Charles Robert Darwin’s gave a theory of natural selection for organic evolution.

Different phases of Darwin’s theory are as under: 

1. Production of off spring in living organisms: Each organism does production of off springs to maintain their race. Example, elephant produces 8 off springs in her life span. It is a slow breeder. A pair of elephant began to breed regularly and engender that all off springs are regularly breeding in the 750 years a pair will generate approximately 1.9 million elephants and number of elephants will be very high. But this does not happen.

2. The struggle for survival: Due to over production of off springs, the struggle for space and food for the growing number of offspring takes place. It is the struggle of survival. This struggle occurs in between animals of own species; and with other species also which is capable of the same shall live. Destruction due to struggle, the number of organisms will remains balanced and consistence in nature.

3. Natural Selection: In struggle of survival only those animals live who adapt them according to nature. If they are not able to do it, then they are destroyed.

4. Origin of new species: Inheritance of useful traits will continue from generation to generation and harmful traits gradually become extinct or remains as Vestigial organ. Sometimes, variations increase so that after new generation is more different from older generation and development of a new race goes.

For example, at the beginning dog, jackal and wolves, three were members of the same race but due to change in atmosphere to adapt themselves accordingly, changes in their size and physical characteristics occurred, After thousands of years dog, fox and wolf, three new species were developed.