Most populations tend to overproduce offspring, but due to limited resources, individuals struggle for existence and populations remain stable in size over time.

Members of the population exhibit herotable variation in their characteristics.

Those individuals with heritable traits best suited to the local environment will generally produce more offspring - natural selection.

Over the generations, heritable traits that enhance survival and reproductive success tend to increase in frequency among a population's individuals. The population adapts to its environment and evolves.