<P> An understanding of the biological meaning of variation and of the evolutionary origin of groups of related species is even more important for the second stage of taxonomic activity, the sorting of species into groups of relatives ("taxa") and their arrangement in a hierarchy of higher categories . This activity is what the term classification denotes; it is also referred to as beta taxonomy . </P> <P> How species should be defined in a particular group of organisms gives rise to practical and theoretical problems that are referred to as the species problem . The scientific work of deciding how to define species has been called microtaxonomy . By extension, macrotaxonomy is the study of groups at higher taxonomic ranks, from subgenus and above only, than species . </P> <P> While some descriptions of taxonomic history attempt to date taxonomy to ancient civilizations, a truly scientific attempt to classify organisms did not occur until the 18th century . Earlier works were primarily descriptive and focused on plants that were useful in agriculture or medicine . There are a number of stages in this scientific thinking . Early taxonomy was based on arbitrary criteria, the so - called "artificial systems", including Linnaeus's system of sexual classification . Later came systems based on a more complete consideration of the characteristics of taxa, referred to as "natural systems", such as those of de Jussieu (1789), de Candolle (1813) and Bentham and Hooker (1862--1863). These were pre-evolutionary in thinking . The publication of Charles Darwin's On the Origin of Species (1859) led to new ways of thinking about classification based on evolutionary relationships . This was the concept of phyletic systems, from 1883 onwards . This approach was typified by those of Eichler (1883) and Engler (1886--1892). The advent of molecular genetics and statistical methodology allowed the creation of the modern era of "phylogenetic systems" based on cladistics, rather than morphology alone . </P> <P> Naming and classifying our surroundings has probably been taking place as long as mankind has been able to communicate . It would always have been important to know the names of poisonous and edible plants and animals in order to communicate this information to other members of the family or group . Medicinal plant illustrations show up in Egyptian wall paintings from c. 1500 BC, indicating that the uses of different species were understood and that a basic taxonomy was in place . </P>

Classical and quantitative methods of taxonomy of animals