Definition for Natural selection
From Biology Forums Dictionary
Natural Selection, in evolution, the process by which environmental effects lead to varying degrees of reproductive success among individuals of a population of organisms with different hereditary characters, or traits. The characters that inhibit reproductive success decrease in frequency from generation to generation. The resulting increase in the proportion of reproductively successful individuals usually enhances the adaptation of the population to its environment. Natural selection thus tends to promote adaptation by maintaining favorable adaptations in a constant environment (stabilizing selection) or improving adaptation in a direction appropriate to environmental changes (directional selection). Charles Darwin and Alfred Wallace first proposed this concept in 1858.