The evolutionary criteria are amino acids and DNA

To reckon a living organism to a particular class, genus, and species is the work of systematic biologists. Biologists of the past (both before and after Darwin) found it easier to systematize the most highly organized representatives of the animal and plant world. But how to systematize, say, bacteria or viruses? In shape (stick, ball, spiral, crystalline)? By embryology (division of bacteria, self-assembly of viruses)? But these signs are very similar! Paleontology is also powerless here: in the deepest antiquity all types of microorganisms already existed, and it is impossible to judge how far they have changed since that time.

To reckon a living organism to a particular class, genus, and species is the work of systematic biologists

Scientists have long been looking for new objective criteria for evolution, most fully and correctly establishing the relationship between organisms. Such criteria were found... in chemistry. They do not rely on external similarity of organisms, but on mathematically exact molecular data. Chemists have proved the relationship of certain molecules of the body. Particularly interesting are the results of comparing the blood hemoglobin of animals standing at different stages of the evolutionary ladder.

Hemoglobin is a protein, its molecules consist of separate "bricks" - amino acids. Such "bricks" in nature are only about 20. And out of 20 amino acids, nature is building a huge number of all kinds of proteins, which differ sharply from each other. Protein chains are very long, up to 100-200 amino acids.

To unravel the structure of the protein, automatic devices now connected. First they determine the percentage composition of individual amino acids in a molecule: how many percent of such an amino acid, how many-such. Then proceed to a sequential analysis, that is, begin, as it were, unwind the tangle of the protein molecule and look at the order in which these amino acids are located in it.

Scientists compared the molecules of hemoglobin of various animals and found them very similar. In the hemoglobin of animals, there is one very convenient for comparison protein chain, the so-called alpha-tselochka. So in the alpha chains of human and horse hemoglobin, for example, 141 amino acids. The result of their comparison struck researchers: in these protein chains, 124 amino acids coincide, and only 17 do not coincide.

Is this result? No, it's not accidental. After all, man and horse belong to the same class of animals - the class of mammals. Even more similarities in human hemoglobin and gorillas. Their molecules differ by only 2 amino acids.

Biochemists have studied the hemoglobin of many animals, and then switched to other protein substances. For example, on cytochrome - a protein that takes oxygen in the blood and "transports" it to places of consumption. The result is the same as in hemoglobin: the closer the relationship, the less differences in the molecules of cytochrome. Man and monkey in the genealogical tree of the animal world, like neighboring branches, their cytochrome molecules differ only by one amino acid. The dog is distant from the person for 10 amino acids, the rabbit for 11, the horse for 12.

Now we know exactly how living proteins are synthesized. Amino acids fit into the protein molecule according to a stencil sent from the cell nucleus from special genes. Genes are fragments of a large, complex molecule of deoxyribonucleic acid - DNA - carriers of heredity. It is the difference and similarity of DNA molecules that determines the difference and similarity of proteins and, hence, of organisms, and the study of the structure of DNA as a criterion of evolution is much more promising. Any changes in heredity are expressed by a change in DNA. And the reasons for them in nature are many, for example cosmic radiation or chemical influences.