How Does Natural Selection Work?
Natural selection is a mechanism by which populations adapt and evolve. In its essence, it is a simple statement about rates of reproduction and mortality: Those individual organisms who happen to be best suited to an environment survive and reproduce most successfully, producing many similarly well-adapted descendants. After numerous such breeding cycles, the better-adapted dominate. Nature has filtered out poorly suited individuals and the population has evolved.
Natural selection is a simple mechanism that causes populations of living things to change over time. In fact, it is so simple that it can be broken down into five basic steps, abbreviated here as V.I.S.T.A.: Variation, Inheritance, Selection, Time and Adaptation.