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.
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.
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.
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