THE POWER OF SLOTH
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First published in Great Britain in 2017 by Doubleday
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Copyright © Lucy Cooke 2017
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1 3 5 7 9 10 8 6 4 2
To the memory of my Dad,
who opened my eyes to the wonders of the natural world.
‘HOW CAN SLOTHS exist when they’re such losers?’
As a zoologist and founder of the Sloth Appreciation Society I get asked this question a lot. Sometimes ‘losers’ is further defined – ‘lazy’, ‘stupid’ and ‘slow’ being perennial favourites. And sometimes the query is paired with the rider – ‘I thought evolution was all about “survival of the fittest”’ – delivered with an air of bemusement or, worse, a whiff of superior species smugness.
Each time it happens, I take a deep breath and, with as much poise as I can muster, explain that sloths are by no means losers. They are, in fact, one of natural selection’s quirkiest creations, and fabulously successful to boot. Skulking about the treetops barely quicker than a snail, and being covered in algae, infested with insects and defecating just once a week might not be your idea of aspirational living, but then you’re not trying to survive in the highly competitive jungles of Central and South America – something the sloth is very good at.
When seeking to understand animals, context is key.
The secret to sloths’ extraordinary endurance is their lethargic nature. They are paragons of low-energy living, with a suite of ingenious, energy-saving adaptations honed over many millennia and worthy of the most eccentric and gifted inventor. I won’t launch into the full list now – you can read all about the sloth’s innovative, upside-down life in chapter 3. Suffice to say, I’m a sucker for an underdog.
The reputation of the sloth was sufficiently besmirched that I felt compelled to found the Sloth Appreciation Society. (Our motto: ‘Being fast is overrated.’) I toured a talk on the unexpected truth about this much-maligned creature to festivals and schools. It traced sloth-based slander back to a clique of sixteenth-century explorers who took it upon themselves to brand this quiet vegetarian pacifist ‘the stupidest animal that can be found in the world’.1 This book grew out of those talks and the need to set the record straight – not just for the sloth, but for other animals as well.
We have a habit of viewing the animal kingdom through the prism of our own, rather narrow, existence. The sloth’s arboreal lifestyle is sufficiently extraterrestrial to make it one of the world’s most misunderstood creatures, but it is by no means alone in this category. Life takes a glorious myriad alien forms, and even the simplest require complex understanding.
Evolution has played some splendid practical jokes by fashioning implausible creatures with an absence of logic and precious few clues to explain itself. Mammals like the bat that want to be birds. Birds like the penguin that want to be fish. And fish like the eel whose enigmatic lifecycle sparked a two-thousand-year search for its missing gonads, driving man to the absolute edge of endeavour – a precipice eel scientists still teeter upon today. Animals do not give up their secrets easily.
Consider the ostrich. In February 1681, the brilliant British polymath Sir Thomas Browne wrote a letter to his son Edward, a physician at the royal court, requesting a rather unusual favour. Edward had come into possession of an ostrich, one of a flock donated to King Charles II by the King of Morocco. Sir Thomas, a keen naturalist, was fascinated by this big foreign bird and eager that his son send him news of its habits. Is it vigilant like a goose? Does it delight in sorrel yet recoil from bay leaves? And does it eat iron? This final query, he suggested helpfully to his son, might be best uncovered by wrapping the metal first in pastry – like some sort of ferrous sausage roll – since ‘perhaps it will not take it up alone.’2
This zoological recipe swap had a decidedly scientific purpose. Browne wanted to test an ancient myth that ostriches were capable of digesting absolutely anything, even iron. According to one medieval German scholar, the ostrich’s taste for the strong stuff was such that the bird’s dinner ‘consists of a church-door key and a horse shoe’.3 As ostriches were bestowed on the courts of Europe by the emirs and explorers of Africa, generations of enthusiastic natural philosophers encouraged the foreign fowl to consume scissors, nails and a glut of other ironmongery.
On the surface this experimentation appears to be lunacy, yet dig a little deeper and there is a (scientific) method to the madness. Ostriches can’t digest iron, but they have been observed swallowing large, sharp stones. Why? The world’s biggest bird has evolved into a rather unusual grazing animal, whose usual diet of grasses and shrubs is tough to digest. And unlike their fellow plant-munchers from the African plains, the giraffe and antelope, ostriches lack a ruminating stomach. They don’t even have teeth. Instead, they must tear the fibrous grasses from the ground with their beak and swallow them whole. They employ the quarry of jagged rocks in their muscular gizzard to do the job of grinding down this stringy dinner into more digestible pieces. They can clunk around the savannah with up to a kilogram of stones in their stomach. (Scientists fancy this up and call them gastroliths.)
Again, understanding the ostrich is about context. But so too we must understand the context of the scientists that have been prodding and poking for the truth about animals for centuries. As such, Browne is just one of a great cast of idiosyncratic obsessives you’ll meet in the pages of this book. There’s the seventeenth-century physician who tried to spontaneously generate toads by placing a duck on a dung heap (an old recipe for creating life). There’s also an Italian Catholic priest with a name befitting a Bond bad guy and the moves to match: Lazzaro Spallanzani wielded a mean pair of scissors in the name of science, whether tailoring tiny, bespoke underpants for his animal subjects or removing their ears.
Although both of these men were products of the earliest days of the Enlightenment, scientists in more recent times have also chosen to pursue bizarre, and often misguided, methods in their search for truth – like the twentieth-century American psycho-pharmacologist whose curiosity compelled him to get a herd of elephants very drunk indeed, with suitably demented results. Every century has its eccentric animal experimenters, and there will no doubt be many more to come. We humans may have split the atom, conquered the Moon and tracked down the Higgs boson, but when it comes to understanding animals we still have a long way to go.
I’m fascinated by the mistakes we’ve made along the way and the myths we’ve created to fill in the gaps in our understanding. They reveal much about the mechanics of discovery and the people doing the discovering. When Pliny the Elder described a hippopotamus secreting crimson liquor from its skin, he reached for the explanations familiar to him – those of Roman medicine – and imagined an animal bleeding itself to stay healthy. Of course he did; he was a man of his time. He was wrong, but the genuine explanation for the hippo’s scarlet ooze is just as extraordinary as the old myth – and it is actually related to self-medication.
I’ve found that taking a dissecting knife to our greatest animal myths often exposes a charming logic, transporting us to times of wondrous naivety, when little was known and anything was possible. Why on earth wouldn’t birds migrate to the Moon, hyenas switch sex with the season and eels spontaneously generate out of mud? Especially when the truth, as we will discover, is no less incredible.
The most nonsensical animal myths sprang to life after the fall of the Roman Empire when, in the Middle Ages, the nascent science of natural history was hijacked by Christianity. This was the heyday of the bestiary. These early compendiums of the animal kingdom were full of gilded illustrations and earnest descriptions of exotic beasts, from sparrow-camels (ostriches) to camel-leopards (giraffes) to sea-bishops (half fish, half clergyman and whole fantasy). But the bestiaries were not the result of some deep commitment to researching the lives of animals. Instead, they all embellished upon one single source, a fourth-century manuscript called the Physiologus, which blended folklore with a sprinkling of fact and a heavy dose of religious allegory. The Physiologus became the medieval equivalent of a massive bestseller (only exceeded at the time by the Bible) and was translated into dozens of languages, spreading absurd animal legends from Ethiopia to Iceland.
These bestiaries are a fabulously bawdy read with much talk of sex and sin, which must have delighted the monks that transcribed and illustrated them for the Church’s libraries. They spoke of extraordinary creatures: the weasel which conceives through its mouth but gives birth through its ear; the bison (or ‘bonnacon’, as it was then known) which avoids a hunter by emitting a fart ‘so foul that its attackers are forced to retire in confusion’ (we’ve all been there); and the stag whose penis has a habit of dropping off following bouts of carnal overindulgence.4 There were more than a few lessons to be gathered and conveyed to flocks of parishioners in such tales. After all, God had created all the animals, and only one – mankind – had lost its innocence. The function of the animal kingdom, in the eyes of the scribes, was to serve as an example for humans. So instead of questioning whether there was any truth to the descriptions in the Physiologus, they looked for the human characteristics of animals and the moral values God had hidden in their behaviour.
This renders some animals in the bestiaries almost unrecognizable. Elephants, for example, were praised for being the most virtuous and wise of beasts, so ‘gentle and meek’ they were even credited with having their own religion.5 They were said to have a ‘great hatred’ of mice but a love of country so deep that just thinking about their homeland could reduce them to tears.6 When it came to fornication, they were ‘the most chaste’, staying with their mates for life – and it was a very long life, lasting three hundred years.7 They were so averse to adultery that they would punish those they caught in the act. All of which would come as something of a surprise to your average elephant, which enjoys a decidedly polygynous sex life.
The urge to look for our reflection in animals and impose moral judgements upon them continued well into more enlightened times. Perhaps the greatest sinner in this department, and the biggest star of this book, is the celebrated French naturalist Georges-Louis Leclerc, Comte de Buffon. The grandiose Comte was a leading figure of the scientific revolution who strove, somewhat paradoxically, to move natural history out from under the shadow of the Church. His epic, forty-four-volume encyclopaedia is, however, a hilariously sanctimonious tome, thanks to a delightfully purple prose which, in the style of most science writing of the period, reads more like a romantic novel than scientific analysis. His withering put-downs of animals whose lives he doesn’t approve of, like our friend the sloth (aka ‘the lowest form of existence’, according to the French aristocrat) are almost as amusingly inaccurate as his overblown adoration of the creatures he exalts.8 One of his pet beasts was the beaver, whose hard work, you will discover, he positively lost his mind over, turning the great Buffon into something of a buffoon, once you know the truth.
Such anthropomorphic impulses persist even today. Pandas are so powerfully cute, they trigger an innate urge to nurture that smothers our judgement. We want to believe they are bumbling, sex-shy bears that cannot survive without our intervention, rather than veteran survivors with a ferocious bite and a taste for rough-and-tumble group sex.
I studied zoology in the early 1990s under the great evolutionary biologist Dr Richard Dawkins and was taught a method of thinking about the world based upon the genetic relationships between species – how their degree of relatedness influences their behaviour. Some of what I was taught has already been surpassed by recent advancements, which show that the way in which a genome is read at a cellular level can be at least as important as its content (which is how we can share 70 per cent of our DNA with an acorn worm and yet be so much more fun at a dinner party). I mention this to make the point that each generation – mine included – think we know more about animals than our predecessors, yet we’re still often wrong. Much of zoology is little more than educated guesswork.
With modern technology we are getting better at our guessing. As a producer and presenter of natural history documentaries, I’ve travelled the world and gained privileged access to some of the most dedicated scientists mining for truth at the coalface of discovery. I’ve met an animal IQ tester in the Maasai Mara, a peddler of panda porn in China, the English inventor behind a sloth ‘bum-o-meter’ (it has a scientific purpose) and the Scottish author of the world’s first chimpanzee dictionary. I have chased after drunk moose, nibbled beaver ‘testicles’, savoured amphibian aphrodisiacs, jumped off a cliff to fly with vultures and attempted to speak a few words of hippo (though not all at once). These experiences have opened my eyes to many surprising truths about animals and the state of animal science. This book is my effort to share these truths with you, to gather together the biggest misconceptions, mistakes and myths we’ve concocted about the animal kingdom, whether the purveyor was the great philosopher Aristotle or the Hollywood descendants of Walt Disney, and create my very own menagerie of the misunderstood.
So, open your mind to these incredible tales. Just don’t expect them all to be true.
There is no animal concerning whose origin and existence there is such a number of false beliefs and ridiculous fables.1
Leopold Jacoby, ‘The Eel Question’, 1879
ARISTOTLE WAS TROUBLED by eels.
No matter how many the great Greek thinker sliced open, he could find no trace of their sex. Every other fish he’d examined on his island laboratory of Lesvos had easily detectable (and often quite delectable) eggs and conspicuous, albeit internal, testicles. But the eel appeared to be entirely sex-less. So, when Aristotle came to writing about them in his pioneering animal almanac in the fourth century BC, this most methodical of natural philosophers was forced to conclude that the eel ‘proceeds neither from pair, nor from an egg’ but was instead born of the ‘earth’s guts’, spontaneously emerging from mud; he thought the worm casts we see in wet sand were embryonic eels boiling out of the ground.2
Aristotle was the first true scientist and the father of zoology. He made acute scientific observations about hundreds of creatures, but I am not surprised he was outfoxed by eels. These slippery characters keep their secrets especially well hidden. The idea that they emerge from the earth is fantastic, but no more so than the truth, since the so-called common freshwater eel, Anguilla anguilla, starts its life as an egg suspended in the depths of an underwater forest in the Sargasso Sea, the deepest, saltiest slice of the Atlantic. As a wisp of life no bigger than a grain of rice, it embarks on an odyssey lasting up to three years, to the rivers of Europe, during which it undergoes a transformation as radical as a mouse turning into a moose. It spends decades living in the mud and fattening itself up only so it can repeat the gruelling 6,000-kilometre journey back to its obscure oceanic womb, where it spawns in the shadowy recesses of the continental shelf and dies.
The fact that the eel only becomes sexually mature after its fourth, and final, metamorphosis at the very tail end of this particularly peculiar life has helped to obscure its origins and bestowed it with a mythical status. Over the centuries, unravelling the mystery has pitted nations against each other, driven man to the remotest reaches of the seas and tormented some of the finest minds in the history of zoology, as everyone seemed to compete with one another to concoct the craziest theory to explain the eel’s genesis. No matter how outlandish, they couldn’t match the true story of the common freshwater eel, which is anything but ordinary: a remarkable tale of eel-starving Nazis, obsessive gonad hunters, gun-toting fishermen, the world’s most famous psychoanalyst – and me.
As a child, I, too, was rather obsessed with eels. When I was about seven my father sank an old Victorian bath in the garden, and converting this sterile tub for human ablution into the perfect pond ecosystem quickly became my principal pastime. I was a geeky child and I took this mission extremely seriously. Every Sunday my dad would accompany me to the ditches of Romney Marsh where I would spend happy hours trawling for any form of life with an improvised underwater animal trap he’d fashioned for me out of a pair of old net curtains. At the end of the day we’d return triumphant, heady with the zeal of Victorian explorers, our underwater booty sloshing around in the back of his aged mini pickup, ready to be identified and introduced to my watery kingdom. The animals came two by two: marsh frogs, smooth newts, sticklebacks, whirligig beetles and pond skaters all joined the party in my bath. Alas no eels. My trusty net collected them, but attempting to transfer their slimy bodies into the bucket was like trying to hold onto water. Every time I grabbed one they’d escape, slithering off to safety overland – more like a snake than a fish out of water. They were elusive creatures and catching them became my Holy Grail.
What I didn’t know was that, if I had succeeded in my mission, the eels would have brought an end to my pleasant pond party by eating all the other guests. Eels spend the freshwater phase of their life like extreme prizefighters bulking themselves up for a championship bout in preparation for the long swim back to the Sargasso to breed. To achieve this they will eat anything that moves – including each other. Their rapacious appetite was exposed in a gruesome experiment conducted by a pair of French scientists in Paris in the late 1930s. The researchers placed a thousand elvers – young eels, about 8 centimetres long – in a tank of water. The fish were fed daily, but even so, a year later there were only seventy-one eels left, now three times as long. Three months later, after what a local journalist reported as ‘daily scenes of cannibalism’, one champion was left: a female measuring one-third of a metre in length.3 She lived a further four years all on her own, until she was accidentally bumped off by the Nazis, who inadvertently cut off her supply of worms during their occupation of Paris.
This horror story would have shocked the past generations of naturalists who believed the eel to be a benign vegetarian with a particular weakness for peas – so much so they were said to leave their watery world and seek out their favourite juicy legumes on land. Such accounts came courtesy of the thirteenth-century Dominican monk Albert Magnus, who, in his book De Animalibus, noted: ‘The eel also comes out of the water in the night time where he can find pease, beans, and lentils.’4 The eel’s hippie diet was still in currency in 1893, when A History of Scandinavian Fishes embellished the monk’s ‘observations’ with delicious sound effects. The Countess Hamilton’s estate was invaded by eels that gobbled up her legumes with ‘a smacking sound, like that made by sucking-pigs when they are eating’.5 Though perhaps lacking the requisite manners, the dowager’s eels were a suitably discerning school that ‘only consumed the soft and juicy skin’ and discarded the rest. Whilst it’s true that eels can survive for a remarkable forty-eight hours out of water, thanks to their slimy, breathable skin – an adaptation that allows them to pond-hop in search of water in times of drought – reports of their lip-smacking, pea-stealing antics were quite delusional.
The eel’s greedy freshwater years lead to an impressive increase in size, though maybe not as great as the ancient naturalist would have us believe. Fish engender themselves to tall tales of ‘the one that got away’. Still, the great Roman naturalist Pliny the Elder’s assertion, made in his epic tome, Naturalis Historia, that eels from the river Ganges grew to be ‘thirty feet long’ – 10 metres – was a cocky overstatement even in this well-worn genre of lies.6 Izaak Walton, author of a seventeenth-century fishing bible, The Compleat Angler, showed a bit more restraint when describing an eel caught in the Peterborough river that he claimed ‘was a yard and three quarters long’, or roughly 160 centimetres.7 Walton was keen to fend off any doubters by adding, perhaps a little too quickly: ‘If you will not believe me, then go and see it at one of the coffee-houses in King street Westminster’ (where it was no doubt happily sipping cappuccinos and regaling customers with stories of its youthful adventures at sea).8 More measured measurements come from Dr Jorgen Nielsen of the Zoological Museum in Copenhagen, who examined the corpse of an eel from a rural pond in Denmark.9 He told Tom Fort, author of The Book of Eels, that the prize-winning specimen punched in at 125 cm. Unfortunately, the slippery monster had met an untimely death when the pond’s owner caught it menacing his beloved ornamental waterfowl and came at it with his shovel.
The eels I caught were quite a bit smaller, not much more than the length and thickness of a pencil. They were no doubt nearer the start of their freshwater life, which can last anything from six to thirty years. Some eels have been known to live much longer. A Swedish specimen nicknamed Putte, caught as an elver near Helsingborg in 1863 and kept in a local aquarium, passed away aged eighty-eight. Her death was mourned with extensive media coverage, her record-breaking age having afforded her the kind of celebrity status not normally available to a long, slimy fish.
Such aged eels have invariably been denied their urge to migrate back to the sea by being kept captive, often as pets. An eel may seem an unconventional choice for an animal companion – not a lot of fun to be had in the snuggling department – but the Roman orator Quintus Hortensius was said to weep at the death of his, ‘which he kept long, and loved exceedingly’.10 All of which makes me somewhat relieved that I never succeeded in catching myself an eel, which I could still be wedded to today.
The eel’s freshwater existence may be long and gluttonous, but it is just one of the fish’s many lives (albeit the only one obvious to me and countless other naturalists over the centuries). It gives no clues about the rest of its lifecycle – its birth, reproduction and death – which are shrouded by the sea, and come in such unlikely alternative guises that they spawned an intense international quest, lasting some two thousand years, to locate the eel’s mysterious gonads.
Aristotle was one of the first to be stymied by the genesis of this apparently sexless fish. He folded the origins of the eel into his theory of spontaneous generation, which he applied liberally to an eclectic collection of critters – from flies to frogs – whose proliferation seemed inexplicable. Several hundred years later, Pliny the Elder took a break from plagiarizing his Greek forebears to trial his own imaginative ideas about eel propagation; he proposed that they reproduced by rubbing themselves against rocks, ‘the scrapings come to life’.11 Hoping to have the last word on the matter, the Roman naturalist concluded with an authoritative flourish: ‘This is the only way they breed.’ But Pliny’s asexual friction was nothing but fiction.
Fantastic rumours of the eel’s reproduction bred like rabbits over the ensuing centuries. Eels were said to emerge from the gills of other fishes, from sweet morning dew (but only during certain months) and from enigmatic ‘electrical disturbances’.12 One ‘reverend bishop’ told the Royal Society he had seen young eels that had been born on the thatching of a roof.13 The eggs, he claimed, had been stuck to the thatching reeds and incubated by the heat of the sun. Not all ecclesiastical naturalists were so open-minded about such fishy tales. In his History of the Worthies, Thomas Fuller poured scorn on the belief widely held in the fenlands of Cambridgeshire that the illicit wives and bastard children of priests were saved from damnation by taking the form of an eel. This, he said, was clearly ‘a lie’.14 To underscore the seriousness of the matter, he added judgementally: ‘No doubt the first founder of so damnable an untruth hath long since received his reward.’ Perhaps by living out the rest of his life as a slug.
The scientific geniuses of the Enlightenment swept aside such fanciful fables with significantly less silly – but no more accurate – theories of their own. In 1692, Antonie van Leeuwenhoek, the Dutch pioneer of microscopic worlds who discovered both bacteria and blood cells, erred towards credibility with his hypothesis that eels, like mammals, were viviparous, that is, their eggs were fertilized internally, with the females giving birth to live young. Van Leeuwenhoek at least embraced contemporary scientific method by basing his supposition on actual observations. He had stared down his magnifying lens and watched what appeared to be baby eels in what he assumed was the fish’s uterus. Unfortunately, these alleged newborns were actually parasitic worms squatting in the eel’s bladder, and had in fact been observed and dismissed as such by Aristotle nearly two thousand years before.
The eighteenth-century Swedish botanist and zoologist Carl Linnaeus also said that eels were viviparous, claiming to have seen what he believed to be baby eels inside an adult female. Surely no one would argue with the great father of taxonomy – a man so pedantic he even Latinized his own name. But they had little choice once it emerged that the classification connoisseur had got his species in a twist. The awkward truth was that Linnaeus hadn’t actually dissected an eel but an eel imposter, a similar-looking beast now known as the eelpout – an unusually viviparous yet altogether unrelated species of fish. Which is not to say his critics had their facts any more straight. One authority who reviewed Linnaeus’s work took him to task for a case of mistaken identity – but, influenced by Aristotle, proclaimed the young eels discovered by the Swede to be parasitic worms, sending the live-birth doctrine into a vortex of inaccuracy and confusion.
Into this lofty academic fray stepped a plucky outsider. In 1862, a Scotsman by the name of David Cairncross announced to the world that he, a humble factory engineer from Dundee, had finally solved the riddle of the eel, which had plagued generations of philosophers and naturalists. ‘The reader may at once be informed that … the progenitor of the silver eel is a small beetle,’ he stated with the bravado of the truly ignorant.15 His enthusiastic, if scientifically baffling, theory – the product of sixty years of ongoing experiments by his own reckoning – took the form of a short book, The Origin of the Silver Eel.
Cairncross began his treatise with an apology for his lack of any interest in learning the rules and norms of contemporary science. ‘I could not be expected to be acquainted with the names and terms used by naturalists in their classifications of the different animals, my knowledge of such books being limited,’ he noted somewhat defensively.16 His unconventional but highly convenient solution was to ‘employ names and terms of my own’.17 This involved a reimagining of animal classification into three nonsensical classes that would have made the great Linnaeus turn in his grave, and succeeded only in creating further challenges to anyone trying to decipher the Scot’s already bewildering theory.
Cairncross’s journey of discovery begins at the tender age of ten, when he observed a number of ‘hair eels’ (his term) in an open drain.18 ‘Where can they come from?’ he wondered. A friend related to him a common folk belief that young eels ‘fall from the tails of the horses while drinking; and the water brings them to life.’19 The young Cairncross scoffed at this highly improbable explanation, before conjuring up his own, equally implausible idea inspired by a number of dead beetles languishing in the bottom of the same drain. Maybe the two animals were connected? This bewitching scene stayed with the Scot for two decades, ‘often did my mind revert to the mystery’, he recalled.20
Then one summer, the adult Cairncross spotted a familiar-looking beetle in his garden in Dundee. He watched it intently, attempting to read its thoughts as it walked with determination towards a puddle and plunged in. The beetle, he reported, then ‘looks about a bit’ before exiting its bath ‘in a very troubled state’.21 How Cairncross arrived at his diagnosis of the beetle’s mental state is not known. But the book’s only illustration provides the reader with valuable assistance in comprehending the insect’s next extraordinary move: entitled ‘the beetle in the act of parturition’, it showed Cairncross’s unlikely hero lying on its back with what appears to be a pair of lassoes emanating from its backside.22 The beetle, according to the Scotsman, was giving birth to two fish.
This was the Eureka moment for Cairncross. He now dedicated himself to furthering his investigation by cutting open beetles, removing ‘hair eels’ and keeping them alive for various, albeit rather limited, periods of time. He freely admitted that his theory ‘may seem strange’ but reassured himself by looking at the behaviour of ‘members of the vegetable kingdom’.23 If one species of tree can be grafted onto another, ‘Could not therefore the Great Creating Gardener graft a foreign nature on that of an insect?’ he mused.24
All manner of Frankenstein animals have been conceived in modern labs: human ears have been grafted onto mice and glow-in-the-dark fish have been created with a judicious sprinkling of jellyfish genes. But the ‘Great Creating Gardener’ had no hand in planting them.
Had Cairncross posed his question to the scholarly community, they would have declared that his ‘hair eels’ were yet another case of pesky parasitic worms and not the fish in an early stage of development. But the factory engineer knew not of peer review. He presented his exceptional findings not to the Royal Society for serious scrutiny, but instead to a pair of farmers he bumped into one day, who were perplexed by the quantities of silver eel in a ditch on their land. So he explained his theory that this profusion of eels had emerged from a beetle’s bum and was delighted by their response. ‘They believed me’, he announced with pride, ‘and rejoiced in the solution of the mystery.’25
Despite the enthusiasm of these local farmers, Cairncross’s theory failed to alter the broader trajectory of eel research. Beavering away in intellectual isolation for sixty-odd years, he was unaware of the radical progress being made in the hunt for the fish’s gonads. Far from Dundee, Europe’s scientific intelligentsia were gripped by ‘the eel question’, and they were about to reach a climax – of sorts.
✜
Leading the charge were the Italians, who embraced the quest to locate the eel’s missing sex organs as an unlikely source of civic pride for their troubled nation.
The Italians had cultivated a longstanding relationship with eels that mostly involved eating them in vast quantities. Eel is an unusually fatty fish – an evolutionary adaptation to fuel its onerous 6,000-kilometre odyssey back to its mating grounds deep in the Sargasso Sea. Unfortunately for the eel, this high lipid content also makes it especially tasty, a quality which did not go unnoticed. The Roman epicure Marcus Gavius Apicius, author of what is arguably the world’s first cookbook, wrote that six thousand eels were served at feasts celebrating the victory of Julius Caesar. He recommended that the ‘eel will be made more palatable’ by serving it with a sauce containing ‘dry mint, rue berries, hard yolks, pepper, lovage, mead, vinegar broth and oil’.26, 27 This doesn’t sound wildly appetizing, but in England we still like to eat them simply boiled and jellied, surely one of the greatest crimes against gastronomy the British have committed in a long and illustrious history of murdering food. Yet, despite such crude recipes, eels were long associated with great feasts and gluttony. Leonardo da Vinci painted the disciples enjoying eels at the Last Supper, and a surfeit of the slippery fish was blamed for the death of the infamous gourmand Pope Martin IV.
The finest tasting eels were said to come from Comacchio and the surrounding vast grey wetlands of the mighty river Po delta. They were home to Europe’s greatest eel fisheries, hauling in three hundred tons of eel a night at the height of the season, and the source of some of the greatest pronouncements and controversies surrounding the eel’s sex. These began in 1707, when a local surgeon noticed an unusually plump eel amongst the many thousands being caught. When the doctor sliced it open, he saw what looked to him like an ovary stuffed with ripe eggs. The pregnant fish was dispatched to his friend, the esteemed naturalist Antonio Vallisneri, who hastily proclaimed the centuries-long search for the eel’s private parts was finally over. The learned professor had already lent his name to the formal classification of a water plant known colloquially as the eelgrass, but the genitals of the female eel would not be a further namesake. Upon closer scrutiny, the discovery was written off as little more than a diseased and distended swim bladder.
Vallisneri’s flirtation with victory inspired the Italian scientific mafia, who now considered it ‘a matter of extreme importance to find the true ovaries of the eel’.28 These were turbulent times for the inchoate nation, as the peninsula was occupied by foreign powers. And whilst many Italians hung their nationalistic hopes on revolution, this small band of intellectuals dreamed instead of empowering their countrymen by laying claim to the delectable eel’s elusive gonads.
The professors devised a plan. Thousands of eels were captured daily around Comacchio; all they need do was offer an enticing reward to the first fisherman who could provide them with a specimen complete with roe. In Germany, a competing plan backfired when the naturalist who had hatched it received so much eel offal in the post that he was moved to ‘cry and beg for mercy’.29 The Italian scheme, however, quickly yielded positive results – or so it seemed. The celebrations were cut short when it was discovered the wily fisherman had simply filled his eel with the eggs of another fish.
This humiliating blow dampened the Italian professors’ zeal for eels for some fifty years. Then in 1777, a fresh, fat, slimy suspect flopped up on the shores of Comacchio. It was immediately examined by the anatomist Carlo Mondini, professor at the nearby University of Bologna, who made an ingenious realization: the frilled ribbons inside the eel’s abdomen were not fringes of fatty tissue, as had been previously supposed, but the female eel’s evasive ovaries.
Italy’s scientists rejoiced, perhaps again a little prematurely. After all, the eel’s testicles were still missing, along with any clear notion of how this enigmatic fish reproduced. Thus, the mission to complete the eel’s genital jigsaw puzzle fell to a rather unlikely candidate: an ambitious young medical student who would later find fame locating the seat of desire, in humans if not in eels. The student’s name: Sigmund Freud.
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As a nineteen-year-old student at the University of Vienna, the founding father of psychoanalysis took up his very first research job, arriving in 1876 at a zoological field station in Trieste, on Italy’s Adriatic coast, with a mandate to find the testicles of the eel.
The only way to determine gender was to slice the fish open, ‘seeing that eels keep no diaries’, Freud opined sardonically in a letter to a friend.30 For weeks he did just that, every day, from eight in the morning until five in the afternoon, in a hot, smelly laboratory. He had been tasked with investigating the claim of a Polish professor named Szymon Syrski, who had said he had discovered the eel’s testes. ‘But since he apparently doesn’t know what a microscope is’, grumbled Freud in his letter, ‘he failed to provide an accurate description of them.’
Four weeks and four hundred disembowelled eels later, Freud gave up. ‘I have been tormenting myself and the eels, but in vain, all the eels which I cut open are of the fairer sex,’ he lamented in a letter littered with doodles of eels wearing thin mocking smiles.31 Freud’s resulting paper, ‘Observations on the Form and the Fine Structure of Looped Organs of the Eel, Organs Considered as Testes’, was his first published work. Although he suspected Syrski was right, he could neither confirm nor deny the Pole’s claims.
It’s anyone’s guess how much those long days spent slicing open phallocentric fish in a fruitless search for their sex influenced Freud’s later theories surrounding the phallic-envy stage of human psychosexual development. In any case, he went on to probe less slippery subjects, like the human psyche, with significantly more success.
Two decades later, a lone male eel finally exposed his private parts. The fortuitous young biologist to make the eel’s acquaintance was another Italian, Giovanni Grassi, who apprehended the fish – his sex organs swollen with sperm – swimming off the coast of Sicily. Grassi had already produced some seminal, if not particularly scintillating, work on the anatomy of termites, and had named a new species of spider after his wife (there’s love for you). But he was on something of a roll when it came to eels. Not only had he won the international eel testicle tournament for Italy, but the year before he had made an equally pivotal discovery by identifying a key stage in the eel’s inscrutable lifecycle.
Since the 1850s, tiny, transparent fish the shape and thickness of a willow leaf with bulbous black eyes and terrifying buck teeth had been documented washing up in great numbers on the shores of Italy. These minuscule monsters were classified as Leptocephalus brevirostris – a perfunctory piece of Linnaean nomenclature that translates to ‘thin-head short-nosed’ – and quickly dismissed as just another of the all too numerous, utterly nondescript marine creatures that inhabit the murky depths.32 Grassi was fascinated by these slivers of life. Suspecting they might be larval, as opposed to adult fish, he pulled a rather cunning trick. He counted up their embryonic vertebrae – which averaged 115 – and looked for a match in another species. He found it in the European freshwater eel. It was a truly momentous revelation, the identification of the missing link in the eel’s mysterious lifecycle.
Several learned minds had already proposed that the freshwater eel must breed far out at sea. It was an unconventional idea – the reverse direction of all other long-distance migrating fish, like salmon, which spread their lives across fresh- and saltwater habitats. But why else would eels swim downriver every autumn in such great numbers and with such determination, with miniature versions of themselves making the reverse journey upriver every spring? Still, there was no evidence supporting this logical hypothesis. No baby eels had ever been found at sea. Now Grassi had not only located the missing larval stage; he had also fingered the eel as a world-class shape-shifter.
Grassi set himself up with an aquarium to observe the miraculous metamorphosis with his own eyes. He was clever to do so, as no one would probably have believed him otherwise. Over the course of several weeks, the leaf-like wisp began to thicken at each end, forming an indisputably eel-shaped creature. Its body length shrank by almost a third, its jagged teeth dissolved and, for obscure alimentary reasons, its anus migrated. After a few days a perfectly transparent, bug-eyed noodle known as a glass eel was swimming around the tank. Giddy with discovery, Grassi proclaimed the Strait of Messina, off the coast of Sicily, to be the breeding ground of all European eels, thereby claiming the lip-smacking fish and its extraordinary lifecycle as the property of the newly united Kingdom of Italy.
But as is the habit of the eel, such hastily grabbed glory quickly slipped out of the Italian’s grasp. Grassi had conveniently ignored the fact that the thin-heads he’d captured were all around 7 centimetres long. So unless they were born from an unfeasibly large egg, these larvae were already quite mature by the time they reached the strait. Could they really have been born so close to Italy’s coast?
One man didn’t think the riddle of the eel was quite so easily solved.
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Like many before him, the oceanographer Johannes Schmidt displayed an almost monomaniacal determination to pin down the obscure breeding ground of the freshwater eel. For nearly two decades the ‘pathalogically ambitions’ Dane combed the vast expanses of the Atlantic Ocean in search of freshly hatched fry the size of pine needles.33 His expedition was so immense and so technically demanding – and led to such an unexpected end – that it would snatch the glory of the eel’s slippery story from Italy’s grasp and deliver it to Denmark.
His mission began in 1903, when the young Schmidt got a job as a fisheries biologist aboard the Thor, a Danish research vessel, studying the breeding habits of food fishes such as cod and herring. One day in the summer of that year, as they were sailing west of the Faroe Islands in the Atlantic, a puny fish larva showed up in one of the boat’s massive, fine-mesh trawls. Schmidt identified the insignificant larva as that of the European eel – the first of its kind to be found outside of the Mediterranean. It was ‘a chance of luck’ that suggested to Schmidt that the birthplace of the eel was not off the coast of Italy but approximately 4,000 kilometres to the north, unless this thin-head had got very lost indeed.34
The Dane became obsessed with locating the eel’s true origins, surpassing even the other eel fanatics – Aristotle, Cairncross, Freud, Mondini or Grassi – who had been seized before him. Fortunately for the tenacious scientist, the year before he had made an auspicious betrothal to the heiress to the Carlsberg Brewery, probably the best lager company in the world for an aspiring thin-head hunter to hitch his wagon to, since the company was known to donate generously to marine research. Whether his bride was as pleased with the deal, which involved losing her new husband to a two-decades-long, seafaring fixation with teeny tiny fish, is anyone’s guess.
Suffused with youthful enthusiasm, Schmidt embarked on an almighty quest to locate the smallest possible thin-heads, which would, he thought, logically lead him to the place of their birth. ‘I had little idea at the time of the extraordinary difficulty which the task was to present,’ he later wrote.35 ‘The task was found to grow in extent year by year, to a degree we never dreamed of.’ He trawled fine nets ‘from America to Egypt, from Iceland to the Canary Islands’, wearing out four large ships, one of which ran aground near the Virgin Islands and sank, nearly taking his precious thin-head specimens with it.36 Then came the First World War. Many of the boats he co-opted to assist in his mission were shot by German submarines.
Whilst battling the oceans, Schmidt was also forced to lay siege to an academic establishment that was infuriatingly reluctant to recognize his painstaking efforts. In 1912 he had published his first findings: that the further from the European coast he travelled, the smaller the eel larvae became, which indicated that the birthplace of the eel must indeed be in the Atlantic. The Royal Society demurred, however, stating that Grassi’s work ‘was considered sufficient’ on the subject, thereby forcing Schmidt back onto a boat and back out to sea.37
A breakthrough came on 12 April 1921, in the southern Sargasso Sea, when Schmidt captured his most Lilliputian larvae: thin-heads just 5 millimetres long, which he presumed were no more than a day or two old. After almost two decades of searching, the Dane’s quest was finally reaching its end. He could at last feel confident in claiming, ‘Here lie the breeding grounds of the eel.’38
It was an astonishing result; even Schmidt was blown away by the import of his discovery. ‘No other instance is known among fishes of a species requiring a quarter of the circumference of the globe to complete its life history,’ he wrote in 1923, ‘and larval migrations of such extent and duration as those of the eel are altogether unique in the animal kingdom.’39 Grassi and the Italians had been vanquished, and the mantle of eel demystification would for ever be worn by a satisfied Schmidt and his Danish homeland.
But one should never say ‘for ever’ – in science or in life.
Almost one hundred years later our understanding of the eel’s lifecycle is still little more than expensive guesswork. Despite billions of dollars and the best of modern technology, no adult Anguilla anguilla has ever been tracked all the way on its journey from the rivers of Europe to the Sargasso Sea. Nor has one been observed mating in the wild. And no eggs have ever been found.
I asked Kim Aarestrup, a senior researcher at the Technical University of Denmark and one of the world’s leading eel scientists, whether we could be absolutely certain that the European freshwater eel really is born in the Sargasso. His answer: a sheepish ‘no’.
in flagrante delicto