The Mechanical Philosophy: Mechanistic and Materialistic Conceptions of Life

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The Mechanical Philosophy: Mechanistic and Materialistic Conceptions of Life


Physiological studies from ancient times to the present have been guided implicitly or explicitly by a philosophical framework that has been either mechanistic or vitalistic. The mechanistic philosophy asserts that all life phenomena can be completely explained in terms of the physical-chemical laws that govern the inanimate world. Vitalist philosophy claims that the real entity of life is the soul, or vital force, and that the body exists for and through the soul, which is incomprehensible in strictly scientific terms. The triumph of Newtonian physics is reflected in the mechanistic materialism of the French philosophes of the Enlightenment and the mechanical philosophy adopted by many naturalists. Among the eighteenth-century naturalists who applied the concepts of mechanical philosophy to their scientific research and writings were Julien de la Mettrie (1709-51); Georges Louis Leclerc, comte de Buffon (1707-1788); and Erasmus Darwin (1731-1802).


New ideas about chemistry, physiology, and medicine were promoted by teachers at Europe's leading medical schools, including Hermann Boerhaave (1668-1738), who taught chemistry, physics, botany, ophthalmology, and clinical medicine at the University of Leiden. Boerhaave's approach to anatomy, physics, and chemistry was widely disseminated by devoted students and disciples, such as Albrecht von Haller (1707-1772). Physiology owes a great debt to von Haller, who carried out an enormous number of experiments and summarized the state of physiology in his Elements of Physiology. For example, von Haller's experiments on the nervous system led him to conclude that the soul had nothing in common with the body, except for sensation and movement that seemed to have their source in the medulla; therefore, the medulla must be the seat of the soul. Eighteenth-century chemists also made major contributions to understanding the relationship between the circulation of the blood and the exchange of gases in respiration. Stephen Hales (1677-1761), who invented the pneumatic trough, investigated the hydraulics of the vascular system, the chemistry of gases, the respiration of plants and animals, and the measurement of blood pressure. Much of this work was reported in Vegetable Staticks (1727) and Statistical Essays, containing Haemastaticks (1733).

According to the mechanical philosophy, also known as materialism, all phenomena, even if not obviously mechanical in nature, can be reduced to primary qualities inherent in matter. In part, the mechanical philosophy represented the rejection of Aristotelian physics and the triumph of the Scientific Revolution, which led to new ways of thinking about the cosmos and the dynamic functions of the body. The mechanical philosophy systematized by the philosopher and mathematician René Descartes (1596-1650), who described animals and the human body as machines, is of special significance to the history of physiology.

The writings of Descartes provided the most influential philosophical framework for a mechanistic approach to physiology. The fundamental platform of Descartes's mechanical philosophy was that all natural phenomena could be explained in terms of matter and motion. Nevertheless, the mechanical philosophy was not necessarily atheistic or incompatible with religious beliefs in a Creator. Pious naturalists could assume that God was not directly involved in the ordinary motions of the universe or the normal activities of living beings.

Cartesian doctrine essentially treated animals as machines and explained their activities as the motions of material corpuscles and the heat generated by the heart. Even human beings could be seen as earthly machines that differed from animals by virtue of the "rational soul," which governed thought, volition, conscious perception, memory, imagination, and reason. Descartes's disciples saw him as the first philosopher to dare to explain human beings in a purely mechanical manner. The Cartesian concept of animals and the human body as machines reached its ultimate expression in the writings of Julien de La Mettrie, author of L'homme Machine (1748). The mechanical philosophy allowed naturalists to investigate nature without relying on the vitalistic "soul" and "spirits" that had characterized ancient and Renaissance science. Only the rational soul of human beings remained as part of natural history. Some natural philosophers, such as La Mettrie, were willing to discard even this "soul" for a fully materialistic and atheistic system.


La Mettrie was quite willing to let his materialistic scientific theories conflict with or contradict Christian dogma. His materialistic interpretations of psychic and physiological phenomena were published in A Natural History of the Soul (1745), L'Homme-machine, Discourse on Happiness (1748), and The Small Man in a Long Queue (1751). La Mettrie argued that we cannot really understand either the soul or matter. Clarity of thought, however, was obviously affected by fevers and other illnesses. This proved that thought, allegedly a function of the rational soul, was actually a function of the brain and was dependent on physical conditions. Because of the problems caused by his unorthodox views, La Mettrie sought refuge in Holland. In L'Homme-machine, which he wrote in Holland, La Mettrie presented man as a machine whose actions were entirely the result of physical-chemical factors. Experiments on animals indicated that peristalsis continued even after death and that isolated muscles could be artificially stimulated to contract. La Mettrie reasoned that if these facts were true for animals, they must also be true for humans. In contrast to Descartes, however, La Mettrie denied the claim that humans were essentially different from animals. For La Mettrie, humans were essentially a variety of monkey, superior mainly by virtue of the power of language. Rejecting the mind-body dualism of Descartes, La Mettrie further argued that even the mind must depend directly on physiochemical processes. Substances such as opium, coffee, and alcohol affected both the body and the mind, affecting thoughts, mood, imagination, and volition. Moreover, diseases attacked the mind as well as the body. La Mettrie taught that atheism was the only road to happiness and that the purpose of human life was to experience the pleasures of the senses. Many aspects of his theories were incorporated into behaviorism and modern materialism. Eventually, La Mettrie found refuge at the court of Frederick II of Prussia, where he was able to write, lecture, and practice medicine until his untimely death.

Although Erasmus Darwin, English naturalist and physician, is now primarily remembered in connection with his grandson Charles Darwin (1809-1882), he was widely known in his own time. Indeed, his wide range of scientific interests established him as the leader of the Lunar Society, an association that included some of the most important British scientists and inventors of the eighteenth century. Erasmus Darwin's major treatise, Zoonomia, or the Laws of Organic Life (1794-1796), deals with medicine, pathology, and the mutability of species. Unlike Descartes, Erasmus Darwin attempted to prove that the same intellectual principle existed in humans and animals. His Zoonomia dealt with essentially all of the central questions of late eighteenth-century biology. He is generally given little credit for originality despite his sweeping speculations, particularly about evolution. According to Erasmus Darwin, all animals arose from a "living filament." In general, his approach to vital phenomena was mechanical, especially his ideas about epigenesis; he believed that all of nature could be explained in terms of matter and motion.

Georges Louis Leclerc, comte de Buffon, the great eighteenth-century French natural historian and mathematician, is primarily remembered for his encyclopedic Natural History (Histoire naturelle, générale et particulière, 44 volumes, 1749-1804), a systematic account of natural history, geology, and anthropology. Buffon was a disciple of Newtonian physics, but he was aware of certain difficulties involving a strict application of the mechanical philosophy to natural history. It seemed impossible to Buffon that simple attraction and repulsion between inert atoms could produce living beings. Instead, he suggested that living matter was made up of "organic molecules" that were directed by an "interior mold." He also postulated a special "penetrating force" that guided the organic molecules to their proper places in the interior mold. Although his writings were very popular, Buffon's ideas about geological history, the origin of the solar system, biological classification, the possibility of a common ancestor for humans and apes, and the concept of lost species were considered a challenge to orthodox religious doctrine. His Epochs of Nature and Theory of the Earth were especially controversial. Buffon was the first naturalist to construct geological history into a series of stages. He suggested that Earth might be much older than church doctrine allowed and speculated about major geological changes that were linked to the evolution of life on Earth. Buffon suggested that the seven days of Creation could be thought of as seven epochs of indeterminate length. These speculations led to an investigation by the theology faculty of the Sorbonne. Buffon avoided censure by publishing a recantation in which he asserted that he had not intended his account of the formation of the earth as a contradiction of scriptural truths.

Mechanical philosophy, however, did not work well when confronted with complex vital phenomena such as reproduction, development and differentiation, nutrition, and growth. Optimism about the explanatory power of mechanical philosophy began to decline by the middle of the eighteenth century. Many physiologists came to the conclusion that mechanical explanations for the activities of living beings were impossible and inappropriate. Naturalists argued that it was more useful to reduce complex vital (living) phenomena to simpler components that could be analyzed, or at least fully described and linked to each other. The new ideas and methods that emerged from the revolution in chemistry provided new ways of understanding some vital phenomena, such as digestion, respiration, and the role of the circulation of the blood. By the second half of the eighteenth century, new ideas from chemistry and experimental physics, especially the study of electricity, were exerting a profound influence on physiology and medicine.


Further Reading


Fulton, John Farquhar, and L. G. Wilson, eds. Selected Readings in the History of Physiology. Chicago, IL: C. C. Thomas, 1966.

Hall, T. S. A Sourcebook in Animal Biology. Cambridge, MA: Harvard University Press, 1952.

Hall, T. S. History of General Physiology 600 b.c. to a.d. 1900. 2 vols. Chicago, IL: University of Chicago Press, 1975.

Hankins, Thomas L. Science and the Enlightenment. New York: Cambridge University Press, 1985.

McNeil, Maureen. Under the Banner of Science: Erasmus Darwin and His Age. Wolfeboro, NH: Manchester University Press, 1987.

Roger, Jacques. Buffon: A Life in Natural History. Ithaca, NY: Cornell University Press, 1997.

Rothschuh, Karl E. History of Physiology. Translated and edited by Guenter B. Risse. New York: Robert E. Krieger, 1973.

Thomson, Ann. Materialism and Society in the Mid-eighteenth Century: La Mettrie's Discours préliminaire. Genève: Droz, 1981.

Wellman, Kathleen Anne. La Mettrie: Medicine, Philosophy, and Enlightenment. Durham: Duke University Press, 1992.

Periodical Articles

Brown, Theodore M. "From Mechanism to Vitalism in Eighteenth-Century English Physiology." Journal of the History of Biology 7 (1974): 179-216.

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The Mechanical Philosophy: Mechanistic and Materialistic Conceptions of Life

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