Classifying plants and animals in hierarchies of superior and subordinate groups. More broadly, systematics is the science involving the naming and classification of living organisms, past or present, and understanding how they have evolved through time and how they function ecologically, biochemically and physiologically.
In its present form, systematic biology (including palaeontology) has proceeded as a continuously building body of scientific knowledge for over two centuries and has underpinned the diversification of the modern biological sciences. However, in recent years there has been a significant reduction in the teaching of systematics in schools and universities. Scientific progress has relegated the systematic natural historian, beloved of the 18th and 19th centuries, to the position of an inferior generalist – who knows "little about a lot" or knows "a lot about the irrelevant". At the same time it has devalued the specialist taxonomic biologist in favour of those working in areas of scientific fashions and booms. The decline in resources for a continued systematic activity in many, if not most, countries of the world, has been gradual but unrelieved.
Some 30 million lifeforms are thought to exist in developing countries, of which at least 85 percent have not been identified. They include the multitudes of mites, moulds, mushrooms, insects and other small organisms. There are thought to be, for example, 2.5 million worms in need of names.
There is continuing debate and reclassification of living things. This is why certain groups of organisms may be in more than one hierarchy.
Up until the 1950s and 60s, textbooks only referred to two kingdoms of living beings, Animals (including protozoa) and Plants (including algae and bacteria). Algae and bacteria were then the "lowest" forms of life – called prokaryotes (organisms without a cell nucleus); the "higher" lifeforms were the eukaryotes (organisms with a cell nucleus) comprising animals and higher plants. Clearly the categories were awkward and became more so with modern microscopic techniques. Whilst plants and animals large enough to be visible are easy to distinguish, on a microscopic level this simple distinction breaks down. There are single-celled organisms that sometimes act like plants (transforming light into food) and sometimes like animals (consuming plants or other organic material); also the bacteria and blue-green algae differ structurally from higher organisms far more than plants differ from animals. In 1959, a paradigm shift was occurred with the the Five Kingdoms hypothesis. The unwieldy dichotomy of plant and animal kingdoms was replaced by: animals, plants, fungi, protista or protoctista, and monera (bacteria and blue-green algae, with only a very simple, prokaryote, cellular structure).
The Five Kingdom approach is attractive in its simplicity, but itself has significant problems. One of these concerns the protists – a wide range of disparate organisms such as amoebae, slime moulds, ciliates, algae, etc. that are grouped together as a kingdom with little justification. Another problem is that anaerobic bacteria found in harsh oxygen-free conditions are genetically and metabolically completely different to other, oxygen-breathing organisms, even other bacteria. These bacteria, called Archaeobacteria, or simply Archaea, are actually "living fossils" that have survived since very early ages, before the Earth's atmosphere even had free oxygen. They are prokaryotes, and they look like bacteria, but in terms of cellular biochemistry and genetics the archaea differ from both eukaryotes and bacteria.
Since the late 1980's, DNA and RNA analysis has shown that instead of five kingdoms there are actually three "Domains", Archaea, Bacteria, and Eukarya (Eukaryota). This last group refers to organisms whose genetic material is contained in a special membrane as the nucleus, and includes all higher organisms from protists to humans. It is now understood to contain over a dozen kingdoms. Viruses are not considered living organisms.
The classification aspect of systematics, called taxonomy, is the basal reference system of biology. It provides an infrastructure which integrates research in ecology, functional morphology, behaviour, genetics and molecular biology, much of which has agricultural, industrial and medical importance. Many areas of science rely on taxonomic research, such as work on disease vectors, biological conservation or agricultural pest control. The fields of biotechnology and petro-geology also require strong systematic support.
At a fundamental level, systematics also explores and reveals the processes of evolution and of ecological and functional interactions. This involves the observation, description and interpretation of patterns of natural variation, and also uses experimental and laboratory studies.
Biodiversity inventorying is the surveying, sorting, cataloguing, quantifying and mapping of landscapes, ecosystems, habitats, populations, species, and genes. Inventories derived from the synthesis of such information give an overview of the state of biodiversity, and enable the identification of key indicators and the analysis of important patterns and processes. Inventories also provide baseline information for the assessment of change and data for conserving and managing biodiversity. Taxonomy, which is the identification, description, classification and naming of organisms, is fundamental to inventorying, and is the core reference system and knowledge base upon which all discussion of biodiversity rests. Biosystematics, which incorporates taxonomy, includes the study of associated biological disciplines such as evolutionary biology and biogeography, and is also an important component of inventorying.
Everything that is furry, feathery or flowering we largely know about. What we don't know about are the "uglies": the insects and the fungi, without which the soil could not function.