The Lagoon

by Armand Marie Leroi

  Every definition is always universal; the physician does not prescribe what is healthy for some particular eye, but rather for every eye or for some determinate form of [afflicted] eye [italics mine].

  Yet there is a difference between Aristotle and the modern biologist. Aristotle is convinced that if you burrow deep enough you will actually be able to delineate stable classes of objects, indivisible forms – true species – that all share some unique, defining causal formula. We, too, are impressed by natural variety, but having seen so much more of it than he did, have surrendered to it completely. Our technology – DNA sequencing is just the latest – shows us that no two sticklebacks, no two cancers, no two people, not even ‘identical’ twins have exactly the same formula. This difference in view is profound, but in practice it doesn’t matter that much. For still we burrow and divide and seek the formulae of things, just as Aristotle did. And if, in our heart of hearts, we know that we’ll never reach that vein of pure causal ore, we also know that we’ll strike it rich on the way down.

  And that is the point. For all its limitations, Aristotle’s theory of demonstration is a genuine scientific method. It is part of ours. Scientists may quarrel about methodology but they also agree about a lot. They understand the domain of science: the kinds of things it investigates. They understand how it delimits things and problems and investigates them piecemeal rather than trying to study and answer everything. They understand the reciprocal role of theory and evidence and the distinction between hypothesis and fact. They understand that science begins with induction to give generalizations from observations and then deduction to give firm causal claims from generalizations. They understand that a scientific claim must be a logical one – and can recognize a logical argument when they hear one. They understand that some causal claims are strong, others weak – and that the trick is to tell them apart. That they understand all this is because Aristotle told them it was so.

  THE

  BIRD

  WINDS

  EPOPS – EURASIAN HOOPOE – UPAPA EPOPS

  XLV

  SEVENTY DAYS AFTER the winter solstice, some time in early March, the ornithiai anemoi, the bird winds, begin to blow. That is when the migrants begin to arrive in Lesbos. In the marshes and pools between Skala and the mouth of the Vouváris, where the Lagoon melds softly into the land, they flutter among the reeds and wade in the shallows, while far above the raptors stream over from Africa. Birders follow them in from Arlanda, Schiphol and Gatwick. They track the birds through telephoto lenses, quarrel like stilts and update their websites with sceptical precision (‘7 May: A common snipe, present at the salt works, and said to be present yesterday too, casts a shadow over yesterday’s claimed great snipe from these pools’). The island swarms with Aristotle’s birds. Here is his description of just one (though it is really a winter migrant): ‘The tyrannos is just a little bigger than a locust, its crest is the colour of sun shining through mist and it is, in every way, a beautiful and graceful little bird.’ That’s the goldcrest, Regulus cristatus, which lives in Lesbos’ pine forests.

  Perhaps, on spring days, when the olive groves at Pyrrha were red with anemones and Olymbos’ summit was swept clear, Aristotle went birding too. The beauty of birds lies in their lucidity. Fish lurk beneath the waves, mammals skulk in the woods, but the lives of birds are open to us. That, I believe, is why when Aristotle wants to explain ‘the more and the less’, the subtle variations in size and shape that kinds within greatest kinds show, it is of them that he often speaks.

  He begins by sorting his birds into groups: carnivorous birds, water birds, marsh birds and the like. These are not taxonomic groups – genē/kinds – but functional classes like the guilds of modern ecology. He explains the features of each class in terms of how the birds make their living. Carnivorous birds (eagles, hawks) have to find and overpower prey – and so have large talons, powerful wings, short necks and very good eyesight. Water birds (ducks, grebes) have to swim, reach down into the water and tear off water plants – and so have short legs and webbed feet rather like oars, long necks and flat bills. Marsh birds (herons, cranes, stilts) live in swamps and catch fish – and so have long legs, long necks and spear-like beaks. Small birds (finches) collect seeds or grasp mites – and so have small, hollow beaks. Some birds are powerful fliers so that they can migrate to distant lands.

  This is exactly where functional explanation in evolutionary biology begins. ‘Seeing this gradation and diversity of structure in one small, intimately related group of birds, one might really fancy that from an original paucity of birds in this archipelago, one species had been taken and modified for different ends.’ People who quote Darwin on the finches of the Galapagos archipelago are usually interested in the one species taken and modified. But forget about that and consider just the gradation and diversity of structure and then the different ends, the fact that one species of finch has a beak adapted to cracking tough, spiny-shelled seeds, another for delicately picking at tiny grains, another for poking holes in boobies to drink their blood, several for eating insects, that one has even taken to using cactus spines the better to winkle insects, woodpecker-like, from the bark of trees; consider all this and you have a thoroughly Aristotelian analysis.

  In The Parts of Animals Aristotle says that ‘nature makes instruments to fit the function, not the function to fit the instrument’. Of course this now seems trite. But it was he who first saw that a bird is not just a cabinet of parts, but a toolbox on the wing.

  XLVI

  WHAT IS IT for the sake of? To fully explain any natural phenomenon we must ask and answer four questions. But, Aristotle is clear, this question is the first. We should begin, as it were, with the end.

  In the best case, Aristotle asserts, individual organisms would be immortal. But, in fact, all individual organisms die. So they do the next best thing: they reproduce. To achieve this they need, in turn, body parts with which to eat, breathe, copulate and so on. His term for such a functional body part is organon from which our ‘organ’.

  Calling body parts ‘instruments’ may suggest that Aristotle’s much vaunted teleology is nothing more than naive functionalism of the Socratic/Platonic/Paleyite type: eyelids are ‘doors for the eyes’ – that sort of thing. He certainly gives plenty of explanations like that. He has the standard textbook list of basic animal capacities – nutrition, respiration, protection, locomotion, sensation – and he parcels out the organs among them, allowing that some do lots of things. Sometimes he finds this easy to do – a stomach is obviously for the sake of nutrition. Sometimes it’s harder – he’s uncertain what the spleen does or whether it does anything at all. Sometimes he thinks it’s easy when it’s not – he’s sure that he knows what the heart and brain do, but he really hasn’t a clue.

  But, right or wrong, this kind of general teleology is only a beginning, for Aristotle’s programme is much more searching and ambitious than anything that Socrates, Plato or Paley even dreamt of. He’s a comparative biologist; his real interest is specific teleology; he wants to know not only why this animal has that feature, but also why others haven’t. To answer this question, and the countless others like it, prompted by all the parts of all the animals in all the world, he devised a system of teleological principles and precepts. It’s the core of a system that has been used ever since. The Parts of Animals, then, is about why some animals fly, some swim and others walk; it’s about teeth and talons, jaws and claws, horns and hooves. It’s about birds and their wings, legs and beaks. And it’s also about the elephant’s nose.

  XLVII

  ‘THE ELEPHANT’S NOSE is unique among animals because of its length and extraordinary versatility.’ The elephant can use it like a hand. He can feed with it. He can defend himself with it. He can trumpet with it. He can even use it to uproot trees. Aristotle may never have seen an elephant, but he has a lot to say about its trunk.

  When Aristotle wants to explain why some animal has the particular features it has, he sometim
es appeals to its lifestyle – its habitat, diet and relations to other living things – in a word, its bios. That is how he explains birds in all their beauty. Occasionally he manages to peer beneath the waves too. ‘In marine animals you can also see many skilled activities [technika] in relation to their lifestyles, for the stories about the batrakhos and the narkē are true.’ He then tells how the frogfish conceals itself in the mud, rears its lure and vacuums up the fish that are drawn to it, and how the torpedo ray narcotizes its prey.

  In this spirit, when Aristotle explains the elephant’s remarkable nose, he also begins with its lifestyle. He thinks, only slightly erroneously, for elephants do love water, that it lives in swamps:

  NARKĒ –TORPEDO RAY – TORPEDO TORPEDO

  Divers, when they stay for a long time in water, provide themselves breathing equipment and use it to breathe in air from outside. Nature makes a similar mechanism for elephants in the length of their nostrils.

  Did ancient divers and ancient elephants really snorkel? I frankly doubted both claims. But D. L. Johnson, in a paper titled ‘Problems in the Land Vertebrate Zoogeography of Certain Islands and the Swimming Powers of Elephants’, reports that African elephants swim the Zambezi, that Asian elephants swim between islets off Sri Lanka and that they do so with a sort of porpoising motion while holding their trunks aloft. Their maximum velocity and range is 1.5 knots and twenty-six nautical miles. He adds that one rarely sees an elephant swimming because they usually do so at night. To silence doubters he supplies a blurry photo.

  The elephant’s swampy habitat doesn’t, however, entirely explain its trunk. Hippos, seals and crocodiles are at least as amphibious and they don’t have one. The elephant must face some unique problem to which a trunk is the best solution. It does. It’s not a single problem though, but rather a cluster of them. Not only is it swamp-bound but it also has to fulfil basic animal functions such as breathing, eating and protecting itself from predators, and it has to do these things while being constrained by other features. Aristotle’s complete explanation for the elephant’s trunk, then, begins with these functions and features and follows their consequences in intersecting causal chains.

  The elephant requires protection. From what Aristotle doesn’t say; presumably nothing less than a triple-tooth-rowed martikhōras can take it down. It defends itself by sheer bulk. That has consequences. Because it’s so big its legs must be thick. Thick legs make inflexible legs, and inflexible legs make the elephant rather slow. Perhaps that doesn’t matter so much on land, but the elephant lives in swamps. It occasionally finds itself in deep water, but can’t dash out to catch its breath, so there it is, wallowing in Indus mire, in mortal danger of drowning. At least it would be had not nature, providentially, given it a snorkel.*

  Aristotle calls this kind of explanation ‘conditional necessity’. It is a principle of the following sort: given some goal, X, and some instrument, Y, for the sake of X, then condition Z is a necessary for Y to fulfil X. The example he gives is banal. If the goal (X) is to cut wood, and the instrument (Y) is an axe, then the axe must be made of something hard (Z), e.g. bronze. But the principle is general: if your goal is to breathe, and you’re a sluggish swamp-dwelling tetrapod, then you need a long nose. It’s his way of expressing and investigating the truth that a living thing is an integrated whole whose every part is adjusted to all others so as to ensure its survival. If you were to shuffle parts randomly among forms, you would get monsters, and hopeless ones at that. That is why Empedocles’ selectionist schemes are so absurd.

  In Historia animalium Aristotle disassembles his creatures to establish the associations among their parts; in the Posterior Analytics he gives a method by which to demonstrate the causes of those associations; in The Parts of Animals he reassembles his creatures and puts the method into practice. The principle of conditional necessity therefore becomes the single most important teleological principle at work in that book. The causal chains multiply and ramify through the text so that it’s hard to see where they start and stop. He even gives another conditional-necessity chain for the elephant’s trunk that ends by explaining its use as a hand, but begins with its toes.

  The thing about the elephant’s toes is that there are many of them. As such, the elephant has a functional affinity with other multi-toed animals such as cats, dogs and humans. Multi-toed animals seize their food with their forelimbs. But the elephant can’t because its legs are inflexible, because they’re thick, because it’s big.* So there’s the elephant starving to death in the teak forest. At least it would be had not nature, providentially, given it a kind of hand. Put this together with the snorkel argument and you really need a causal diagram to see that it all makes sense. It does, but you wonder how Aristotle got by, as he presumably did, without one.

  XLVIII

  ARISTOTLE’S ANALYSIS OF avian anatomy is so clear, so obvious, that you expect The Parts of Animals to be filled with more of the same. You expect to find a full-blown adaptationist programme demonstrating the exquisite – the adjective is rarely absent – fit of animals to their environments.

  It isn’t there. Yes, Aristotle does occasionally explicitly explain animal adaptations in terms of their lifestyles, but the principle of conditional necessity – the explanation of parts in terms of each other – dominates. One reason for this is his taxonomic focus. Some biologists paint the canvas of life in the broadest strokes, comparing the great phyla with each other, oblivious to the legions of species that they embrace; others construct intimate family portraits of just one group, tiger beetles, say; many study just one species, the mouse, the fly, the worm, ourselves. Aristotle does it all. His gaze wanders up and down his taxonomic hierarchy, sometimes coming to rest on humans, sometimes on all blooded animals. In The Parts of Animals, however, it is to the differences among the greatest kinds that he mostly attends.

  It is the obvious thing to do. It is among the greatest kinds that most of life’s variety can be found. The parts of the greatest kinds differ, not as those of birds do, by ‘the more and the less’, but in the entire order of their bodies. If their organs are similar, then they are so only by analogy. And yet it is also among the greatest kinds that specific teleological explanations are most elusive. Birds have beaks and tetrapods have teeth – why? Most animals have a mouth at one end of their bodies and a rectum at the other, but not cephalopods – why? Some animals have blood, others do not – again, why? Each of the greatest kinds is so different from every other, and embraces so much variety, that it is hard to correlate form with lifestyle unless trivially so. Yes, fish have fins rather than legs, and gills rather than lungs, because they live in water and not on land – Aristotle does indeed tell us so. But, in general, when contemplating the diversity of his greatest kinds he doesn’t even try.*

  It may seem that Aristotle has come to the end of explanation. He has just begun. His approach is as follows. For each greatest kind he takes certain features as primitive (in the epistemological rather than evolutionary sense). They are givens, not necessarily to be explained. They are, however, starting points for explanations. Aristotle often indicates primitive features by saying that they are part of the ‘definition [logos] of the entity [ousia]’ of an animal. For birds, flying is a feature of this sort; for fishes, swimming is. For birds (and presumably others) having a lung is. For live-bearing tetrapods (= most mammals), egg-bearing tetrapods (= most reptiles and amphibia), birds and fishes, having blood is; for all animals, sensation is. Aristotle only explicitly identifies a few features as givens of this sort, but he acts as though many are.

  Such as bird beaks. Aristotle never explains why birds have beaks rather than teeth; they just do. But he does chart the consequences. Because birds have beaks, rather than teeth, they cannot chew their food. To compensate for this deficiency they store and ‘concoct’ (digest) their food using a variety of other devices. Some birds (pigeons, pelicans, partridges) have a crop; others (crows) have a broad oesophagus or else (kestrels) an expanded part
of the stomach (proventriculus). Most birds have a fleshy and hard stomach (the gizzard). Marsh birds have neither a crop nor a wide oesophagus because their food is easily ground up. All this anatomy is broadly correct. So is Aristotle’s reasoning: they do so because they lack teeth.

  BIRD ALIMENTARY TRACTS LEFT: ALEKTōR – CHICKEN – GALLUS DOMESTICUS RIGHT: AIETOS – EAGLE – AQUILA SP.

  Aristotle uses the same logic to explain why some grazing animals (horses, asses, onagers) have the same number of teeth in their upper and lower jaws and simple stomachs, but others (cows, goats, sheep) have an unequal number of teeth in their jaws and have complex stomachs. Or why some fish have single gills, but others double. Or why the ostrich cannot fly. Or why . . . but such examples could be multiplied, for nearly every line of The Parts of Animals is an explanation.

  XLIX

  IN THE PORT OF Mithymna, the pretty Turkish town on Lesbos’ northern cape, I once found the desiccated remains of a sea-urchin species that I had never seen before. I found it on the quay, evidently discarded by a fisherman who had tied up there to sort and clean his nets. I recognized it as one described by Aristotle who says that it has a small body and large, hard spines and so is very different from the fat, fragile-spined sea urchins of the Lagoon. Characteristically, he does not give it a name but he does say that it lives far off shore, a hundred metres (‘60 orguiai’) down – which fits with the location, for Mithymna looks out over the strait of Mytilene where the sea floor drops to three hundred metres or more.