The use of BiologyBiology is the science of living systems. It is inherently interdisciplinary, requiring knowledge of thephysical sciences and mathematics, although specialities may be oriented toward a group oforganisms or a level of organization. BOTANY isconcerned with plant life, ZOOLOGY with animallife, algology with ALGAE, MYCOLOGY withfungi, MICROBIOLOGY with microorganismssuch as protozoa and bacteria, CYTOLOGY withCELLS, and so on. All biological specialties,however, are concerned with life and itscharacteristics. These characteristics includecellular organization, METABOLISM, responseto stimuli, development and growth, andreproduction. Furthermore, the informationneeded to control the expression of suchcharacteristics is contained within each organism.FUNDAMENTAL DISCIPLINES Life is dividedinto many levels of organization--atoms,molecules, cells, tissues, organs, organ systems,organisms, and populations. The basic disciplinesof biology may study life at one or more of theselevels. Taxonomy attempts to arrange organisms innatural groups based on common features. It isconcerned with the identification, naming, andclassification of organisms. The seven majortaxonomic categories, or taxa, used inclassification are kingdom, phylum, class, order,family, genus, and species. Early systems usedonly two kingdoms, plant and animal, whereasmost modern systems use five: MONERA(BACTERIA and BLUE-GREEN ALGAE),PROTISTA (PROTOZOA and the otherALGAE), FUNGI, PLANT, and ANIMAL. Thediscipline of ECOLOGY is concerned with theinterrelationships of organisms, both amongthemselves and between them and theirenvironment. Studies of the energy flow throughcommunities of organisms and of the environment(the ecosystem approach) are especially valuablein assessing the effects of human activities. Anecologist must be knowledgeable in otherdisciplines of biology. Organisms respond tostimuli from other organisms and from theenvironment; behaviorists are concerned withthese responses. Most of them study animals--asindividuals, groups, or entire species--in describingANIMAL BEHAVIOR patterns. These patternsinclude ANIMAL MIGRATION, courtship andmating, social organization, TERRITORIALITY,INSTINCT, and learning. When humans are
included, biology overlaps with psychology andsociology. Growth and orientation responses ofplants can also be studied in the discipline ofbehavior, although they are traditionallyconsidered as belonging under development andPHYSIOLOGY, respectively. Descriptive andcomparative EMBRYOLOGY are the classicareas of DEVELOPMENT studies, althoughpostembryological development, particularly theaging process, is also examined. The biochemicaland biophysical mechanisms that control normaldevelopment are of particular interest when theyare related to birth defects, cancer, and otherabnormalities. Inheritance of physical andbiochemical characteristics, and the variations thatappear from generation to generation, are thegeneral subjects of GENETICS. The emphasismay be on improving domestic plants and animalsthrough controlled breeding, or it may be on themore fundamental questions of molecular andcellular mechanisms of HEREDITY. A branch ofbiology growing in importance since the 1940s,molecular biology essentially developed out ofgenetics and biochemistry. It seeks to explainbiological events by studying the molecules withincells, with a special emphasis on the molecularbasis of genetics--nucleic acids in particular--andits relationship to energy cycling and replication.Evolution, including the appearance of newspecies, the modification of existing species, andthe characteristics of extinct ones, is based ongenetic principles. Information about the structureand distribution of fossils that is provided bypaleontologists is essential to understanding thesechanges. Morphology (from the Greek, meaning"form study") traditionally has examined theANATOMY of all organisms. The middle levelsof biological organization--cells, tissues, andorgans, are the usual topics--with comparisonsdrawn among organisms to help establishtaxonomic and evolutionary relationships. Asimportant as the form of an organism are itsfunctions. Physiology is concerned with the lifeprocesses of entire organisms as well as those ofcells, tissues, and organs. Metabolism andhormonal controls are some of the special interestsof this discipline. HISTORY OF BIOLOGYOrigin and Early Development. The oldestsurviving archaeological records that indicate somerudimentary human knowledge of biologicalprinciples date from the Mesolithic Period. Duringthe NEOLITHIC PERIOD, which began almost
10,000 years ago, various human groupsdeveloped agriculture and the medicinal use ofplants. In ancient Egypt, for example, a number ofherbs were being used medicinally and forembalming. Early Development As a science,however, biology did not develop until the last fewcenturies BC. Although HIPPOCRATES, knownas the father of medicine, influenced thedevelopment of medicine apart from its role inreligion, it was ARISTOTLE, a student of Plato,who established observation and analysis as thebasic tools of biology. Of particular importancewere Aristotles observations of reproduction andhis concepts for a classification system. As thecenter of learning shifted from Greece to Romeand then to Alexandria, so did the study ofbiology. From the 3d century BC to the 2dcentury AD, studies primarily focused onagriculture and medicine. The Arabs dominatedthe study of biology during the Middle Ages andapplied their knowledge of the Greeks discoveriesto medicine. The Renaissance was a period ofrapid advances, especially in Italy, France, andSpain, where Greek culture was beingrediscovered. In the 15th and 16th centuries,Leonardo da Vinci and Michelangelo becameskilled anatomists through their search forperfection in art. Andreas VESALIUS initiated theuse of dissection as a teaching aid. His books,Fabrica (1543) and Fabrica, 2d ed. (1550),contained detailed anatomical illustrations thatbecame standards. In the 17th century, WilliamHARVEY introduced the use of experimentationin his studies of the human circulatory system. Hiswork marked the beginning of mammalianphysiology. Scientific Societies and Journals. Lackof communication was a problem for earlybiologists. To overcome this, scientific societieswere organized. The first were in Europe,beginning with the Academy of the Lynx (Rome,1603). The Boston Philosophical Society, foundedin 1683, was probably the first such society to beorganized in colonial America. Later, specializedgroups, principally of physicians, organizedthemselves, among them the American Associationfor the Advancement of Science (AAAS),founded in 1848. Much later, in 1951, theAmerican Institute of Biological Science (AIBS)was formed as an alliance of the major biologicalsocieties in the United States. The first journals topresent scientific discoveries were published inEurope starting in 1665; they were the Journal des
Savants, in France, and Philosophical Transactionsof the Royal Society, in London. Over the years,numerous other journals have been established, sothat today nearly all societies record theirtransactions and discoveries. Development andEarly Use of the Microscope. Before 1300 opticallenses were unknown. At that time, except forcrude spectacles used for reading. Modern opticsbegan with the invention of the MICROSCOPEby Galileo Galilei about 1610. Microscopyoriginated in 1625 when the Italian FrancescoStelluti published his drawings of a honeybeemagnified 10 times. The 17th century producedfive microscopists whose works are consideredclassics: Marcello MALPIGHI (Italy), Antoni vanLEEUWENHOEK and Jan SWAMMERDAM(Holland), and Robert HOOKE and NehemiahGREW (England). Notable among theirachievements were Malpighis description of lungcapillaries and kidney corpuscles and HookesMicrographia, in which the term cell was firstused. Basis for Modern Systematics. Consistentterminology and nomenclature were unknown inearly biological studies, although Aristotle regularlydescribed organisms by genos and eidoes (genusand species). Sir Isaac NEWTONs Principia(1687) describes a rigid universe with an equallyrigid classification system. This was a typicalapproach of the period. The leading botanicalclassification was that used in describing themedicinal values of plants. Modern nomenclaturebased on a practical binomial system originatedwith Karl von Linne (Latinized to CarolusLINNAEUS). In addition to arranging plants andanimals into genus and species based on structure,he introduced the categories of class and order.Jean Baptiste LAMARCK based his system onfunction, since this accommodated his view of theinheritance of acquired characteristics. In 1817,Georges, Baron CUVIER became the first todivide the entire animal kingdom into subgroups,for example, Vertebrata, Mollusca, Articulata, andRadiata. Explorations and Explorers. During the18th and 19th centuries numerous importantbiological expeditions were organized. Three ofthese, all British, made outstanding contributions tobiology. Sir Joseph BANKS, on Captain Cooksship Endeavor, explored (1768-71) the SouthSeas, collecting plants and animals of Australia.Robert BROWN, a student of Banks, visitedAustralia from 1801 to 1805 on the Investigatorand returned with more than 4,000 plant
specimens. On perhaps the most famous voyage,Charles DARWIN circumnavigated (1831-36)the globe on the Beagle. His observations of birds,reptiles, and flowering plants in the GalapagosIslands in 1835 laid the foundation for his theorieson evolution, later published in On the Origin ofSpecies (1859). The Discovery ofMicroorganisms. Arguments about thespontaneous generation of organisms had beengoing on since the time of Aristotle, and variousinconclusive experiments had been conducted.Louis PASTEUR clearly demonstrated in 1864that no organisms emerged from his heat-sterilizedgrowth medium as long as the medium remained insealed flasks, thereby disproving spontaneousgeneration. Based on Edward JENNERs studiesof smallpox, Pasteur later developed a vaccine foranthrax and in 1885 became the first tosuccessfully treat a human bitten by a rabid dog.Beginning in 1876, Robert KOCH developedpure-culture techniques for microorganisms. Hiswork verified the germ theory of disease. One ofhis students, Paul EHRLICH, developedchemotherapy and in 1909 devised a chemicalcure for syphilis. The value of ANTIBIOTICSbecame evident when Sir Alexander FLEMINGdiscovered penicillin in 1928. An intensive search,between 1940 and 1960, for other antibioticsresulted in the development of several dozen thatwere used extensively. Although antibiotics havenot been the panacea once anticipated, their usehas resulted in a decreased incidence of mostinfectious diseases. The Role of the Cell.Following Hookes use of the term cell, biologistsgradually came to recognize this unit as commonthroughout living systems. The cell theory waspublished in 1839 by Matthias Schleiden a plantanatomist. Schleiden saw cells as the basic unit oforganization and perceived each as having adouble life, one "pertaining to its owndevelopment" and the other "as an integral part ofa plant." Schwann, an animal histologist, noticedthat not all parts of an organism are comprised ofcells. He added to the theory in 1840 byestablishing that these parts are at least "cellproducts." Between 1868 and 1898 the celltheory was enlarged as substructures of thecell--for example, plastids andmitochondria--were observed and described.Basic Life Functions. Until the 17th century it wasbelieved that plants took in food, preformed, fromthe soil. Jan Baptista van HELMONT, the first
experimental physiologist, around 1640 concludedthat water is the only soil component required forplant growth. Stephen HALES showed (1727)that air held the additional ingredient for foodsynthesis. In 1779, Ingenhousz identified this ascarbon dioxide. The study ofPHOTOSYNTHESIS began with ademonstration by Sachs and Pringsheim in themid-19th century that light is the energy source ofgreen plants. Blackman showed (1905) that not allparts of this process require sunlight. Results ofwork done during the 1920s and 30s proved thatchloroplasts produce oxygen. Subsequently, it wasshown that the light-dependent reactions causetwo types of high-energy molecules to be formedthat use the energy from light. The route of carbondioxide in photosynthesis was worked out byMelvin CALVIN in the early 1950s, using theradioisotope carbon-14. His results provedBlackman correct: there exist two distinct butclosely coordinated sets of chloroplast reactions,one light-dependent and the otherlight-independent. High-energy products of thelight-dependent reactions are required forincorporation of carbon dioxide into sugars in thelight-independent reactions. The earliestdemonstration of ferments (the word ENZYMEwas not coined until 1878) in pancreatic juice wasmade by Claude BERNARD in France. Bernardalso experimentally determined numerous functionsof the liver as well as the influence of vasomotornerves on blood pressure. In the 1930s, OttoWARBURG discovered a series of cellularenzymes that start the process of glucosebreakdown to produce energy for biologicalactivity. When Hans KREBS demonstrated(1950s) an additional series of enzyme reactions(the citric acid cycle) that completes the oxidationprocess, the general respiration scheme of cellsbecame known. Chemical synchronization of bodyfunctions without direct control by the nervoussystem was discovered in 1905 by Sir William M.BAYLISS and Ernest Henry STARLING (thefirst to use the term hormone). Steroids werediscovered in 1935. Continuity in Living Systems.The early biologists known as preformationistsbelieved that animals exist preformed, either insperm (the animalculists view) or in the egg (theovists belief). Embryology actually began whenKarl Ernst von BAER, using the microscope,observed that no preformed embryos exist.Modern interpretations of developmental control
in embryogenesis can be traced to HansSPEMANNs discovery in 1915 of an "organizer"area in frog embryos. More recent research hasshown the importance of other factors, such aschemical gradients. Genetics, the study of heredity,began with the work of Gregor Johann MENDEL,who published his findings in 1866. Mendelsextensive experiments with garden peas led him toconclude that the inheritance of each characteristicis controlled by a pair of physical units, or genes.These units, one from each parent (the law ofsegregation), were passed on to offspring,apparently independent of the distribution of anyother pairs (the law of independent assortment).The gene concept was amplified by therediscovery and confirmation of Mendels work in1900 by Hugo DE VRIES in Holland, Karl ErichCorrens in Germany, and Gustav Tschermak vonSeysenegg in Austria. De Vriess mutation theorybecame the foundation of modern genetics. Thechromosome theory is based on the speculationsof Pierre Paul ROUX in 1883 that cell nucleicontain linear arrangements of beadlikecomponents which replicate (produce exactcopies) during cell division. Many importantcontributions were made early in the 20th centuryby the American Thomas Hunt MORGAN. Theseincluded sex-linked inheritance and the associationwith gene theory of the crossing over ofchromosomes. The discovery by Geoffrey Hardyand William Weinberg of the equilibriumrelationship that exists between frequency ofalleles (a term originated by William Bateson in1909 for alternate forms of a gene) in a populationled to formulation of the law bearing their names.The role of genetics in evolution was publicized in1937 by Theodosius DOBZHANSKYs Geneticsand the Origin of Species. Molecular biology, themost recent branch of biology, began early in the20th century with Archibald Garrods work on thebiochemical genetics of various diseases. Theconcept of one gene producing one enzyme wasestablished in 1941 by George W. BEADLE andEdward L. TATUM. The work on proteinsynthesis by Jacques MONOD and FrancoisJACOB and others in 1961 has modified the onegene-one enzyme concept to one gene-oneprotein. Essential to the understanding of proteinsynthesis were the advances made in the 1940sand 50s in understanding the role and structure ofnucleic acids. The structural model proposed in1953 by James D. WATSON and F. H. C.
CRICK is a landmark in biology. It has givenbiologists a feasible way to explain the storage andprecise transmission of genetic information fromone generation to the next. Knowledge ofbiological processes at the molecular level has alsoenabled scientists to develop techniques for thedirect manipulation of genetic information, a fieldnow called GENETIC ENGINEERING. UNITYOF LIVING SYSTEMS Despite the astoundingdiversity of organisms that have been discovered,an equally astounding degree of unity of structureand function has been discerned. The structure offlagella is essentially the same in all cells havingnuclei. The molecules involved in growth andmetabolism are remarkably similar, and often theyare constructed of identical subunits. Furthermore,enzymes, the catalysts of biological chemistry, arenow known to act similarly in all organisms.Phenomena such as cell division and thetransmission of the genetic code also appear to beuniversal. Larry A. GiesmannBibliography:Angros, Robert, and Stanciu, George, The NewBiology (1987); Antebi, Elizabeth, and Fishlock,David, Biotechnology (1987); Asimov, Isaac, AShort History of Biology (1964; repr. 1980), andThe Intelligent Mans Guide to the BiologicalSciences (1968); Borek, Ernest, The Sculpture ofLife (1973); Darnell, James, et al., Molecular CellBiology (1986); Ebert, J. D., et al., Biology(1973); Ehrlich, Paul, The Machinery of Nature(1987); Ehrlich, Paul R., et al., IntroductoryBiology (1973); Gardner, Eldon J., History ofBiology, 3d ed. (1972); Hanawalt, P. C., andHaynes, R. H., eds., The Chemical Basis of Life(1973); Handler, Philip, ed., Biology and theFuture of Man (1970); Lanham, U. N., TheOrigins of Modern Biology (1968); MaynardSmith, John, The Problems of Biology (1986);Mayr, Ernst, The Growth of Biological Thought(1982); Medawar, P. B., and J. S., Life Science(1978); Pauley, Philip, Controlling Life (1987);Swanson, Carl P., and Webster, Peter, The Cell,4th ed. (1977); Watson, J. D., et al., MolecularBiology of the Gene, 2 vols., 4th ed. (1987).