Natural selection was first described by Charles Darwin, who used it to support his theory of evolution. He discovered through observing finches that each species had its own advantages in the form of different shaped beaks, and that this significantly correlated with the type of seeds on their islands. The selection pressure of seed dispersal had caused differentiation, which lead to the evolution of multiple species.
Darwin discovered the key to natural selection, changes in individuals in a population that increase fitness can increase survival and reproductive chances, making the traits more common as they are passed through generations with only the fittest young surviving to pass on desired traits.
Natural selection has been accepted ever since, so we have a lot to thank our ancestors DNA errors for, and Darwin of course, thanks Darwin.
From Crash Course: Biology on YouTube by Hank Green.