The Lagoon

by Armand Marie Leroi

  Cockles, clams, razorfish and scallops generate spontaneously on sandy bottoms; oysters grow in slime; the pinna in sand and slime; ascidians, limpets, nēreitēs (a snail, probably Monodonta), sea anemones and sponges on rocks; hermit crabs come from soil. In Cnidos there’s a kind of mullet that springs from sand or mud, as do some kind of small fry. Fish lice are generated from the slime of fish. Worms (helminthes) generate spontaneously in our guts. Insects and suchlike seemingly generate spontaneously everywhere: fleas are produced in putrefying matter; lice in the flesh of animals; ticks in couch grass; cockchafers and flies in dung;* horseflies from timber; pseudoscorpions in books; clothes moths in clothes. Other insects come from the morning dew on leaves. Fig wasps are generated spontaneously in figs. Every conceivable habitat, it seems, produces its own form of life. When Aristotle begins to talk about spontaneous generation, it becomes apparent that he thinks that the inanimate world is endlessly fecund.

  He does not ask his readers to accept this vision at face value, but provides evidence for it. A naval squadron, he says, once anchored off Rhodos and a lot of earthenware was thrown overboard. The pots collected mud and then living oysters. Since oysters can’t move on to pots, or indeed anywhere, they must have arisen from the mud. He has another oyster anecdote. Some Chians once transported a lot of oysters from the Lagoon at Pyrrha to their island south of Lesbos, and deposited them in a strait ‘where the currents meet’. The oysters grew in size, but did not multiply.

  The argument has a lovely symmetry: first he shows that oysters can appear without reproduction; then he shows that they don’t reproduce; and then he explains away the structures that less scientific thinkers believe are their reproductive organs.

  But, as Thomas Kuhn was so fond of reminding us, empirical evidence, no matter how good, is never decisive when big scientific issues are at stake – you also need a new theory. Aristotle apparently feels this tension too. (In The Heavens he remarks, ‘It is, however, wrong to remove the foundations of a science unless you can replace them with something more convincing.’) Here he addresses the problem by giving a recipe for making an oyster. Place water (seawater is especially good) and earthy material in a cavity of some sort, mix, heat with pneuma (abundant in seawater) or else place in the sun. The mixture will concoct and then foam. Some putrefied residue will form – a by-product of the concoction. After a while, earthy material will begin to congeal and form the shell; the living material will be inside. Life: it’s as simple as that.

  Most of Aristotle’s spontaneous generators are bloodless animals, invertebrates. There’s one spectacular creature, however, whose reproductive organs he does not have to argue away for it does not have any. ‘The eel’, says Aristotle in Book IV of Historia animalium, ‘is neither male nor female and produces no offspring.’ In Book VI he adds: ‘eels do not come into being by copulation nor do they lay eggs’. These two sentences contain four factual claims, all of them wrong. Contra Aristotle, eels are either male or female, do pair, do lay eggs and do produce offspring. Nor does this exhaust the list of Aristotle’s errors about the eel; in fact, he got little right about them. For all that, when zoologists consider Aristotle on eels, they have tended to the charitable. That is because he is the Ur-Hero of one of their greatest quests. He showed them that the eel was a problem.

  The problem is that eels don’t have gonads. Cut an eel open, says Aristotle, and you never find milt or eggs. In this he’s perfectly correct – at least in Greek waters. Where the gonads of fish are generally filled with semen or eggs, the eel’s are generally not. Aristotle’s response is to add the eel to his list of spontaneous generators. He has, of course, to consider rival theories. One turned on the shape of the eel’s head. Some eels have broad heads that give them a vaguely frog-like aspect; others have delicately narrow snouts, and some people evidently thought that the dimorphism was sexual. Aristotle disposes of this briskly: ‘One difference between male and female eels, so people claim, is that the male’s head is larger and longer, the female’s smaller and more snub-nosed. But what they are talking about is a difference not of gender but of kind [genos].’* And then there were those who claimed that eels are viviparous. For these theorists he has only scorn: ‘People say that eels can occasionally be seen with what looks like hair, worms or sea-weed attached to them. These are ill-considered claims resulting from observational failure.’

  His own solution is an account of the eel’s ontogeny. They are, he says, generated from the gēs entera, the ‘guts of the earth’, a sort of worm that grows near the edges of rivers and marshes where there is plenty of sunbaked putrefying matter. The gēs entera are the mothers or hosts of the infant eels – Aristotle is not very clear; at any rate if you open one you will sometimes find small eels inside. It’s an ingenious and wholly specious theory. He’s probably talking about burrowing arenicolid worms; their casts litter beaches and mudflats and do, indeed, look like small heaps of coiled intestines.* I suppose that the gēs entera are an attempt to make sense of eels. Many of the other marine spontaneous generators (clams, oysters, snails, sponges, etc.) are, in his view, very simple animals; he often compares them to plants. An eel is nothing like a plant: it’s a large, fiercely active, blooded predator, and there are lots of them. Aristotle was bold; but even he baulked at manufacturing a major fishery of metre-long animals annually out of mud, and so he gave them a larva.

  LXXVII

  ARISTOTLE’S THEORY OF spontaneous generation had a baleful effect on early modern science. Descartes, Liceti, even Harvey, were all in its thrall. Van Helmont, no fool, reported spontaneous generation of mice from a mixture of rags and wheat. The theory’s fall was, oddly, precipitated by a passage from Homer. There has been a battle and corpses litter the ground. Achilles weeps by the remains of his friend Patroclus, and implores his mother, the nymph Thetis of the silver feet:

  But I am very much afraid that the flies might in the meantime alight on the open wounds of Patroclus and breed worms in them. Then his corpse will be defiled, for there is no life left in him, and his flesh will rot.

  Francesco Redi, who had learnt his Aristotle at Pisa, read Iliad XIX and wondered whether Homer might have been right after all. The experiments that he carried out in the laboratories of Ferdinand II, Archduke of Tuscany, were simple and convincing. He placed into separate flasks, dead snakes, some river fish, eels from the Arno and slices of veal. Some flasks he sealed with paper or else a kind of fine muslin called velo di Napoli; others, the controls, he left open. The open flasks generated swarms of flies; the sealed ones did not. He followed the fly through the course of its life cycle and published his results, in 1668, in a work titled Esperienze intorno alla generazione degli insetti – ‘Experiments on the Generation of Insects’.

  Leeuwenhoek took care of the oyster. In 1695 he bought a bushel of the animals at Zierikzee in the Zeeland deltas. Wielding his microscope, he cracked open their shells, peered into their mantle cavities and described the oyster’s sperm and eggs. He also found thousands of veliger larvae complete with embryonic shells. He does not name Aristotle, but reserves his ire for contemporaries: ‘I place these observations before the world thus stopping the mouths of those pig-headed fellows who still pretend that Shellfishes are generated spontaneously from mud.’ Leeuwenhoek also saw the deeper problem with spontaneous generation. In an unconscious echo of the Iliad he wrote: ‘For if from exhalations there come forth Animals, why is it that after a Battle in which fifty thousand men and more are defeated, who are left putrefying in the Field, there do not come forth a great many young children or Adults, or something resembling a Human Being or a Horse, for while in a Battle many Men are defeated, many Horses are also killed.’ Once you allow that some animals can arise spontaneously, why not all?

  More than a century later, biologists sieving Europe’s coastal waters with nets of silk found the larvae of Aristotle’s remaining ostrakoderma in the plankton. In 1826 John Vaughan Thompson identified the cyprid larva of a barnacle in Cork
Harbour; in 1846 Johannes Müller fished the strange Pluteus paradoxus from the German Bight and watched it transform into a sea urchin; in 1866 Anton Kowalevsky discovered the tadpole larva of a sea squirt in the Bay of Naples. The larvae themselves are exquisite. At 100 diameters magnification they look like machines made of Venetian glass. Their discovery changed the order of nature. Where Aristotle thought that the sea squirt was the lowliest of animals, Kowalevsky’s discovery that its larva had gill slits, a dorsal nerve cord and a notochord showed that it was chordate. Far from arising from rock slime, the sea squirt was our close relation.

  By the early nineteenth century most animals had been removed from the roll call of spontaneous generators. Not all, for parasitic worms, with their opaquely complex life cycles, were still on it. Microbes remained suspect until Pasteur’s experiments of 1859. In Northern Europe, popular belief in the eel’s spontaneous origins persisted until the end of the seventeenth century.

  In Greece it still does. We were long-lining for eels at the Vouváris’ mouth when Dimitris, who knew that I was interested in that sort of thing, mentioned that scientists do not know where the eel comes from, but that it grows out of mud. This seemed to be based on local lore and personal observation rather than reading Aristotle. Of course, scientists do know where the eel comes from. And it was Redi who described what Aristotle only hints, that the eel is a migratory fish. Adults live in rivers and lakes, sometimes for many years, migrate down to the sea, embark on an obscure voyage, reproduce and die. Their progeny then return as glass eels which, between January and April, invade European estuaries by the millions en route to the rivers that their parents came from.

  And yet the eel’s gonads remained missing. Some thought, contra Aristotle, that the eel was viviparous. Leeuwenhoek claimed that he’d found an eel’s womb full of young eels ready to be born. In fact he’d found an eel’s bladder full of parasitic nematodes. In 1777 Carlo Mondini, professor at Bologna, finally identified the ovary of the eel. It proved to be a frilled ribbon of tissue that runs the length of the animal and that had previously been mistaken for fat. The testes were more elusive; they were found by Simon Syrski at Trieste only in 1874. It is easy to see why Aristotle missed them: the gonads of both sexes are more or less empty until the eel is well at sea. (Even now, few gravid animals have been caught; one was taken from the stomach of a mid-Atlantic sperm whale.) Aristotle did not know that; but then neither did Sigmund Freud who, as a twenty-year-old research student, dissected 400 eels in a search for their sperm, failed to find them and then turned his mind to more tractable problems. Some years later Grassi and Calandruccio working at Messina showed that the weird pelagic leptocephalus was the eel’s true larva. It was only in 1922 that Johannes Schmidt sailing in the Dana finally located where the eel mates, dies and comes to be: 22° 30’ N, 48° 65’ W, the Sargasso Sea.

  LXXVIII

  ARISTOTLE’S LOVE OF spontaneous generation seems perverse. We can hardly censure him for not knowing where eels spawn, or for not having seen the oyster’s larva, but why does he think that flies are spontaneously generated? After all, he knows that flies copulate and engender maggots and also knows that maggots develop into flies. The conclusion is – or should have been – obvious. Even Homer understood it. Yet he resists it, and so fails to give the fly the life cycle it manifestly has.

  The inconsistencies are not just empirical. Spontaneous generation also runs against the grain of some of his deepest theory. For Aristotle, order does not, cannot, depend on the properties of matter alone but also requires a formal cause. A sexually reproducing animal gets its form from its paternal parent; form is the information that shapes the dynamic organization of the soul. But spontaneous generators, by definition, lack parents. So how do they come to be? Does a snail not have a soul?

  Aristotle’s recipe for a spontaneous generator is evidently an attempt to solve, or at least paper over, some of these problems. It’s obviously based on his model of sexual reproduction. There’s a substrate (a material cause) analogous to the mother’s menses; there’s a source of movement (an efficient cause), a source of soul-heat analogous to the pneuma in semen; there’s concoction, foam, and the emergence of order and life. It is an explanation, but a very thin one. In the absence of a father, what ensures that a particular form of animal will be produced, an oyster, say, rather than a clam? Why are there so many different kinds of spontaneous generators?

  Aristotle’s answer isn’t very clear, but specificity somehow depends on the exact mix of ingredients. That’s why he is at such pains to tells us the exact kind of habitat in which each of his spontaneous generators can be found: the larva of the dung fly, myia, comes from dung, but the larva of the horse fly, myōps, comes from timber. It also has to do with the shape of the cavity in which the cooking takes place. Together, these variables determine how ‘honourable’ – he means roughly how ‘complex’ – a creature will emerge from a given reaction. But, since the raw materials are collectively ubiquitous, it seems likely that life will emerge anywhere; indeed, as he blandly assures us, ‘in a way, all things are full of soul’.

  It’s a wonder that he finds this account convincing. It is scarcely different from the materialist theories that he so dislikes and it shares all their flaws. In Physics II, 8 Aristotle insists that spontaneous events do not ‘normally come about in a given way’ – they’re unusual, even rare. Yet oysters, clams, flies and fleas are among the most abundant animals that he knows; how, then, can they be the product of spontaneous events? Aristotle also insists that spontaneous events do not have goals, but only appear to. Yet, by his own account, spontaneous generators have – reproductive parts aside – the same sort of organs that sexual animals do. An eel may not participate in eternity, yet it is otherwise as much a teleological construct as a sardine: they both have mouths, stomachs, gills and fins that they use in exactly the same way. Having brought forms down from their Platonic realm, and having made them the centrepiece of his theory of inheritance and ontogeny, he then apparently discards them. And he does so because he cannot work out where eels keep their gonads and how oysters mate.

  And so puzzle remains. Aristotle believes in spontaneous generation even though the animals that he knows best all have parents. He believes it even when his own data on particular animals – those pesky flies – point the other way. He believes it even though to make it work he has to distort his own – brilliant – theory of development. He believes it even though it contradicts his metaphysics and gives the game, the hard-fought game, to his materialist opponents. He believes it even though there’s a simple alternative explanation ready to hand. So why does he believe it?

  The beliefs of any scientist depend at once on the theories he inherits from his predecessors, the theories he formulates for himself and the evidence of his own eyes. Aristotle does not tell us where he got the theory of spontaneous generation from, but it was certainly a commonplace in his day. Theophrastus says that many of the physiologoi, Anaxagoras and Diogenes among them, thought it was true. It was likely wrapped up with origin-of-life theories.

  A passage in the Problems, a pseudo-Aristotelian text, makes the connection explicit. The author, probably one of Aristotle’s students, is wondering why some animals generate spontaneously while others need sex to do so. He starts by asserting that all animal kinds ultimately originated from the ‘compounding of certain elements’. But, he continues, as the physiologoi have explained, a full-scale zoogony requires ‘powerful changes and movements’. We are, evidently, to imagine large-scale chemical turmoil of the sort present when the cosmos was young. (Prebiotic-soup scenarios of belching volcanoes and flashing lightning bolts spring irresistibly to mind.) These days, however, things are calmer, so the only animals spontaneously generated are small; big ones have to reproduce sexually.

  The average Greek certainly didn’t need elaborate theories of that sort. Popular belief held that the cicada was spontaneously generated from soil; as a mark of their autochthony Athenia
n girls wore golden cicadas in their hair. Then, too, bread, meat, wine, wood, cloth – almost any organic substrate at all – will, if left unattended for long enough, spring to life and produce seething swarms of animals. Even a tub of water will develop an ecology. What could be more natural than to suppose that the creatures originated there? Even cautious Theophrastus admits that some plants really do spontaneously generate.

  It can’t be that Aristotle’s love of spontaneous generation is just relict popular or Pre-Socratic belief. He’s usually so quick to correct his predecessors and so scornful when he does. Still, intellectual inertia can’t be completely discounted either. Perhaps what happened was this. Aristotle, beginning, as he always does, with popular belief and expert opinion (but ignoring Homer) holds that some animal kinds are spontaneous generators. It is, for them, his null hypothesis. He then begins to investigate them, accumulating evidence that will tell either for or against the idea. He takes an empirical stance, refusing to believe that an animal has a complete life cycle unless he’s seen the whole thing. For example, he says that some writers assert that all grey mullets are spontaneous generators, but that this is empirically wrong – only one is. He does not consider that spontaneous generators are the product of invisible seeds since he’s generally sceptical about the existence of microscopic objects such as atoms. He develops an explanation for spontaneous generators that is as consistent as possible with his model of sexual generation and simply elides its difficulties. He retains the Pre-Socratic epithet ‘spontaneous’ for generation of this sort even though his own definition of spontaneous events, given in the Physics, is much more restricted. Here, as so often, he uses a single term in several quite different senses and forgets to tell us which usage he is employing.