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.