Natural selection

Natural selection is the process by which heritable traits that improve survival or reproduction become more common in a population over generations. It produces adaptation when differences in reproductive success are consistently associated with inherited variation.

Heritability: The proportion of variation in a trait within a population that is associated with genetic differences. Selection can shift a trait across generations only when relevant differences are heritable.
Mutation: A change in the DNA sequence that can create new genetic variants. Mutation supplies new inherited variants on which selection can act.
Peppered moth evolution: The change in frequencies of light and dark forms of the peppered moth in response to environmental conditions. Industrial pollution and later cleanup altered camouflage and predation, producing a documented case of changing selection.
Genetic drift: Random changes in allele frequencies caused by chance sampling across generations. Drift can change a population even when variants have no consistent fitness differences.
Fitness (biology): An organism's relative contribution of offspring to later generations in a particular environment. Differences in reproductive success are the immediate mechanism through which selection changes trait frequencies.
Recombination: The exchange and reshuffling of genetic material that creates new combinations of alleles. Recombination assembles existing variants into new combinations that selection may favor or remove.
Antibiotic resistance: The ability of microorganisms to survive and reproduce despite exposure to drugs that would normally inhibit or kill them. Antibiotic use favors resistant variants, making their inherited resistance more common.
Gene flow: The movement of alleles between populations through migration and reproduction. Gene flow alters trait frequencies by importing or exporting variants, not by differential reproduction within the population.
Allele frequency: The proportion of copies of a particular allele among all alleles at a genetic locus in a population. Changes in allele frequencies can reveal selection across generations.
Population genetics: The study of genetic variation and its change within populations over time. It provides the mathematical framework for tracking selection alongside other evolutionary forces.

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