In the Renaissance, when the study of human nature took center stage, medicine, astronomy, and physics finally broke out of the cage of Aristotelian and Galenic thought. The Renaissance was a time of rediscovery and reassessment, during which scholars combed the globe for ancient manuscripts. It was not the discovery of modern scientific methods that allowed Renaissance physicians to break with Galen and Aristotle; it was the discovery of ancient magical manuscripts. The arguments of the ancient magicians were based on the correspondence between the human body and the universe as a whole, and they led to the development of alchemical medicine. For example, in his book Of Natural and Supernatural Things, the Benedictine monk and alchemist Basilius Vesalius provides a recipe for “Spirit of Mercury . . . which cures all diseases, be it dropsie, consumption, gout, stone, falling sickness, apoplexy, leprosy, or howsoever called in general”—a recipe, surely, that would be more likely to cause apoplexy than to cure it.
The main proponent of this new medicine was the Swiss physician Paracelsus (1493–1541), born Phillippus Aureolus Theophrastus Bombastus von Hohenheim. (While apparently the word bombastic is not based on Hohenheim’s middle name, he certainly was that: “Let me tell you this: every little hair on my neck knows more than you and all your scribes, and my shoe buckles are more learned than your Galen and Avicenna, and my beard has more experience than all your high colleges.”) Even though Paracelsus’s alchemical medicine was often no better than the old Greek medicine, his decisive break with the ancient Greek tradition and his emphasis on using chemistry were an important step forward. At times, Paracelsus sounded amazingly modern: “Medicine is not only a science; it is also an art. It does not consist of compounding pills and plasters; it deals with the very processes of life, which must be understood before they may be guided.”
The various approaches to medicine—traditional and herbal medicines, Galenic medicine based on the balance of humors, and the new alchemical medicine of Paracelsus—coexisted and were vigorously debated, often on what appears to us today as dubious grounds. Yet, that they were debated ushered in the era of modern critical science.
The Mechanical Philosophy
The battle between ancient and alchemical medicine was raging when a new idea emerged: the idea that human bodies were merely machines and that the body’s function could be understood as the workings of discrete parts. An inadvertent hero of the mechanical view of life was the English physician William Harvey (1578–1657), a thoroughgoing vitalist who still believed in Galen’s vital spirits. Yet Harvey was the first to understand the true function of the heart. According to Galenic medicine, the heart was the source of heat in the blood and the place where blood mixed with air to create “vital spirits.” Galen believed that the arteries originated in the heart, and the veins in the liver. The arteries and the veins were separate systems, connected only through the porous septum in the heart.
Although little evidence supported the porous nature of the septum, few physicians were brave enough to criticize Galen’s theories. The famous physician Andreas Vesalius (1514–1564), who published some of the most influential and detailed books on human anatomy, could not find any porosity in the heart; nevertheless, in the first edition of his De fabrica he accommodated Galen: “The septum is formed from the very densest substance of the heart. It abounds on both sides with pits. Of these none, as the senses can perceive, penetrate from the right to the left ventricle. We wonder at the art of the Creator which causes blood to pass . . . through invisible pores.” But by the second edition of his book, Vesalius had to admit, with some regret, that there was simply no way that Galen’s theory could be correct.
The path was now clear for Harvey, who, like Vesalius before him, had studied at the University of Padua. The way Harvey disproved Galen was enormously influential: Going beyond dissections and observations, Harvey used a simple quantitative argument, which was unprecedented and powerful. If the heart was the source of blood, the total amount of blood generated in the heart could easily be estimated by multiplying the volume of the heart with the rate of pumping. This would result in 540 pounds of blood every hour—a giant amount. Where would it all go? The only reasonable explanation was that a limited amount of blood circulated through the body; and whatever the heart pumped out, came back to the heart a short time later. Harvey’s mathematical reasoning had an enormous impact on the subsequent history of the life sciences: Life, like the rest of nature, could yield to quantitative analysis and, with it, careful experimentation.
Despite Harvey’s modern scientific methods, his work drew praise from the Paracelsian physician Robert Fludd (1574–1637). Fludd saw in the circulation of blood a confirmation of his alchemist views that the macroscopic world of the stars was reflected in the microscopic world of the human body: As the planets go around the sun, so the blood circulates around the heart. But Harvey’s findings also received nods from more modern scientists and philosophers, especially René Descartes (1596–1650), who in The Description of the Human Body vigorously championed Harvey and argued that the body was a machine.
Descartes’s philosophical ideas were an important step toward a mechanical view of life. Performing (sometimes gruesome) experiments on animals, he discerned that the body acted like a machine with pumps and pipes. He was one of the first natural philosophers to argue for the investigation of the body from a mechanical perspective, devoid of any mysterious forces. These ideas landed Descartes in hot water with the Catholic Church, despite his being a devout churchgoer. Descartes tried his best to reconcile what he saw in nature with Catholic theology. His solution was to divorce “mind” from the mechanical worldview he espoused. The mind or spirit was to be the realm of the soul and the divine, while the body was pure machine. The soul, which once explained everything, from the growth of plants to the human mind, had now been confined to mind alone. Everything else was matter in motion.
The first modern atomists, after the almost complete suppression of atomism during the Middle Ages, were Isaac Beeckman (1588–1637), a Dutch philosopher and scientist, and Pierre Gassendi (1592–1655), a French Jesuit priest. Beeckman, Descartes’s teacher and friend, was considered one of most educated men of Europe at the time. Gassendi followed Beeckman in arguing for a revival of atomism and strived to make Epicurean atomism palatable for the Catholic Church. Gassendi had a different approach from that of Descartes: Whereas Descartes created dualism, the separate realms of matter and soul, Gassendi animated his atoms with the power of God, returning to an animistic view of the universe. If atoms were responsible for life, the necessary intelligence had to be built into them. And who endowed the atoms with this intelligence? God, of course.
This idea was later adopted by the German philosopher Gottfried Leibniz (1646–1716), who replaced atoms by “monads,” atomic units of thought. Later materialist philosophers, however, would discard God altogether and instead endow atoms with uncreated purpose, an idea that during the Enlightenment, the French philosopher Voltaire (1694–1778) found laughable. According to Voltaire, the idea of some kind of uncreated intelligence inherent in atoms was ridiculous. Wasn’t it simpler to just believe in God? After two thousand years of debate, it seemed that philosophers had not advanced much beyond Aristotle and Democritus.
But this would be unfair: The mechanical worldview, the revival of atomism, and the combination of rational examination and experiment were the foundation for one of the most influential periods in the history of science, the scientific revolution, which lasted from the late sixteenth to the eighteenth century. During this period, modern science was born and natural philosophers began to distinguish science from mysticism. The towering figures of this period were Galileo Galilei (1564–1642) and Isaac Newton (1642–1726). Both Galileo and Newton were atomists and believed in using experiment and reason to find new truths about nature. Newton had a Lucretian idea of how atoms form macroscopic matter; he thought of matter as made of small, hard particles that stick together to make larger particles. This i
dea explained how materials can break apart, as they break “not in the midst of solid particles, but where those particles are laid together, and only touch in a few points.”
Newton stood at the threshold between Renaissance mysticism and modern science, and much has been made of his interest in alchemy and obscure theological pursuits. Yet his alchemy led him to value experimental approaches and validated his atomism. Newton appeared to know the difference between mysticism and science and kept his alchemy and theology neatly separated from his scientific and mathematical writings. He even went so far as to defend his scientific findings from those who thought that he was advocating new occult forces: “These Principles I consider, not as occult Qualities, supposed to result from the specifick Forms of Things, but as general Laws of Nature, by which the Things themselves are form’d; their Truth appearing to us by Phænomena, though their Causes be not yet discover’d.”
The mechanical philosophy and the new atomism compelled scientists during the scientific revolution to look ever more closely at the living world, and advances in optics provided new instruments for the search of the “atoms” of nature. The microscope was invented in the late 1500s in the Netherlands by two Dutch spectacle makers, Zacharias Janssen and his son Hans. Improvements to the microscope were completed by Galileo (1609) and Cornelius Drebbel (1619). In 1614, Galileo observed that flies had “fur.” Others observed mites and studied the structure of a fly’s eye. The most famous early book on microscopic observations was Hooke’s Micrographia of 1665. Robert Hooke (1635–1703), a master experimenter, used his homebuilt microscope to look at everything from flees to “gravel” in urine. The early microscopists discovered what Hooke called “small machines of nature,” from the legs of flees to single-celled animals. Hooke was the first to see cells in cork. The first animal cells, red blood cells, were discovered shortly thereafter by Antonie Philips van Leeuwenhoek (1632–1723), but neither he nor Hooke realized that these cells were the smallest units of all living beings.
Hooke and his contemporaries discovered that life was a wondrous menagerie of mechanisms, from the smallest “animalcules” to the body of a human. The search for smaller and smaller units continued for over two hundred years, leading to the cell theory in the mid-1800s. For Hooke and his fellow microscopists, the mechanical philosophy compelled them to look carefully at the components of living beings. What they saw confirmed their mechanical view of life. Observing the growth of mold, Hooke noted: “I must conclude, that as far as I have been able to look into the nature of this Primary kind of life and vegetation, I cannot find the least probable argument to perswade me there is any other concurrent cause then such as is purely Mechanical.”
L’homme machine
Some people just don’t know when to shut up.
Julien Offray de La Mettrie (1709–1751), Brittany native, medical doctor, and radical Enlightenment philosopher, certainly didn’t (Figure 1.2). When his first venture into philosophy, A Natural History of the Soul (1745), was burned in Paris for its impiety, he followed with an attack on the less-than-competent physicians of France. Having thoroughly upset both the medical and the religious establishments, he fled to Holland. Then, in 1747, he continued his attacks with The Vengeful Faculty, against the physicians, and Man a Machine (L’homme machine), against the priests. Holland was no longer safe, and La Mettrie found refuge at the court of Frederick the Great in Berlin. The Prussian king loved the French and the Enlightenment, and you couldn’t be more Enlightenment than La Mettrie.
FIGURE 1.2. Julien Offray de La Mettrie. Another laughing materialist philosopher, although unlike Democritus, he has no beard.
What had La Mettrie written in L’homme machine that so upset his contemporaries?
After receiving his medical doctorate from the University of Rheims, La Mettrie had served as medical officer to the French Guards and participated in a number of bloody battles. Through this experience, he developed a profound distaste for the slaughter of war and saw what savagery and injury could do to the human mind. He came to realize that reason and emotion, supposedly part of the soul, could be thoroughly altered by injury. Didn’t this clearly show that Descartes’s last refuge of soul—the mind—could ultimately be explained by pure mechanism? No wonder La Mettrie’s more religious contemporaries were displeased.
Because of his provocative writings, La Mettrie is sometimes seen as the bad boy of the Enlightenment. The rumor that he died while overeating expensive pheasant pâté did not help his reputation (although it seems likely he died of food poisoning). However, under the combative veneer of his writing, there was a thoughtful philosopher and one of the most uncompromising representatives of the mechanical philosophy.
La Mettrie was a better provocateur and philosopher than scientist. But we can hardly fault him for that: While his explanations of procreation or “irritability” (see next paragraph) seem to us naive or laughable, he based them on what little was known about human physiology at a time when alchemical and ancient Greek ideas were still common. But his philosophy did not depend on such details.
At the heart of his most famous work, L’homme machine, were two observations: First, the functions of body and mind could be greatly altered by physical influences and therefore could not be independent of them. Second, living tissue, such as muscle, could move on its own, even when removed from the body. Experiments performed during La Mettrie’s time demonstrated that isolated tissues could move when “irritated.” This so-called irritability indicated to La Mettrie that life possessed “inherent powers of purposive motion.” He put irritability at the center of his arguments, providing a list of ten examples, some quite gruesome, such as the frantic fluttering of headless chickens. In light of these observations, La Mettrie concluded that we cannot divorce the functions of the body or the mind from their physical nature. Instead, the functions must be the result of the physical and mechanical makeup.
La Mettrie’s denial of the soul led to his being charged as an atheist (the standard charge for all philosophers who spoke out against Church doctrine). But he was more of a sincere agnostic: “I [do not] question the existence of a supreme being; on the contrary, it seems to me that the greatest degree of probability is in its favor. But that doesn’t prove that one religion must be right, against all the others; it is a theoretical truth that serves very little practical purpose.” For him, metaphysical and theological speculations about the soul served little purpose when a meal could make the “soul” happy and content and when we could see “to what excesses cruel hunger can push us.” La Mettrie, tongue-in-cheek, observed that “one could say at times that the soul is found in our stomach.” Observing that hunger, injury, drugs, and sleep affected people’s minds, he felt certain that the soul was just part of the body, even if he could not explain in detail how it worked: “It is folly to waste one’s time trying to discover its mechanism. . . . There is no way of discovering how matter comes to move.”
La Mettrie was wrong to state that “there is no way” to discover how organized matter moves, but we can agree with him that a supernatural soul is probably not needed to render us alive, as Aristotle believed, because the soul is so dependent on the physical state of the body. La Mettrie concluded that the “soul’s abilities” clearly depend on the “specific organization of the brain and the whole body.” Therefore, the soul was nothing other than the organization of the body and, as a separate concept, empty. It had taken two thousand years before somebody could freely acknowledge that a soul was not necessary to explain the motions of the body.
La Mettrie’s agnosticism gave him a modern outlook on the methodology of science (although modern scientists are more diplomatic) and a somewhat religious awe of nature governed by necessity. He wondered “why would it be absurd to believe that there exist physical causes for everything that has been made.” Was it not “our absolutely incurable ignorance of these causes that has made us resort to a God?” For him, the answers for the mystery of life and mind lay not in
chance, nor in God, but in nature.
La Mettrie’s rejection of chance was very much in the spirit of the pre-Darwinian world. It was difficult to see what role chance could play in the emergence of the organized state of matter we call life. La Mettrie believed that a purely physical explanation of life was possible—but a mechanical explanation had to explain all aspects of life previously explained by religion. When God became an “unnecessary hypothesis,” nature had to fill the gap and produce life and the human race out of necessity. The mechanical philosophy, like other explanations that relied on the fashionable ideas of the day, compared living beings to mechanical contraptions such as clocks.* Clocks, when well maintained, leave nothing to chance; they are the epitome of necessity.
For La Mettrie, nature acted on many levels, from the simple to the complex. He opposed artificial barriers to physical explanations and rejected the idea that there was a wall beyond which physics could not tread. The difference between a falling rock and a human mind was not one of different matter or different laws of nature, but one of a tremendous increase in complexity. And even if this complexity prevented us from completely explaining how a human mind works, this failure did not warrant the insertion of soul or God into this gap in our understanding. “Just as, given certain physical laws, it would not be possible for the sea to not have its ebb and flow, the same . . . laws of motion . . . would form eyes which see, ears that hear, nerves that feel, tongues that can or cannot talk depending on their organization; and finally, would fabricate the organ for thought. Nature has made in the human machine another machine, which finds itself capable of retaining ideas and creating new ones . . . it has made, blindly, eyes that can see; it has made without thought, a machine that thinks.”
Life's Ratchet: How Molecular Machines Extract Order from Chaos Page 3
