Is Nature Mechanical?
Many people who have not studied science are baffled by scientists’ insistence that animals and plants are machines, and that humans are robots too, controlled by computer-like brains with genetically programmed software. It seems more natural to assume that we are living organisms, and so are animals and plants. Organisms are self-organizing; they form and maintain themselves, and have their own ends or goals. Machines, by contrast, are designed by an external mind; their parts are put together by external machine-makers and they have no purposes or ends of their own.
The starting point for modern science was the rejection of the older, organic view of the universe. The machine metaphor became central to scientific thinking, with very far-reaching consequences. In one way it was immensely liberating. New ways of thinking became possible that encouraged the invention of machines and the evolution of technology. In this chapter, I trace the history of this idea, and show what happens when we question it.
Before the seventeenth century, almost everyone took for granted that the universe was like an organism, and so was the earth. In classical, medieval and Renaissance Europe, nature was alive. Leonardo da Vinci (1452–1519), for example, made this idea explicit: “We can say that the earth has a vegetative soul, and that its flesh is the land, its bones are the structure of the rocks . . . its breathing and its pulse are the ebb and flow of the sea.” William Gilbert (1540–1603), a pioneer of the science of magnetism, was explicit in his organic philosophy of nature: “We consider that the whole universe is animated, and that all the globes, all the stars, and also the noble earth have been governed since the beginning by their own appointed souls and have the motives of self-conservation.”
Even Nicholas Copernicus, whose revolutionary theory of the movement of the heavens, published in 1543, placed the sun at the center rather than the earth was no mechanist. His reasons for making this change were mystical as well as scientific. He thought a central position dignified the sun:
Not unfittingly do some call it the light of the world, others the soul, still others the governor. Tremigistus calls it the visible God: Sophocles’ Electra, the All-seer. And in fact does the sun, seated on his royal throne, guide his family of planets as they circle around him
Copernicus’s revolution in cosmology was a powerful stimulus for the subsequent development of physics. But the shift to the mechanical theory of nature that began after 1600 was much more radical.
For centuries, there had already been mechanical models of some aspects of nature. For example, in Wells Cathedral, in the west of England, there is a still-functioning astronomical clock installed more than six hundred years ago. The clock’s face shows the sun and moon revolving around the earth, against a background of stars. The movement of the sun indicates the time of day, and the inner circle of the clock depicts the moon, rotating once a month. To the delight of visitors, every quarter of an hour, models of jousting knights rush round chasing each other, while a model of a man bangs bells with his heels.
Astronomical clocks were first made in China and in the Arab world, and powered by water. Their construction began in Europe around 1300, but with a new kind of mechanism, operated by weights and escapements. All these early clocks took for granted that the earth was at the center of the universe. They were useful models for telling the time and for predicting the phases of the moon; but no one thought that the universe was really like a clockwork mechanism.
A change from the metaphor of the organism to the metaphor of the machine produced science as we know it: mechanical models of the universe were taken to represent the way the world actually worked. The movements of stars and planets were governed by impersonal mechanical principles, not by souls or spirits with their own lives and purposes.
In 1605, Johannes Kepler summarized his program as follows: “My aim is to show that the celestial machine is to be likened not to a divine organism but rather to clockwork . . . Moreover I show how this physical conception is to be presented through calculation and geometry.”4 Galileo Galilei (1564–1642) agreed that “inexorable, immutable” mathematical laws ruled everything.
The clock analogy was particularly persuasive because clocks work in a self-contained way. They are not pushing or pulling other objects. Likewise the universe performs its work by the regularity of its motions, and is the ultimate time-telling system. Mechanical clocks had a further metaphorical advantage: they were a good example of knowledge through construction, or knowing by doing. Someone who could construct a machine could reconstruct it. Mechanical knowledge was power.
The prestige of mechanistic science did not come primarily from its philosophical underpinnings but from its practical successes, especially in physics. Mathematical modelling typically involves extreme abstraction and simplification, which is easiest to realize with man-made machines or objects. Mathematical mechanics is impressively useful in dealing with relatively simple problems, such as the trajectories of cannonballs or rockets.
One paradigmatic example is billiard-ball physics, which gives a clear account of impacts and collisions of idealized billiard balls in a frictionless environment. Not only is the mathematics simplified, but billiard balls themselves are a very simplified system. The balls are made as round as possible and the table as flat as possible, and there are uniform rubber cushions at the sides of the table, unlike any natural environment. Think of a rock falling down a mountainside for comparison. Moreover, in the real world, billiard balls collide and bounce off each other in games, but the rules of the game and the skills and motives of the players are outside the scope of physics. The mathematical analysis of the balls’ behavior is an extreme abstraction.
From living organisms to biological machines
The vision of mechanical nature developed amid devastating religious wars in seventeenth-century Europe. Mathematical physics was attractive partly because it seemed to provide a way of transcending sectarian conflicts to reveal eternal truths. In their own eyes the pioneers of mechanistic science were finding a new way of understanding the relationship of nature to God, with humans adopting a God-like mathematical omniscience, rising above the limitations of human minds and bodies. As Galileo put it:
When God produces the world, he produces a thoroughly mathematical structure that obeys the laws of number, geometrical figure and quantitative function. Nature is an embodied mathematical system.
But there was a major problem. Most of our experience is not mathematical. We taste food, feel angry, enjoy the beauty of flowers, laugh at jokes. In order to assert the primacy of mathematics, Galileo and his successors had to distinguish between what they called “primary qualities,” which could be described mathematically, such as motion, size and weight, and “secondary qualities,” like color and smell, which were subjective. They took the real world to be objective, quantitative and mathematical. Personal experience in the lived world was subjective, the realm of opinion and illusion, outside the realm of science.
René Descartes (1596–1650) was the principal proponent of the mechanical or mechanistic philosophy of nature. It first came to him in a vision on November 10, 1619, when he was “filled with enthusiasm and discovered the foundations of a marvellous science.” He saw the entire universe as a mathematical system, and later envisaged vast vortices of swirling subtle matter, the ether, carrying around the planets in their orbits.
Descartes took the mechanical metaphor much further than Kepler or Galileo by extending it into the realm of life. He was fascinated by the sophisticated machinery of his age, such as clocks, looms and pumps. As a youth he designed mechanical models to simulate animal activity, such as a pheasant pursued by a spaniel. Just as Kepler projected the image of man-made machinery onto the cosmos, Descartes projected it onto animals. They, too, were like clockwork.8 Activities like the beating of a dog’s heart, its digestion and breathing were programmed mechanisms. The same principles applied to human bodies.
Descartes cut up living dogs in order to study their hearts, and reported his observations as if his readers might want to replicate them: “If you slice off the pointed end of the heart of a live dog, and insert a finger into one of the cavities, you will feel unmistakably that every time the heart gets shorter it presses the finger, and every time it gets longer it stops pressing it.”
He backed up his arguments with a thought experiment: first he imagined man-made automata that imitated the movements of animals, and then argued that if they were made well enough they would be indistinguishable from real animals:
If any such machines had the organs and outward shapes of a monkey or of some other animal that lacks reason, we should have no way of knowing that they did not possess entirely the same nature as those animals.
With arguments like these, Descartes laid the foundations of mechanistic biology and medicine that are still orthodox today. However, the machine theory of life was less readily accepted in the seventeenth and eighteenth centuries than the machine theory of the universe. Especially in England, the idea of animal-machines was considered eccentric. Descartes’ doctrine seemed to justify cruelty to animals, including vivisection, and it was said that the test of his followers was whether they would kick their dogs.
As the philosopher Daniel Dennett summarized it, “Descartes . . . held that animals were in fact just elaborate machines . . . It was only our non-mechanical, non-physical minds that make human beings (and only human beings) intelligent and conscious. This was actually a subtle view, most of which would readily be defended by zoologists today, but it was too revolutionary for Descartes’ contemporaries.”
We are so used to the machine theory of life that it is hard to appreciate what a radical break Descartes made. The prevailing theories of his time took for granted that living organisms were organisms, animate beings with their own souls. Souls gave organisms their purposes and powers of self-organization. From the Middle Ages right up into the seventeenth century, the prevailing theory of life taught in the universities of Europe followed the Greek philosopher Aristotle and his leading Christian interpreter, Thomas Aquinas (c. 1225–74), according to whom the matter in plant or animal bodies was shaped by the organisms’ souls. For Aquinas, the soul was the form of the body. The soul acted like an invisible mold that shaped the plant or the animal as it grew and attracted it toward its mature form.
The souls of animals and plants were natural, not supernatural. According to classical Greek and medieval philosophy, and also in William Gilbert’s theory of magnetism, even magnets had souls. The soul within and around them gave them their powers of attraction and repulsion. When a magnet was heated and lost its magnetic properties, it was as if the soul had left it, just as the soul left an animal body when it died. We now talk in terms of magnetic fields. In most respects fields have replaced the souls of classical and medieval philosophy.
Before the mechanistic revolution, there were three levels of explanation: bodies, souls and spirits. Bodies and souls were part of nature. Spirits were non-material but interacted with embodied beings through their souls. The human spirit, or “rational soul,” according to Christian theology, was potentially open to the Spirit of God.
After the mechanistic revolution, there were only two levels of explanation: bodies and spirits. Three layers were reduced to two by removing souls from nature, leaving only the human “rational soul” or spirit. The abolition of souls also separated humanity from all other animals, which became inanimate machines. The “rational soul” of man was like an immaterial ghost in the machinery of the human body.
How could the rational soul possibly interact with the brain? Descartes speculated that their interaction occurred in the pineal gland. He thought of the soul as like a little man inside the pineal gland controlling the plumbing of the brain. He compared the nerves to water pipes, the cavities in the brain to storage tanks, the muscles to mechanical springs, and breathing to the movements of a clock. The organs of the body were like the automata in seventeenth-century water gardens, and the immaterial man within was like the fountain keeper:
External objects, which by their mere presence stimulate [the body’s] sense organs . . . are like visitors who enter the grottoes of these fountains and unwittingly cause the movements which take place before their eyes. For they cannot enter without stepping on certain tiles which are so arranged that if, for example, they approach a Diana who is bathing they will cause her to hide in the reeds. And finally, when a rational soul is present in this machine it will have its principal seat in the brain, and reside there like the fountain keeper who must be stationed at the tanks to which the fountain’s pipes return if he wants to produce, or prevent, or change their movements in some way.
The final step in the mechanistic revolution was to reduce two levels of explanation to one. Instead of a duality of matter and mind, there is only matter. This is the doctrine of materialism, which came to dominate scientific thinking in the second half of the nineteenth century. Nevertheless, despite their nominal materialism, most scientists remained dualists, and continued to use dualistic metaphors.
The little man, or homunculus, inside the brain remained a common way of thinking about the relation of body and mind, but the metaphor moved with the times and adapted to new technologies. In the mid-twentieth century the homunculus was usually a telephone operator in the telephone exchange of the brain, and he saw projected images of the external world as if he were in a cinema, as in a book published in 1949 called The Secret of Life: The Human Machine and How It Works.21 In an exhibit in 2010 at the Natural History Museum in London called “How You Control Your Actions,” you looked through a Perspex window in the forehead of a model man. Inside was a cockpit with banks of dials and controls, and two empty seats, presumably for you, the pilot, and your co-pilot in the other hemisphere. The ghosts in the machine were implicit rather than explicit, but obviously this was no explanation at all because the little men inside brains would themselves have to have little men inside their brains, and so on in an infinite regress.
If thinking of little men and women inside brains seems too naïve, then the brain itself is personified. Many popular articles and books on the nature of the mind say “the brain perceives,” or “the brain decides,” while at the same time arguing that the brain is just a machine, like a computer.22 For example, the atheist philosopher Anthony Grayling thinks that “brains secrete religious and superstitious belief” because they are “hardwired” to do so: