fred Hoyle and Chandra Wickramasinghe, while studying the interstellar matter properties, noted that the cosmic dusts infrared spectra are very similar to the organic matters spectra, to the dry bacteria, in particular. These scientists observations served the basis for putting forward the idea of the microorganisms possible existence in the interstellar space cosmic dusts clouds. They suggested that within the period of 4.63.8 billion years ago, the life occurrence on Earth was the result of the microorganisms ingress from outer space. According to their calculations, a large number of space spores annually enter the upper atmosphere of Earth as the remnants of solid material scattered in the solar system. According to their ideas, comets are the life embryos carriers that were earlier formed in the interstellar space.
Francis Crick, the Nobel Prize winner for the DNA code discovery, also suggested in his book «Life Itself: Its Origin and Nature» (1982) that life on Earth did not occur by itself, it occurred through controlled panspermia, that is, through Earths deliberate colonization by microorganisms delivered on unmanned spacecraft by a developed alien civilization, which may have tried to perform terraforming for future colonization.
M. Sherman, a professor of Boston University, put forward the hypothesis of the «universal genomes» artificial occurrence in Cambria to explain the causes of the so-called Cambrian explosion in the evolution of multicellular organisms. Moreover, he insists on the possibility of his hypothesiss scientific verification.
In favour of their views, supporters of the panspermia hypothesis provide two indirect evidences in favour of their views: the genetic code universality and the need of molybdenum availability for the normal metabolism for all living creatures, which is currently extremely rare on the planet. Supporters of the comet panspermia theory deny the life spreading from one planet to other one processs controllability, and suggest its spontaneity and chance.
Taking into consideration the fact that the life spontaneous occurrences probability on Earth is extremely negligible, the panspermia hypothesis is the most real in comparison with both the evolutionary theory and religious beliefs. Its disadvantage is that it does not explain how and where the first microorganisms to come to Earth were formed; it only indicates the other place where it could have occurred, but does not explain the process and the reasons for the given occurrence.
1.3. THE EVOLUTIONARY THEORY
The evolution theory is highly ranked in the study of the history of the origin of life on Earth. Jean-Baptiste Lamarck was the first to identify two most common trends of the life on Earths development: the upward development from simplest forms to more complex and advanced ones and the adaptations formation in organisms depending on environmental conditions (vertical and horizontal development). In his works, the scientist noted the organisms historical development, which is not of random but of regular nature and occurs in the direction of gradual and steady improvement. He believed that the organisms development is not a spontaneous process. In his opinion, «the natures drive for progress», «the drive for perfection» was originally inherent in all organisms and laid down in them by the Creator. He argued in his paper «Philosophy of Zoology» that subsequent generations are able to inherit acquired useful properties thus forming new species. For example, in his opinion, giraffes generated from antelopes due to the constant extension of their necks when they tried to reach the leaves on the tops of trees.
Ch. Darwin, being inspired by similar examples, continued the Lamarckian series of assumptions. In his book «The Origin of Species through Natural Selection,» he revealed the main organic worlds evolution factors. Approximately at the same time, Alfred Russel Wallace published an article entitled «On the Law Which Has Regulated the Introduction of New Species», in which he came up with the idea of «survival of the most adapted ones».
Ch. Darwin grounded the theory of the gradual evolution of some species into other ones under the influence of such factors as the survival of the most adapted, the struggle for existence, natural selection, and adaptability to environmental conditions.
The essence of evolutionary doctrine lies in the following main points:
1. All the living creatures types that inhabit Earth have never been created by anyone.
2. Having occurred in a natural way, organic forms slowly and gradually transformed and improved in accordance with the surrounding conditions.
3. The species transformation in nature is based on such organisms properties as heredity and variability, as well as natural selection constantly occurring in nature.
4. Natural selection is carried out through a complex interaction of organisms with each other and with factors of inanimate nature; Ch. Darwin called this relationship a struggle for existence.
5. The adaptability of organisms to their living conditions and the diversity of species in nature is the result of evolution.
According to the mentioned above provisions, a variety of species possessing new specific features allowing a better adaptation to the environment (habitat) can be formed within each species. If the newly acquired qualities are inherited, then genetic differences are amplified in subsequent generations due to the selection of properties that ensure the genotypes survival and the new mutations accumulation. The mentioned above variety of species adapts better to existing conditions, phenotypically moving away from the parent species. Intraspecific competition leads to the deliberate (selective) removal of the least adapted to the environment individuals and an increase in the number of individuals whose properties favour the survival and reproduction in this habitat. According to the evolutionary theory proponents, such a natural selection is the main mechanism for the new species occurrence. Evolution is a process of long-term and gradual qualitative changes that ultimately result in the new species occurrence.
According to some evolutionary theorys advocates, the palaeontological, biogeographic, systematics, plant and animal breeding, morphological, comparative embryology and comparative biochemistry data confirm the evolutionary occurrence of species through natural selection, although they are not indisputable evidence. Three groups of facts are used to confirm the theory. The first group represents examples of species minor changes observed within a geologically short period of time in the wild nature, as well as the results of agricultural plants and domestic animals breeding. The second group is the fossil record, which indicates a significant variability of life throughout the history of Earth. The third group of evidences deals with the similarity of the morphological features of the all organisms structure, which may indicate their common origin. All explanations of the facts discovered are reduced to a spontaneous random process without any intellectual interference in the programming system.
Charles Darwin formulated his theory of evolution in accordance with the morphological and physiological characteristics, using the natural selection ideas, but did not determine the source of variability in the population. A synthetic theory of evolution combining the Darwinian natural selections idea with the laws of heredity and population genetics was developed in the middle of the last century. Currently, it is the most developed system of ideas regarding the speciations processes. The hypothesis of the new genes recessivity was the impetus for its development; according to it mutations constantly arise in each reproducing group of organisms during the gamete maturation as a result of errors in the DNA replication. Therefore, the mutation process is the most important evolutionary factor, and the bulk of evolutionary material is represented by various forms of mutations, which are manifested by means of changes in the hereditary properties of organisms that occur naturally or are caused by artificial means. After the different types of isolations occurrence between populations, they begin to evolve independently, and as a result, genetic differences are gradually accumulated between them, and with time genetic incompatibility is achieved, and crossing becomes impossible.
Charles Darwin formulated his theory of evolution in accordance with the morphological and physiological characteristics, using the natural selection ideas, but did not determine the source of variability in the population. A synthetic theory of evolution combining the Darwinian natural selections idea with the laws of heredity and population genetics was developed in the middle of the last century. Currently, it is the most developed system of ideas regarding the speciations processes. The hypothesis of the new genes recessivity was the impetus for its development; according to it mutations constantly arise in each reproducing group of organisms during the gamete maturation as a result of errors in the DNA replication. Therefore, the mutation process is the most important evolutionary factor, and the bulk of evolutionary material is represented by various forms of mutations, which are manifested by means of changes in the hereditary properties of organisms that occur naturally or are caused by artificial means. After the different types of isolations occurrence between populations, they begin to evolve independently, and as a result, genetic differences are gradually accumulated between them, and with time genetic incompatibility is achieved, and crossing becomes impossible.
Julian Huxley, the English biologist and naturalist, indicates in his famous book «Evolution: The Modern Synthesis» (1942) that the species is a system of populations that are reproductively isolated from other species populations, and each species is ecologically isolated; speciation lies in the genetic isolating mechanisms occurrence and is carried out mainly in conditions of geographical isolation. According to the J. Huxleys ideas, reproductive isolation is the main criterion that indicates the speciations completion.
According to the synthetic theory of evolution, the formation of new species occurs as a result of the separation of individuals of one species into groups that do not interbreed, and the very evolution is defined as the populations genetic structure change over time. The alleles frequency changes thus becoming more or less common compared to other forms of this gene. The acting evolution forces lead to changes in the allele frequency in this or that direction. The change disappears when the new allele reaches the fixation point it completely replaces the ancestral allele or disappears from the population. Mutations increase the populations variability due to the emergence of new genes allelic variants mutational variability. If any allele increases the organisms adaptability more than other ones of the given gene, then the share of this allele in the population will increase with each generation, i.e., selection takes place in favour of this allele. Evolution through the natural selection is a process in which mutations increasing the organisms adaptability are fixed. As a result, three processes are necessary for the evolutions implementation: mutational (to generate new variants of genes with a low phenotypic expression); recombination (to create new phenotypes of individuals), and selection (to determine the compliance of these phenotypes with the given living conditions or growth).
Judging by the palaeontological chronical and by the mutations speed indexes, this concept advocates believe that it takes in average 3 million years to reach the complete incompatibility of genomes, which makes crossing impossible. Therefore, it is a rear event to witness the new species formation in natural environment.
In addition to mutational, there is also the combinatorial variability distinguished, which is determined by recombination, but it leads not to the allele frequencies changes but to their new combinations.
The gene drift is one more factor contributing to the allele frequencies changes.
The synthetic theory of evolution differs from the Ch. Darwins evolution in the following points:
1. It distinguishes a population in which the same species individuals are able to interbreed, and but not an individual or a separate species.
2. It considers a steady change in the population genotypes change the process of evolution.
3. Mutational processes and isolation are treated as the leading factors.
4. The mutational and recombinative variability are the material for evolution.
5. Natural selection is considered as the main reason for the adaptations and speciations development.
In accordance with the synthetic theory of evolution speciation is a time-consuming process. However, J. B. S. Haldane found a discrepancy between the real speciation speed and the expected one based on the population genetics models (Haldanes dilemma) by means of mathematical calculations. He published an article «Cost of Natural Selection» on the basis of his research in the «Journal of Genetics» scientific edition. D. Haldane calculated the mathematical relationship between the intensity of selection and rate of the existing alleles substitution in the population by other, more adapted ones. He also evaluated the mortality rate caused by the positive natural selection, while maintaining the mutant gene. According to his calculations, the speciation would have taken much more time for the stage-to-stage formation than it has actually taken (according to the paleontological data) for the implementation of speciation would require much more time than is actually observed (according to palaeontological data).
Later, M. Kimura, while studying the rate of amino acid substitutions in proteins, found that for mammals the substitution rate for the genome per generation was several hundred times higher than the Haldanes estimation. Kimura showed that in order to maintain a constant population size while preserving mutational substitutions, the rate of occurrence of which stands to one substitution in two years, each parent should produce 3.27 106 descendants so that one of them survives and begins to breed. The mismatch of this impressive number with real data served as the basis for the «Neutral Molecular Evolution Theory» development.
Another argument in favour of this theorys development was the fact that the assumption regarding more frequent occurrence of favourable mutations (in reality, such mutations are rather rare compared to the adverse ones) was necessary in order to explain the molecular evolution rate provided it proceeds under the natural selection influence.
The «neutral evolution» hypothesis main content lies in the point that majority of the changes at the macromolecular level are not controlled by natural selection as Darwins theory states, but are determined by the random drift of neutral mutations. According to the authors, this theory is proved by a number of direct and indirect arguments. At the same time, the neutral molecular evolution theory does not turn down the role of natural selection in the development of life on Earth, but emphasizes the proportion of mutations that possess adaptive significance. This theory has demonstrated that the processes associated with speciation are still far from a final explanation based on population-genetic models.
Modern synthetic theory of evolution has a number of disadvantages. It makes no distinction between macroevolution and microevolution, considering one the continuation of other one on a larger scale. Such views advocates have detected genetic changes from the populations original composition from generation to generation, in various laboratory scientific experiments, including the model organisms development (drosophila, mice, and bacteria). It gave the grounds to assume that both microevolution and macroevolution are based on the same mechanisms and, in their view, minor changes can lead to significant ones over time, but the authors provide no evidences to prove it. Experts have no doubts regarding the microevolutionary processes within the species, for example, the hair colour or skin colour change, the beak shape, etc., due to which many types of breeds and sorts can exist within the same species. However, microevolution is determined by the alleles frequencys change in a population (i.e. genetic variability due to such processes as selection, mutation, genetic drift), while the macroevolution involves changes at the species level or higher.