Biogeography. Types of evolutionary change

The main types of evolutionary change are divergence, convergence and parallelism. Divergence is the separation of the traits of a common ancestor through adaptation to different environments; new species, genera and families arise (Galápagos finches; the orders of mammals – insectivores, carnivores, hoofed animals, rodents; homologous organs). Convergence is the appearance of similar traits in unrelated groups through adaptation to similar conditions: the streamlined body of a dolphin (mammal), a shark (fish) and an ichthyosaur (extinct reptile); the wings of birds, bats and insects (analogous organs); spiny water-storing stems in desert plants of Africa and South America (cacti and euphorbias). Parallelism is the independent appearance of similar changes in the same direction in closely related groups; for example, among mammals the cetaceans and the pinnipeds moved into water independently and both developed paddle-like limbs (flippers); the reason is that similar mutations arise in similar genes of related groups. N. Vavilov’s law of homologous series explains parallelism. Coevolution is the joint change of two species through mutual influence: flower and pollinating insect (a long-tubed flower – a long-tongued moth), predator and prey (a fast deer – a fast predator), parasite and host. Evolution is pictured as a branching tree: groups with a common ancestor spread from one branch, while convergent similarity arises independently on different branches.