Conditions for natural selection
The excess fecundity, and consequent competition to survive, in every species provides the precondition for the process Darwin called natural selection. Natural selection is easiest to understand as a logical argument, leading from premises to conclusion. The argument requires the four conditions listed below.
1. Reproduction. Entities must reproduce to form a new generation.
2. Heredity. The offspring must tend to resemble their parents: roughly speaking, 'like must produce like'. This condition is provided by Mendelian inheritance.
3. Variation in characteristics of the members of the population.
4. Variation in the fitness of organisms associated with these characteristics.
Provided these conditions are met for any property of a species, natural selection automatically results, as in the case of the peppered moth. If any are not, it does not. Thus entities, like planets, that do not reproduce cannot evolve by natural selection. But when the four conditions apply, the organisms with the property conferring higher fitness will leave more offspring, and the frequency of that type of organism will increase in the population.
The biologist Richard Dawkins argues that there is possibly only one condition for natural selection.