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classification, in biology, the systematic categorization of organisms into a coherent scheme. The original purpose of biological classification, or systematics, was to organize the vast number of known plants and animals into categories that could be named, remembered, and discussed. Modern classification also attempts to show the evolutionary relationships among organisms (see the table entitled Examples of Systematic Classification). A system based on categories that show such relationships is called a natural system of classification; one based on categories assigned only for convenience (e.g., a classification of flowers by color) is an artificial system.
Modern classification is part of the broader science of taxonomy, the study of the relationships of organisms, which includes collection, preservation, and study of specimens, and analysis of data provided by various areas of biological research. Nomenclature is the assigning of names to organisms and to the categories in which they are classified.
A modern branch of taxonomy, called numerical taxonomy, uses computers to compare very large numbers of traits without weighting any type of trait—in contrast to the traditional view that certain characteristics are more significant than others in showing relationships. For example, the structure of flower parts is considered more significant than the shape of the leaves in flowering plants because leaf shape appears to evolve much more quickly. Much of the science of taxonomy has been concerned with judging which traits are most significant. If new evidence reveals a better basis for subdividing a taxon than that previously used, the classification of the group in question may be revised. A considerable number of classification changes as well as insights in recent years have been the result of comparisons of nucleic acid (genetic material) sequences of organisms.
See also cladistics.
The broadest division of organisms has been into kingdoms. Traditionally there were two kingdoms, Animalia and Plantae, but many unicellular and simple multicellular organisms are not easily classified as either plants or animals. In 1866 the zoologist Ernst Heinrich Haeckel proposed a third kingdom, the Protista, to include all protozoans, algae, fungi, and bacteria. In the 20th cent. his proposal was refined, and a grouping became widely accepted that was made up of five kingdoms: animals; plants; Protista, including protozoans and some algae; Monera, comprising the prokaryotic bacteria and cyanobacteria (blue-green algae); and Fungi. Other groupings have been proposed from time to time.
Analysis of genetic sequences in various organisms has recently suggested placement of the Archaebacteria into a separate major group called the archaea. In this system, the second and third major groups are the other bacteria and the eukarya (or eukaryotes), organisms that have cell nuclei and include the fungi, plants, and animals.
The Lower Taxa
Kingdoms are divided into a hierarchical system of categories called taxa (sing. taxon). The taxa are, from most to least inclusive: phylum (usually called division in botany), class, order, family, genus, and species. Intermediate divisions, such as suborder and superfamily, are sometimes added to make needed distinctions. The lower a taxon is in the hierarchy, the more closely related are its members.
The species, the fundamental unit of classification, consists of populations of genetically similar interbreeding or potentially interbreeding individuals. If two populations of a species are completely isolated geographically and therefore evolve separately, they will be considered two species once they are no longer capable of mixing genetically if brought together. In a few cases interbreeding is possible between members of closely related species—for example, horses, asses, and zebras can all interbreed. The offspring of such crosses, however, are usually sterile, so the two groups are nonetheless kept separate by their genetic incompatibility. Populations within a species that show recognizable, inherited differences but are capable of interbreeding freely are called subspecies, races, or varieties.
The genus (pl. genera) is a grouping of similar, closely related species. For example, the domestic cat and the jungle cat are species of the genus Felis; dogs, wolves, and jackals belong to the genus Canis. Often the genus is an easily recognized grouping with a popular name; for example, the various oak species, such as black oak and live oak, form the oak genus (Quercus). Similarly, genera are grouped into families, families into orders, orders into classes, and classes into phyla or divisions.
The present system of binomial nomenclature identifies each species by a scientific name of two words, Latin in form and usually derived from Greek or Latin roots. The first name (capitalized) is the genus of the organism, the second (not capitalized) is its species. The scientific name of the white oak is Quercus alba, while red oak is Quercus rubra. The first name applies to all species of the genus—Quercus is the name of all oaks—but the entire binomial applies only to a single species. Many scientific names describe some characteristic of the organism (alba=white; rubra=red); many are derived from the name of the discoverer or the geographic location of the organism. Genus and species names are always italicized when printed; the names of other taxa (families, etc.) are not. When a species (or several species of the same genus) is mentioned repeatedly, the genus may be abbreviated after its first mention, as in Q. alba. Subspecies are indicated by a trinomial; for example, the southern bald eagle is Haliaeetus leucocephalus leucocephalus, as distinguished from the northern bald eagle, H. leucocephalus washingtoniensis.
The advantages of scientific over common names are that they are accepted by speakers of all languages, that each name applies only to one species, and that each species has only one name. This avoids the confusion that often arises from the use of a common name to designate different things in different places (for example, see elk), or from the existence of several common names for a single species. There are two international organizations for the determination of the rules of nomenclature and the recording of specific names, one for zoology and one for botany. According to the rules they have established, the first name to be published (from the work of Linnaeus on) is the correct name of any organism unless it is reclassified in such a way as to affect that name (for example, if it is moved from one genus to another). In such a case definite rules of priority also apply.
The earliest known system of classification is that of Aristotle, who attempted in the 4th cent. B.C. to group animals according to such criteria as mode of reproduction and possession or lack of red blood. Aristotle's pupil Theophrastus classified plants according to their uses and methods of cultivation. Little interest was shown in classification until the 17th and 18th cent., when botanists and zoologists began to devise the modern scheme of categories. The designation of groups was based almost entirely on superficial anatomical resemblances.
Before the idea of evolution there was no impetus to show more meaningful relationships among species; the species was thought to be uniquely created and fixed in character, the only real, or natural, taxon, while the higher taxa were regarded as artificial means of organizing information. However, since anatomical resemblance is an important indication of relationship, early classification efforts resulted in a system that often approximated a natural one and that—with much modification—is still used. The most extensive work was done in the mid-18th cent. by Carolus Linnaeus, who devised the presently used system of nomenclature. As biologists came to accept the work of Charles Darwin in the second half of the 19th cent., they began to stress the significance of evolutionary relationships for classification.
Although comparative anatomy remained of foremost importance, other evidence of relationship was sought as well. Paleontology provided fossil evidence of the common ancestry of various groups; embryology provided comparisons of early development in different species, an important clue to their relationships. In the 20th cent., evidence provided by genetics and physiology became increasingly important. Recently there has been much emphasis on the use of molecular genetics in taxonomy, as in the comparison of nucleic acid sequences in the genetic makeup of organisms. Computers are increasingly used to analyze data relevant to taxonomy.
See E. Mayr, Principles of Systematic Zoology (1969); T. Savory, Animal Taxonomy (1972); H. M. Hoenigswald and L. F. Wiener, eds., Biological Metaphor and Cladistic Classification (1987); F. A. Stafleu and R. S. Cown, Taxonomic Literature: A Selective Guide to Botanical Publications and Collections (1988); N. Eldredge, Fossils: The Evolution and Extinction of Species (1991).
- the hierarchical distinctions that exist between individuals or groups (e.g. occupational groups) within a society. In this general sense class is an alternative general term to SOCIAL STRATIFICATION. The term ‘social class’ is also widely used as a general synonym for ‘class’.
- any particular position within a social stratification system or class system, e.g. ‘middle class’, ‘working class’, etc.
- (social classes) the descriptive classificatory categories used by the Registrar General in the collection and analysis of CENSUS data; in 1961, for example, the Registrar General's division of the population into five ‘social classes’.
- (occupational class) descriptive classification of the total population into broad ‘occupational classes’ or ‘socioeconomic status groups’, e.g. ‘manual and non-manual’ classes, as well as more elaborated classifications (see OCCUPATIONAL SCALES).
- the particular form of‘open’, rather than ‘closed’, stratification of class system found within modern industrial societies, in which individual and collective SOCIAL MOBILITY is relatively commonplace (compare CASTE, ESTATE).
- (MARXISM) the economically determined and inherently conflictual divisions of society based on ownership and non-ownership of property, e.g. lord and serf in feudal society (see FEUDALISM AND FEUDAL SOCIETY), BOURGEOISIE and PROLETARIAT in capitalist societies, which characterize all large-scale societies and which are held ultimately to determine the destiny of each type of society. Marx also identifies a multiplicity of lesser classes and groupings which influence the outcome of political and social conflicts.
- (WEBER, 1922) differences between categories or groups of persons in their ‘typical probabilities’ of ‘procuring goods’, ‘gaining positions in life’ and ‘finding inner satisfaction’ – LIFE CHANCES. Thus, for Weber, ‘class’ means ‘all persons in the same class situation’, what ever the basis of this and whatever its implications may be for the longer-term destiny of societies (see also CLASS, STATUS AND PARTY). Weber identified a number of overlapping possible bases of class situation, based on ownership and non-ownership of property and also including reference to different kinds of property and the different kinds of income that this yields. In particular, he identifies:
- property classes;
- commercial classes, somewhat misleadingly so-called, since these include individuals able to safeguard their position through political or organization activity, e.g. professionals or others monopolizing qualifications, as well as entrepreneurs possessing other bases of monopoly;
- social classes, the ‘totality’ of such class situations, defined in terms of situations within which ‘individual and generational mobility is easy and typically occurs’. The main ‘social classes’ identified by Weber in this sense are: (i) the working class, (ii) the petty bourgeoisie, (iii) the ‘propertyless’ intelligentsia and specialists, (iv) classes privileged by property and education.
In the UK, the first dictionary use of‘class’ occurred in the 17th century, in T. Blount's Glossographia. Apart from military and school usage, he noted that the term described a ‘distribution of people according to their several Degrees’. The term came into general use in a similar way; as one which described differences of birth, occupation, wealth, ability, property, etc.
An overall, but no absolute, distinction can be drawn between those conceptions of class’ which set out to be mainly ‘descriptive’ (e.g. senses 3 and 4) and those which are more ‘analytical’ (e.g. senses 6 and 7 ).
Analytical conceptions of class: Marx. Of the analytical approaches to class, the most influential uses in sociology undoubtedly stem from MARX, although he acknowledged that the term had originated earlier, in particular in the work of Enlightenment social theorists and French socialists.
In Marx's own work the term has a number of different applications, but the essential aspects of Marx's general model of social class are clear:
- Every society has to produce a surplus to feed, house and clothe dependent children, the sick and the elderly Class differences begin when one group of people claim resources that are not consumed for immediate survival as their private property;
- Classes therefore are defined in terms of ownership (or non-ownership) of productive property which makes the taking of the surplus possible. At different times in human history different forms of property (e.g. slaves, water, land, capital) have been crucial in shaping social relationships, but all class systems are characterized by two major classes. The most important class relationship as far as Marx was concerned was that found in CAPITALISM, between the bourgeoisie and the proletariat;
- The historical importance of classes, for Marx, is that they are intrinsically exploitative: one class, because it takes the surplus produced by another class, exploits and oppresses that class, and therefore conflict is an inevitable product of class relationships. The conflicts associated with class antagonisms are the most important factor in social change: ultimately it is class conflicts, associated with underlying social and economic CONTRADICTIONS, which transform societies;
- Marx distinguishes between the ‘objective’ aspects of class, as set out in (b) above, and the 'S ubjective’ aspects, i.e. the fact of membership of a class is not necessarily accompanied by an awareness of membership or a feeling of political identity with the interests of a class. It is only when members of a class realize their common interests and act together to gain them that one can fully talk about a social class.
It should be noted that the above is a theoretical model and, as such, should not be taken as simply descriptive of any historical situation but as indicating the most important structure and processes for understanding social relations and for directing empirical work. In his own empirical work Marx introduced a number of factors into his understanding of social class. In The 18th Brumaire of Louis Bonaparte (1852), for example, he discusses the French peasantry of the mid-19th century and he comes close to a formal definition of class which includes variables such as a shared culture and a national political organization.
Major problems arising out of Marx's work have inspired most of the subsequent sociological work on class:
- the fact that Marx's account of classes and the role of class in pre-capitalist societies was relatively limited leads to questions as to whether class has the centrality of importance in the generation of change in these societies, e.g. see CLASS-DIVIDED SOCIETY;
- the existence and growth of important groups other than the proletariat and the bourgeoisie;
- divisions within classes which have often proved as significant. politically, as divisions between classes (e.g. see CONTRADICTORY CLASS LOCATIONS);
- the important effect of factors other than social class on people's lives, GENDER and race in particular;
- the fact that CLASS CONSCIOUSNESS, in practice, has never shown evidence of a simple correspondence with Marx's view of objective class situation and, historically, for subordinate classes, has normally been much at variance with ‘objective’ conditions as defined by Marx.
Analytical conceptions of class: Weber. The most influential alternative theory of class is found in Max WEBER's work. Unlike Marx, Weber emphasized other factors which promoted inequality In particular he considered status or honour and prestige as a distinct variable. He also emphasized the link between class and opportunity, arguing that a class is a category or group of people who share similar ‘life chances’. With Marx, he saw ownership and non-ownership as a basic criterion, but Weber stressed divisions within classes (partly based on social STATUS) and empirical changes in class boundaries to a much greater extent than Marx. Examples are Weber's distinction between ownership and commercial classes, and also the way that different skill levels divided the working class in terms of life chances. Here Weber is emphasizing the importance of ‘markets’ rather than simply ownership or non-ownership of property as the basis of inequality, i.e. level of skill and demand for skills determining differences in rewards. Weber also differs from Marx in seeing BUREAUCRACY, as well as class, as a fundamental nexus of power in modern societies.
Weber's stress on a variety of factors influencing opportunities and rewards (see also CLASS, STATUS AND PARTY) has made his approach to the analysis of class and social stratification very influential in sociological theory. In British sociology, for example, LOCKWOOD (1958), and later GOLDTHORPE and Lockwood et al. (1968 and 1969), emphasized the importance of taking account of'S tatus’ as well as ‘market situation’ and ‘work situation’ (see also MULTIDIMENSIONAL ANALYSIS OF SOCIAL STRATIFICATION, BLACK-COATED WORKER, AFFLUENT WORKER). GIDDENS (1981) has taken the emphasis on the market situation of individuals as important in qualifying Marx's view of class and power. Earlier critics of Marx's work also emphasized Weberian themes, notably theorists of MANAGERIAL REVOLUTION, STABLE DEMOCRACY, END-OF-IDEOLOGY THESIS (see also DAHRENDORF).
Analytical conceptions of class: modern approaches: Most recent approaches have tended to take either Marx or Weber as a starting point. There have been numerous attempts to adapt or refute elements of the classical approaches. Efforts to repair deficiencies in Marx's work, for example, as seen in studies by Poulantzas (1973), Carchedi (1977) and Wright (1978 and 1985), have been widely discussed. A common preoccupation of all these theorists is the problem of CLASS BOUNDARIES, of accounting for the position of the ‘middle classes’ (see INTERMEDIATE CLASSES AND INTERMEDIATE STRATA) within the Marxist theory of class. They all accept the deficiencies of the orthodox Marxist view of such groups as professionals, managers and white-collar workers, but they differ in their attempted solutions to the problem posed by the continued existence and role of this group, which the classical Marxian theory assumed in the long run would simply be assimilated into one or other of the two main classes in capitalism, or disappear.
Poulantzas follows ALTHUSSER's conception of the MODE OF PRODUCTION to argue that there are three relatively autonomous aspects of class relations: economic (PRODUCTIVE versus UNPRODUCTIVE LABOUR), political (supervision versus nonsupervision) and ideological (mental versus manual labour); and, hence, the definition of social classes cannot be purely economic. The direct production of commodities (the economic role) is still seen as the main criterion which defines the proletariat, but the situation is complicated by further relations of power. Any worker, productive or not, who occupies a subordinate position in any of the three spheres should be seen as a member of a distinct class: the ‘new petty bourgeoisie’. Carchedi proposes a variation on this approach. He distinguishes between ownership and functional aspects of the capitalist labour relation. He argues that, as capitalism developed, production became more and more a collective process and, similarly, the function of the capitalist in controlling and organizing the labour force became separated from ownership with the growth of managerial hierarchies. The NEW MIDDLE CLASS exercises the function of capital (control and surveillance) without being part of the class which owns capital. Similarly, Wright (1978) distinguishes between ownership and control, arguing that people who do not own the means of production but have important powers as managers or semiautonomous professionals were in CONTRADICTORY CLASS LOCATIONS. In a later critique (1985), Wright re-emphasized ideas of property and exploitation as central to an understanding of class relations. Each of these approaches attempts to overcome the problems which the ‘new middle classes’ pose for Marxian accounts of class by treating power and control of the LABOUR PROCESS as in some way independently definitive of class relations. These ‘new’ approaches, therefore, despite their location within the Marxian tradition and different conceptual frameworks, bear, at some points, a striking resemblance to aspects of Weber's approach, the difference being, however, that they see their new approach as rehabilitating the Marxian view. The ultimate basis of class, and the fundamental dynamics of society, remain ‘objective’ economic class interests.
Many other writers have preferred to look more directly to Weber rather than to Marx to develop a more satisfactory theory of class. Among the most influential of these, along with Lockwood and Goldthorpe, has been Parkin (1971; 1974; 1979). Parkin draws on Weber's discussion of SOCIAL CLOSURE, the idea that groups try to monopolize resources and opportunities for their own benefit, and to deny resources and opportunities to others. The key point here is the idea of exclusion of nonmembers. In different societies, criteria of eligibility for membership of dominant classes differ: religion, ethnicity, gender, for example, are bases for exclusion in different societies. Birth into a particular group is a common criterion, so kinship and descent are crucial, and, in this type of rigid system, privileged groups can maximize closure to their own benefit very successfully Closure in modern societies is not based upon descent, but distinct strategies of exclusion are nevertheless employed.
It should be noted that much empirical work on ‘class’ and social mobility operates with ‘occupational definitions rather than with ones based on ‘property’ (see SOCIAL STRATIFICATION). Sociological approaches to class have also been much criticized recently for their ‘gender blindness’, that is, for being models of inequality relating to males only, and treating women's class positions as dependent on those of their male partners (see GENDER STRATIFICATION, MEDIATED CLASS LOCATIONS).
In Britain recently some theorists have seemed to propose an end to class and to the saliency of class analysis (e.g. Pahl, 1989). However, stripped of rhetoric, such claims represent less a call for a revaluation of the centrality of class (e.g. compare LIFESTYLE analysis) than a preference for particular versions of class analysis.
the grouping of farm animals in classes established by judging the animals in terms of a set of features.
The rules for assigning animals to a particular class are determined by the directions for the valuation of various species developed by the Ministry of Agriculture of the USSR. The indexes of ratable features for first class (liveweight, exterior, productivity) are the basic ones and correspond to the requirements for the registration of the animals in the State Herdbook. More valuable animals are classed as elite and elite record; less valuable animals are assigned to second class, third class, and fourth class. Animals in breeding stock that fall outside these classes are culled from the herd.
The class is an index of the breeding value and economic worth of livestock; according to the class, prices are established and the animals are set aside either for breeding or for use.
in biology, one of the higher taxonomic categories of animals and plants. A class embraces related orders of animals or plants. The class Mammalia comprises many orders, including the orders Rodentia, Insectivora, and Carnivora. In turn, classes with members that are similar in their general structure and have common ancestors are grouped in a phylum. For example, the phylum Chordata comprises the classes Pisces, Amphibia, Reptilia, Mammalia, and others. The classes Monocotyledonae and Dicotyledonae constitute the phylum Angiospermae. The concept of class was introduced into taxonomy by the French botanist J. de Tournefort and was subsequently adopted by C. Linnaeus in his Systema naturae (1735).
(in logic), a concept expressing an aggregate (set) of objects satisfying some condition or criterion (a distinction is sometimes made between the concepts “class” and “set”; this is connected with special problems in set theory); for these objects, it is said that they are elements of the (given) class (the relation of belonging to a class is usually denoted by the symbol ∊; the notation a ∊ A is read “a is an element of the class Ā”). It is assumed that for every property (or concept of a property) it is possible to find the class of objects having that property; for example, the class of all even numbers corresponds to the property of being an even number.
The class corresponding to a certain property may consist of any finite number of objects (finite classes are often given by an enumeration of their objects—by a list of their names); it may be infinite (for example, the aforementioned class of all even numbers); or it may be empty (that is, it does not contain any elements at all; the empty class is usually denoted by ʌ or Ø). A class consisting of only one element is called unitary or singular (Aristotle did not introduce singular or empty sets into the construction of his system of syllogisms). In contrast to the empty class is the universal class (denoted by V), specifying the range of the objects under study and composed of all objects under consideration in the object domain. Classes are usually depicted geometrically by figures bounded by simple closed curves (for example, circles in the plane).
We now consider operations upon classes and relations between them. There are several operations upon classes. The intersection of classes A and B is the class (usually denoted by A ∩ B) consisting of all those, and only those, elements contained in both class A and class B; the union of classes A and B is the class A ∪ B consisting of all those, and only those, elements contained in at least one of the classes A or B; the complement of a class A is the class Ā consisting of all those, and only those, objects of the universal class that do not belong to the class A. Relations between (two arbitrary) classes include identity (coincidence), inclusion (one set is part of [a subclass of] another), partial coincidence (when the classes have at least one common element), and exclusion (when they have no common elements). The properties of operations upon classes and relations between classes are studied in the logic of classes.
REFERENCESHubert, D., and W. Ackerman. Osnovy teoreticheskoi logiki. Moscow, 1947. (Translated from German.)
Tarski, A. Vvedenie v Logiku i metodologiiu deduktivnykh nauk. Moscow, 1948. (Translated from English.)
Ianovskaia, S. A. “Logika klassov.” In Filosofskaia entsiklopediia, vol. 3. Moscow, 1964.
Kuzichev, A. S. Diagrammy Venna. Moscow, 1968.
Mendelson, E. Vvedenie v matematicheskuiu logiku. Moscow, 1971. (Translated from English.)
A. S. KUZICHEV
What does it mean when you dream about being in class?
A dream of a school group in which one is a participant or the teacher may symbolize learning life’s lessons or being the authority in matters of life. In certain esoteric traditions, dreaming of being in a classroom is interpreted as meaning that the soul attends classes on the “inner planes” during sleep. Such a dream may also relate to one’s social, political, or economic status, or even to one’s uniqueness (e.g., “in a class of her own”). Divisions, often prejudicial, of race, color, or creed may also be indicated by such a dream (e.g., class consciousness, most significantly as practiced in India). (See also School, Seminar).
Classes are related in a class hierarchy. One class may be a specialisation (a "subclass") of another (one of its "superclasses") or it may be composed of other classes or it may use other classes in a client-server relationship. A class may be an abstract class or a concrete class.
See also signature.
class(1) In object technology, a user-defined data type that defines a collection of objects that share the same characteristics. An object, or class member, is one instance of the class. Concrete classes are designed to be instantiated. Abstract classes are designed to pass on characteristics through inheritance. See instantiate.
(2) In networking, a categorization of a packet based on attributes such as protocol, port and source and destination addresses.