Natural selection

Individuals in a population can have different inherited characteristics. If a characteristic helps an individual survive or reproduce in its environment, that individual may leave more offspring than others. Over generations, the inherited characteristic can become more common in the population. This process is called natural selection.

A phenotype is an individual's observable characteristics. Some differences in phenotype are heritable: they are influenced by alleles that can be passed from parents to offspring. Natural selection acts when individuals with different heritable phenotypes differ in their survival or reproductive success.

Selection pressures

A selection pressure is a feature of the environment that affects survival or reproduction. Predation, disease and competition can all be selection pressures. For example, if predators more easily spot some individuals than others, individuals with inherited colouring that makes them harder to see may be more likely to survive and reproduce.

An advantageous phenotype is one that improves survival or reproductive success under the prevailing conditions. If conditions change, the same phenotype may no longer provide an advantage.

Natural selection and evolution

Individuals with an advantageous phenotype are more likely to reproduce and pass the alleles contributing to that phenotype to their offspring. Not every individual with the advantage will reproduce, but if they leave more offspring on average, those alleles can become more common over generations.

The gene pool is the collection of alleles in a population. Evolution is a change in the frequencies of alleles in a population over time. Natural selection is one process that can produce this change: individuals are selected through differences in survival and reproduction, while allele frequencies change in the population across generations.