Microevolution describes changes in allele frequencies within a population over generations.
An allele is one version of a gene, and a population’s allele frequencies can change through natural selection, genetic drift, gene flow, or mutation. For example, if an inherited color pattern helps insects avoid predators, the associated allele may become more common in later generations.
Microevolution does not mean evolution is unimportant or necessarily slow. It refers to the population-level scale of change rather than a fixed speed. Macroevolution describes larger patterns above the species level, such as the origin of new species and long-term diversification, and it is built from genetic changes occurring in populations.