"From the amoeba to the human being" - this is our usual concept of the route followed by evolution. Yet in olden times, when most knowledge was obtained through observation by the naked eye, it was a commonplace to contrast man as the "crown of life" with the "contemptible worm crawling in the dust". Why was the worm accorded such contempt? Why has the term "worm" become a synonym of nonentity? For its simple structure and requirements, perhaps? As for the bee, it has always commanded everyone's respect - and not for its usefulness (the hen is also useful) but, first of all, for its diligence and highly complex, almost intelligent behaviour. Incidentally a high degree of perfection was ascribed to other insects as well. For example Lucian, living in the 2nd century, wrote "In Praise of the Fly", and one thousand years earlier the merits of this importunate insect were appreciated by the famous Homer. In his "Iliad" the goddess Athena, inspiring king Menelaos to battle, strengthened his body and
"... put strength into his shoulders and his knees, and in his breast set the daring of the fly, that though it be driven away never so often from the skin of a man, ever persisteth in biting, and sweet to it is the blood of man; even with such daring filled she his dark heart within him..."
(translated by A.T.Murray, published by William Heinemann Ltd, London, 1963):
Discovery of the microscope discredited the idea of "the lower" as being simple and imperfect. All creatures turned out to be complex. By the middle of the 19th century it had become clear that the basic unit of all living beings is the cell - a little lump of protoplasm capable of growth and reproduction. A multicellular organism was seen as some kind of political union of cells possessing autonomy.
The last quarter of the 19th century acquired the name "golden age of cytology". The cell nucleus and chromosomes were discovered, and their behaviour in cell division was described. All this was of great importance for postulating and substantiating the chromosomal theory of heredity. At the same time discoveries using the microscope demonstrated the organizational level of cells to be independent of the position of their owners in the evolutionary tree. That is why cytologists often choose for their investigations "exotic" species (as a rule, from the lower parts of the tree) where various phenomena of cellular life are expressed most clearly (Wilson, 1937). For example, the mitotic apparatus is best studied in sea urchins, the fate of heterochromatic chromosomal regions in an ascarid worm or a cyclops, and morphology of chromosomes in orthopteran insects or tailed amphibians. Occasionally in the lower organisms one can encounter cells of great complexity. It is sufficient to mention the miniature harpoon guns hidden in the nettle cells of coelenterates.
However, the maximum complexity of cellular structure is achieved in the Protozoans. For example, the infusorian Paramecium is a free-living two-nucleus cell with multiple structures (organelles) performing the functions of the organs of multicellular organisms. The most impressive is the reproductive system, where ordinary cell divisions alternate with a specific sexual process in the course of which the smaller nucleus (micronucleus) plays the role of a generative cell.
Nevertheless, in spite of all the cytological discoveries, information about subcellular organization was scarce, and up to the mid 20th century the cell was considered as quite simple, almost a structureless mass.
In the 20th century there appears on the scene a major new source of information about the structure of living matter - biochemistry. Due to advances in this science there began to develop a magnificent landscape of synthesis and degradation pathways of the main chemical components of organisms - proteins, fats, carbohydrates and nucleic acids. It became clear that almost every chemical transformation is governed by special protein catalysts - the enzymes. This meant that thousands of different chemical reactions taking place in an organism were steered by the same number of enzymes. Furthermore, an analysis of protein structure showed that all the properties (including catalytic) were unequivocally determined by a sequence of several hundred aminoacid residues. Moreover, billions of molecules of a certain type of protein shared an identical structure. Such an unbelievable precision turned out to be provided by a special, hitherto unknown template principle of chemical synthesis.
Protein molecules are produced from RNA templates where each triplet of nucleotides (codon) corresponds to a certain aminoacid residue. RNA templates, in turn, are synthesized under the control of special DNA templates stored in chromosomes - the mysterious genes of classical genetics. Thus, a typical gene turned out to be a segment of DNA coding for the information about the aminoacid sequence of a protein. Besides, coding sequences in chromosomal DNA are as a rule adjacent to regions determining the gene's activity, that is, intensity of RNA production. These operating sequences of DNA interact specifically with regulatory proteins - products of other genes (regulators) which, in turn, can be under control too (Lewin, 1994).
Thus, chromosomes harbour several thousand genes, each of them being an unique sequence of hundreds or even thousands of nucleotides. They encode dozens of RNA variants (attending different stages of information transfer from a gene to a protein) and several thousands of various proteins performing catalytic, regulatory and structural functions. The majestic landscape of molecular transformations overwhelmed by its complexity and perfection all previous biological knowledge to such a degree that voices (including some rather authoritative ones (Crick, 1981)) were heard arguing for the extraterrestrial origin of life, since too little time - only about one billion years - separates the newly created Earth from its first inhabitants.
An analysis of processes connected with the synthesis and destruction of the main chemical components of an organism, as well as the storing, copying and coding of hereditary information, leads to the following conclusions. First, in all living beings these processes are organized in virtually the same way. This fundamental unity was expressed in the famous phrase of Jacques Monod: "What is true for E.coli is true for an elephant". Second, it is not impossible that complexity of organisms, regardless of their position on the 'ladder of creatures', at the molecular level exceeds by several orders of magnitude everything commonly studied by such disciplines as anatomy, histology and physiology. Finally, from the point of view of logical Darwinism all organisms are equally adapted to their environments and in this sense both "the higher" and "the lower" are equally perfect.
Returning to the evolutionary route from the worm - it would be better to say 'from the sponge' - to the human being, we must discard all illusions connected with the terms "higher" and "lower". We must admit that the progress achieved by creatures along this route is not absolute, since it concerns only levels of organization above that of the cell. However, the achievements of evolutionary progress should by no means be underrated. Suffice it to mention that the cellular diversity of a human is not less than 50 times that of the sponge. And how many new organs have arisen? But immediately arises the disturbing question: "What is it all for?" Probably, merely in order to obtain more food and to build biomass from it. But in this respect humans fall far behind coelenterates and even sponges. Those who doubt this need only walk along the southern coast of the Azov Sea in early September and look at the sparkling heaps of jellyfish Rhizostoma pulmo.
But where does evolution lead to? And what are its motive forces? How has this amazing conglomeration of living creatures come about, in which "the lower" - far from 'eating dust' - not infrequently flourish, while "the higher" drag out a miserable existence? However, we shall make an attempt to answer these questions. Although the reader should have some acquaintance with such "dull" and mathematical parts of biology as population genetics and the genetics of quantitative traits, the author has tried his best to simplify and animate the text, and hopes that anybody interested in the causes of evolutionary progress will master the book without serious difficulties.