In the fourth century B.C., Aristotle devised a system of classification of organisms. He grouped organisms into divisions according to similar characteristics. Several of these divisions are still used. An example is the division of animals into vertebrates (animals with backbones) and invertebrates (animals without backbones). For 2,000 years no significant advances were made in classifying organisms.
Beginning in the late 1400’s, explorers and scientists began to travel extensively. People discovered new species around the world, and naturalists developed new classification schemes. In the 17th century, the English naturalist John Ray introduced the modern concept of the species as the basic unit of classification. In the 18th century, Carolus Linnaeus, a Swedish naturalist, developed a more complex classification based upon Ray's definition of a species and established the two-name system for species. Both Ray and Linnaeus believed that species were fixed at the time of creation and never changed. Toward the end of the 18th century, Antoine-Laurent de Jussieu, a French botanist, grouped plants into 100 families. His work influenced Augustin de Candolle, a Swiss botanist who later devised a plant classification system. De Candolle was the first to use the term taxonomy.
Since World War II, rapid advances in the science of biochemistry have revolutionized the study of the structure and functions of organisms. More recently, the use of such techniques as DNA sequencing has allowed scientists to analyze and compare the genetic material of different species. This research has led to many revisions in the classification of organisms.
Some scientists are developing an alternative set of rules for naming organisms called the PhyloCode which would eliminate all taxa above species level. The naming of a new group would include information about where the group fits into the overall phylogeny (evolutionary history). However, many biologists are critical of this system.