The Lagoon Page 9
Aristotle can think of several reasons why not. But, to understand them, it’s necessary to have Aristotle’s version of selection clearly in mind. It probably isn’t Empedocles’, for the Sicilian’s extant verses tell only of recombination-selection events that occurred in some remote historical past; ever since then the forms of the survivors – the plants and animals we see – have been fixed. Aristotle, by contrast, supposes that selection is working today. But Aristotelian selection isn’t Darwin’s either; it’s much more radical. Darwinian natural selection supposes that organisms have a system of inheritance that transmits their features more or less intact from one generation to the next, that the inherited material varies slightly nevertheless, and that this subtle variation is the substrate for natural selection. Aristotelian–Empedoclean selection, however, assumes that every individual forms itself de novo by a variational-selection mechanism. The womb contains, as it were, a formless soup from which selection produces a child complete with teeth. Aristotle, in short, turns a cosmological model into an embryological one.
Which he demolishes with ease. His arguments are fascinating, for some of them have been used against the theory of evolution by natural selection. (1) Spontaneous events are rare, but the signature of genuinely purposeful events is that they are common: teeth always come up in exactly the same way. This is a probabilistic argument for the existence of a purposeful agent and, like all such arguments, it is wrong, for selection can regularly produce order from disorder.* Admittedly, Empedocles helps Aristotle to this conclusion by making his cosmogonies indeterminate: ‘[sometimes] it may happen to run one way, but often it ran otherwise’ – the line is quoted by Aristotle. (2) It’s not just the end of development that has the appearance of purpose; it’s also the process. Every step in development is obviously directed towards a final goal, rather like each step in the construction of a house. These steps must be the product of an intelligence that has the final product in mind. (3) Although development is very regular, mistakes do happen (in The Generation of Animals he has a lot to say about conjoined twins and dwarfs), but they are mistakes – deviations from some existing, purposeful programme that must be already in place. Indeed, even Empedocles’ original recombinant animals could not have come from nothing; they must have sprung from ‘some corruption of some principle corresponding to what is now the seed’. (4) Besides, we simply don’t see that much variation. Granted, monstrous progeny sometimes appear, some perhaps even as monstrous as Empedocles’ man-headed calf, but why don’t we see the same thing in plants, an olive-headed vine sapling, say? ‘An absurd suggestion’ – and one wishes that one could have shown him a homeotic mutant flower. (5) Organisms inherit their forms from their parents. A given seed doesn’t develop into any creature, but rather into a specific one: a cicada, a horse or a man. Selectionism can’t do that. Aristotle’s right – his version of it can’t.
The heart of Aristotle’s rejection of materialism is his conviction that the cosmos, and the creatures it contains, have order and purpose. His dismissal of Democritus’ conviction that order can simply arise spontaneously is, perhaps, understandable. His objection to Empedocles is less certain, for selection – even non-Darwinian selection – can bring about order from disorder; it is, indeed, the only known naturalistic explanation for it. Aristotle seems to have painted himself into a corner. Where, then, does order come from? And what is its purpose?
XXXI
SPEAKING OF THE physiologoi, Aristotle concedes that one of them wasn’t completely clueless. ‘Whoever said that, in nature as in animals, mind was present as the cause of all order and arrangement appeared like a sober man compared to the random utterances of those before him.’ The object of this backhanded compliment was Anaxagoras of Clazomenae (c. 500–428 BC). In Anaxagoras’ cosmology, for he too had one, the cosmos began with a mixture of various kinds of eternally existing matter. This mixture was set in motion by the action of nous – ‘Intelligence’ – so that a partial separation of ingredients occurred to give the various kinds of matter that we see. The fragments do not tell us what the ingredients were, the recipes for any existing matter or the source of the Intelligence; but it seems that Anaxagoras’ Intelligence was not so much a designer as the cosmological mixer’s power source.
In Phaedo Socrates expresses his disappointment with this. Back in the day, he says, when he was still interested in natural science, hearing that Anaxagoras had made Intelligence the order and cause of things, he had hoped that he, Anaxagoras, would also explain why things were arranged as they were, why indeed they were arranged for the best. But then he bought Anaxagoras’ books and found that ‘the fellow made no use of Intelligence and assigned to it no causality for the order of the world, but adduced to it causes like air and aithēr and water and many other absurdities’.
That’s just the sort of reaction we expect from Socrates. Unexpectedly, Aristotle has much the same complaint. For, a few pages after complimenting Anaxagoras on his invocation of Intelligence, Aristotle retracts and accuses him of using Intelligence as a deus ex machina, dragging it in only when he’s at a loss, and generally explaining events by appealing to all sorts of other causes. The problem is not that Anaxagoras invokes Intelligence; the problem is that he doesn’t give it full rein. When we find Socrates–Plato and Aristotle, the first so hostile to science, the other so utterly committed to it, united in their disparagement of a third (or is it a fourth?) philosopher, we can be sure that we have found a deep connection between them. And so it proves. For Aristotle’s conviction that the cosmos must be explained in terms of goals or ends is one that he learnt at Plato’s knee.
Explanations that appeal to goals, or purposes, or final causes are known as ‘teleological’ explanations. The word is derived from telos – ‘end’ – and was coined in 1728 by the German philosopher Christian Wolff. The perennial fascination of teleological explanations is that, in attributing purpose to the world, they appear to demand the existence of purposeful agents; indeed, the phenomena they explain become evidence that such agents exist. It was for that reason that William Paley in his Natural Theology (1802) limned the functional perfection of the eyelid:
Of the superficial parts of the animal frame, I know none which, in its office and structure, is more deserving of attention than the eyelid. It defends the eye; it wipes it; it closes it in sleep. Are there, in any work of art whatever, purposes more evident than those which this organ fulfils? or an apparatus for executing those purposes more intelligible, more appropriate, or more mechanical?
And for that same reason Socrates did too:
And besides all this, do you not think this looks like a matter of foresight, this closing of the delicate orbs of sight with eyelids as with folding doors, which, when there is need to use them for any purpose, can be thrown wide open and firmly closed again in sleep?
Socrates goes on to argue that the foresight and purpose manifest in the eyelid comes from God, ‘a wise artificer full of love for all living things’. It is the first appearance in history of the Argument from Design, the argument upon which Paley’s Natural Theology and The Bridgewater Treatises (1833–40) depend. It is a gesture towards the sort of account that Socrates sought from Anaxagoras and the other physiologoi, one that would lead him from the phenomenal world to the beautiful and the good and the Divine. It is almost certainly Socrates’ argument, for it appears in Xenophon’s Memorabilia rather than in Plato’s works. But if Socrates merely gestured towards an account of the world, Plato wrote one – or something that looks like one.
The Timaeus may be a ‘myth’, but it is a myth written by Plato and so, between the jokes and the moralizing, pullulates with ideas. Of course Genesis and the Rig Veda contain ideas too, and those in The Timaeus would be as irrelevant to the history of science as theirs are, were it not that Aristotle read The Timaeus and transmuted its conceptual lead into the gold of scientific explanation.
The myth that Plato tells is one of intelligent design. The cosmos an
d its creatures exist and are beautiful because a divine craftsman, the Dēmiourgos, made them so. Plato, no zoologist, mentions only six kinds of living things: the heavenly gods (a.k.a. stars and planets), humans, land animals, birds, fish and shellfish. Even so, he has a good deal to say about how and why the Dēmiourgos made them as he did.
His account of our digestive tract reveals the Dēmiourgos’ design priorities. Our intestines are, Plato says, looped into coils to ensure that nourishment does not pass through them too quickly. The coils, therefore, restrict how much food we can eat. That’s good, because when we eat we become ‘deaf to the command of the divinest part of our nature’ – we literally stuff ourselves silly – and so cannot think, and that’s bad. Philosophy, it seems, begins in our bowels.
The Dēmiourgos is also remarkably farsighted. Plato explains that we have fingernails ‘for our framers knew that some day men would pass into women and also into beasts, and that many creatures would need nails (claws and hoofs) for many purposes; hence they designed the rudiments of this growth from the very birth of mankind’. One is tempted to suppose that Plato is thinking of evolution here, and that fingernails are pre-adaptations for claws. That would make this a weird but interesting passage; in fact, it’s weird but boring. It’s just another of his transmutationist bizarreries, rather like the one that has astronomers becoming birds.
It’s not that there aren’t some interesting ideas in The Timaeus. Aristotle uses many of them in his zoology. But Plato, characteristically, does not think that we should accept his divine teleology on its scientific merits. In Laws he explains that materialism – the materialism of Empedocles and Democritus – is malignant, for, dispensing with divine purpose, it leads to atheism and so social disorder. There’s a moral sting in every Platonic tale.
XXXII
UPON PLATO’S UNNATURAL teleology Aristotle built a functional biology. When Aristotle invokes a teleological explanation, he often uses the phrase to hou heneka – ‘that for the sake of which’ – or a grammatical variant thereof. He gives a crisp definition of the term in The Parts of Animals: ‘We all say x is for the sake of something when some movement is unimpeded in its progress towards an apparent goal.’ He identifies this teleological impulse with natures, the internal principle of change, and then goes on to give a concrete example, the development of a horse. Thus, he is saying: when we see processes that, by their nature, are directed towards an end (for example, the development of a horse from its parent’s seed into a foal and finally an adult), then we should explain that process in term of ‘this is for the sake of that’, where ‘this’ is some feature of the animal, and ‘that’ is the adult animal itself.
Aristotle was deeply impressed by the resemblance between organisms and artefacts, particularly machines. In passage after passage he draws on axes, beds, houses and, more mysteriously, automata to explain and elucidate various features of animal life. Sometimes they provide mechanical models for explaining how animals work. In The Movement of Animals he compares the workings of a limb to those of a puppet. But Aristotle’s real interest in comparing organisms and artefacts is that both of them ‘come to be’: they grow or are made. And both bear the stamp of design.
This talk of artefacts is all very Platonic. And it may seem that Aristotle, too, is working his way towards an intelligent designer. Yet repeatedly and decisively he denies that there is a divine craftsman who made it all. There’s no room for a Dēmiourgos in Aristotle’s cosmos because it was not made; it’s always been there. Besides, a craftsman isn’t needed. Consider, he says, the apparently purposeful actions of animals: the way a spider weaves its web or a swallow makes its nest. Some people suppose that this ability must make them as intelligent as human craftsmen. But that clearly isn’t so for even plants, devoid of intelligence, show purpose in how they grow. In the same way the various parts of organisms may look as if they have been designed by an ingenious external mind, but they have not: each animal and plant is the result of its very own nature; each living thing crafts and maintains itself, like a doctor doctoring himself.
Aristotle denies that Plato ever used ‘that for the sake of which’-type explanations. This is odd. The Timaeus seems to be full of them and Plato even used the phrase. Perhaps Aristotle thought that his kind of teleology was very different from Plato’s. It is. In The Timaeus Plato gave a teleological explanation for the coils of the intestinal tract and in The Parts of Animals Aristotle gives one too; the explanations are related, for both argue that intestinal morphology regulates appetite; but where Plato explains that human gut is designed just so by a divine craftsman to make sure that we philosophize, this is what Aristotle has to say:
When feeding, some animals require greater moderation (i.e. they do not have a space in the lower stomach, nor a straight gut, but many spirals). Space creates desire for bulk. Straightness speeds up desire. Such animals end up gluttonous in either speed or quantity.
No divine philosophy-loving craftsman there; just comparative digestive physiology.
Such examples could be multiplied – The Parts of Animals is full of them. ‘Every part of the body is for some action: so what the body as a composite whole is for is a multifaceted action.’ And although Aristotle’s explorations of these profound truths are delightfully detailed and endlessly ingenious it appears that he has impaled himself on the horns of a dilemma. He sees, as Socrates and Plato did before him, the evidence of purpose writ across the face of the world; sees too that material forces alone cannot explain it, but refuses to yield to the expedient of a cosmic designer. So the question remains: from where do plan and purpose in nature come? Aristotle’s answer to this question is brilliantly subversive. He appropriates another of Plato’s doctrines, one that underpins his, Plato’s, entire ontology and epistemology, one that is indeed the very mainspring of his contempt for the perceptible world, destroys it, rebuilds it and turns it to the service of science. There is much to dislike in Plato: his anti-science, his totalitarianism and the seductive charm of his prose; but to his credit let this be said: he taught Aristotle.
XXXIII
COMING ON THE heels of Democritus’ atomic cosmology, Plato’s creationism may seem like a throwback to the naive natural theology of Hesiod’s Theogony. And so it would be had not Plato underpinned it with a whole new ontology. Seeking a source of stability in a shifting, mutable world, Plato argued that the physical entities that we see are but imperfect copies of abstract, immaterial entities that he called Forms. It is an obscure doctrine, but if we think of Forms as blueprints in the mind of God we will approach, perhaps, what he had in mind. The entire cosmos is but a copy of a Form. In The Timaeus, Plato calls its original the ‘Intelligible Living Creature’, a title that reflects his conviction that the cosmos is alive. This ultimate Form contains within it countless subordinate Forms, the blueprints for all the objects that the cosmos contains. Beds, birds and men are all but hazy reflections of unseen ideals.
Plato’s theory of Forms is the ancestor of all species of idealism. Modern scientists are generally realists and so will find it incomprehensible or bizarre. So did Aristotle. He wanted to explain the features of the physical world. But, if Forms are eternal and static how then, he asks, can they actually do anything? And what does it mean to say that the physical world ‘participates’ in the world of Forms? And if a Form is merely a mental conception, then does not any one physical object have as many Forms as ways that you can think about it? And if a Form exists for any given physical object, say Socrates, then why should there not be two, three or an infinite number of copies of Socrates walking about? Platonic Forms, he concludes, are merely empty words and poetical metaphors. They annihilate the study of nature.
It is all the more remarkable, then, that this unpromising theory was the source of one of Aristotle’s deepest ideas. For Aristotle believes that the nature of a living thing, or at least the most important part of it, is in fact its form – if not its Form. The term he uses for ‘form’ is the term th
at Plato used, eidos. It is one of the most vital organs of his thought.
Aristotle holds that any sensible object is a compound of form (eidos) and matter (hylē). One can speak of ‘form’ and ‘matter’ in the abstract, but in practice they’re actually inseparable. To explain what he means Aristotle appeals to various metaphors. If wax is hylē, then eidos is the impression made in it by a signet ring. In its most general sense, eidos is the way in which matter is structured to make the things we see. That seems fairly clear. However, when he applies the term to the world of living things, he uses it in several distinct, but related, senses.
The first biological sense in which Aristotle uses eidos is close to the English meaning of ‘form’ – as the appearance of an animal. His word for a taxon of animals is genos (pl. genē) – which I translate as ‘kind’. Some genē are small – the sparrow kind; others are large – the bird kind. So when he wants to describe the features that make a sparrow a sparrow rather than a crane, or a bird a bird rather than a fish, he speaks of its eidos.
When using eidos in this sense Aristotle usually speaks of forms within a kind: ‘There are many eidē of fishes and birds.’ Which brings us to the second sense of eidos – as the fundamental unit of biodiversity, that is, close to what we mean by ‘species’. Indeed, the traditional Latin translation of eidos is precisely species, just as genus is of genos.* One could, then, rewrite the above passage as: ‘There are many species of fishes and birds.’
The ambiguity is problematic. To say that there are many different species of birds or fishes is a much richer claim than saying that they come in many forms, and it’s often hard to know which of these Aristotle means. Older translations of the biological works often simply use ‘species’ for eidos. Read William Ogle’s de Partibus animalium (1882) or D’Arcy Thompson’s Historia animalium (1910) and it’s hard to resist the conclusion that Aristotle’s sense of the reality of species isn’t that different from Linnaeus’. These days most scholars agree that Aristotle rarely uses eidos in this second sense. Sometimes he’ll refer to an atomon eidos – an ‘indivisible form’ – as when he says that Callias and Socrates share an atomon eidos. He obviously doesn’t mean that they are identical, but that they have the same essential features. That seems to correspond to our ‘species’. But he names very few indivisible forms, among them, humans and horses, sparrows and cranes.