In constructing phylogenetic series, evolutionary biologists, in addition to paleontological data, widely use the comparative method with which they establish similarities in the structure of organisms, their biochemical reactions, reproduction characteristics, or other properties by which it is possible to judge the development paths of a group from a common ancestor.
The following characteristic types of evolutionary changes are distinguished: parallelism, convergence and divergence. Sometimes one phylogenetic series may contain examples of changes of various types.
Parallelism. Two different species of porcupine evolve independently in Africa and South America. More than 7 mil. years ago, they lived together, their common ancestor looked like a large woolly rat. When the two continents separated, the population divided into two parts, each of which developed independently of the other. But they are very close in structure and image.
Convergence. When two or more species not related by close kinship become similar to each other. So large water predators arose in four completely different groups: among fish, reptiles, birds and mammals. Their external similarity arose in the process of evolutionary development under the influence of lifestyle and environmental factors with completely different initial positions of organisms. This similarity hides the profound differences in the internal structure and metabolism of the result of the profound differences in their evolutionary history.
Homology and analogy. In parallel and convergent evolution, the similarity of the external structure can be the result of homology – the origin from a common ancestor or analogy – the independent evolution of those organ systems that perform similar functions. So the wings of birds and insects have a different origin – this is an example of an analogy. Homologous structures already in the embryonic period develop according to the same genetic programs. Similar structures, on the contrary, perform the same functions but do not have a common genetic basis. Birds and flies fly in the same environment, but do not have a common winged ancestor and travel different routes in evolutionary history.
Divergence. Evolution or radiation: a common ancestor gave rise to two or more forms which, in turn, became the ancestors of many species and genera. So, the class of mammals was divided into numerous orders that differ in their external structure, ecological features, and the nature of physiological and behavioral adaptations (insectivorous, bats, beetles, cetaceans, etc.).
|Types of Evolutionary Change
||The result is the appearance of similar traits in related organisms.
||cetaceans and pinnipeds independently moved to living in the aquatic environment and acquired fins. The similarity of the structure of African and American porcupines
||Two or more unrelated species are becoming more and more alike. This is the result of adaptation to similar environmental conditions.
||Looks like a dolphin, shark and penguin; marsupial flyer and flying squirrel. The presence of wings in butterflies and birds
||Represents an evolutionary tree with diverging branches. A common ancestor gave rise to two or more forms, which, in turn, became the ancestors of many species and genera. Divergence – diverging evolution – almost always reflects the expansion of adaptation to new living conditions
||The class of mammals broke up into groups, whose representatives differ in structure, environmental features, and the nature of physiological and behavioral adaptations (insectivorous, predatory, cetacean)