Termodynamic Trends in Biological Evolution

THEORETICAL BIOLOGY
Thermodynamic Trends in Biological Evolution

G. P. Gladyshev

Semenov Institute of Chemical Physics, Russian Academy of Sciences, ul. Kosygina 4, Moscow, 117977 Russia. Received September 27,1993

Abstract - The available data on the thermodynamic stability of supramolecular biological structures and variations in the chemical composition of living organisms have allowed a macrothermodynamic model of biological evolution to be developed experimentally. In this model, the tendency toward a minimum of the specific Gibbs function of the formation of supramolecular structures of living organisms causes variations in the chemical composition and structure of living systems. It is shown that, during the course of ontogenesis and phylogenesis, as well as long-lasting stages in the evolution of the organic world, the biosystems (as a result of the thermodynamic direction of evolutionary processes of the formation of supramolecular structures) are enriched with energy-intensive chemical substances, which displace water from these biosystems. The change in the composition and structure of biostructures of an adaptive character is also explained from the angle of macrothermodynamics.

1.THE HIERARCHY OF STRUCTURES AND MACROTHERMODYNAMICS

There are reasons to assume that biological evolution as a whole, phylogenesis, and ontogenesis (like the general evolution of the Universe and the Earth's geological evolution) have a thermodynamic tendency (Gladyshev, 1988; Gladyshev, 1993). This tendency is conditioned by the second principle of thermodynamics, whose validity is not doubted.

It was noted earlier that understanding the specifics of the biological evolution of matter in the light of the general laws of thermodynamics is made simpler by consideration of the evolutionary process within the framework of structural formation, which results in the emergence of structures (j+1, j+2, ..., j+n) of a higher hierarchical order from the structures (j) of a lower hierarchical order (Gladyshev, 1988; Gladyshev, 1993; Gladyshev, G. and Gladyshev, D., 1993).

It was shown that there is a correspondence between some of the series of natural hierarchical structures (identified by the energies of their formation) and the series of the average lifespan (relaxation) of these structures. For instance, for an individual community of some closely related species of organisms it may be written

where t is the average lifespan of the "free" metabolite molecules, supramolecular structures, organelles, biological tissue cells, organisms, populations, and communities.

There is a correspondence between series (1) and another, oppositely directed, hypothetical series of the times of the establishing of imagined quasi-equilibriums between different uniform structures inside one hierarchy in a preset biomass volume.

Series (1) presents a geometric progression of the type , where t_n is the average lifespan of structures of the nth hierarchy in the identified biosystem; n = 1,2,3,..., n; t₀ is the standard time equal to the average lifespan of the structure of the lower (standard) hierarchy (0) of the series under review; and b is the constant for a given series.

Law (1) makes it possible to lay the foundations of hierarchic thermodynamics or macrothermodynamics (heterogeneous systems), which integrates methods of classical thermodynamics, i.e., thermostatics and macrokinetics - relatively slow, quasi-equilibrium processes. It is essential that series (1) makes it possible to identify the thermostat (the environment) and the system j under study, which forms, together with its thermostat (j+1), a complete thermodynamic system [j+(j+1)]. This complete thermodynamic system [j+(j+1)] is quasi-closed (at the times of the existence of the system under study), since it is contained in a thermostat of a higher hierarchical order (j+2). The latter points to the existence in the biological world of quasi-closed systems (which function against a background of practically constant kinetic factors determining the flow of matter from the environment - the thermostat) and, to a certain extent, helps avoid insuperable difficulties in applying the functions of state to the description of the behavior of open systems of this type. Indeed, in a general case, the functions of state of open systems, such as, say, the Gibbs function (G) and the Helmholtz function (F), cannot attain extreme values in these systems. In this situation, classical thermodynamics, naturally, cannot predict the directions of processes.

Investigation of quasi-closed biosystems isolated with the aid of series (1) and the use of a macrokinetic adsorption model (Gladyshev, 1988; Gladyshev, 1993) has allowed an important postulate to be formulated: the specific values (per unit of volume) of the Gibbs function of intermolecular interactions (where "-" means the specific character of a value and "~" emphasizes the heterogeneous character of the system) tend toward a minimum during the formation of the supramolecular and supracellular structures of organisms:

where V is the volume of the system (m is the mass of the microvolume) and x, y, z are the coordinates. This causes a change in the local and general chemical composition of living organisms and the accumulation of chemically energy-intensive matter by biosystems. In accordance with the model, organisms must accumulate mainly those of the most energy-intensive substances, which (in accordance with the aforesaid postulate) have a relatively increased absolute value of the Gibbs function of the formation of supramolecular structures (structural stabilization). It follows from the model that it is possible to find a correlation between the specific value of the Gibbs function of the formation of chemical compounds of atoms or simple substances and the specific value of the Gibbs function of the formation of supramolecular structures of these chemical compounds - molecules - . In accordance with the model, biostructures must form mainly from relatively high melting substances in the case of enthalpy-controlled self-organization or from relatively low melting structures in the case of entropy-controlled self-organization.

With the aggregation of chemical substances in the water systems of living organisms, these energy-intensive substances displace water relatively slowly from organisms in the process of life.

Note that macrothermodynamics operates with the lifespans (relaxation) of t_l, biostructures. This means that it also relies on the kinetic principle. However, according to the model, t_l depends primarily on the change in the thermodynamic function of state -the Gibbs function - during the formation of the structure . Thus, the adsorption model we use implies that , where R is the gas constant.

The macrothermodynamic approach was also used to propose the theory of the behavior of biological systems on the basis of Le Chatelier-Braun's principle. The latter's application to quasi-closed systems (interchanging matter with its thermostat) is strictly valid only with definite restrictions (de Heer, 1957, 1958). Nevertheless, it has proved possible to trace a qualitative link between the intensity of some physical influences on the organism and its reaction to them, as well as to substantiate the Weber-Fechner empirical law.

2. THE APPROXIMATE CHARACTER OF THE MODEL

The studies carried out suggest a local and general thermodynamic tendency in evolutionary processes. However, the real world of biostructures is certainly more complex than the model, which is by definition inaccurate, since it is based not only on thermostatics but also on macrokinetic principles. Moreover, some of the mathematical problems of the model are insoluble in principle, as are those of any other models of the thermodynamics of complex systems, in which not only the work of expansion is performed (Denbigh, 1971; Sychev, 1981).

As noted above, according to our model, the isolated open system j has (as does each of its locally isolated parts) its own thermostat (j+1), whose parameters remain practically unchanged throught the lifespans of the system (or part of it). The open system j under study, together with its thermostat (j+1), forms a complete thermodynamic system [j+(j+1)]. The model implies at the same time that practically all transformations take place within the open system itself. The model also implies that the formation of supramolecular structures of different types is determined, as is that of the structures of higher hierarchical orders, by thermodynamic factors alone. This is proved by the fact that the energetics of supramolecular interactions is commensurate in scope with k_BT (k_B - Boltzmann constant, T - temperature), and local equilibriums are established relatively quickly. The thermostat parameters are temperature (T): pressure (p); chemical composition ; tension of electric, magnetic fields, etc.). Of course, these parameters often fluctuate noticeably in the space of minutes, hours, 24-hour periods, and years, and organisms, as a rule, have to adapt to such fluctuations. Moreover, each species (like each organism) has its own thermostat (habitat), whose parameters undergo fluctuations in time-scales shorter than the life of this species. The same is true of other biostructures, for instance, cells functioning in biological tissues: their own thermostats of macromolecules are contained in the relevant physiological fluids, etc.

Hence, it is obvious that the thermodynamic tendency in the processes of suprastructural formation (with constant kinetic factors ensuring an inflow of substructures into the system) can be clearly seen at times when the essential (in Tolman's terminology) thermostat parameters are averaged. This can take place with good approximation in cellular ontogenesis, the ontogenesis of organisms, and even in phylogenesis of many species. As for evolution over long periods of time, the real picture is even more approximate. However, the available unambiguous experimental findings on changes in the chemical composition of the biological tissue of different animal and plant species suggest that in this case, too, it would be reasonable to assume the existence of thermostats in the relevant time periods with averaged parameters.

It should be re-emphasized for clarity that with this model it can be assumed that all transformations occur in the isolated open biosystem itself, while the formation of supramolecular structures of different types is determined (as is that of the structures of higher hierarchical orders) practically by thermodynamic factors alone.

On the other hand, sometimes the thermostat parameters change substantially (a sharp climatic change, artificial modification of environmental conditions, artificial selection, etc.). In such cases, there is evidence of revolutionary changes in the environmental parameters and the transformation of the system under study into a new one (with a new thermostat). In the process of revolutionary change, the system becomes essentially unbalanced and open; it can be assumed that the behavior of this system cannot always be studied by macrothermodynamic methods. A system of this type can be studied in principle by kinetic methods with the aid of the thermodynamic models of systems distant from the state of equilibrium (Prigozhin, 1985).

The overall impression is that the fragmentation of biosystems into their hierarchical components is a promising method of study, because it helps establish the thermodynamic tendency (local and general) of evolutionary changes. It appears that the motivating force of evolution is the "thermodynamic force," which operates against a background of fluctuations of the environmental parameters on either side of their averaged values. Note that these fluctuations are accompanied by the adaptive reactions of biosystems that also have a thermodynamic tendency. The said fluctuations are the "source" of work: the environment performs work on the system. Evidently, this work (on a par with work performed using solar and chemical energy) is necessary to support life. The biosystem periodically expands and contracts, as it were, absorbing and expelling matter, i.e., it is a living "sponge" functioning against a background of relatively small fluctuations of T, p, concentrations of chemical substances, and other parameters of the relevant thermostat, with regard to some of the averaged values of these parameters.

Let us examine some examples of variations in the chemical composition and structure of individual molecules, macromolecules, and complex supramolecular systems in ontogenesis and phylogenesis. The phenomena observed will be interpreted from the angle of the macrothermodynamic model.

3. FACTUAL DATA

Some facts referring to variations in chemical composition and confirming the validity of the macrothermodynamic model are discussed in a number of works (Gladyshev, 1988; Kanungo, 1982).

It is perhaps appropriate here to look at the change in the chemical composition and structures of biostructures and biosystems in vivo, which correlate with the melting (denaturation) temperature of these structures, as well as with the body temperatures of homoiothermal animals or the upper temperature limit of the habitats of poikilothemial animals. The study of such correlations is interesting, because a temperature change in phasic transitions often permits judgement on variations in the thermodynamic stability of structures.

3.1. Theoretical considerations. For closed systems, the dependence of the change in the Gibbs function on T is determined by the Gibbs-Helmholtz equation:

where D H is the change in enthalpy during the process, and T and p are the temperature and pressure, respectively. A similar equation was also written for open systems (p and V are constant), whose composition was inconstant. Such an assumption can be considered accurate only for i-substances having identical values , , and , where the index m_i refers to the melting point of i-substances. Nevertheless, it was found that the assumption made was reasonable for a definite range of variations in the thermodynamic characteristics of substances, since a correlation was revealed between the specific Gibbs function of the unbalanced phasic transition of overcooled liquid ® solid body (with standard temperature of 298K) and D T (T_m-298K) for a wide range of organic compounds with T_m in the range of 273-373K. The calculation was based on our approximate equation, an analogue of the Gibbs-Helmholtz approximate equation:

where T₀=298K, while the upper index im indicates that the process of matter condensation is under study. The corresponding results (Gladyshev, G. and Gladyshev, D., l 993) are presented in Fig.1. It can be seen that the aforesaid postulate is correct, with a definite degree of approximation. Indeed, substances with an increased show a tendency to form more thermodynamically stable crystals, i.e., solid structures (a more negative value ), since the processes of crystallization of pure substances must be considered to be mainly enthalpy-controlled. Note that the chemical energy capacity of uniform natural compounds () also grows with an increase in their .

In the case of entropy-controlled processes (for instance, the aggregation of cells under the self-organization of cellular structures, the denaturation of some proteins, etc.), the growth of the thermostability of structures may be accompanied by a decrease in .

Note that our approach agrees with the approximate models of P.Flory, who used the Gibbs-Helmholtz equation to establish the connection of T_m synthetic copolymers with their composition and structure (Flory, 1953; Mandelkern, 1964).

3.2. Variation in the composition of fatty acids participating in the synthesis of fats. There is much data providing evidence that the cells of microorganisms, plants, and animals adaptively change the composition of fatty acids (fats) with a change in the temperature of the environment. When the temperature of an organism T_l is below the optimum level, there is an increase in the content of unsaturated fatty acids (fatty acid residue) having a lower melting point T_m (as compared with saturated and other unsaturated acids). This increase is easily detected by the increase in the iodine number of the relevant fatty acid fractions. When the temperature is above the optimum level, the cells show an increase in the proportion of saturated acids having a higher melting point.

The aforesaid is illustrated by Frenkel and Hoppe's classic data on the relationship of the iodine number of phosphatides (lipids) or larvae Calliphora erythrocephala and Phormia terranova to the maturation temperature of flies (Aleksandrov, 1975, p.274). It can be seen in Fig.2 that at increased maturation temperatures the number of unsaturated acids (characterized by a heightened iodine number and a lowered T_m) drops. Other research results are given in a monograph (Aleksandrov, 1975) and numerous reference publications (Libermann and Petrovsky, 1960; Marsh, 1990).

Ignoring kinetic problems, i.e., the question of the mechanisms responsible for compensatory change in the composition of fatty acids, and examining this phenomenon from the angle of the macrothermodynamics of the formation of lipid structures (against a background of constant kinetic factors), we can draw the following conclusion.

The regularities observed can be easily interpreted on the basis of our macrothennodynamic model, reasonably assuming that the correlation of enthalpy-entropy control during the formation of "solid" uniform structures containing fatty acids changes insignificantly in the adaptive temperature interval.

Let us examine the data of Table 1 and show by examples that the observed change in the chemical composition of fatty acids (fats) of biological tissues in ontogenesis with a change in temperature is thermodynamically advantageous.

Table 1 Several fatty acids whose residuals are contained in natural fats*

*Values of T_m and are taken from reference literature [16]. The estimations for are done using Eq. (7) for the case of crystallisation (hardening) of substances from over-cooled state at 25 and 5° C. **The values of are positive since the standard temperature 25° C (5° C) is higher than T_m. Under this condition, crystallisation of matter is impossible.

According to the model, the unit of volume V_i of adipose tissue (cell) receives a flow of matter from the thermostat (environment), in which a constant concentration of fatty acids (fats) is maintained (the thermostat temperature within its physiological values has no substantial influence on the values of ). The volume V_i under review is like a chromatographic column adsorbing incoming substances. Its calculation (Gladyshev, 1988; Gladyshev, 1993) is based on the following obvious correlation:

where c_s and c_l are fatty acid concentrations in the volume V_i in solid (adsorbed) and liquid state, respectively; is the change in the Gibbs function with the adsorption of fatty acids. Assuming that are close to values of the crystallization of individual acids (Table 1), let us make these simple operations:

For example, for palmitic acid at 25°C, . This means that, in accordance with this model, from 1 mole (for convenience, calculation is based on 1 mole, although the amount of matter in volume V is much less) of this acid received from the thermostat by the adipose tissue cell, 0.917 of a mole will pass into the solid phase and 0.083 of a mole will remain in the liquid phase. At 5°C, 0.982 of a mole will go to the solid phase and 0.018 of a mole will stay in the liquid phase. Thus, the amount of palmitic acid in the solid phase at a temperature decrease from 25 to 5°C increases times.

For elaidic acid, at 25°C, 0.723 of a mole will pass into the solid phase and 0.277 of a mole will remain in the liquid phase; at 5°C, 0.890 of a mole will pass into the solid phase and 0.110 of a mole will remain in the liquid phase. Hence,

For oleic acid, at 25°C, 0.408 of a mole will pass into the solid phase and 0.592 of a mole will remain in the liquid phase; at 5°C, 0.624 of a mole will pass into the solid phase and 0.375 of a mole will remain in the liquid phase. Hence,

Thus, according to the model calculation, on changing the temperature of biological tissue from 25 to 5°C the amount of palmitic, elaidic, and oleic acids will increase 1.07, 1.23, and 1.53 times, respectively. Although our simple model ignores a number of effects, its results are in complete agreement with the known facts indicating that with a decrease in animal body temperature the relative amount of unsaturated acids (substances with a relatively low T_m increases and that of saturated acids decreases.

Such conclusions can be drawn from qualitative assessments directly for the fats (lipids) themselves. In the future, it would be wise to make computer-aided calculations of variations in the composition of different natural fats, depending on the fatty tissue temperature of an animal.

Note that we have used for assessment an approximate equation (3) for a relatively wide temperature range. However, this does not alter the general tendency of the phenomena, because corrections for the change in thermal capacity with a temperature in the cases we have studied, even though they are essential, are commensurate in the cases under review (Ullmann's Encyclopedia ..., 1987; Stull et al., 1969).

Besides, we compared the value of only for fatty acids rather than for fatty tissue itself. Nevertheless, this circumstance does not change the general picture of the phenomenon either, because the strict correlations between the thermodynamic characteristics of fatty acids and fats (T_m and D H_m) and their content of various fatty acid residues (Ullmann's Encyclopedia ...,1987) are well-known.

Thus, the model calculations (made with relatively high precision for added conviction) unambiguously confirm the applicability of the macrothermodynamic model to the evolution of adipose tissue of organisms, explaining the causes of variations in the chemical composition of fatty acids (fats) in terms of the adaptation of organisms to the temperature conditions of their environment.

Relying on the macrothermodynamic model, it is possible to understand the nature of change in the composition of adipose tissue in the ontogenesis and phylogenesis of animals. However, in these cases conclusions should be drawn taking into consideration the type of adipose tissue, sex, fatness, and the conditions of keeping the animals (the character of feed, etc.). With all the essential characteristics of the animal and the environmental conditions remaining constant, the process of ontogenesis shows a regular decrease in the water content of adipose tissue, which increases its chemical energy capacity (). The fatty acid composition of tissues in ontogenesis also changes (Table 2): evidently, the relative content of unsaturated acids often increases (the iodine number grows), which also brings about an increase in the chemical energy capacity of adipose tissue ().

In addition, a number of known examples indicate that the capacity of the organism (biological tissue) to absorb lipids increases with the age of animals. For instance, vitamin A and cholesterol absorption by the small intestine of rats in ontogenesis increases substantially (Table 3; Cristofalo,1985).

Thus, despite some limitations of the simple model used and the influence of many factors (including genetic ones) on the thermodynamic parameters of lipid-containing living systems, one can draw this conclusion: adaptive and evolutionary changes in the lipid composition of living systems evidently always have a thermodynamic tendency.

3.3. Variations in the structure and composition of collagen. It is an accepted view (Nikitin et al., 1977) that change in the properties of collagen structures in ontogenesis has an adaptive character. It has been found that the temperature of collagen denaturation in homoiothermal animals is close to their body temperature and in poikilothermal animals is close to the upper temperature limit of their environment (i.e., the highest body temperature of an animal).

Figure 3 shows the generally known dependence of the temperature of denaturation T_d of collagen molecules on body temperature (homoiothermal animals) or on the upper temperature limit of the environment (poikilothennal animals), T_l, (Rigby, 1971; Nikitin et al., 1977). In view of the macrothermodynamic model, it can be assumed that adaptation of the composition and structure of collagen tissue in vivo, just as in the case of fats, has a thermodynamic character. Naturally, T_d > T_l

and hence , has a negative value in the formation of collagen structures. The values D T_d= T_d-T_l for the collagen structures of all the animal species studied vary insignificantly. This means that the relative thermodynamic stability of the collagen structures of animals referred to T, of each type is practically identical.

This confirms the reasons for using the concept of Aleksandrov et al. (1975) concerning the semistable state of biological macromolecules. However, the "absolute" thermodynamic stability of collagens referred to, standard T₀ [(see equation (3)], is evidently determined primarily by their T_m(T_d) and in the icefish, cod, tuna, snail (cow, rat, human), and swine series tends to grow. At the same time, ignoring the variation in the structure and chemical composition of collagen, it is difficult to draw from Fig. 3 an unambiguous conclusion on the thermodynamic tendency of evolution. Also unclear are the role and fluctuations of the thermostat parameters of the environment and the changes

Fig. 3. The relationship of the denaturation temperature (T_d) of collagen molecules to the body temperature (homoiothermal animals) or to the upper temperature limit of the environment (poikilothermal animals): (1) swine, parasitic nemathelminthic worms - Ascaris and Acanthocephala; (2) human, rat, cow; (3) snail; (4) tuna; (5) cod; (6) icefish.

in the degree of entropy control which come about as a result of temperature changes with the formation of protein structures (Brandt and Hunt, 1967; Tiktopulo et al., 1979; Cantor and Schimmel, 1980; Hochachka and Sommero, 1973).

On the whole, however, the known facts create the impression that the evolution of collagen structures, although it is determined primarily by genetic factors, has a thermodynamic tendency. For instance, there is a certain parallelism in the temperature increase of the hydrothermal contraction of collagen-containing tissues in both the transition from lower to higher verterbrates and the ontogenesis of mammals. It is believed (Nikitin et al., 1977) that this phenomenon is primarily an ontogenetic recapitulation of the process of increasing the thermal stability of supramolecular collagen structures, which occurred in the phylogenesis of vertebrates.

It is assumed that among the factors determining the thermal stability of collagen-containing tissues only one coincides in phylogenesis and ontogenesis - the increasing degree of intermolelcular interactions. This is a key factor in ontogenesis, while in phylogenesis (when the genetic factor is in operation) its role is not significant. Nevertheless, it appears that the general change in , counted off from the standard level is determined by the sum total of changes in the Gibbs function associated with the adaptation of the organism and evolutionary changes proper (in ontogenesis and phylogenesis).

The thermodynamic tendency in ontogenesis can be linked, for instance, to the loss in the water content of the native Achilles tendons of animals (Table 4; Nikitin et al., 1977, p. 128) as they grow old.

It is clear that one of the factors responsible for the increase in the thermal stability of the supramolecular structures of collagen in phylogenesis is the change in its chemical composition, which is associated primarily with an increase in the relative amount of imino acid residues in protein macromolecules.

There are also many other data on the evolution of collagen, which can be interpreted in the light of the thermodynamic tendency of evolution. However, it should be re-emphasized that the evolutionary change in the composition and structure of proteins is associated with a complex of thermodynamic and purely genetic factors. The role of the latter is determined by the DNA structure.

3.4. The change in the composition and structure of nucleic acids. Just as in the case of lipids and proteins, many facts (Aleksandrov, 1975, 1985; Saenger, 1984; Cantor and Schimmel, 1980) point to the thermodynamic nature of the correspondence between the melting temperature of nucleic acids, their supramolecular structures, and the temperature conditions of the life of the species (i.e., the temperatures of the relevant thermostats). This does not contradict Aleksandrov's kinetic principle of semistability and allows quantitative assessment (through values) of the "conformational strength" of biological supramolecular structures.

On the other hand, there are known examples of a thermodynamic tendency in the variation of the composition and structure of nucleic acids (chromatin) in ontogenesis. It has been found that the thermodynamic stability of nucleic acids is determined by the content of G-C pairs, as well as by the ability of these biopolymers to form complexes with proteins and various low-molecular substances, and other known factors (Cantor and Schimmel, 1980; Gladyshev, 1988). Hence it is clear that efforts to accurately identify the general correlation between the degree of an animal (plant) evolution and the composition of nucleic acids have failed. For instance, the classic data (Marmur and Doty, 1962) on the relationship of the denaturation temperature (T_m) of different DNA to their content of G-C pairs gives no reason to conclude that this relationship is linked with the evolution of the organic world. It appears that only some cases contain dependable evidence of a relationship between the trend of evolution and the content of G-C pairs, whose growth (on a par with other factors) contributes to the increased thermodynamic stability of submolecular structures formed with the participation of DNA and RNA (Gladyshev, 1988).

The increase in the melting temperature of chromatin in ontogenesis, as is assumed, unambiguously indicates its evolutionary aging in ontogenesis (Gladyshev, 1988). This conclusion correlates with a certain reduction in the metabolic activity of DNA at the final stages of ontogenesis, which is associated with the increased stabilization of this nucleic acid. Let us assume that the average value of in the formation of the chromatin structure (referred to the pair of complementary bases - nucleotides) is equal to -0.025 kcal/(Kґ unit). Using the equation (3), it is easy to estimate the gain in changing the Gibbs function by increasing T_m of the chromatin by 1K in ontogenesis (when the DNA composition is unchanged):

Now lei us examine one of the models of biological evolution primarily associated with DNA evolution.

Under the action of solar energy, substances that are thermodynamically stable in the primeval conditions of the Earth transform (as they do today) into various photosynthesis products (Calvin, 1969; Ponnamperuma, 1972). Then, as a result of "dark reactions," these products transform into various substances, and are selected by kinetics, in accordance with the laws of chemical thermodynamics. After this, the local thermodynamics of supramolecular processes selects the most stable suprastructures from the full range of chemical substances, a process that is facilitated by the tendency of im biostructures toward a minimum, and these suprastructures accumulate in the micro- and macrovolumes of systems. Individual macromolecules and suprastructures are reduplicated by possible matrix mechanisms. The selected compounds are primarily nucleic acids, whose composition and structure slowly adapt (under the action of thermodynamic factors) to environmental nature, and include proteins, whose composition is determined by DNA itself. This explains the feedback between protein structure and DNA. In our model, this link is of a thermodynamic nature.

The existence of correlations between T_m of chemical substances and the thermodynamic stability of suprastructures (crystals) forming during crystallization from an overcooled state confirms the presented model.

The degradation processes of the disintegration of chemical compounds parallel the synthesis processes. However, living systems resist this and tend to preserve their state. This tendency is of a thermodynamic nature. The biosystems reproduce perishing supramolecular structures. In the meantime, as noted above, thermodynamics contributes to selecting the most stable structures.

It is thermodynamically advantageous for macromolecular chains to pair with similar chains and surround themselves (through supramolecular contacts) with the renewed "young" matter of living organisms. Therefore, evolution selects those thermodynamically preferable processes that contribute to cell division and DNA preservation. All this occurs against a background of fluctuations in the thermostat (environment) parameters, which, on a par with other factors, support life. Thermodynamic factors contribute to the stabilization of all complex biological structures, thus creating higher hierarchical orders of the biological world.

Thus, it can be assumed that adaptive and evolutionary changes in the composition and structure of supramolecular structures containing nucleic acids have a thermodynamic tendency. However, for the time being it is rather difficult to ascertain this tendency in view of the influence of many factors.

4. CONCLUSION

The model we have proposed makes it possible to identify, relying on the principles of macrothermodynamics and static approaches, the tendency of the evolutionary processes of structural formation leading to the emergence and existence of hierarchical biostructures. Similarly to classical thermodynamics (thermostatics), macrothermodynamics "sets" the axis of time and can only study change occurring in time in the specific functions of state during the structural formation in biosystems of preset hierarchical orders.

Macrothennodynamics is not concerned with the mechanisms of phenomena. However, despite these limitations, the macrothermodynamic method can prove quite effective in the study of ontogenesis, phylogenesis, and biological evolution in general on a solid physical foundation.

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