Macroevolution refers to changes in populations of plants and animals so that new species develop from old ones. Microevolution refers to changes in allele frequencies within a species. Adaptation results from the possession of features that promote the chance of an organism's survival and reproduction. The natural selection of Darwin's concept of evolution is the process, and adaptation is the result. Genetic polymorphism refers to genes that have more variation than can be explained by mutation.
Invertebrates are more polymorphic than vertebrates.
The variation provided by genetic polymorphism is a significant source of raw material upon which natural selection can act. Migration, mutation, genetic drift, nonrandom mating, and selection will cause a shift in the Hardy-Weinberg equilibrium. Gene flow is the movement of genes from one population to another through migration or hybridization. Gene flow is affected by the distance between populations, how much individuals move during or before they reach reproductive age, and the distance over which mating takes place. Genetic drift is loss of an allele from a population.