Morphophysiological and biochemical evolution

Abstract

The article describes the biochemical approaches to the natural system of organisms: the problem of “genotaxonomy,” i.e., the classification of organisms based on a study of the genome, and the problem of “molecular evolution,” based on a study of the amino acid sequence in homologous proteins of different organisms. It is emphasized that these areas of chemotaxonomy should not replace, but supplement classical taxonomy based on a study of morphological characteristics, on the data of comparative anatomy, embryology, and paleontology. Recent investigations show that it is not easy to connect and correlate evolutionary changes in morphological characteristics and changes in biochemical characteristics, for example, in the primary structure of proteins. In other words, these two processes are largely independent, as is shown, for example, by experiments on the hybridization of species of mammals, birds, and amphibians. Mammals evolved rapidly morphologically and physiologically and quickly lost the capacity for interspecific hybridization, although they frequently remained very similar in a biochemical respect (in structure of the proteins). Birds and amphibians, on the other hand, evolved much more slowly and retained the capacity for interspecific hybridization for a long time, even in the presence of very considerable differences in the amino acid composition and sequence of the proteins. It is suggested that the rapid morphological and functional evolution of mammals is connected with the rapid evolution of the regulatory region of their genome. On the other hand, the evolution of the structural genes (cistrons) that code peptides and proteins proceeded at the same uniform rate in different classes of vertebrates. This explains why in mammals, in contrast to amphibians and birds, often in the presence of considerable biochemical similarity, there are significant differences in morphological and functional characteristics and successful interspecific hybridization is impossible.