The first system for classifying species was proposed in 1735 by Carl Linnaeus, a Swedish naturalist. He developed a binomial system to identify each species of plant and animal. Although he was a creationist, he realized that different species maintained anatomical similarities. The Linnaean system of classification is still in use today.

According to his system of binomial nomenclature, each species has two names, the genus and the species. The genus is always written with an uppercase letter and can include multiple similar species. The second name, species, is not capitalized. For example, Homo sapiens, Homo erectus, and Homo habilis are three species of hominids belonging to the genus Homo, each of them carrying a specific species name. Each species is then grouped into larger and larger umbrella categories: family, order, class, phylum, and kingdom. The species Homo sapiens belongs to the Hominidae family, the Primate order, the Mammalia class, the Chordata phylum, and the Animalia kingdom.