Key concepts/ terms: artificial selection, heavy-metal tolerance, stabilizing, crop mimicry, directional and disruptive selection, herbicide resistant weeds, heterostyly. Industrial melanism: types of selection: artificial vs. natural, modes of selection, examples of selection: evolution by pollution, evolution in agriculture. Natural selection can be defined as the differential survival and reproduction of genotypes in response to factors in the environment. It can only occur when genotypes differ in fitness. Fitness is measured by genotype"s rate of increase relative to other genotypes in a population. Artificial selection is sometimes used as a model for natural selection but there is a big difference, natural selection has no purpose. For any given generation it results because of difference between individuals with respect to their capacity to produce progeny. Natural selection is a self-generated outcome of interactions between organisms and their environment. In contrast, artificial selection is a purposeful process. It has a goal that can be visualized (eg. increase in yield) and a selector humans.