How did the complication of organisms actually take place in evolution?
In the course of evolution, any of these side regulatory effects can be isolated, enhanced, and fixed (for example, a new specialized protein may appear that enhances this effect, which, as a result, will cease to be a side effect).
Of course, this is only the most general idea of the structure of the regulatory-metabolic network, which forms the basis of any living system, which, therefore, can be roughly characterized by its “functions” (in this approach, the main role is assigned to enzymes) and “regulatory effects” (with their the main role is played by regulatory proteins).
If we compare a living system with a computer program, then we can liken “functions” to operators that perform some specific actions with data, that is, perform data transformation (for example, assignment operators); and “regulatory effects”, with this analogy, correspond to conditional jump operators, which, depending on certain conditions, “turn on” or “turn off” (regulate) the actions of operators (or “functions”).
Based on this, one can try to determine what should be understood by the complication of a living system. By complication we mean an increase in the number of heterogeneous elements of the regulatory and metabolic network. In other words, it is either the emergence of a new “function” – a new enzyme that catalyzes some kind of reaction, or the emergence of a new “sustained” regulatory effect.
Different meaning of evolution at different stages
How did the complication of organisms actually take place in evolution?
The fossil record is a gigantic array of data that is absolutely impossible to cover in all details within a single publication. Therefore, I will only outline the most important milestones and stages.
As you know, the age of the Earth is about 4.5 billion years, but, unfortunately, the first 700 million years of its existence did not leave us any paleontological evidence, because about 3.8 billion years ago, the primary crust was destroyed and remelted in the mantle. So the oldest surviving sedimentary rocks are no more than 3.8 billion years old. But the most amazing thing is that even in such breeds there are already certain signs of life. And in rock samples up to 3.5 billion years old, fossil remains of bacteria have already been reliably found.
Prokaryotes. So far, we can not accurately date either the moment of the appearance of life, or the moment of the appearance of the first real cells. It is only clear that both happened in the first 700-1000 million years of the existence of the Earth. But we can say with a high degree of certainty that in the second billion years of earthly existence (3.8–2.7 billion years ago), the biosphere was entirely prokaryotic. In other words, only bacteria existed – unicellular organisms that did not have a nucleus.
Progress in such a biosphere consisted mainly of the emergence of new “functions”, that is, the emergence of new enzymes that gave rise to new chemical reactions. The regulatory systems of prokaryotes, due to the peculiarities of their structure, could not develop beyond the most primitive, initial level.
Traces of ancient life
Fossil organisms are found primarily in sedimentary rocks, but the oldest known sedimentary rocks (the Ishua Formation in Greenland) are about 3.8 billion years old. And they already have traces of life. True, it is not entirely clear which one: the original RNA life or the modern DNA-protein one. These traces are purely chemical, associated with the isotopic composition of carbon.
Some experts attribute the origin of the RNA world to the interval of 4.3–3.8 billion years ago.
Eukaryotes. The first great breakthrough in the evolution of life took place about 2 billion years ago, when the first eukaryotes appeared. Their main difference from prokaryotes (bacteria) is that they have formed a cell nucleus, and thus the area of active metabolism (cytoplasm) was separated from the area of storage, reading and regulation of the genome. This opened up the opportunity for the development of complex regulatory systems.
The consequences of this event were colossal. The nature and meaning of evolutionary progress has radically changed. New “functions” (enzymes and metabolic pathways) have ceased to be its content from now on. Progress henceforth consisted in the emergence of new regulatory effects.
The development of complex regulatory systems allows eukaryotes to form completely different types of cells with the same genome, depending on the conditions. Bacteria are practically incapable of this. It is thanks to this property that eukaryotes were able to become multicellular.
Multicellular organisms. As you know, any multicellular organism develops from one cell – an egg. The egg divides, and the daughter cells formed as a result of division end up in different conditions (different positions in the embryo, different environments and, as a result, different concentrations of substances in the external environment surrounding the cell). Depending on the conditions in which a given germ cell falls, certain groups of genes are included in it. As a result, different germ cells develop in different ways, and different tissues and organs are formed from them. Thus, if we consider a multicellular organism precisely in the course of ontogenesis, as a program of individual development (and this is exactly how it should be considered, speaking of evolution, since it is ontogenesis that evolve, and not adults), it turns out that all the diversity of the structure of multicellular organisms actually comes down to certain regulatory effects (operators of conditional transitions) included in the development program.
So, the progress of eukaryotes (and especially multicellular ones) consisted not of new “functions” (enzymes), as in bacteria, but new regulatory effects. And from this thesis is already deduced as a consequence of the nature of the complication of the structure of adult organisms. For example, there was an organism with 10 pairs of identical legs. If he has two more pairs of the same legs, this cannot be considered a complication of the structure of the body – no new regulatory connection has appeared. It just boiled down to some new “revision” of the definition of the old conditional branch operator. The operator of the type “shape legs until there are 10 pairs” was replaced by the operator “shape legs until there are 12 pairs”. But if the first pair of legs in this organism began to differ from the others, say, by the presence of an additional claw, then this is already progress, since this means that a new conditional transition operator has appeared in the ontogenetic program of the type “if I am the rudiment of a leg of the first pair, then it follows to form an additional claw “.
This second stage of evolution, when progress consisted in the complication of regulatory effects, continued until the advent of Homo sapiens.
The modern stage. At the current (third) stage of evolution, progress is no longer concentrated in the field of genome regulation, but in the sociocultural sphere. I will not dwell on the characteristics of human progress. I will only note that there is a clear continuity here, because the mind (or consciousness) is actually a higher-level regulatory system.
Chronology of evolution
So, we can distinguish three main stages of evolution, each of which is characterized by its own content (direction) of evolution:
Progressive evolution of biochemical functions. Prokaryotic biosphere. The biochemistry of organisms is developing. Progressive evolution of regulation (control) of functions. Eukaryotic biosphere. The morphology (structure) of organisms develops. Progressive evolution of consciousness, or regulation of regulations (?!). Anthroposphere. Sociocultural systems are developing.
The main features of evolutionary progress
In addition to the noted periodization of evolutionary progress, attention is drawn to several of its most important features, identified, in particular, from the analysis of paleontological data:
New, more complex organisms usually do not displace or replace their primitive ancestors. Simple forms continue to exist along with complex ones – more and more complex organisms accumulate in the biota and a general increase in the diversity of life (for example, the bacterial world continues to exist and flourish to this day, along with much more complex eukaryotic organisms).However, after the largest aromorphoses (transitions to a higher level of organization), further evolutionary progress is concentrated mainly in a new layer of biota, consisting of more complex organisms. So, with the advent of eukaryotes, the progressive evolution of bacteria practically stopped – some bacteria have existed to this day since the Archean era (almost 3 billion years) almost unchanged. There are also serious grounds to believe that with the advent of man, the progressive evolution of animals and plants ceased (or at least seriously slowed down).The third feature is related to the second: there is a general pattern that the more complex an organism is, the higher the likelihood of its further complication. In this sense, evolutionary progress seems to be accelerating.Progressive complication is a fairly rare evolutionary event. The frequency of such events is many orders of magnitude lower than the frequency of transformations occurring at the same level of complexity or with a decrease in this level, i.e., with simplification.
Is spontaneous progress of living systems possible?
The progressive nature of evolution raises many questions. This is especially often mentioned: is spontaneous progress possible if in inanimate nature we see that “by itself” everything usually only collapses and becomes simplified, but almost never becomes more complicated?
Spontaneous complication of systems, as was thought earlier, contradicts the second law of thermodynamics – the law of entropy growth (only chaos grows spontaneously, but not organization). However, the well-known physicist and chemist, one of the founders of the thermodynamics of nonequilibrium systems and the Nobel laureate I.R. That is, progress in the understanding accepted in this article. An example is the formation of regular hexagonal convective cells when certain viscous liquids are heated.
Thanks to Prigogine’s discoveries, progressive evolution ceased to contradict the laws of nature and the foundations of the materialistic worldview. They were of particular importance for understanding the problem of the origin of life and such a phenomenon as catalytic cycles. Cyclic chemical processes are known in which the products formed at individual stages of the cycle serve as catalysts for subsequent stages. The result is a self-reproducing, self-sustaining chemical system, from which, generally speaking, it is not far from even the most primitive forms of life.
A new form of life
An interesting example can be found in recent discoveries in molecular biology and medicine. Perhaps, quite recently, literally before our eyes, a new form of life appeared on Earth. We are talking about the notorious prions (infectious agents of a protein nature that cause brain damage – encephalopathy – in humans and animals). These were originally normal proteins found in mammalian nerve cells. They performed their own role and did not attract the attention of scientists. But one day (it seems, in the first half of the 19th century), most likely in some cow, one molecule of such a protein for some completely unknown and accidental reasons “folded” incorrectly – after all, the protein molecules, after they are synthesized, must be certain curl up, fold into a kind of globule (and this book 1884 spatial configuration of the molecule largely determines its properties). And this prion molecule folded “incorrectly” and as a result quite accidentally acquired two new properties: resistance to proteases (enzymes that catalyze the breakdown of proteins) – in other words, the body is unable to destroy this protein; and the ability to stimulate the same misfolding of other prions. And the result was a kind of quasi-organism of a new type, something like a virus, only without genes! The thing turned out to be completely indestructible: such a “incorrectly” folded prion is not digested in the stomach, gets into the peripheral nervous system and, as if in a chain reaction, makes all prions in nerve cells fold in the same way – this wave of “incorrect folding” reaches the brain, where the “incorrect” protein “envelops” all neurons (after all, it is indestructible), as a result of which a person goes crazy and soon dies. One of the most striking manifestations of the potential of prions was the very spongy encephalitis (“mad cow disease”), which not so long ago almost destroyed the animal husbandry and meat industry in a number of countries.
To stop such an autocatalytic (self-accelerating) cycle, it is necessary to destroy every “wrong” prion to the last. This example shows that the autocatalytic cycle can become a terrible force: once it has arisen, it will actively reproduce and support itself, and it turns out to be very difficult to stop it. So it reminds one of the embryo of that very mysterious “life force” that has been more than once tried to be presented as the driving force of evolution.
The role of RNA in the origin of life
The primary autocatalytic system with which life on Earth began, most likely, could be a short RNA molecule capable of catalyzing the synthesis of its own copies. The resulting autocatalytic system had to immediately absorb other abiogenically synthesized RNA molecules – such RNA (with polymerase activity) would synthesize not only its own copies, but also copies of other “neighboring” RNAs, which thereby become material for selection. And here it is quite appropriate to note that, as shown in laboratory experiments, selection and even the struggle for existence are clearly manifested already in the simplest autocatalytic cycles – the most “successful” (effective) catalytic cycles quickly “expand” and “displace” their less effective “rivals. “.
So, given the recently discovered ability of RNA to perform various catalytic (enzymatic) functions, a so-called RNA organism, a precursor of a living cell, could rather quickly form from such a primary RNA system. This RNA organism was already able, “involving” short and then longer proteins into its metabolic network, to improve the mechanisms of protein synthesis based on RNA enzymes, which gradually led to the formation of the genetic code and modern mechanisms of protein synthesis.
Evolution cannot be reduced to probability theory
One of the characteristic objections to the classical theory of evolution is that the creation of any complex element – for example, a new enzyme – as a result of the accumulation of random mutations (random enumeration of variants) is impossible from the point of view of the theory of probability. A typical “functional” protein consists of several hundred combinations of amino acids (there are only 20 essential amino acids). Hence, the creationists argue, in order to obtain a “functional” protein of at least 100 amino acids by random enumeration, it is necessary to enumerate so many options that the entire time of the existence of the Universe will not be enough for this.