Ways to carry out evolution
Evolutionary processes can be carried out in different ways. The ways of evolution include divergence, convergence and parallelism.
Divergence is a gradual divergence of signs in related organisms that live in different conditions.
Divergence is based on the division of a species into several new species as a result of the action of disruptive selection. The differences between the species of the same group deepen over time, but the general features of the structure remain. The similarity of organisms indicates a common origin, and the differences indicate adaptation to different conditions.
As a result of divergence, homologous organs are formed.
- different subspecies of finches in the Galapagos Islands;
- limbs of terrestrial and aquatic mammals;
- mouthpieces of various types in insects;
- the size and color of flowers in angiosperms;
- different types of fruits in angiosperms.
Convergence is the independent development of similar traits in unrelated groups of organisms living in similar conditions.
The basis of convergence is selection under the same conditions of the habitat, into which groups of organisms that are not related by kinship fall. An adaptation to similar conditions occurs and an external similarity of organs arises, but their essential features do not change.
As a result of convergence, similar organs are formed.
- wings of birds, insects and bats;
- similar body shape in sharks, ichthyosaurs and dolphins;
- burrowing limbs of a mole and a bear;
- thorns of cacti (modified leaves), white acacia (stipules) and hawthorn (modified shoots);
- gills of fish and gills of dragonfly larvae.
Parallelism is a process of evolutionary development in a similar direction of several previously divergent groups.
Similar signs are formed in related groups.
- the development of saber-toothed in felines;
- the appearance of flippers in cetaceans and pinnipeds;
- the similarity of mammals of tropical forests living on different continents.