Natural selection causes populations to become adapted or increasingly well suited to their environment and requires existing heritable variations in a group. It increases the frequency of characteristics that make individuals better adapted and decreases the frequency of other characteristics leading to changes within the species.
Natural selection is a cornerstone of modern biology. It is a key process in the evolution of a population. It acts on the phenotype, the characteristics of the organism which actually interact with the environment. While genotypes can slowly change by random genetic drift, natural selection remains the primary explanation for adaptive evolution.
Natural selection causes populations to become adapted, or increasingly well suited to their environments over time.