- a hereditary program, recorded in the aggregate of genes (genome), i.e., in the corresponding nucleotide sequences of deoxyribonucleic acid (DNA);
- self-reproduction following this program.
The code by which the hereditary program is recorded is universal, so that all living beings use the same universal scheme for encoding, transferring (and translating) information and biosynthesis. In these processes, two types of molecules predominate nucleic acids as carriers of the “legislative” principle and proteins as carriers of the “executive” principle.
The genome (hereditary program) of an organism can be conditionally subdivided into constitutive and facultative. The constitutive genome is the sum of the structural genes encoding the biologically active macromolecules (proteins and enzymes, ribosomal and transport ribonucleic acid-RNA, etc.) that are present in the genome, mainly ensuring the heredity conservatism, the stability of this specific hereditary program that determines the development and functioning of the organism. An optional genome is that part of it that is labile, optional, and contains so-called mobile genetic elements that can change their position in the genome, “enter” into it or leave “hard” places, as well as numerous types of repeating DNA sequences that are hypervariable. The optional genome provides for genetic variability of the genome: most of the spontaneous (not caused by any external influences) mutations (changes in genes) are caused by movements of mobile genetic elements, and relatively frequent quantitative and qualitative changes in repeating DNA sequences can induce significant functional shifts, sometimes leading to diseases.
Thus, at the heart of life lies a specific and rather complex genetic program, which is realized through metabolism, metabolism, as the second necessary element of any form of life. Only by continually using the influx of free energy, the system can be continuously updated and this slows down its descent into the state of thermodynamic equilibrium, which E. Schrödinger called the land of death. The dynamical order inherent in life processes can be maintained only through constant compensation of entropy production.
Finally, the molecules and specific ordered supramolecular formations that have arisen through intermolecular interactions have a limited lifetime due to thermal motion. In order not to lose the information accumulated in them, they must manage to have at least one identical copy containing the plan for the structure and functioning of the original structure before it decays. Consequently, life activity based on the realization of the genetic program does not die out due to the process of self-reproduction proceeding according to the plan recorded in the hereditary program, as a result of which the descendants acquire those features of the organization and functions that were inherent in the ancestors.
On the issue of the origin of life on Earth, there are three hypotheses:
- the hypothesis of the natural origin of life,
- the hypothesis of skidding life from the Cosmos,
- the hypothesis of the creation of the living.
The preference of a hypothesis is more to do with faith than with knowledge since none of them is provided with the necessary and sufficient evidence of scientific truth by the factual material. One of the main difficulties in constructing the first hypothesis is the lack of reliable information about the state of the planet during the “birth” of life. Moreover, the ideas about the conditions that existed on it at the time of such a “birth” are constantly changing, and the formulation of a concrete scheme for the emergence of a living system depends on this, which, therefore, with every discovery changes beyond recognition, often quite the opposite.
The contradictory nature of such views serves as a significant obstacle to the creation of a convincing concept of the origin of life. In addition, the specificity of the organization of living systems is not usually taken into account, namely that they can not occur consistently and gradually, because each of the constituent parts of them is meaningless in itself: for example, the ribosome, the cellular organoid involved in protein synthesis, is characterized by complex structure, consists of many (several dozen) components, strictly “tied” to each other, it has a “meaning” only as a whole. Nevertheless, life on Earth appeared very early – the first living creatures of approximately 4.25 billion years ago. Mechanisms of photosynthesis arose 3.7-2.5 billion years ago, rather complex living organisms (eukaryotes) – 1.6-1.35 billion years ago. Therefore, numerous “sketches” that paint a picture of the gradual emergence of a living system from the inanimate (whatever form they take on) are purely speculative.
The possibility of experimental formation of some components from which living organisms (amino acids, nitrogenous bases, carbohydrates, nucleosides, nucleotides, lipids) are built does not at all prove the hypothesis of the natural origin of life. First, these components did not arise naturally but were obtained by reasonably planned experiments in the laboratory, and secondly, the distance from these components to living matter is too large to make it possible to make some experiments far-reaching conclusions. In fact, they do not even reveal the veil over the mystery of the origin of life on Earth, and regarding solving this problem are unpromising.
The concept of the introduction of the living from the Cosmos does not explain the origin of life, but only pushes its solution to another plane and another point of the universe. Some authors (for example, an astronomer from India Vikramasinghe) suggest that the Cosmos from time immemorial is filled with the simplest forms of life, spreading to its various “regions” and reached by unknown circumstances of our planet. But views of this kind can only be accepted as faith and in a certain sense equivalent to the third hypothesis. In this regard, the Russian paleontologist Boris Sokolov believes that it would be more correct and accurate to speak not about the origin, but about the appearance of life on Earth. The question of how it appeared is still open.
At the same time, it is undeniable that the various forms of the living have undergone a process of evolutionary transformation after their appearance. This is evidenced by the data of paleontology, pointing to the fact that in various strata of the earth’s crust there are found essentially different remains of living beings and, consequently, different periods of the Earth’s existence were characterized by a change in flora and fauna. And although the mechanisms of evolutionary transformations are not sufficiently studied and in many respects remain undeciphered, the very fact of their existence can be considered proven.