That was Aristotle’s view as well. It is why he identifies psychē as the actualization of eidos. It is only a beginning. Soul appears in his book on developmental biology and heredity – The Generation of Animals; in his book on animal locomotion – The Movement of Animals; in his functional anatomy – The Parts of Animals; and, most of all, in his physiology – The Length and Shortness of Life and Youth & Old Age, Life & Death. Soul, in short, pervades Aristotle’s biology. When we survey all that he says about its workings it becomes apparent that he has given a detailed and coherent account, embracing many levels of biological organization, of how animals abstract matter from the environment, transform it, distribute the transformed matter throughout their bodies and use it to grow, maintain themselves, reproduce, perceive the world and respond to it – and that the form, structure or organization of all this activity is the soul.
The result is a vision that is at once disturbingly alien and surprisingly familiar. It is alien when we consider that we have been talking about ‘soul’, a word that by religious and philosophical tradition is usually applied to entities only tangentially connected to the physical world, if at all; but it is very familiar when we ignore the word itself and attend to what Aristotle is trying to understand – the moving principle of life.
LVI
ARISTOTLE DIVIDES THE soul among its functions. All living things have a ‘nutritive’ soul responsible for nourishment – trophē – and all that flows from it, but only animals (and humans) have a ‘sensitive’ soul that controls perception, appetite and locomotion. (He thinks that plants can neither sense their environment nor respond to it.) Humans also have a ‘rational’ soul. These sub-souls are components of a larger whole; sub-systems of the soul tout court.
The nutritive soul is the first soul to appear in an animal’s development. Its powers are wide. It reigns over the acquisition, transformation and distribution of nutrition and hence the growth and maintenance of living things, their destruction by ageing and the perpetuation of their forms by reproduction. It holds them together and stops them from crumbling into dust. To put it more succinctly, when Aristotle talks about a creature’s nutritive soul, he’s talking about the structure and control of its metabolism.
Metabolism: from the Greek metabolē – literally ‘transformation’. It’s a very Aristotelian word. A metabolism is the system by which an organism acquires matter from the world, transforms it into the stuff that it needs, and then redistributes to the places where it needs it. It is an open chemical system – which is what Schrödinger meant when he spoke of life feeding on negative entropy. Aristotle also perceived that living things were open systems:
We must understand this [a growing uniform part] in terms of a constant flow of water. Different parts, one after another, are coming into being. This is how the matter, of which flesh consists, grows: some is eroded in the flow and some arrives in addition. Additions to every part do not take place, but every part that belongs to the shape and form.
Aristotle often compares the making of an animal to the making of human artefacts: axes, statues, beds and houses. But here he’s saying that an animal is not like a house at all. When an animal self-assembles it doesn’t just add bits of flesh to flesh like so many bricks until it’s complete; the material dynamics of animals are much more complicated for, even as they grow, they also maintain themselves. There is, in the jargon of biologists, a continual ‘turnover’ of materials, and growth is due to the accession of matter over and above this turnover. This idea is central to Aristotle’s physiology and the starting point for any modern physiological model of growth as well.
The belief that living things transform food into uniform parts hardly seems like a stunning insight, yet it seems to have been original to him. He says that his predecessors had two views about how the uniform parts grow. Some held that creatures make more of x (flesh, bone, whatever) simply by eating x. Call it the ‘additive’ model of nutrition. Others were more subtle: they held that creatures make more of x by eating its opposite. This ‘anti-matter’ theory is hard to understand and Aristotle’s illustration of it, that ‘water may be said to feed fire’, isn’t very helpful, but it does contain – albeit in peculiar form – the idea of transformation. Aristotle acknowledges, then, that the ‘antimatter’ theory contains a germ of truth. Even so, he’s clear that a much more general theory of transformation is needed.
Some chemical notation shows what an advance his theory was over his predecessors’. If the ‘additive’ theory is written x → x, and the ‘anti-matter’ theory is anti-x → x, then Aristotle’s general theory is x → y. Or, to use his words, one kind of matter, x, ‘passes away’ even as another, y, ‘comes to be’. But actually that’s too simple, for Aristotle thinks that uniform parts arise from a system of serial and parallel transformations: x → y → z etc. or x → y + x → z etc. That is, he thinks that metabolic transformations are ordered as a chain or even a network. From this simple, yet pregnant, idea Aristotle constructs an entire system.
In blooded animals food is masticated by the teeth, broken down by the alimentary system, transported to the mesentery, liver and spleen where it is transformed into purer nutrition and then transported further, via the veins, to the heart where it is transformed again. The product of this last transformation is blood, the key intermediate from which all animal uniform parts are derived. Blood is distributed throughout the body via the vascular system and transformed locally into flesh, fat, bone, semen and so on. Aristotle tells us how each uniform part is derived from, or related to, the others. Flesh is derived first from the ‘purest’ nutrient, leaving other uniform parts to be derived from the residue; what’s left over is excreted. Nowhere does Aristotle present his model in toto, but if you ferret through his texts, you can draw a diagram that resembles a modern metabolic network and that accounts for the origin of all the uniform parts, fluids and waste residues that he mentions.* It is Aristotle’s vision of the body’s economy in full.
LVII
THAT MATTER FLOWS through living things, is transformed by them into the various uniform parts that they need to live and is distributed among those various uniform parts in a way constrained by economic laws – these are the elements of any metabolic theory. But any such theory must be underwritten by chemistry. Aristotle has a chemistry, but it is a poor one.
It begins with the traditional four elements. Food and all its derivatives – the uniform parts – are compounds composed of these elements in particular proportions. Aristotle credits Empedocles with this idea, and Empedocles actually gives a formula for bone: E2W2AoF4, where E is earth, W is water, A is air and F is fire. Aristotle, by contrast, is very vague about the formulas of the uniform parts and generally speaks of them as being composed of just earth and water: hard uniform parts (bone, nails, hooves, horns, etc.) have lots of earth but little water; soft uniform parts (fat, semen, menstrual fluid) have little earth but lots of water; flesh is something in between. Aristotle suggests that such a formula is a step towards the definition of any uniform part. That makes sense since the recipe dictates its functional properties.
All this is intuitive enough. But probe deeper, and difficulties appear. Aristotle berates Empedocles for merely thinking of the uniform parts as mixtures – agglomerated heaps of elements. They’re not, he says; they’re compounds – genuinely new substances. Very well, but how are such compounds formed? Our chemistry is based on a molecular theory of material substance. It is precisely the truth of this theory that makes it so rich, for it permits a multitude of possible transformations – ‘reactions’ – and countless molecular species each with its own distinctive physical properties. But Aristotle has rejected Democritean atomism, so his compounds are made of completely continuous matter down to the finest microscopic scale.
How can different kinds of continuous matter combine to form a new kind? Aristotle gives us no model or metaphor to explain it and I can’t think of one that will. He says that when elements form a mix
is they are transformed into something entirely new, yet he insists that those elements still exist, or do so ‘potentially’.* In fact, the elements must exist within a mixture for his chemistry relies on their re-emergence during transformation. The root of the problem is plain. When Aristotle rejected atomism he also rejected any molecular theory of chemical combination. In doing so, he rejected any theory that allows elements to be the building blocks of new substances and yet remain themselves unaltered and available for recycling by living things as they please.
Heat transforms food into the various uniform parts. But Aristotle struggles to understand the nature of heat. He notes that ‘hot’ and ‘cold’ can be used in many senses, which is certainly true. It’s unfortunate, then, that he uses them so indiscriminately. All living things, he believes, have an internal source of ‘vital heat’ (except for embryos which obtain their heat from their parents), which is why they feel warm to the touch. This internal fire, which is not the same as conventional fire, is sustained by nutrition – ‘Fire’, he says, ‘is always coming into being and flowing like a river’ – and, like all fires, it needs to be fed.* This internal fire drives ‘concoction’, a process analogous to ‘cooking’, ‘broiling’ or ‘boiling’, all of which – he thinks – drive off a mixture’s internal heat and moisture leaving varying proportions of earthy material behind. Concoction seems, and is, a rather crude device, but Aristotle argues that the subtle, iterative application of heat to raw nutrition, blood and then to more derived compounds can yield all the different kinds of matter of which creatures are made.
It may seem that in describing Aristotle’s metabolic model and the chemistry that underlies it I have forgotten about the soul. But in fact I have been talking about the soul all along. The system that I have described – the structure of the metabolic network – is the nutritive soul, or at least a part of it. The ends to which a creature puts its nutrients, how much of each kind of uniform part it will make and when and where it will do so, its growth, its reproduction and its death – all of these depend on the organization of metabolism and all depend, Aristotle tells us, on the nutritive soul. Yet there is more to the nutritive soul than this:
Some think the fire itself is the main cause of nutrition and growth. It’s not – the soul is; though it may be a contributory factor. Fires will always grow so long as there’s fuel but the size and growth of all naturally composed (i.e. living) things is limited and defined: this is the job of the soul not the fire, of defining characteristics not matter.
We must imagine Aristotle sitting in front of a hearth (as Heraclitus was said to do), staring into the fire, occasionally poking it, thinking about the fire that rages inside him, that keeps him alive, that permits his thoughts to flow apparently without cease, devouring the world. ‘Fire is always coming into being and flowing like a river’ – how very true. But no fire can rage unchecked for ever lest it consume itself. All fires must be fuelled, stoked, damped – regulated – if the tenuous flame of existence is to be maintained. That, too, is the work of the soul.
LVIII
ARISTOTLE SAYS THAT tortoises hiss, copulate and have shells. They also have large lungs, small spleens, simple stomachs and a bladder; male tortoises have internal testes and seminal ducts that converge in an ‘organ’. So he evidently dissected one. At least one tortoise came under his knife while still alive for he also says that if you cut out a tortoise’s heart and then put its shell back on it will keep wiggling its legs. Aristotle doesn’t have pets: he has specimens.
He vivisected with an enthusiasm that is no longer fashionable. ‘After being cut open along its entire length, it’ – the chameleon – ‘continues to breathe for a long time.’ Insects, too, seem to be able to survive being cut in half for a surprisingly long time. (He appears to assume, no doubt correctly, that his readers know that chickens, goats, dogs and men do not live for long without their hearts.) It all seems rather brutal, but these observations are carefully considered, for when Aristotle vivisects he’s after the seat of the soul.
Where is the soul located? The Aristotelian answer is ‘everywhere’ and ‘nowhere’. A creature’s soul is, after all, not a physical object but the sum of its functional features. That truism, however, does not preclude the possibility that some organ or other is particularly important in its regulatory functions. In blooded animals – vertebrates – Aristotle supposes that organ is the heart.
This may strike us as an odd choice: why not the brain? But that’s easily answered: the soul’s first job is nutrition, and that’s obviously no job for the brain. Very well – but what has the heart to do with nutrition? Everything, replies Aristotle. This is where his physiology becomes strange. To be sure, insofar as nutrition is carried in the blood, the cardio vascular system must somehow be involved, but Aristotle puts the heart front and centre in his nutritional physiology. He thinks that it is the main site of concoction; in fact the ‘boiling’ action of concoction is what keeps the heart in motion. The heart is the main site of concoction because it is also the site of the ‘internal fire’. We think that it’s a pump; he thinks it’s a chemical reactor. He calls it the ‘citadel of the body’ and says it has ‘supreme control’.
KHELŌNĒ – TORTOISE – TESTUDO SP. LONGITUDINAL SECTION
Of course, not all animals have blood. But at least some bloodless animals have something like blood and something like a heart too. That is why he’s so quick to misidentify the cuttlefish’s mytis as a heart-analogue. He does not, however, make the mistake of applying his cardiocentric model of the soul to all animals. Since certain insects continue moving ‘when divided into parts’ it follows that each body part must have ‘all the parts of the soul’. All the parts? That seems like an exaggeration, though the ability of, say, a male praying mantis to continue coitus even as his mate chews off his head makes the point. In fact, he is probably thinking of centipedes and millipedes since he says that they’re like ‘concretions of many animals’. All this vivisection leads Aristotle to conclude that plants, insects, reptiles and mammals have successively more centralized souls. He thinks that centralized souls are ‘better’ than distributed ones. It was during these investigations that he vivisected a tortoise. I haven’t repeated Aristotle’s observation, but one unusually empirically minded philosopher says he has. He claims to have obtained Aristotle’s result too even though he didn’t really follow his protocol, having first compassionately decapitated his terrapin.
LIX
AESCHYLUS WAS VISITING Sicily when an eagle, mistaking his bald head for a rock, dropped a tortoise on it and killed him. The tortoise probably died too since the only part of the story that’s certainly true is that golden eagles do seize tortoises, carry them aloft and release them in order to crack them open like nuts. Neither the playwright nor the tortoise matters here; one is only an accidental anvil and the other is food; the interest of the story is how the eagle accomplished this feat.
A neurophysiologist, sketching the mechanisms involved, would describe a causal chain that begins with a goal (bodily maintenance), that requires an ‘appetitive motivational drive’ (hunger), perception (of the tortoise and Aeschylus’ head), a variety of computations (how and when to seize, carry and drop the tortoise) and motor-responses to execute them by. He would say that the physiology underlying some of these processes is well understood, that some of them are obscure, and that how it all works together is quite unknown. He would point out that we struggle to give a computational model of a worm wriggling across a petri dish never mind an eagle on the hunt.
Aristotle also attempts a mechanistic explanation of animals in motion. He sketches how the senses work, how they transmit information to the sensorium, how this information is integrated with respect to the animal’s goals and how it is transformed into mechanical action in its limbs. This system has even been given (by two classical philosophers) a very scientific-sounding acronym, the CIOM model, which stands for Centralized Incoming Outgoing Motions. Aristotle simply calls
it the sensitive soul. By any name its anatomy is hazy, its physiology wrong, but its structure percipient.
Perception obviously requires the transmission of information about the world from the world to within an animal. As Aristotle puts it, perception is the transmission of an object’s form without its matter. This process begins with the five senses: sight, smell, taste, hearing, touch and their respective organs. He assumes that perception involves a qualitative change in a sense organ. That implies that the perceived object must make contact with it.
It’s easy to see how contact-dependent change works in touch, taste, hearing and, perhaps, smell. Vision is trickier. Empedocles and Plato argued that the eyes contain a fire and that light rays from this fire travel to the object of sight. Aristotle trenchantly points out that if this torch-beam theory were true, we’d be able to see in the dark. We might reasonably assume that his own theory of light is merely the reverse: that light rays emanate from some source and enter our eyes where they effect some change. That, however, is Newton, not Aristotle.
Aristotle supposes that some media – air and water – have the property of being either opaque or transparent. When such a medium is exposed to the sun or a fire it becomes transparent. Light, then, is not a ray, a wave or a particle, but a quality, an actualization of a potential. When we look at an object through a transparent medium, its shape and colours initiate movements in the medium that travel to our eyeballs where they effect a change.
The Lagoon Page 17
