Evolution is the gradual and slow process of change that occurs in living species. The living organisms adapt themselves to the environment and slowly change their biological systems and processes in order to live more efficiently in that environment.
Organisms also have the capability to reproduces species that are more capable than the previous generations. Due to improvements in the genes and traits, the successive generations of species evolve in each organ of the body. The shape, size, constitution, and purpose of organs change to the better. Some unused organs will slowly disappear from the species.
The evolution depends on the flexibility of the organism in learning the new environment and changing its metabolism and other processes throughout its body. Evolution happens through mutation in the DNA, RNA genomes.