Natural selection is evolution in the wild. While many selective pressures select against living things by killing them off, many more simply lower the number of offspring an organism produces. Natural selection neither produces perfect traits nor entirely eliminates bad traits.

Artificial selection is the method by which people breed plants and animals to suit their own purposes. It differs from natural selection in several important respects, the two most important being the tremendously strong selective pressure applied during the artificial selection and the use of selective breeding. While artificial selection has created all of man's domestic plants and animals, it's limited by the rate of mutation creating new desirable traits and the difficulties of selective breeding.

People developed genetic engineering to address the limitations of artificial selection. Since genetic engineering adds specific Instructions to living things it's more precise than artificial selection. Genetic engineering also isn't limited by the rate of mutations. Several different methods are presently used to add Instructions to living things: gene guns, retroviruses, and agrobacter. Genetic engineering is presently limited to making only small changes in living things.