generations before ever proving to be useful to an individual or population. Individuals with genes that help them perpetuate themselves in new conditions of existence are said to be pre-adapted to the new condition.
A reproduction differential between two groups of individuals is the state where some individuals have adaptations that favor their chance of passing on their genes while some individuals lack such adaptations. Differential reproduction, then, is the idea the every factor associated with reproduction had several different phenotypic expressions and that some of the expressions of each factor favor individuals' chances to pass on their genes while some of the expressions of each factors are less favorable to individuals' chances to pass on their genes. Factors such as the selection of a mate, the frequency of mating, fertility, the percentage of zygotes that survive to birth, and the percentage of young that survive to reproduce all have different phenotypic expressions within a population. Thus, because expressions of factors that help or deter an individual's reproduction lead to an increase or decrease, respectively, in the frequency of that gene or gene combination, differential reproduction may be said to be synonymous with natural selection.
Natural selection can affect the direction of a group's evolution in a variety of ways. The effects of natural selection that act upon aspects of a whole population are know as group selection. Most phenotypic characters on which selection acts are determined by a variety of different genes many of which have multiple alleles within
