The process of natural selection requires 3 ingredients, 1) variation, 2) a struggle for survival, and 3) survival of the fittest. 1) Variation. For the process of natural selection to occur there must be variation among individuals in a population and this variation must have a genetic basis. The variation may be in morphological, physiological or behavioral characteristics. As humans, we are most aware of the variation among members of our own species, exhibited by the girls in this picture, but there is variation among individuals of every species.