Evolution

In biology, evolution is change in the heritable traits of a population from one generation to the next. At its simplest it is a shift in how common different versions of genes, called alleles, are in a population's gene pool. Over long periods these changes accumulate and split lineages into new species, so all living things are related through descent from common ancestors. Charles Darwin called this process descent with modification.

Four main mechanisms drive evolution. Mutation creates new genetic variation; natural selection makes traits that improve survival and reproduction more common; genetic drift changes allele frequencies by chance, especially in small populations; and gene flow moves alleles between populations. Darwin and Alfred Russel Wallace independently arrived at natural selection, presenting their papers together in 1858, and Darwin published On the Origin of Species in 1859.

Evidence for evolution comes from fossils, homologous and vestigial structures, embryos, the geographic distribution of species and, most powerfully, DNA and protein sequences. Individuals do not evolve during their lifetimes; populations do. Evolution has no goal, and in science a theory, such as the theory of evolution, is a thoroughly tested explanation rather than a guess.