BIOLOGY.

Biology comes from the Greek word for life, bis, and the Greek word for thought or reasoning, logos. It denotes the science that studies life, the properties and processes that sustain life, the evolutionary history of life, and particular living organisms. It is a science of enormous diversity, breadth, and heterogeneity unified only by the conceptual framework provided by the theory of evolution. Indeed, as famously noted in 1973 by the Russian evolutionary geneticist Theodosius Dobzhansky (1900–1975), "Nothing in biology makes sense except in the light of evolution"—a quote now replicated in so many university-level textbooks that it is almost a dictum in modern biology.

One reason for the diversity of biology comes from the staggering diversity of organisms that can be considered living. These range from viruses, bacteria, and fungi to plants and animals, including humans. Another reason is that life can be studied on various levels in a hierarchy that ranges from the organic-macromolecular level to genes, cells, tissues, organs, and entire organisms. Furthermore, organisms interact in, and can be organized into, families, communities, societies, species, populations, biomes or biota, and perhaps even the global systems (as in the controversial Gaia hypothesis, which postulates that the earth itself is a living organism). To a large extent, biological subdisciplines are organized around each of these levels of activity or organization. Thus, for example, cellular biology, or cytology (coming from the Greek word cyto for cell), deals specifically with the study of cells, while ecology (coming from the Greek word oikos for habitat) deals with interactions between populations, species, communities, and biomes and the processes that sustain them. Since biology deals immediately with living organisms and processes, it has a large applied component. It touches on medical and health-related areas, pharmacy, agriculture, forestry, and biological oceanography. In contemporary society, the promises and problems associated with applications of biology are staggering. They range from stem-cell research, the development and use of genetically modified organisms, and the use of biological tools as identity markers (as in DNA "fingerprinting") to the possibility of designer babies and human cloning. Whereas the physical sciences and their applications dominated science for much of the history of science, the biological sciences now dominate both popular and scientific discussions, especially after the discovery of the structure of DNA in 1953. Viewing the revolution precipitated by the applications of biology to society at the closing of the twentieth century, many commentators anticipate that the new century will be the century of biology.

The Origins of Biology

Though biology is generally regarded as a modern science with late origins in the early to mid-nineteenth century, it drew on varied traditions, practices, and areas of inquiry beginning in antiquity. Traditional histories of biology generally target two areas that merged into modern biological science: medicine and natural history. The tradition of medicine dates back to the work of ancient Greek medical practitioners such as Hippocrates of Kos (b. 460 b.c.e.) and to figures such as Galen of Pergamum (c. 130–c. 200), who contributed much to early understanding of anatomy and physiology. The tradition of natural history dates back to the work of Aristotle (384–322 b.c.e.). Especially important are his History of Animals and other works where he showed naturalist leanings. Also important is the work of Aristotle's student Theophrastus (d. 287 b.c.e.), who contributed to an understanding of plants. Aristotle and Theophrastus contributed not only to zoology and botany, respectively, but also to comparative biology, ecology, and especially taxonomy (the science of classification).

Both natural history and medicine flourished in the middle ages, though work in these areas often proceeded independently. Medicine was especially well studied by Islamic scholars working in the Galenic and Aristotelian traditions, while natural history drew heavily on Aristotelian philosophy, especially in upholding a fixed hierarchy of life. The Roman naturalist Caius Plinius Secundus (23–79), known as Pliny, also had a major influence on natural history during the middle ages, notably through his compendium Natural History (later shown to be rife with errors of fact). Without doubt the most outstanding contributor to natural history in the middle ages is Albertus Magnus (1206–1280), recognized for his superb botanical studies and for his work in physiology and zoology. A lesser known figure is Holy Roman Emperor Frederick II (1194–1250), whose treatise The Art of Falconry is one of the first serious accounts of ornithology.

Though animals traditionally drew the attention of many naturalists, the study of zoology remained underdeveloped during the middle ages, relying heavily on illustrated books of animals modeled on medieval bestiaries. Botany, on the other hand, flourished in the Renaissance and early modern period. The study of plants was important in medicine, as well as natural history (and in fact constituted one of the few early points of common focus in the two areas), because plants were regarded as materia medica, substances with noted medicinal properties. These medicinal properties drew medical attention to plants. Hence it became standard practice to plant gardens next to primary centers of medical instruction, and professors of medicine were very often experts in materia medica and served as garden curators. Indeed, noted taxonomists of the early modern period—individuals such as Andrea Cesalpino (1519–1603) and Carl Linnaeus (1707–1778), both of whom are considered fathers of modern botany for their work in reforming taxonomy—were simultaneously physicians and botanists. An exception was John Ray (1627–1705), an English taxonomist who also worked with animals.

Also leading to the growing interest in and need for taxonomy and to an unprecedented development of natural history were the voyages of exploration associated with the establishment of colonies from the late fifteenth century. Largely to meet the demand to classify the collections made by explorers and travelers in order to exploit these natural commodities, gardens and museums of natural history were created in European centers associated with colonial conquests, especially Madrid, Paris, and London. A new period of scientific exploration dawned with the first voyage of Captain James Cook, whose expeditions included not only astronomers and artists but also botanists, such as Joseph Banks (1743–1820). On returning to London, Banks was instrumental in helping to found the Royal Institution of Great Britain, as well as in continuing to expand Kew Garden and the Royal Society. He also encouraged these institutions to serve the interests of both natural history and the expanding British Empire in the late eighteenth and early nineteenth centuries.

While botany and medicine were closely linked, anatomy and physiology followed other trajectories. After Galen, the next major figure in the history of anatomy is Andreas Vesalius (1514–1564) of Belgium. Unlike many anatomists (such as Galen, who relied on dissections of animals such as pigs and Barbary apes), Vesalius drew his knowledge of the human body from detailed dissections on human cadavers. He was unusual for his time in believing that the authority of nature should supercede the authority of ancient texts. His seven-volume atlas of human anatomy, De Humani Corporis Fabrica (On the fabric of the human body), covered skeletal and muscular anatomy as well as the major organ systems of the body. Skillfully illustrated by some of the leading Renaissance artists, the atlas was considered a work of art as well as of anatomical science. Although Vesalius challenged many of tenets held by Galen and his numerous commentators, he nonetheless retained some erroneous conventions present in Galen's anatomy, such as the existence of pores in the septum of the heart and "horned" appendages in the uterus (present in the pig uterus but not in the human uterus). Vesalius's work was shortly followed by the work of anatomical specialists such as Bartolomeo Eustachio (1510–1574) and Gabriele Falloppio (1523–1562). Eustachio specialized in the anatomy of the ear, and Falloppio specialized in the female reproductive tract.

Developments in anatomy that turned interest to the parts and organs of the body were accompanied by questions dealing with organ function. In the sixteenth century, physiology, the science that deals specifically with the functioning of living bodies, began to flourish. The major animal physiologist of this period was William Harvey (1578–1657). Harvey performed numerous dissections and vivisections on a range of animals to determine that blood circulates through the body and is not manufactured de novo, as Galenic tradition had dictated. Harvey's influence was felt not only in medicine, but also in comparative physiology and comparative biology, since he performed his experiments on diverse animal systems. His experiments and major treatise, An Anatomical Disputation concerning the Movement of the Heart and Blood in Living Creatures (1628), are considered one of the first demonstrations of the method of hypothesis testing and experimentation. While Harvey frequently drew analogies between the pumping action of the heart and mechanical pumps, he resisted the idea that the body entirely obeyed mechanistic principles. Unlike his contemporary René Descartes (1596–1650), who held mechanistic theories of the functioning of animal bodies, Harvey maintained that some kind of nonmechanistic special forces, later called "vitalistic," were responsible for the life processes of animate matter.

The mechanical philosophy—the belief that the universe and its constituent parts obeyed mechanical principles that could be understood and determined through reasoned observation and the new scientific method—thus made its way into the history of biology. This engendered a lively discussion between mechanism and vitalism, between the idea that life obeyed mechanistic principles and the idea that life depended on nonmechanistic "vital" principles or somehow acquired "emergent properties." The debate cycled on and off for much of the subsequent history of biology, up to the middle decades of the twentieth century.

During the Renaissance, the mechanical philosophy did gain some proponents in anatomy and physiology, the most notable figure being Giovanni Borelli (1608–1679), who sought to understand muscle action in animal bodies in terms of levers and pulleys. Some early embryologists, as followers of Descartes, espoused the belief that development too followed mechanistic principles. In what came to be known as preformation theory or "emboitement," the seeds of mature but miniaturized mature adult forms or homunculi were thought to be embedded entirely intact in mature organisms (as though they were encased in a box within a box, hence the name "emboitement"). Prominent advocates of this view included Marcello Malpighi (1628–1694) and Jan Swammerdam (1637–1680). This stood in contrast to the idea of "epigenesis," the belief dating back to Aristotle and his commentators that development began from initially undifferentiated material (usually the ovum) and then followed an epigenetically determined path of development after fertilization. One of the more prominent proponents of this theory was Pierre Louis Maupertuis (1698–1759), who argued that preformationist theories could not explain why offspring bore characteristics of both parents.

In the seventeenth and eighteenth centuries, theories of embryology and development were superimposed with theories of sexual reproduction, along with a number of theories on the origins of life, most of which upheld the idea of spontaneous generation. During this period debates raged over spontaneous generation, the idea that life was spontaneously created out of inanimate matter. The popular belief that living organisms propagated from mud in streams, dirt and detritus, or environments such as rotting meat was supported by a number of scholars from antiquity on. William Harvey's research into reproduction, published in 1651 as Exercitationes de Generatione Animalium (Essays on the generation of animals), began to cast doubt on spontaneous generation. Harvey believed that all life reproduced sexually, a view he pithily stated with his famous dictum Ex ovo omnia ("Everything comes from the egg"). In 1668 the Italian physician Francesco Redi (1626–1697) performed a famous experiment that further detracted from the theory of spontaneous generation. By carefully covering rotting meat so that it was not accessible to flies, he showed that maggots did not spontaneously emerge. The idea that sexual reproduction characterized much of life was further reinforced when Nehemiah Grew (1641–1711) demonstrated sexuality in plants in 1682. Later, in 1768, the Italian physiologist Lazzaro Spallanzani (1729–1799) offered additional evidence disproving spontaneous generation, and in 1779 he gave an account of the sexual function of ovum and sperm. Despite this accumulating experimental evidence against spontaneous generation, new developments continued to fuel belief in spontaneous generation. In 1740, for example, Charles Bonnet (1720–1793) discovered parthenogenesis ("virgin birth"—an asexual form of reproduction) in aphids, and in 1748 John Turberville Needham (1731–1781) offered evidence of what he thought were spontaneously generated microbes in a sealed flask of broth (this was later challenged by Pierre-Louis Moreau de Maupertuis [1698–1759]). Finally, the discovery of microbial life supported the idea that living organisms spontaneously emerged from natural environments such as pond water. The seventeenth and eighteenth centuries thus witnessed a number of debates that were only resolved much later in the late nineteenth century when distinctions were made between the very different processes associated with reproduction, the origins of life, and embryological or developmental unfolding. Belief in spontaneous generation was finally put to rest in 1860 by the celebrated "swan-necked flask" experiments of Louis Pasteur (1822–1895).

Other notable developments in the origins of biology came as the result of new instruments and technologies, the most important of which was the microscope. Developed independently by Robert Hooke (1635–1703) in England and Antony Van Leeuwenhoek (1632–1723) in the Netherlands, the microscope revealed a previously unseen and entirely unimagined universe of life. Robert Hooke first observed repeating units he described as "cells" in his Micrographia (1665), while Leeuwenhoek observed varied motile organisms he described as "animalcules." While the microscope opened up cytological and microbiological explorations, it also shattered Aristotle's notion that life is organized along a scala naturae (ladder of nature), since new and minute animal forms were not easily located on the ladder of creation. It also fueled the belief in spontaneous generation. Pioneering the use of the microscope and its application to anatomy, Marcello Malphighi (1628–1694), Italian professor of medicine and personal physician to Pope Innocent XII, drawing on the previous work of Andrea Cesalpino and William Harvey, studied the circulatory and respiratory systems of a range of animals (especially insects). He was one of the first to study major organ groups such as the brain, lungs, and kidneys in diverse organisms.

Modern Biology

Though there is some disagreement among historians of biology about the precise origins, the transition to modern biology appears to have occurred from the late eighteenth century to the early nineteenth century. A confluence of developments brought about this transition. In France naturalists reformed taxonomy and began to recognize the extinction of life forms. This progress resulted from the work of natural historians such as the Compte de Buffon (1707–1788), Georges Cuvier (1769–1832), Étienne Geoffroy de Saint Hilaire (1772–1844), and Jean-Baptiste de Lamarck (1744–1829) at institutions such as the Jardin du Roi. New sciences emerged, including comparative anatomy and paleontology, areas in which Cuvier is still recognized as the founding father. French anatomists such as Xavier Bichat (1771–1802) and physiologists such as François Magendie (1783–1855), by experimenting on animal systems (sometimes to questionable excess in the case of Magendie), refined and enhanced understanding of fundamental physiological processes, and thereby revolutionized physiological understanding of life. In Germany the insights of natural philosophers such as Johann Wolfgang von Goethe (1749–1832) and Lorenz Oken (1779–1851) began to generate a serious interest in a unified science of life.

All of this activity was echoed by a number of early references to biology in a number of obscure German contexts beginning in the late eighteenth century. Traditional histories generally pinpoint the first general use of the term biology at 1800 in the medical treatise Prapädeutik zum Studium der gesammten Heilkunst (Propaedeutic to the study of general medicine) by Karl Friedrich Burdach (1776–1847), who used it mostly for the study of human morphology, physiology, and psychology. It appeared again in 1802 in the work of the German naturalist Gottfried Treviranus (1776–1837) and in the work of Jean-Baptiste de Lamarck, the French botanist and early proponent of transmutationism. Although the word gained some currency by the 1820s, especially in the English language, it was largely through the efforts of August Comte (1798–1857), the French social philosopher, that the term gained its most widespread currency. For Comte, biology, one of the "higher sciences" in his philosophy of positivism, was the discipline of knowledge that organized the study of life and sought the principles of life.

Especially critical to the development of modern biology was the period between 1828, when Friedrich Wöhler (1800–1882) artificially synthesized the organic compound urea in the laboratory (fueling the debate between mechanism and vitalism), and 1866, the year Gregor Mendel (1822–1884) published his theory of heredity. During this time the conceptual foundations of the new science were laid, and many of the defining criteria of nearly all the major subdisciplines of biology were established.

The first areas for which groundwork was laid were cytology (now part of the more general discipline of cell biology) and histology (the study of tissues). Advances in optics in the 1830s by workers such as Giovanni Battista Amici (1784–1863) significantly enhanced the resolving power of the microscope and diminished or entirely eliminated such disruptive phenomena as chromatic aberration. Techniques for selectively dyeing and staining cellular components and enhancements in sectioning that led to thinner and thinner sections further enabled researchers to see more clearly increasingly finer structures. As a result of improvements in microscope technology, a series of plant and animal observations from 1833 led to recognition of a number of cellular structures, beginning with the nucleus, first observed in orchid cells by the English microscopist Robert Brown (1773–1858). Observations on the cells of plants and animals culminated in the establishment of the cell theory in the late 1830s, the recognition that cells were the basic unit of organization in all living tissues. The establishment of the cell theory resulted from observational work by the botanist Matthias Schleiden (1804–1881) and by the animal physiologist Theodor Schwann (1810–1882). Rudolf Virchow (1821–1902) extended this theory in 1840 to include the observation that all cells come from cells, and in 1858, in his Cellular Pathology, he provided new foundations for understanding disease in terms of cellular disruption. The germ theory of disease, a theory that Louis Pasteur proposed in the 1860s as a result of his work in microscopy, suggested that microorganisms were the causes of infectious diseases. Advances in microscopy in the nineteenth century thus laid the foundations not only of cytology and histology but also of the new science of microbiology (the study of microbial life), which continued to explore smaller and smaller life forms well into the twentieth century.

Yet another area that drew heavily on microscopy was knowledge of heredity (later designated as the science of genetics), especially in the late nineteenth century after structures such as chromosomes were first observed and cellular reproduction was understood in terms of meiosis and mitosis. The chromosome theory of heredity, first proposed by Walter Sutton (1877–1916) and Theodor Boveri (1862–1915), largely integrated knowledge of the fine structure and behavior of chromosomes with Mendelian genetics to suggest that chromosomes were the material carriers of heredity. This theory was not articulated until early in the twentieth century, between 1902 and 1903. This development occurred so late because Gregor Mendel's experimental insights into the process of heredity, which had been published in 1866, was not appreciated until its rediscovery in 1900. The modern science of heredity, which William Bateson (1861–1926) designated as genetics, began in the early years of the twentieth century, with initial inquiry determining the extent to which Mendelian principles operated in the natural world. The second area of interest sprung from the pioneering research of the American geneticist Thomas Hunt Morgan (1866–1945) and his laboratory on Mendelian genetics in the fruit fly, Drosophila melanogaster. Beginning roughly in the 1910s and peaking in the 1930s, this classic school of genetics worked on the transmission of a number of characteristics by studying mutant forms of Drosophila.

Microscopic techniques also played an active role in other important areas of nineteenth-century biology, areas such as embryology, and brought into relief the interplay between heredity, development, cytology, and evolution. By the late nineteenth century, persistent questions of biological development were being tackled with techniques and insights gleaned from cytology and cellular physiology, leading to a renewal of the debate between mechanism and vitalism. Just when figures such as August Weismann (1834–1914) had articulated mechanistic theories linking heredity with development and evolution, leading to movements such as developmental mechanics, individuals such as Hans Driesch (1867–1961) challenged strict mechanism in biology by experimentally demonstrating that almost any part of the cellular constituents of embryonic tissues had the potential to develop into mature forms. Driesch's experimental efforts were rivaled by those of Wilhelm Roux (1850–1924), the leading advocate of developmental mechanics.

The middle decades of the nineteenth century also witnessed improvements in animal physiology, especially through the efforts of the German school associated with Johannes Müller (1801–1858) and later through the pioneering efforts of Hermann von Helmholtz (1821–1894). Increasingly, work in physiology, especially that of Helmholtz, drew heavily on the physical sciences. This research further supported the view that life obeys mechanistic principles and is reducible to such sciences as chemistry and physics. Proponents of this view increasingly dominated physiology, an arch example being Jacques Loeb (1859–1924), the German-American biologist most associated with mechanistic and reductionistic approaches to biology. His essays in The Mechanistic Conception of Life (1912) summarized this point of view.

Unquestionably, a major development in the critical early period of modern biology was the articulation and acceptance of evolution as based largely on the mechanistic process of natural selection. Drawing on a number of transmutation theories (especially those of Buffon, Lamarck, and Robert Chambers [1802–1871]), Charles Darwin (1809–1882) and Alfred Russel Wallace (1823–1913) independently formulated similar theories of species change through the mechanism of natural selection, jointly publishing their insights in a paper read to the Linnaean Society in 1858. Darwin articulated his theory more fully in his celebrated work On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life (1859). Though the mechanism of evolutionary change continued to resist full understanding by scientists, the fact that life on earth had had an evolutionary history became widely accepted by the late nineteenth century. Because the mechanism remained uncertain, evolutionary theory remained controversial in the closing decades of the nineteenth century. Suggested alternative mechanisms included neo-Lamarckism, directed evolution, aristogenesis, and mutation theory—an entirely new theoretical formulation that drew on the new experimental science of genetics. The turn of the twentieth century is frequently known as the "eclipse of Darwin," not so much because he fell into disfavor, but because alternatives to his theory of natural selection were being favored instead.

Between 1930 and 1950 scientists became certain about the mechanism of natural selection by integrating insights into heredity from Mendelian genetics with insights from traditional natural-history-oriented areas such as systematics, botany, and paleontology to formulate what has been called the "synthetic theory of evolution." At this time evolutionary biology was organized as a discipline, in order to study the process of evolution from a range of perspectives. This "evolutionary synthesis"—an integration of Darwinian selection theory with the newer Mendelian genetics—is generally recognized as a major event in the history of twentieth-century biology. With the establishment of the synthetic theory of evolution, scientists began to feel that a mature, unified, modern science of biology had emerged. Theodosius Dobzhansky, whose own work in evolutionary genetics served as catalyst for this synthesis, has maintained that evolution went a long way toward unifying biology.

Much of the work of twentieth-century biologists served to integrate biology. In addition, new technologies (such as the first electron microscopes in the 1930s), as well as developments and refinements in existing technologies, led to a staggering range of new discoveries in the twentieth century. In 1895 the Dutch biologist Martinus Beijerinck (1851–1931) designated what is known now as viruses—tiny living aggregations of protein and nucleic acid—as "filterable agents" because they passed through fine filters that could contain bacteria. It was known that these filterable agents could induce disease, but their structure was unknown until 1935, when W. M. Stanley (1904–1981) first crystallized the tobacco mosaic virus. This opened up further inquiry into viruses as disease-causing agents, into proteins and nucleic acids as the sole components of this very simple form of life, and into biochemical techniques instrumental for carrying out this research. By the late 1930s molecular biology and biochemistry were gaining traction. The reductionistic, mechanistic approaches of these sciences further pushed biological thinking about life in those directions. There was acute interest in the molecular structure of important proteins such as insulin, whose structure was determined in 1955 by Frederick Sanger (b. 1918), and in the role played by proteins and nucleic acids in reproduction and genetics.

Properties of Living Organisms

A capacity for evolution

A capacity for self-replication

A capacity for growth and differentiation via a genetic program

A capacity for self-regulation, to keep the complex system in a steady state (homeostasis, feedback)

A capacity (through perception and sense organs) for response to stimuli from the environment

A capacity for change at the level of phenotype and of genotype

source: Ernst Mayr, This is Biology: The Science of the Living World (1997).

In 1953 vitalistic approaches and philosophies received two body blows. First, the discovery of the structure of DNA (deoxyribonucleic acid), by Rosalind Franklin (1920–1958), Maurice Wilkins (b. 1916), James D. Watson (b. 1928), and Francis Crick (1916–2004) made the mechanism of the replication of genetic material understandable at the macromolecular level and moved genetics in the direction of molecular genetics. More than any discovery in recent biology, the discovery of the structure of DNA brought forth a revolution in biology, not just because of the theoretical knowledge gleaned, but also because of the potential applications of this knowledge.

The second body blow to vitalism was delivered in the same year by news of the celebrated experiment simulating the origins of life under early conditions on earth by Stanley Miller (b. 1930) and Harold C. Urey (1893–1981) at the University of Chicago. Miller and Urey enclosed the constituents of the early atmosphere of earth (methane, ammonia, and hydrogen gas) in a glass vessel and applied a high-energy electrical discharge to it, "sparking" it to simulate lightning. A container of boiling water constantly supplied water vapor and heat. The cooling and condensing water vapor simulated rain. After letting the apparatus run for a number of hours and eventually weeks, Miller and Urey collected a brown-red pastelike substance and chemically analyzed it to reveal a number of amino acids, the building blocks of proteins, and other macromolecules usually associated only with living organisms. The Miller-Urey experiment thus provided evidence that the basic building blocks for life could be generated by the kinds of conditions present in the early atmosphere of the earth. Subsequent experiments simulating conditions on other planets supported the view that life may also have originated in space, on other planets, or wherever similar conditions are found. For this area of study integrating research on the origins of life on earth with research on the existence and specific character of life on other planets, the molecular geneticist Joshua Lederberg (b. 1925) coined the term "exobiology," the biology of organisms outside earth. Its sibling science is esobiology, or earth-based biology.

After World War II, biology boomed, and with it emerged new societies and institutions to organize the growing science. In 1947 the first umbrella organization for the biological sciences, the American Institute of Biological Sciences, was created in the United States. Other institutions, such as the National Science Foundation in the United States, established large divisions (and budgets) to fund research in the biological sciences. Both trends helped shape the direction and character of subsequent biological research. As with many other sciences in the postwar period, the dominant site of activity in the biological sciences had shifted from its older European centers in Germany, France, and England to the United States. At the height of the Cold War, the Soviet launch of the Sputnik satellite drove a panicked U.S. government to offer even stronger support of scientific research. The biological sciences, too, benefited from this turn of events and received generous funding for research and biological instruction. Textbooks such as the popular Biological Sciences Curriculum Study drew on a virtual industry of biologists and educators to produce a series of widely read and influential textbooks for American high school students. Research in the United States continued at specialized research centers such as that at Cold Spring Harbor (in 2004 a center for molecular biology) and more traditional research settings including public and private universities, land-grant colleges, hospitals and medical centers, museums and gardens. In university education, biology as a subject area is considered so vital that it has become a requirement for general education programs. It is rapidly becoming one of the most popular majors for university students not just in the United States but worldwide.

Early Definitions of Biology

From Lamarck, 1802: Biology: this is one of the three divisions of terrestrial physics; it includes all which pertains to living bodies and particularly to their organization, their developmental processes, the structural complexity resulting from prolonged action of vital movements, the tendency to create special organs and to isolate them by focusing activity in a center, and so on.

From Treviranus, 1802: The objects of our research will be the different forms and phenomena of life, the conditions and laws under which they occur and the causes whereby they are brought into being. The science which concerns itself with these objects we shall designate Biology or the Science of Life.

source: As translated by William Coleman in Biology in the Nineteenth Century: Problems of Form, Function, and Transformation (1971), p. 2.

Despite arguments for the unity of the increasingly diverse biological sciences, controversies and debates erupt between biologists about fundamental concepts in the biological sciences. Differences are especially pronounced between more reductionistic, physicalist, laboratory-driven, and experimental sciences such as molecular biology and biochemistry and more integrative, field-oriented, observational, and historical sciences such as evolutionary biology and ecology. In the mid-1960s, university biology departments became divided over differences in conceptual foundations, goals, methodology, philosophy, and scientific style. As a result, at locations such as Harvard University, departments of biology formally divided into departments of molecular biology and organismic biology, an area defined as an integrative approach to the biological sciences that includes a strong historical and ecological component. Roughly at this time ecology—a science of enormous heterogeneity drawing on a range of approaches, practices, and methodologies and rooted in questions pertaining to adaptive responses to varying environments—became integrated with evolutionary approaches and instituted in departments of ecology and evolution. Often located within ecology and evolution departments are systematics and biodiveristy studies, a newer area concerned with biodiversity, including classification and conservation.

In 1961 the evolutionary biologist, historian, and philosopher Ernst Mayr, reflecting on some of these growing differences between biologists, provocatively suggested that biology in fact comprises two sciences. The first is a biology based on proximate causes that answers questions of function (molecular biology, biochemistry, and physiology). The second is a biology based on ultimate causes that seeks historical explanation (evolutionary biology, systematics, and the larger discipline of organismic biology). While the biology of proximate causes is reductionistic and physicalist, the biology of ultimate causes is historical and is characterized by emergent properties. Much of Mayr's reflections on the structure of the biological sciences has formed the backbone of the history and philosophy of biology and has made its way into some textbooks in the biological sciences. While vitalism is no longer tenable in biology, there is considerable support for the belief that complex properties emerge from simpler strata in biology and for the idea that such emergent properties are useful in explaining life.

See also Evolution ; Genetics ; Life .

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Vassiliki Betty Smocovitis

BIOLOGY

BIOLOGY. The science of biology as such did not exist in the early modern period; the term biology itself came into use only around 1800. Nonetheless, research in subjects now encompassed by biology was avidly pursued, principally by physicians but also by natural philosophers. The philosopher of science Francis Bacon (1561–1626) called for intensified descriptive study of physical forms ("natural history") and the analytical study of their functions, classified as part of "physic." Institutional sites for inquiry included the universities, with those in southern Europe dominant earlier and those in northern Europe later in the period. Private individuals often worked with the support of aristocratic, princely, and ecclesiastical patrons. In the seventeenth century omnibus scientific societies were founded in Rome and Florence. The Royal Society of London (founded 1660) and the Academy of Sciences in Paris (founded 1666) were highly influential. Specialized learned societies came into existence only at the end of the period. Instruments were less important than in physical science, but the microscope proved crucial to advances in knowledge. Much inquiry was tied to the pursuit of fine and technical arts (painting and sculpture, optics, printing and illustrating) and to collecting practices ("cabinets of curiosities"). Public gardens and zoological collections were essential to naturalists from the seventeenth century forward.

NATURAL PHILOSOPHY

At the beginning of the period the natural philosophy taught in the universities was dominated by Aristotelianism as recast by the late Scholastics to harmonize with Roman Catholic orthodoxy. Aristotelian philosophy established the linguistic and conceptual framework for inquiry and conveyed specific doctrines such as the "great chain of being," a posited hierarchy of natural forms ranging from the simplest to the most complex. Aside from Aristotelian influence, medicine was dependent on the legacy of the Greek physician Hippocrates (460–c. 370 b.c.e.), especially the doctrine of the humors, and of the Hellenistic surgeon and Roman court physician Galen (129/130–199/200 c.e.), whose general teleology and specific teachings in anatomy and physiology undergirded universitybased medical training. Competing intellectual traditions derived from Plato (427–348/347 b.c.e.) as well as the occult sciences of the cabala, natural magic, hermeticism, astrology, and alchemy.

The greatest master of the occult sciences in medicine was Philippus Aureolus Theophrastus Bombast von Hohenheim, called Paracelsus (1493–1541). Paracelsus rejected the study of anatomy, basing pathology and therapeutics instead on the doctrine of correspondences between the macrocosm and the microcosm. His "ontological" theory of disease, which held that the "seeds" of all maladies are present in every organism, undermined humor theory and encouraged the search for specific remedies, especially new ones derived from metals. Paracelsianism spread most rapidly in Protestant lands and Protestant enclaves in Catholic Europe. Its diffusion contributed to the decline of Aristotelianism, which was, however, principally undermined by the emergent "mechanical philosophy." Mechanism, which viewed living bodies as sophisticated machines, was dominant from the later seventeenth century until challenged around 1750 by vitalists who posited a distinctive "principle of life" or individuated vital "forces." By the eighteenth century many investigators rejected all "systems" and embraced a scientific ethos based on observation and experimentation.

HISTORICAL CONTEXT

European contact with the New World resulted in a challenge to existing conceptions of creation, the lineage of humankind, and the number and types of living creatures. Other influences included the continuing recovery of the heritage of Greco-Roman antiquity; the emergence of centralizing "new monarchies" and elaborated forms of princely and municipal government; and long-term economic revival from the ravages of the pandemic of plague that first struck Europe in 1348. In connection with these changes, new and fuller editions of the works of ancient philosophers and physicians appeared; the arts and sciences enjoyed expanded prestige and public patronage; and new commodities, both natural and manufactured, came into use. The Protestant Reformation destroyed the religious unity of Europe and encouraged challenges to tradition. The absolutist state emergent in the seventeenth century established new guardians of orthodoxy but also provided new resources for learned inquiry. More powerful government, coupled with economic growth and differentiation, encouraged the spread of literacy and the extension of modes of communication and transportation. These combined forces unsettled social hierarchies based on bloodlines, corporate status, and gender. The self-styled "Enlightenment" of the eighteenth century was marked by a commitment to the methods and values of "science," variously defined, and by a heightened critical spirit. Broader historical developments were linked both as cause and effect to changes in the world of learning that, by the period's end, encouraged the emergence of modern life science.

ANATOMY AND PHYSIOLOGY

Because in Aristotelian-Galenic medicine the heart was considered central, many Renaissance-era inquirers were drawn to the study of this organ. Aristotle viewed the heart as the center of the body, the seat of the "vital heat" that empowered its functions. Galen delineated the structure and functions of the heart and other organs dominant in three body "centers" of head, chest, and abdomen. In his system, blood flowed only as part of an ebb and flow to and from the dominant organ to peripheral structures; arterial blood produced in the right ventricle of the heart seeped into the left ventricle via "pores" in the septum. In his anatomical atlas De humani corporis fabrica (1543), the anatomist and professor at Padua Andreas Vesalius (1514–1564) questioned the existence of the septal pores without challenging the overall outlines of Galenic physiology. After Vesalius, other investigators at Padua contributed to the study of the heart. Realdo Colombo (1510–1559) described the "lesser circulation" (the transit of blood from the right to the left side of the heart via the lungs), and Girolamo Fabrici (1533–1619) described the valves in the veins. The Padua tradition was crowned by the achievement of William Harvey (1578–1657), who studied with Fabrici. After taking his medical degree in 1602, Harvey returned to England, where he became a staff physician at St. Bartholomew's Hospital, Fellow of the College of Physicians, and court physician to the Stuart kings.

A committed Aristotelian, Harvey upheld Aristotle's conception of the heart as the vivifying center of the body and the principle of the perfection of the circle. Yet Harvey was also a powerful innovator methodologically and conceptually. He designed and performed experiments using a wide range of cold- and warm-blooded animals. He drew compelling analogies between the work of the heart and vessels and mechanical actions. Most tellingly, he quantified the amount of blood that passed through the body with each beat of the heart. Judging it too great to be produced by nutritional activity, he was convinced that the blood must move in one great circulatory motion throughout the body. This discovery was incorporated in his Anatomical Treatise on the Movement of the Heart and Blood (1628). Although the impact of Harvey's work was delayed because of an entrenched Galenism, in time his findings revolutionized thinking about the heart and blood as well as general physiology. Harvey's work also lent great prestige to the emergent "mechanical philosophy," although Harvey himself was not a mechanist.

The chief intellectual force behind the body-machine analogy was the French philosopher René Descartes (1596–1650). Descartes's cosmology sought to explain all known physical phenomena, including, in his posthumously published treatise Man (1664), mechanisms of digestion, respiration, reproduction, and other vital activities. Fruitful applications of mechanist thinking were found in works such as Giovanni Alfonso Borelli's On the Motions of Animals (1680–1681), which explored the mechanics of the human muscular and skeletal systems. Mechanist thinking also had a profound impact on inquiry into the cluster of problems called "generation."

THE PROBLEM OF GENERATION

Learned interest in processes of reproduction, including heredity, developed in response both to internal scientific dynamics and to sociocultural pressures for clarity in respect to family lineages, gender roles, and rules for inheritance. Aristotelian teaching posited a union in reproduction of male "form," embodied in semen gathered from throughout the body, with female "matter" (menstrual blood), presenting the male as the "perfect" result while the female was a continuously appearing "monster" of nature. A competing, Galenic account of generation posited two "semens," one male and one female. Inspired by Aristotle, Fabrici and other inquirers at Padua pursued a comparative study of the embryos of horses, sheep, and other animals. Harvey conducted extensive experiments designed to elucidate developmental processes. The most famous was his dissection during and after mating season of does in whom he found no trace of male semen. His Anatomical Treatise on the Generation of Animals (1651) declared that "all living beings arise from eggs." This was the beginning of "ovism," which held that the female alone contributed materially to the embryo.

This view was contradicted by Antoni van Leeuwenhoek (1632–1723), who, using a microscope, identified the spermatozoon ("animalcule") in 1677. Ensuing controversy pitted "ovists" against "animalculists," who held that the male contributed all parts of the embryo. In most cases both ovists and animalculists rejected Aristotle's view that the embryo developed in a process of epigenesis, the progressive elaboration of new structures. Both generally favored the "preformationist" view that each individual exists as a preformed miniature in the matter present at conception and develops through mechanical enlargement. The epigenesistpreformationist debate culminated in an exchange between the Swiss physiologist Albrecht von Haller (1708–1777) and the German naturalist Caspar Friedrich Wolff (1733–1794). Initially a preformationist, Haller converted to epigenesis after studying the discovery by Abraham Trembley (1710–1784) of the regenerative capacities of the freshwater polyp. He later settled on ovist preformationism, fearing the irreligious implications of epigenesist theories like that of Georges Louis Leclerc Buffon (1707–1788), who postulated an "interior mold" that shaped development and disregarded the role of the creator. Challenging Haller, Wolff argued for a vis essentialis, or essential force, responsible for patterns of differentiation evident in development. Wolff made extensive use of plants to study development and thus effected a juncture with this branch of natural history.

NATURAL HISTORY AND CLASSIFICATION

Early description and ordering of plants and animals was undertaken as an adjunct to both the search for remedies and the humanist effort to identify references in works of the ancients. Herbals based principally on classical, Arabic, and Medieval Latin sources were among the first printed books. Sixteenth-century naturalists such as Conrad Gessner (1516–1565) began organizing local collecting expeditions. Accurate description and representation of distinctive external characteristics of leaf, flower, and fruit were emphasized. The number of species described steadily increased until, in the 1680s, the English naturalist John Ray (1627–1705) described some eighteen thousand species.

Interest in the comparative structure of the parts of plants distinguished the work of Andrea Cesalpino (1519–1603), medical professor first at Pisa and then Rome. Cesalpino sought unifying principles of classification and, after an interval, was followed in that effort by Joachim Junge (1587–1657), also a medical professor. The quest for a "natural" system of classification culminated in the work of Carl Linneaus (1707–1778), the Swedish naturalist whose work formed the basis for modern taxonomy.

Animals were similarly the focus of joint artistic and learned pursuits. Leonardo da Vinci (1452–1519) did his own dissections and compared the structure of body parts in humans, horses, bears, cats, monkeys, and other animals. The humanist lexicographer William Turner (1508–1568) compiled existing accounts of birds and added observations of his own. French naturalists including Pierre Belon (1517–1564) and Guillaume Rondelet (1507–1566) undertook comparative studies of fish. Much seventeenth-century work on the comparative morphology of animals was tied to the investigations into generation discussed above.

The natural history of plants and animals was of keen interest to both trained investigators and the educated public by the late seventeenth century. Religious feeling was central to the popularity of "natural theology." While the mechanical philosophy dispensed with direct intervention in nature by the deity, natural histories such as Spectacle of Nature (1732–1750), by Noël-Antoine, the Abbé Pluche, drew attention to the marvels of God's creation. The most influential naturalists of the eighteenth century, Linnaeus and Buffon, focused not on religious but scientific themes, especially the problem of how best to approach classification itself. Buffon's Natural History, a general history of the earth and living creatures, was published in many volumes beginning in 1749. Determinedly non-religious, it largely ignored biblical chronology and posited the passage of eons in which natural forms had altered.

HISTORIOGRAPHY

Conventional history of science divided the early modern era into the Renaissance (1400–1550), the scientific revolution (1550–1700), and the Enlightenment (1700–1800), and generally treated life science as peripheral to the revolutionary changes under way in physical science. An alternate scheme divides the era into two phases, roughly 1450–1670 and 1670–1800, more appropriate to biology, with the break marked by a decisive rejection of both Aristotelian thinking and competing occult traditions in favor of inquiry based first on deductive reasoning and, finally, modern inductive science.

Twentieth- and twenty-first-century scholarship has been much affected by the work of the French philosopher Michel Foucault (1926–1984), who overturned traditional labels and periodization. Historians following his lead have questioned presumed continuities with modern science, recovered texts and formulations previously regarded as merely "curious," and investigated the interconnections between learned "discourses" and structures of power. Historical revisionism is also evident in the work of social "constructivists" who emphasize the social creation of knowledge rather than its emergence from autonomous intellectual dynamics.

See also Anatomy and Physiology ; Aristotelianism ; Buffon, Georges Louis Leclerc ; Gessner, Conrad ; Haller, Albrecht von ; Harvey, William ; Leeuwenhoek, Antoni van ; Linnaeus, Carl ; Mechanism ; Medicine ; Museums ; Natural History ; Paracelsus ; Ray, John ; Scientific Revolution ; Vesalius, Andreas.

BIBLIOGRAPHY

Ackerknecht, Erwin H. A Short History of Medicine. Rev. ed. Baltimore, 1982. A brief account of medical history, with some attention to larger issues in life science.

Butterfield, Herbert. The Origins of Modern Science: 1300–1800. Rev. ed. London and New York, 1957.

Clark, William, Jan Golinski, and Simon Schaffer, eds. The Sciences in Enlightened Europe. Chicago, 1999. Chapters on biopolitics, monsters, and natural history in the Enlightenment, with emphasis on the social foundations of knowledge.

Crombie, A. C. Medieval and Early Modern Science. Vol. 2, Science in the Later Middle Ages and Early Modern Times: 13th–17th Centuries. Garden City, New York, 1959. A standard survey of early modern science.

Daston, Lorraine, and Katharine Park. Wonders and the Order of Nature, 1150–1750. New York and Cambridge, Mass., 1998. A Foucauldian study focused on the place of marvels in conceptions of natural order.

Foucault, Michel. The Order of Things: An Archaeology of the Human Sciences. New York, 1971. An early work of the French philosopher who has revolutionized intellectual and cultural history.

Hall, Thomas S. History of General Physiology, 600 B . C .to A . D . 1900. 2 vols. Chicago, 1975. Essential account of the history of physiology.

Impey, Oliver, and Arthur MacGregor, eds. The Origins of Museums: The Cabinet of Curiosities in Sixteenth and Seventeenth-Century Europe. Oxford and New York, 1985. A valuable work of institutional history.

Lovejoy, Arthur O. The Great Chain of Being: A Study of the History of an Idea. Cambridge, Mass., 1936. Classic study by the master of the "history of ideas."

Magner, Lois N. A History of the Life Sciences. 2nd ed. New York, 1994. Places early modern developments within the larger history of biology from the ancients to the era of genetics and molecular biology.

Roger, Jacques. The Life Sciences in Eighteenth-Century French Thought. Edited by Keith R. Benson. Translated by Robert Ellrich. Stanford, 1997. Translation of Les sciences de la vie dans la pensée française au XVIIIe siècle: La génération des animaux de Descartes à l'Encyclopédie. Magisterial work on the problem of generation, chiefly but not exclusively on French inquirers.

Elizabeth A. Williams

44. Biology

See also 16. ANIMALS ; 54. BOTANY ; 72. CELLS ; 244. LIFE ; 302. ORGANISMS ; 319. PLANTS ; 430. ZOOLOGY .

abiogenesis

the process of generation of living organisms from inanimate matter; spontaneous generation. —abiogenetic, adj. —abiogenetically, adv.

agamogenesis

asexual reproduction. —agamogenetic, adj.

agrobiology

the branch of biology that studies the relation of soil management to the nutrition, growth, and erop yield of plants. —agrobiologist, n. —agrobiologic, agrobiological, adj.

amensalism

the living together of two organisms in a relationship that is destructive to one and has no effect on the other.

anamorphism

gradual change in type, usually from a lower to a higher type. Also anamorphosis , (Obsolete) anamorphosy . —anamorphic, adj.

anastomosis

connection between parts that have branched off from each other at some earlier point. —anastomotic, adj.

anisogamy

a form of reproduction in which dissimilar gametes, often dirfering in size, unite. —anisogamous, anisogamic, adj.

apomixis

any of several processes of asexual reproduction. Cf. parthenogenesis.

astrosphere

1. the central part of an aster, containing the centrosome.

2. the whole aster excluding the centrosome.

autecology

the branch of ecology that studies the relation of an organism to its environment. Cf. synecology.

auxanography

the branch of microbiology that studies the rate of growth or inhibition exhibited by individual organisms in various plateculture media. —auxanographic, adj.

auxesis

growth, especially owing to an increase in cell size. Cf. merisis. —auxetic, adj.

biodegradability

the capacity of some substances to decompose readily by biological process. —biodegradable, adj.

biogenesis, biogeny

1. the process by which living organisms develop from other living organisms.

2. the belief that living organisms can only develop from other living organisms. —biogenic, biogenetic, adj. —biogenetically, biogenically, adv.

biogeography

the branch of biology that studies the geographical distribution of animals and plants.

biologism

a theory or doctrine based on a biological viewpoint. —biologistic, adj.

bioluminescence

the property of some organisms, as fireflies, of producing light. —bioluminescent, adj.

biometrics, biometry

1. the calculation of the probable extent of human lifespans.

2. the application to biology of mathematical and statistical theory and methods. —biometric, biometrical, adj.

bionomics, bionomy

ecology. —bionomist, n. —bionomic, bionomical, adj.

biophysiology

the branch of biology that studies the growth, morphology, and physiology of organs. —biophysiologist, n.

bioscience

any of the sciences that deal with living organisms.

biosphere

that part of the earth where most forms of life exist, specifically, where there is water or atmosphere.

biosynthesis

the formation of chemical compounds by living organisms, either by synthesis or degradation. —biosynthetic, adj.

biosystematics

biosystematy.

biosystematy, biosystematics

the science of the classification of living things. —biosystematic, biosystematical, adj.

biotypology

the science or study of biotypes, or organisms sharing the same hereditary characteristics. —biotypologic, biotypological, adj.

cataplasia

degeneration of cells or tissues. —cataplastic, adj.

cetology

the study of whales. —cetologist, n. —cetological, adj.

chemotropism

growth or motion in response to a chemical stimulus. —chemotropic, adj.

chiasmatypy

the formation of chiasma, the basis for crossing over or the interchange of corresponding chromatid segments of homologous chromosomes with their linked genes. —chiasmatvpic, adj.

chorology

Biogeography. the study of organisms, especially their migrations and distribution. —chorologic, chorological, adj.

commensalism

the living together of two organisms in a relationship that is beneficial to one and has no effect on the other. —commensal, adj.

consortism

a relationship of mutual dependency between two living organisms.

crustaceology

the study of crustaceans. —crustaceologist, n. —crustaceological, adj.

cryptobiosis

Medicine. a state in which the signs of life of an organism have weakened to the point where they are barely measurable or no longer measurable. —cryptobiotic, adj.

ctetology

the branch of biology that studies the origin and development of acquired characteristics. —ctetologic, ctetological, adj.

cytogenetics

the branch of biology that studies the structural basis of heredity and variation in living organisms from the points of view of cytology and genetics. —cytogeneticist, n. —cytogenetic, cytogenetical, adj.

cytology

the branch of biology that studies the structure, growth, and pathology of cells. —cytologist, n. —cytologie, cytological, adj.

diakinesis

the final stage of prophase prior to the dissolution of the nuclear membrane. —diakinetic, adj.

dialysis

the process whereby colloids and crystalloids separate in solution by diffusion through a membrane. —dialytic, adj.

diapause

a period of rest or quiescence between phases of growth or reproduction.

digenesis

successive reproduction by two different processes, sexual in one generation and asexual in the following generation. —digenetic, adj.

digitigradism

Zoology. the condition of walking on the toes. —digitigrade, adj.

dysmerogenesis

a form of generation characterized by irregularity of constituent parts, which differ in function, time of budding, etc. Cf. eumerogenesis. —dysmerogenetic, adj.

ecdysis

the process of shedding skin or other covering, typical of snakes and some insects. Cf. endysis. —ecdysial, adj.

ecology, oecology

1. the branch of biology that studies the relations between plants and animals and their environment. Also called bionomics, bionomy .

2. the branch of sociology that studies the environmental spacing and interdependence of people and institutions, as in rural or in urban settings. —ecologist, oecologist, n. —ecological, oecological, adj. —ecologically, oecologically, adv.

electrobiology

the study of electrical activity in organisms and of the effect of electricity on them. —electrobiologist, n. —electrobiological, adj.

embryogeny

the formation and growth of an embryo. —embryogenic, embryogenetic, adj.

endogenesis, endogeny

the formation of cells from within. —endogenous, adj. —endogenicity, n.

endysis

the growth of new scales, hair, plumage, etc. Cf. ecdysis. —endysial, adj.

enzymology

the branch of biology that studies fermentation and enzymes. Also called zymology. —enzymologist, n. —enzymologie, enzymological, adj.

epicenism

the state or quality of combining characteristics of both sexes. —epicenity, n. —epicene, adj.

epigenesis

the biological theory that germ cells are structureless and the embryo develops through the action of environment on the protoplasm. Cf. preformation. See also 46. BIRTH ; 122. DISEASE and ILLNESS ; 179. GEOLOGY . —epigenetic, adj.

epigenesist

a supporter of the theory of epigenesis.

eumerogenesis

generation by unit parts, as in the tape worm, in which each part repeats the one before. Cf. dysmerogenesis. —eumerogenetic, adj.

galactosis

the process of producing milk.

galvanotropism

growth or movement of an organism in response to an electric current. —galvanotropic, adj.

gamogenesis

the process of reproduction by the joining of gametes, a form of sexual reproduction. Also called zoogamy. —gamogenetic, adj.

genetics

the branch of biology that studies heredity and variation in plants and animals. —geneticist, n. —genetic, adj.

gnotobiotics

a branch of biology that studies animals under germ-free conditions.

Haeckelism

theories and doctrines of Ernst Haeckel (1834-1919), German biologist and philosopher, especially the notion “ontogeny recapitulates phylogeny.” —Haeckelian, adj.

heterogamete

a gamete differing from the gamete with which it unites in sex, structure, size, or form. Cf. isogamete .

heterogamy

1. the condition of being heterogamous, or reproducing sexually and asexually in alternating generations.

2. the process of indirect pollination. Cf. heterogenesis. —heterogamous, adj.

heterogenesis

1. reproduction by a sexual and asexual process alternately. Cf. heterogamy .

2. reproduction in which the parent bears offspring different from itself. Cf. xenogenesis. —heterogenetic, adj.

3. abiogenesis.

heterolysis

the destruction of the cells of one species by the enzymes or lysins of another species. —heterolytic, adj.

heterotopism

heterotopy.

heterotopy, heterotopia

deviation from the normal ontogenetic sequence with regard to the placing of organs or other parts. Also heterotopism . See also 56. BRAIN . —heterotopous, adj.

hexiology, hexicology

the study of the effects of environment on an organism’s growth and behavior. —hexiological, hexicological, adj.

histogenesis, histogeny

the growth of organic tissues. —histogenic, histogenetic, adj.

histography

a treatise or other work on organic tissues, or histogenesis. —histographer , n. —histographic, histographical, adj.

histolysis

the disintegration or dissolution of organic tissues. —histolytic, adj.

homodynamy

the homology of serial segments. Cf. parhomology.

homogenesis

the normal course of generation in which the offspring resembles the parent from generation to generation. Cf. heterogenesis. —homogenetic , adj.

homology

1. similarity of form or structure in two or more organisms owing to common descent.

2. similarity in form or structure between different parts of an organism owing to common origin. Cf. homodynamy. —homologous, adj.

isogamete

a gamete that is not sexually differentiated from the other gamete with which it unites. Cf. heterogamete.

isogamy

reproduction by means of the union of isogametes. —isogamous, adj.

isogenesis

the state or process of deriving from the same source or origins, as different parts deriving from the same embryo tissues. Also isogeny.

isogonism

production of similar reproductive parts from stocks that are dissimilar, as with certain hydroids. —isogonic, adj.

isomorphism

similarity in the form or structure of organisms that belong to a different species or genus. —isomorph , n. —isomorphic, adj.

karyology

a specialty within cytology that studies the anatomy of cell nuclei with emphasis upon the nature and structure of chromosomes. —karyologist , n. —karyologic, karyological, adj.

kinetogenesis

1. the genesis of organic structure by kinetic processes.

2. the belief that the structure of animals is determined and produced by their movements. —kinetogenetic, adj.

Lysenkoism

the theories of the 20th-century Russian geneticist Trofim Lysenko, who argued that somatic and environmental factors have a greater influence on heredity than orthodox genetics has found demonstrable; now generally discredited.

macrobiotics

the branch of biology that studies longevity. —macrobiosis, n. —macrobiotist, n.

malacology

the study of molluscs. —malacologist, n.

Mendelianism

the principles or use of Mendel’s law. —Mendelian, n., adj.

merisis

any form of growth, especially as a product of cell division. Cf. auxesis. —meristic, adj.

merogenesis

the process of segmentation in which similar parts unite and form a complex individual entity from the aggregate of the parts. —merogenetic, adj.

metagenesis

alternation of generations across reproductive cycles. Cf. xenogenesis. —metagenetic, metagenic, adj.

Michurinism

the biological theory of Ivan Michurin who asserted the fundamental influence of environmental factors on heredity in contradiction of orthodox genetics. —Michurinist , n. —Michurinite, adj.

microtomy

the science or practice of preparing extremely thin slices of tissue, etc, cut by a microtome, for study under the microscope. —microtomist , n. —microtomic, adj.

mimicry

the ability of some creatures to imitate others, either by sound or appearance, or to merge with their environment for protective purposes. See also 310. PERFORMING . —mimic, mimical, adj.

mitosis

the normal process of cell division. —mitotic, adj.

monogenesis

1. asexual processes of reproduction, as budding.

2. development of an ovum directly into a form like that of the parent, without metamorphosis. —monogenetic, adj.

monosymmetry

the state of being zygomorphic, or bilaterally symmetrie, or divisible into symmetrical halves by one plane only. Cf. zygomorphism. See also 316. PHYSICS . —monosymmetric, monosymmetrical, adj.

morphology

the study of the form and structure of plants and animals. —morphologist , n. —morphologic, morphological, adj.

mutualism

the living together of two organisms in a mutually beneficial relationship.

neontology

the scientific study of recently living plants and animals. —neontologist, n. —neontologic, neontological, adj.

ontogenesis

ontogeny. —ontogenetic, ontogenetical, adj.

ontogeny

the life cycle, development, or developmental history of an organism. Also ontogenesis. —ontogenic, adj. —ontogenic, adj.

oogamy

the union of sexually differentiated reproductive cells. —oogamous, adj.

oogenesis

the formative process of the ovum in preparation for fertilization and subsequent development. —oogenetic, adj.

ooscopy

observation of the development of an embryo inside an egg by means of an ooscope.

organogenesis, organogeny

the origin and growth of organs. —organogenetic, organogenic, adj.

organography

the scientific description of the organs of plants and animals. —organographist , n. —organographic, organographical, adj.

organology

the study of the structure and organs of plants and animals. —organologist , n. —organologic, organological, adj.

organonomy

1. the laws of organic life.

2. the doctrine upon which these laws are based. —organonomic, adj.

organonymy

the nomenclature of organs. —organonymal , —organonymic, adj.

orthogamy

the property or process of self-fertilization, as in certain plants and animals. —orthogamous, adj.

orthogenesis

progressive evolution, leading to the development of a new form, as can be seen through successive generations. See also 376. SOCIETY . —orthogenetic, adj.

ovism

the theory that the female reproductive cell contains the entire organism and that the male cell does not contribute anything, merely initiating the growth of the female cell.

ovology

the study of the formation and structure of animal ova. —ovologist , n. —ovological, adj.

palynology

the science that studies live and fossil spores, pollen grains, and other microscopic plant structures. —polynologist, n. —polynological, adj.

parabiosis

the uniting of two individual organisms or animals anatomically and physiologically, under either experimental or natural conditions. —parabiotic, adj.

parasitism

the living together of two organisms in a relationship that is beneficial to one and destructive to the other. —parasitic, parasitical, adj.

parasitology

the branch of biology that studies parasites and parasitism. —parasitologist , n.

parhomology

the biological process of imitative homodynamy. —parhomologous , adj.

parthenogenesis, parthogeny

reproduction without fertilization, as certain ova, seeds and spores, insects, algae, etc. Also called unigenesis . —parthenogenetic, parthenogenic, adj.

photoperiodism, photoperiodicity

the effect on the growth and reproduction of plants or animals of varying exposures to light and darkness. Cf. thermoperiodism. —photoperiod, n. —photoperiodic, adj.

photosynthesis

the synthesis of complex organic substances from carbon dioxide, water, and inorganic salts, with sunlight as the energy source and a catalyst such as chlorophyll. —photosynthetic, adj.

phototropism

growth or motion in response to light. —phototropic, adj.

physiogeny

the history or science of the development or evolution of vital activities in the individual and the genesis of organic functions; a division of ontogeny. Also called physiogenesis. —physiogenetic, physiogenic, adj.

phytobiology

plant biology. —phytobiologist, n. —phytobiological, adj.

pleomorphism, pleomorphy

the existence of a plant or animal in two or more distinct forms during a life cycle. Also called polymorphism. —pleomorphic, pleomorphous, adj.

polygenesis

1. derivation from more than one kind of cell in the generative process.

2. Also called polygenism . the theory that different species have descended from different original ancestors. Cf. monogenesis. —polygenic, polygenetic, adj.

polyphagia, polyphagy

the tendency to eat a wide variety of food. —polyphagist , n. —polyphagic, adj.

polyzoism

the character of being made up of a number of smaller organisms that are acting as a colony. —polyzoic, adj.

preformation

the theory that germ cells contain every part of the future organism in miniature form, future development being only a matter of increase in size. Cf. epigenesis .

preformationism

the theory that an organism is fully formed at conception and that reproduction is thereafter simply a process of growth. —preformationist, n.

protozoology

the study of protozoa, especially of those that cause disease. —protozoological, adj. —protozoologist , n.

psychobiology

1. the branch of biology that studies the interactions of body and mind, especially as exhibited in the nervous system.

2. psychology as studied in terms of biology. —psychobiologist, n. —psychobiologic, psychobiological, adj.

speciation

the formation of new species.

spermism

an obsolete biological theory that stated that sperm contained the preformed germ or the embryo. —spermist, n.

spongology

the science and study of the sponges. —spongologist, n.

sporogenesis

1. the process of reproduction by means of spores.

2. the formation and growth of spores. —sporogenetic, sporogenous, adj.

stereotaxis

orientation or movement of an organism in response to the stimulus of a solid object. Cf. stereotropism. —stereotactic, adj.

stereotropism

growth or movement determined by contact with a solid. Cf. stereotaxis. Also thigmotropism. —stereotropic, adj.

stirpiculture

selective breeding to develop strains with particular characteristics. —stirpicultural, adj.

superfetation

a conception occurring during a pregnancy from an earlier conception.

symbiosis

the living together of two dissimilar organisms; the relationship may be beneficial to both (mutualism and symbiosis), beneficial to one without effect on the other (commensalism ), beneficial to one and detrimental to the other (parasitism ), detrimental to the first without any effect on the other (amensalism), or detrimental to both (synnecrosis ). —symbiotic, adj.

symphytism

Rare. the tendency of two separate elements to grow together. —symphytic, adj.

synecology

the branch of ecology that studies the relation of various groups of organisms to their common environment. Cf. autecology.

synnecrosis

the living together of two organisms in a mutually destructive relationship.

teratology

the branch of biology that studies abnormal formations in animals or plants. —teratologist , n. —teratologie, teratological, adj.

testaceology

the study of the shell-bearing animals. —testaceological, adj.

thermoperiodism, thermoperiodicity

the effect on the growth and reproduction of plants or animals of timed exposures to varied temperatures. —thermoperiod, n. —thermoperiodic, adj.

therology

the study of animals. —therologist , n. —therologic, therological, adj.

thigmotaxis

involuntary response or reaction to the touch of outside objects or bodies, as in motile cells. —thigmotactic , adj.

thigmotropism

stereotropism. —thigmotropic , adj.

ultrastructure

the submicroscopic, elemental structure of protoplasm. —ultrastructural , adj.

unigenesis

parthenogenesis. —unigenetic , adj.

uterogestation

the process of gestation taking place in the womb from conception to birth.

xenogenesis, xenogeny

1. abiogenesis; spontaneous generation.

2. metagenesis, or alternation of generations.

3. production of an offspring entirely different from either of the parents. —xenogenetic, xenogenic, adj.

zoogamy

gamogenesis. —zoogamous, adj.

zygomorphism

the state or quality of being bilaterally symmetrical, as certain organisms. Cf. monosymmetry. —zygomorphic, zygomorphous, adj.

zygosis

the biological process of conjugation; the union of cells or gametes. —zygose , adj.

zymogenesis

the process in which a zymogen becomes an enzyme, as in the fermentation process. —zymogenic, zymogenous, adj.

zymology

enzymology. —zymologist , n. —zymologic , adj.

Biology

Biology is the scientific study of the processes of life. Biology gradually came into existence as a coherent field of study in the nineteenth century. It combined into a single field what had previously been called natural history and natural philosophy as well as elements of medicine, zoology, physiology, botany, chemistry, and pharmacology. Biology is an empirical, experimental science, which means that hypotheses made about the character and functioning of life processes are proven through repeatable experiment. Because biology is the science of life processes and reproduction is considered one of the key processes that defines life itself, biology has always been bound up with issues of sex and reproduction. Although biology is an empirical science, it has also long reflected cultural attitudes about sex and gender, both as foundational concepts for theories of life and as categories to be questioned and investigated. In its development of new theories about reproduction, physiology, behavior, and heredity, biology continues to grapple with understandings of sex and gender as well as the ways biological science has produced itself around and through gender and sexual difference.

The term biology combines the Greek root bios, or life, with the Greek ology, or study of, and was introduced in Germany in 1800 by German physiologist Karl Friedrich Burdach (1776–1847). The idea of combining botany and zoology was soon taken up simultaneously by both German naturalist Gottfried Reinhold Treviranus (1776–1837) in his 1802 book Biology or Philosophy of Living Nature and influential French botanist and early theorist of evolution Jean-Baptiste Lamarck (1744–1829), the major proponent of Lamarckism, or the idea that parents could pass on acquired traits. The concept of a science of life gained support throughout the nineteenth century, catalyzed through the discoveries of German botanist Matthias Schleiden (1804–1881) and German biologist Theodor Schwann (1810–1882) in 1838 that plants and animals were composed of cells. The idea of a single field of life studies was also advanced in 1858 by English naturalists Charles Darwin (1809–1882) and Alfred Wallace (1823–1913) whose development of a theory of evolution disagreed with Lamarck's idea that acquired traits could be passed from generation to generation. In the latter half of the nineteenth century, French biologist Louis Pasteur (1822–1895) developed the field of microbiology, demonstrating the connections between microorganisms and disease. Austrian Botanist Gregor Mendel (1822–1884) published his findings on patterns of heredity in 1866. Although his ideas were ignored until they were rediscovered in 1900, they formed the basis for the modern study of genetics.

Perceiving the continuities among what had been diverse fields of study enabled the development of more comprehensive theories of life, including Darwin's theory of evolution, but also including the germ theory of disease advocated by Pasteur, and the discovery of viruses in 1898. In the early twentieth-century American biologist Walter S. Sutton (1877–1916) and German Theodor Boveri (1862–1915) independently discovered that human chromosomes are paired and are the agents of heredity. In 1905 American researchers Edmund B. Wilson (1856–1939) and Nettie Stevens (1861–1912) independently discovered the chromosomes that determine the sex of humans. Working with fruit flies, American zoologist Thomas Hunt Morgan (1866–1945) linked heredity to evolution and developed ways to map genes on chromosomes and link specific genes to traits. With the invention of technology such as the X-ray in 1895 and the electron microscope in the 1930s, as well as advances in the fields of biochemistry, genetics, physiology, microbiology, and medicine, biologists were able to investigate phenomena happening on the smallest scale. With the development of sophisticated statistical methods, a better understanding of the geological history of the earth, and better modes of gathering data, scientists made advances in studies of paleontology, population genetics, ecology, and evolutionary biology.

The discipline of biology in the early twenty-first century examines molecular and cellular phenomena and issues involving whole organisms as well as their environments and interrelation with other organisms. Molecular biology studies life processes as matters of molecular chemistry and includes studies in biochemistry, biophysics, genetics, and cell biology. Studies involving whole organisms focus on the relations among organisms or between organisms and their environments—ecology, ethology—or on the evolution or development of organisms—evolutionary biology, paleontology, developmental biology, and population studies.

HISTORY OF CONCEPTS ABOUT LIFE, SEX, AND REPRODUCTION

From the time of the Greeks, natural philosophers, such as Aristotle (384–322 bce), were interested in the nature of reproductive processes. They and those who followed devised a series of theories for how humans and other organisms reproduced, almost all of which assumed the superiority of the male contribution. As with other sciences, biology was influenced by cultural ideas about sex and gender, which it reflected in its assumptions, hypotheses, and theories. Until the mid 1950s most biologists assumed that the male of the species was the more developed and superior entity, and used the male as a model for most interrogations of life processes. They perceived the male as the source of form and intelligence and the female as the source of matter, ideas that indeed go back to ancient times. Assumptions about the character of genders across species have affected most aspects of zoological and biological inquiry from its study of cell processes to reproduction and even to its conceptions of DNA.

Ancient Greek philosophers such as Hippocrates (c. 460–c. 377 bce), Plato (428–c. 347 bce), and Aristotle considered the qualities and causes of life and offered various approaches to understanding the nature of existence. Hippocrates, who worked as philosopher and clinical physician, believed that nature could be explained through reason rather than through recourse to supernatural devices, and his approach to medicine involved observation and experience over theorizing. Hippocrates's theory of health was that healthy life required a balance and disease was evidence of an imbalance. Hippocrates believed that the body was governed by the actions of four fluids, or humours: black bile, yellow bile, phlegm, and blood. When these humours got out of proper balance and one or another dominated, illness ensued. Hippocrates's notion of the four humours persisted until the Enlightenment.

Plato thought that human life was split among spirit, reason, and appetites, each located in a specific organ: spirit in the heart, reason in the brain, and the appetites in the liver. Advocating measure in all things, Plato was far more a philosopher than an observer; the importance of observation was advocated by his pupil Aristotle. Aristotle believed in the reasoned and careful observation of all kinds of natural phenomena, from the weather to animals to plants. He believed that in nature everything had a function, and he sought to find both what caused phenomena and what those phenomena themselves caused. Aristotle dissected animals and discerned that the heart and blood seemed to be the first causes of life in living organisms.

Aristotle's empirical approach to nature enabled him to provide his own account of the agents of reproduction, which disagreed with the account formulated earlier by Hippocrates. Hippocrates had formulated the theory of pangenesis to account for how parental traits were passed on to offspring. He believed that sperm concentrated elements from all of the organs of the body as well as physical changes and traits that an individual acquired over a lifetime. Sperm then carried all of this forward in creating offspring. The female might also contribute her seed, though that contribution was also imagined to be like semen, because the female was understood to be a lesser-developed version of the male.

Aristotle introduced a different concept of how semen worked. He believed that semen had a vital heat that molded new individuals by its heating action on menstrual blood. He also believed that the parts of individuals developed gradually from this original heating action. Aristotle disagreed with Hippocrates's idea that acquired traits could be passed on, showing that individuals who lost limbs did not father limbless children. He, too, included the female as a part of the reproductive process, but as the contributor of brute matter upon which the shaping action of semen worked. The idea that semen was the primary determinant of the characteristics of a new generation persisted until the eighteenth century.

Galen (129–c. 199) was a Greek doctor who practiced and theorized about medical care during the Roman Empire. An enthusiastic anatomist, he identified the functions of many of the organs. In contrast to the Aristotelean model in which sexual difference was a matter of degree rather than kind, Galen envisioned two sexes whose genital parts were different but which were rearrangements of one another; the uterus, for example, was the counterpart of the scrotum. As with Hippocrates, Galen believed that reproduction was the result of the contribution of two seeds, both of which were versions of semen. During the Middle Ages, Islamic philosopher Avicenna (980–1037) picked up Aristotle's ideas about sexual difference, as well as the idea that sperm was like the agent that clots milk and female sperm like the milk itself.

During the Renaissance, which witnessed the revival of Aristotelean ideas in Europe, British physician William Harvey (1578–1657) introduced a refinement of Aristotle's theory about the mechanism of human reproduction: epigenesis. Epigenesis adopted Aristotle's idea that organs were not all present from the beginning, but developed gradually as the fetus developed. This was in contradistinction to another widely held theory about reproduction, preformationism, which held that each sperm contained a minute, fully formed individual, called a homunculus. The ideas of preformationists came from what early microscopists thought they saw when they looked at magnified sperm. Still there was no real role for the female in these theories. Partly this was because of cultural preconceptions about the superiority of the male. It was also partly because human eggs were not available to be observed through the microscope.

When scientists did look at eggs, as Aristotle had and as German anatomist Caspar F. Wolff (1734–1794) did in the late eighteenth century, they noticed that more seemed to occur in the egg than could be accounted for by a preformed, sperm-conveyed individual. By studying chicken eggs, Wolff reaffirmed Harvey's notion that individuals developed gradually. Mathematician and natural philosopher Pierre de Maupertuis (1698–1759) revived Hippocrates's notion of pangenesis, at least in so far as he believed that sperm carried particles from every organ. Maupertuis also assigned a role to the egg, although he believed that the qualities carried by the sperm were dominant.

Darwin also ascribed to a theory of pangenesis, believing that sperm carried gemmules from around the father's body that were passed on to offspring. Lamarck also believed in a theory of pangenesis. Only in 1863 did German biologist August Weismann (1834–1914) disprove the idea that parents passed on acquired characteristics.

The paternal bias of all of these theories of reproduction accompanied, paradoxically, the fact that without circumstantial corroboration, one could never be absolutely certain of who was a child's father. The role of the mother, so obvious in pregnancy and gestation of the fetus, was ignored or denied in the matter of passing on traits. The idea that maleness was the source of reason and form and that the female supplied only matter was so pervasive and unquestioned that only the invention of microscopy, the discovery of human chromosomes, the development of genetic studies, and diligent and unbiased observation finally showed that parents each contributed one-half of the genetic material for each child.

With the advent of sophisticated understandings of genetics as well as advanced concepts of physiology and development, the role of the female has become in many ways more central and important in human reproduction than the role of the male. Modes of artificial insemination and in vitro fertilization have made the contribution of genetic material less a challenge than the gestation of a child. The interaction of genetic contributions from each parent has become a matter of hypothesis and study, especially as the x chromosome, contributed by the female, carries many traits that are only expressed by male children.

SEXUAL DIFFERENCE AND PHYSIOLOGY

Theories about human reproduction depended upon and reflected ideas about the differences between the sexes. Understandings of reproduction as the action of formative semen upon the more material female required an understanding of the sexes as being the same, different only in degree of development. From the time of the ancient Greeks until the eighteenth century, male and female anatomies were seen as counterparts of one another that differed only in their relative arrangement and size. Male reproductive parts had equivalents among female reproductive parts. Both males and females contributed semen; both had testes. Male testes, however, were large; female testes were small. According to Galen, the penis and vagina were homologous, and the female's exterior genitalia (labia, clitoris, vulva) were analogous to the head of the penis at the end of a vagina shaft.

The one organ that was considered to be specifically female was the uterus (despite Galen's attempts to compare it to the scrotum). The uterus was believed to generate a host of ills and female diseases, as it was also believed to be the repository of poisons that caused female diseases. Even through the nineteenth century, many believed that the uterus could get loose and wander around the body, causing a number of symptoms—a condition referred to as hysteria from the Greek word for womb. Speculation about the nature and functioning of the uterus produced a number of theories—from the idea that the character of the uterus determined the sex and quantity of offspring, to the notion that it had a chamber for every day of the week, to the theory that it was divided into male-producing and female-producing sides (and sometimes with a center section that produced hermaphrodites), to the hypothesis that women had two uteruses that matched the number of breasts, to the belief that the uterus had horns—all gleaned from analogies to mammalian physiology. Anxieties about female difference were displaced on to the uterus as the locus of difference. At the same time, quandaries about the origins of sexual difference and disease were resolved by recourse to the mysterious qualities of the uterus.

The male reproductive system did not receive the same kind of fascinated attention, partly because the organs were visible and partly because they served as the norm against which the female differed. Because both males and females were believed to have semen, much more attention was devoted to trying to discern its origin. Where did semen originate: In the brain? From blood? The persistent notion of male and female commonality also supported the belief that if males lost portions of their reproductive anatomy, they would become like females. Venetian surgeon Alessandro Benedetti (c. 1450–1512) noted that when males lost their testicles, they became more like women, an opinion seconded a few centuries later by Harvey. Until the Renaissance many anatomists also believed that females could turn into males at puberty, having their interior organs drop out.

Only in the sixteenth century did scientists discover more details about the female anatomy, which made it much more difficult to support the idea that men and women were two versions of the same sex. In 1559 anatomist Realdo Colombo (1515–1559) identified the clitoris, which undid the neat symmetry that Galen had contrived. Anatomist Gabriele Falloppio (1523–1563) described the fallopian tubes, though their function was a mystery. By the latter half of the seventeenth century, Dutch anatomist Reinier de Graaf (1641–1673) found what he thought were the eggs of the human female (but which were in fact the ovarian follicles). De Graaf's discovery of the follicles and naming of the ovaries, however, supplied a new source for the possible location of a preformed homunculus in the egg and challenged the notion that females contributed little other than matter to the reproductive project.

SEXUAL DIFFERENCE, HORMONES, AND BEHAVIOR

In most patriarchal cultures, sexual difference has been interpreted as a difference in the intrinsic qualities and capabilities of individuals. Male and female have been regarded as oppositions and as complementary to one another. Males have been perceived as strong, wise, reasonable, intelligent, governing, aggressive, and generally more developed than females, who have been considered correspondingly weak, less wise, less intelligent, followers, of a passive disposition, and generally less developed than males. Males were form; females were matter. The biological basis for these differences was for centuries thought to be a difference in development instead of anatomy. But from the Renaissance, with its burgeoning studies of human anatomy, internal differences between males and females, such as the uterus, offered other bases for understanding sexual difference.

In the late nineteenth century and the twentieth century, the discovery of hormones and their regulatory roles provided another way to understand the differences between the sexes based on the effects of hormones that derived from the reproductive organs. In 1849 German physiologist Arnold Berthold (1803–1861) demonstrated that testes secreted a substance into the bloodstream. Other glands and their role in the body became a topic of interest, particularly the thyroid gland, which was affected by goiters, but also the adrenal gland and adrenaline, which was the first hormone to be synthesized outside of the body. The term hormone was introduced in 1905, and research continued into the role of the pituitary gland (linked to growth), the hypothalamus (linked to regulation of the pituitary), and the pancreas and its production of insulin.

Sex hormones were also a subject of interest. The part played by the testes had been suspected for a long time, because Renaissance anatomists noticed the effects the loss of testicles had. Because the testes were visible and their effects known, male sex hormones such as androsterone and testosterone received initial attention. Testosterone was isolated and synthesized in the 1930s by scientists who ground up animal testicles. Female sex hormones were more difficult to isolate, partly because they came from more than one source in the body—the ovaries, the follicles—and menstrual cycles and pregnancies involved a more complex interplay of several hormones—progesterone, progesterol, estrogen, estriol, and estradiol. Discovering and understanding the role of hormones in body development and regulation enabled the development of pregnancy tests and the birth control pill.

In the early twenty-first century scientists attributed many gender characteristics to the actions of hormones, although these attributions still reflect old ideas about the inferiority of women. Testosterone endows strength, whereas estrogen causes irrational emotion, unreliability, and moodiness. These ideas come from the differences sex hormones produce in their actions on the body. Androgens, estrogens, and progestins, which both males and females have in differing amounts, spur sexual development in the womb and at puberty, regulate sex drive, and control reproduction. Androgens such as testosterone, produced by the testes but also by the adrenal gland, influence the apparent sex of a fetus. Androgens present in the womb stimulate the development of male genitalia, which even occurs in female embryos if too much testosterone is present. Male fetuses that develop in the womb without sufficient androgens will not develop normal male genitals.

At puberty high concentrations of sex hormones (testosterone for males, estrogen for females) spurs the development of secondary sex characteristics, such as facial and body hair and vocal chord and genital growth in males, and the development of body hair, growth of breasts, and the onset of menstruation in females. Sexually mature males have a constant supply of testosterone, whereas mature females experience menstrual cycles governed by the complex interplay of estrogen and progestin that govern uterine lining, the release of eggs, and the shedding of the uterine lining. Pregnancy is also governed by sex hormones: When the ovaries reduce their production of estrogen, female humans enter into menopause, which is when menstrual periods cease.

SEXUAL DIFFERENCE AND GENETICS

Even the production of sex hormones is itself an effect of the actions of genes, whose discovery and function have been the object of much research since the twentieth century. Sexual difference plays through genetics in two main ways. First, the sex of individuals is determined by the kinds of chromosomes they receive from their parents. One set of the twenty-three pairs of human chromosomes is called the sex chromosomes, and this pair consists of two different kinds of chromosome—an X chromosome and a Y chromosome. Females have two X chromosomes and males have one X chromosome and one Y chromosome. Gametes (eggs and sperm) each carry one-half of a set of chromosomes. Female parents contribute gametes with X chromosomes only. Sperm can carry either an X or a Y chromosome. X chromosomes are longer than Y chromosomes and contain more genes. In the other pairs of chromosomes, the genes from each of the pair are matched, which means that dominant and recessive forms of a gene often temper one another. Recessive genes for various diseases may not be fully expressed when the other gene of the pair is a normal variant.

In the pairing of X and Y chromosomes, however, the recessive traits for such problems as colorblindness and hemophilia have no corresponding gene on the Y chromosome, and so they express themselves in male children. These traits are called sex-linked traits and involve primarily males. Occasionally gametes may carry more than one sex chromosome as the result of a mistake. Children born with three or more sex chromosomes express different varieties of sex/gender traits. Some individuals are born with genes for both male and female sex organs; these individuals are called hermaphrodites.

A growing belief in the genetic basis for behaviors also offers a way to understand the differences between genders. Genders—feminine and masculine—represent one way cultures and individuals have interpreted the qualities of sexual difference—a difference in reproductive gonads and roles. Femininity and masculinity have been considered effects of nurture and culture instead of nature since the work of Austrian Austrian psychoanalyst Sigmund Freud (1856–1939) and other psychologists and sexologists at the turn of the twentieth century. Discovering that the behaviors of fruit flies were partly determined by genes, genetic researchers turned to human behavior, looking for genes that account for aggressiveness, antisocial behavior, nurturing, and homosexuality. Because human behaviors are far more complex than the behaviors of fruit flies, and because behavior is also culturally taught and reinforced, genes can likely only partly explain gender behavior.

The second way sexual difference plays through the genes is in the ways genes from each parent govern different developmental or life processes, with genes from the father, for example, governing the development of the placenta or social skills and genes from the mother dominating matters of brain function. Research continues into how genes affect one another, how they influence sex and gender expression and behaviors, and the vast variation there is in the possible combinations of sex and gender in human beings.

BIOLOGY AND GENDER

As with all sciences, biology is affected by cultural ideas and preconceptions. For example, the kinds of phenomena scientists choose to examine are sometimes defined by their ideas of what phenomena are important, which is in turn influenced by assumptions about the relative centrality of males and females. Twentieth-century investigations of heart disease, for example, focused on males, not only because males were believed to be more afflicted by heart disease, but also because females were still assumed to be lesser versions of males. Studies of reproduction in females lagged behind understandings of male contributions. Only by the late twentieth century did scientists begin to undertake more systematic studies of major diseases specifically in women, acknowledging the differences between female and male biology and physiology. The understanding that some processes and diseases are specific to females or males has also enabled a wider recognition of male-specific disorders, such as prostate problems.

Feminist scholars such as Evelyn Fox Keller, Anne Fausto-Sterling, and Sandra Harding have examined the ways scientists, including biologists and geneticists, incorporate presumptions about sexual difference into the ways they define issues to examine and hypotheses to offer, how they decide to test these hypotheses, and the relative importance of various issues. The argument that female reproductive mechanisms are more monstrous and less influential than male contributions delayed research into female anatomy as well as specifically female diseases such as ovarian cancer. The assumption that all mammals pattern their behaviors on human sexual difference skewed the ways zoologists understood the complexities of animal social organizations, such as packs. Assuming the empirical truth of a cultural phenomenon such as gender (instead of sexual difference) turns objective empiricism into a protocol marred by biases. Assuming that there are only two sexes produces the conclusion, for example, that hermaphroditic or intersex children must be made to conform with cultural gender norms, a conclusion that then supports invasive surgeries and other types of coercion aimed toward making the children comply with a rigid type. Assuming that culturally defined genders and sexualities are natural spurs some scientists into looking for genes that produce such behaviors.

Perhaps the greatest problem of all is the way females have long been understood as irrational and emotional and thus not good scientists. The bias of the sciences toward a rational, empirical norm that barely veils the masculinist assumption has made it difficult for female scientists to contribute to scientific research. The result is a dearth of important female scientists and the consequent marginalization of influential biologists, such as Barbara McClintock (1902–1992), in the scientific community.

BIBLIOGRAPHY

Fausto-Sterling, Anne. 1992. Myths of Gender: Biological Theories about Women and Men. New York: Basic Books.

Harding, Sandra. 1986. The Science Question in Feminism. Ithaca, NY: Cornell University Press.

Keller, Evelyn Fox. 1985. Reflections on Gender and Science. New Haven, CT: Yale University Press.

Laqueur, Thomas. 1992. Making Sex: Body and Gender from the Greeks to Freud. Cambridge, MA: Harvard University Press.

Porter, Roy. 1998. The Greatest Benefit to Mankind: A Medical History of Humanity. New York: Norton.

Ridley: Matt. 2003. The Red Queen: Sex and the Evolution of Human Nature. New York: Perennial.

Rodgers, Joann. 2003. Sex: A Natural History. New York: Owl Books.

                                                 Judith Roof

Biology

Important discoveries in biological science

Resources

Biology is the scientific study of all forms of life, including plants, animals, and microorganisms.

Among the numerous fields in biology are microbiology, the study of microscopic organisms like bacteria; cytology, the study of cells; embryology, the study of embryo development; genetics, the study of heredity; biochemistry, the study of the chemical structures in living things; morphology, the study of the anatomy of plants and animals; taxonomy, the identification, naming, and classification of organisms; and physiology, the study of how organic systems function and respond to stimulation. Biology often interfaces with subjects like psychology. For example, animal behaviorists would need to understand the biological nature of the animal they are studying in order to evaluate the animal’s behavior.

Important discoveries in biological science

The history of biology begins with the careful observation of the external aspects of organisms and continues with investigations into the functions and interrelationships of living things.

The ancient Greek philosopher Aristotle is credited with establishing the importance of observation and analysis as the basic approach for scientific investigation. By AD 200, studies in biology were centered in the Arab world. Most of the investigations during this period were made in medicine and agriculture. Arab scientists continued this activity throughout the Middle Ages.

When ancient Greek and Roman writings were revived in Europe during the Renaissance, scientific investigations began to accelerate. Renaissance artists Leonardo da Vinci (1452–1519) and Michelangelo (1475–1564) produced detailed anatomical drawings of human beings. At the same time da Vinci and others were dissecting cadavers (dead bodies) and describing internal anatomy. By the seventeenth century, formal experimentation was introduced into the study of biology. William Harvey (1578–1657), an English physician, demonstrated the circulation of the blood, initiating the biological discipline of physiology.

So much work was being done in biological science during this period that academies of science and scientific journals were formed, the first of which being the Academy of the Lynx in Rome in 1603. In Massachusetts, the Boston Philosophical Society was founded nearly a hundred years before the American Revolution. The first scientific journals were established in 1665 with the French Journal des Savants and the British Philosophical Transactions of the Royal Society.

The invention of the light microscope opened the way for biologists to investigate living organisms at the cellular level, and ultimately at the molecular level. The first drawings of magnified life were made by Francesco Stelluti, an Italian who published drawings of a honeybee at a ten-times magnification in 1625.

During the eighteenth century, Carolus Linnaeus (1707–1778) proposed a system for naming and classifying plants and animals is the basis of that used today. In his book Species plantarum, published in 1753, Linnaeus described 6, 000 plants, each one assigned a binomial name—genus and species. For example, the binomial name for the wolf is Canis lupus, and for humans, Homo sapiens.

In the nineteenth century, many explorers contributed to biological science by collecting plant and animal specimens from around the world. In 1859

KEY TERMS

Genetic engineering— The manipulation of genetic material to produce specific results in an organism.

Germ theory of disease— The theory that some types of disease are caused by microorganisms.

Metabolism— The chemical changes within an organism’s cells that produce energy for vital activity and the assimilation of nutrients.

Microorganisms— Living units that cannot be seen without magnification under a microscope.

Molecular biology— The study of the cellular structure of living units.

Prokaryote— A cell that lacks a distinct nucleus, such as bacterium or alga.

Spontaneous generation— Also known as abiogenesis. The belief that living organisms could arise from nonliving matter; this belief was used to explain the origin of life.

Charles Darwin (1809–1882) published On the Origin of Species, in which he outlined the theory of evolution by means of natural selection. This was an important postulate; it refuted the idea that organisms generated spontaneously. Later, French chemist Louis Pasteur (1822–1895) discovered that certain bacteria caused diseases. Pasteur also developed the first vaccines. By the end of the nineteenth century the germ theory of disease was established by Robert Koch (1843–1910), and by the early twentieth century, chemotherapy was developed. The use of antibiotics began with penicillin in 1928 and steroids were discovered in 1935.

From the nineteenth century until the present, the amount of research and discovery in biology has been voluminous. Two fields of rapid growth in biological science today are molecular biology and genetic engineering.

See also Biodiversity; Biological community; Biological rhythms; Botany; Ecology; Ecosystem; Evolution, convergent; Evolution, divergent; Evolution, evidence of; Evolution, parallel; Evolutionary change, rate of; Evolutionary mechanisms.

Resources

BOOKS

Byatt, Andrew, et al. Blue Planet. New York: D.K. Publishing, 2002.

Campbell, Neil A., and Jane B. Reese. Biology, 6th ed. San Francisco: Benjamin/Cummings, 2001.

Perlman, Dan L., and Edward O. Wilson. Conserving Earth’s Biodiversity Washington, DC: Island Press, 2000.

Purves, William K. Life: The Science of Biology, 6th ed. New York: W.H. Freeman, 2001.

Starr, Cecie, and Ralph Taggart. Biology: The Unity and Diversity of Life. Pacific Grove, CA: Brooks/Cole Pub. Co., 2000.

Wilson, Edward O. The Diversity of Life New York: W.W. Norton, 1999.

OTHER

Estrella Mountain Community College. “Online Biology Book” <http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookTOC.html> (accessed November 1, 2006).

University of Arizona. “The Biology Project” <http://www.biology.arizona.edu/> (accessed November 1, 2006).

WGBH Educational Foundation and Clear Blue Sky Productions. “Evolution: A Journey into Where We’re from and Where We’re Going” <http://www.pbs.org/wgbh/evolution/> (accessed November 1, 2006).

Vita Richman