IELTS Academic Reading — Đề mẫu 01

The camel family

Camels are so closely tied in the popular imagination to the deserts of Africa and Asia that it comes as a surprise to learn that the family they belong to began its history on another continent altogether. The camelids first appear in the fossil record of North America some forty-five million years ago, and for most of their existence they were an exclusively North American group. Only in the last few million years did some of them cross the land bridge into Asia, while others moved south into what is now South America. The North American originals then died out completely, leaving the family with a curiously divided modern range: three species in the deserts and steppes of the Old World, and four in the mountains and grasslands of the New.

The living camelids fall into two groups. The Old World camels are large animals with humps; the South American camelids are smaller, humpless and adapted to altitude rather than heat. The dromedary, with a single hump, is the animal of the Arabian and North African deserts. It has been domesticated for perhaps three thousand years and no longer exists in the wild anywhere, although a substantial feral population roams the interior of Australia, descended from animals imported in the nineteenth century for transport and never gathered up again once motor vehicles arrived. The domesticated Bactrian camel, which has two humps, belongs to the colder deserts and steppes of Central Asia, where winter temperatures can fall far below freezing.

A third Old World species was recognised only recently. The wild Bactrian camel of the Gobi was long assumed to be a feral descendant of domesticated stock, but genetic work has shown it to be a separate species that parted from the domesticated line long before domestication began. Fewer than a thousand survive, in a handful of populations on the Mongolian and Chinese sides of the desert, and it is among the most endangered large mammals in the world. It is also the only camelid able to live on water too salty for the domesticated form to drink.

In South America the pattern of wild and domesticated forms is repeated. The guanaco is a wild animal of the Andes and the Patagonian plains, and from it the llama was domesticated, several thousand years ago, as a pack animal — the only beast of burden the pre-Columbian Andes possessed. The vicuna, the smallest of the family, lives on high grassland above three and a half thousand metres and is the wild ancestor of the alpaca, which was bred not for carrying but for its fleece. Vicuna fibre is the finest produced by any animal, and under the Inca the animals were rounded up, shorn and released again in a communal drive; the practice was revived in the twentieth century after hunting had cut the species to a few thousand.

What unites all seven species is a set of adaptations that have very little to do with humps. The most striking is in the blood: camelids are the only mammals whose red blood cells are oval rather than round. The shape allows the cells to keep flowing when the blood thickens through water loss, and to swell without bursting when the animal drinks again. A dromedary can lose a quarter of its body water — a level that would kill most mammals — and then replace it in a single long drink.

The hump itself stores fat, not water, and the distinction matters: fat gathered into one mass on the back leaves the rest of the body free to shed heat, whereas an even layer of the same fat would trap it. A camel also allows its body temperature to drift upwards through the day rather than sweating to hold it steady, and only begins to sweat when it passes about 41 degrees Celsius. The saving in water is considerable. Other features are more obvious: nostrils that close against blowing sand, two rows of eyelashes, and a transparent third eyelid that can be drawn across the eye without blinding the animal.

The feet are not hooves. Each foot ends in two toes resting on a broad elastic pad, which spreads the animal's weight over soft ground and is the reason camels cross sand that would defeat a horse. The same pad serves the vicuna on loose mountain scree. Camelids are also commonly called ruminants, which is not quite right: they chew the cud and ferment their food in a chambered stomach, but the stomach has three chambers rather than the four of cattle and sheep, and the two groups arrived at the arrangement independently.

The family's economic importance has shifted rather than declined. Camels are no longer the freight system of the Sahara, but camel milk — lower in fat and higher in vitamin C than cow's milk — has found an export market, and racing has made breeding stock valuable. Alpaca fleece supports thousands of small Andean producers. The wild species have fared less well: the guanaco has lost most of its range to sheep, and the wild Bactrian camel now competes for water with mining operations in a desert that, until recently, almost nobody else wanted.

The camel family

Camels are so closely tied in the popular imagination to the deserts of Africa and Asia that it comes as a surprise to learn that the family they belong to began its history on another continent altogether. The camelids first appear in the fossil record of North America some forty-five million years ago, and for most of their existence they were an exclusively North American group. Only in the last few million years did some of them cross the land bridge into Asia, while others moved south into what is now South America. The North American originals then died out completely, leaving the family with a curiously divided modern range: three species in the deserts and steppes of the Old World, and four in the mountains and grasslands of the New.

The living camelids fall into two groups. The Old World camels are large animals with humps; the South American camelids are smaller, humpless and adapted to altitude rather than heat. The dromedary, with a single hump, is the animal of the Arabian and North African deserts. It has been domesticated for perhaps three thousand years and no longer exists in the wild anywhere, although a substantial feral population roams the interior of Australia, descended from animals imported in the nineteenth century for transport and never gathered up again once motor vehicles arrived. The domesticated Bactrian camel, which has two humps, belongs to the colder deserts and steppes of Central Asia, where winter temperatures can fall far below freezing.

A third Old World species was recognised only recently. The wild Bactrian camel of the Gobi was long assumed to be a feral descendant of domesticated stock, but genetic work has shown it to be a separate species that parted from the domesticated line long before domestication began. Fewer than a thousand survive, in a handful of populations on the Mongolian and Chinese sides of the desert, and it is among the most endangered large mammals in the world. It is also the only camelid able to live on water too salty for the domesticated form to drink.

In South America the pattern of wild and domesticated forms is repeated. The guanaco is a wild animal of the Andes and the Patagonian plains, and from it the llama was domesticated, several thousand years ago, as a pack animal — the only beast of burden the pre-Columbian Andes possessed. The vicuna, the smallest of the family, lives on high grassland above three and a half thousand metres and is the wild ancestor of the alpaca, which was bred not for carrying but for its fleece. Vicuna fibre is the finest produced by any animal, and under the Inca the animals were rounded up, shorn and released again in a communal drive; the practice was revived in the twentieth century after hunting had cut the species to a few thousand.

What unites all seven species is a set of adaptations that have very little to do with humps. The most striking is in the blood: camelids are the only mammals whose red blood cells are oval rather than round. The shape allows the cells to keep flowing when the blood thickens through water loss, and to swell without bursting when the animal drinks again. A dromedary can lose a quarter of its body water — a level that would kill most mammals — and then replace it in a single long drink.

The hump itself stores fat, not water, and the distinction matters: fat gathered into one mass on the back leaves the rest of the body free to shed heat, whereas an even layer of the same fat would trap it. A camel also allows its body temperature to drift upwards through the day rather than sweating to hold it steady, and only begins to sweat when it passes about 41 degrees Celsius. The saving in water is considerable. Other features are more obvious: nostrils that close against blowing sand, two rows of eyelashes, and a transparent third eyelid that can be drawn across the eye without blinding the animal.

The feet are not hooves. Each foot ends in two toes resting on a broad elastic pad, which spreads the animal's weight over soft ground and is the reason camels cross sand that would defeat a horse. The same pad serves the vicuna on loose mountain scree. Camelids are also commonly called ruminants, which is not quite right: they chew the cud and ferment their food in a chambered stomach, but the stomach has three chambers rather than the four of cattle and sheep, and the two groups arrived at the arrangement independently.

The family's economic importance has shifted rather than declined. Camels are no longer the freight system of the Sahara, but camel milk — lower in fat and higher in vitamin C than cow's milk — has found an export market, and racing has made breeding stock valuable. Alpaca fleece supports thousands of small Andean producers. The wild species have fared less well: the guanaco has lost most of its range to sheep, and the wild Bactrian camel now competes for water with mining operations in a desert that, until recently, almost nobody else wanted.

The camel family

Camels are so closely tied in the popular imagination to the deserts of Africa and Asia that it comes as a surprise to learn that the family they belong to began its history on another continent altogether. The camelids first appear in the fossil record of North America some forty-five million years ago, and for most of their existence they were an exclusively North American group. Only in the last few million years did some of them cross the land bridge into Asia, while others moved south into what is now South America. The North American originals then died out completely, leaving the family with a curiously divided modern range: three species in the deserts and steppes of the Old World, and four in the mountains and grasslands of the New.

The living camelids fall into two groups. The Old World camels are large animals with humps; the South American camelids are smaller, humpless and adapted to altitude rather than heat. The dromedary, with a single hump, is the animal of the Arabian and North African deserts. It has been domesticated for perhaps three thousand years and no longer exists in the wild anywhere, although a substantial feral population roams the interior of Australia, descended from animals imported in the nineteenth century for transport and never gathered up again once motor vehicles arrived. The domesticated Bactrian camel, which has two humps, belongs to the colder deserts and steppes of Central Asia, where winter temperatures can fall far below freezing.

A third Old World species was recognised only recently. The wild Bactrian camel of the Gobi was long assumed to be a feral descendant of domesticated stock, but genetic work has shown it to be a separate species that parted from the domesticated line long before domestication began. Fewer than a thousand survive, in a handful of populations on the Mongolian and Chinese sides of the desert, and it is among the most endangered large mammals in the world. It is also the only camelid able to live on water too salty for the domesticated form to drink.

In South America the pattern of wild and domesticated forms is repeated. The guanaco is a wild animal of the Andes and the Patagonian plains, and from it the llama was domesticated, several thousand years ago, as a pack animal — the only beast of burden the pre-Columbian Andes possessed. The vicuna, the smallest of the family, lives on high grassland above three and a half thousand metres and is the wild ancestor of the alpaca, which was bred not for carrying but for its fleece. Vicuna fibre is the finest produced by any animal, and under the Inca the animals were rounded up, shorn and released again in a communal drive; the practice was revived in the twentieth century after hunting had cut the species to a few thousand.

What unites all seven species is a set of adaptations that have very little to do with humps. The most striking is in the blood: camelids are the only mammals whose red blood cells are oval rather than round. The shape allows the cells to keep flowing when the blood thickens through water loss, and to swell without bursting when the animal drinks again. A dromedary can lose a quarter of its body water — a level that would kill most mammals — and then replace it in a single long drink.

The hump itself stores fat, not water, and the distinction matters: fat gathered into one mass on the back leaves the rest of the body free to shed heat, whereas an even layer of the same fat would trap it. A camel also allows its body temperature to drift upwards through the day rather than sweating to hold it steady, and only begins to sweat when it passes about 41 degrees Celsius. The saving in water is considerable. Other features are more obvious: nostrils that close against blowing sand, two rows of eyelashes, and a transparent third eyelid that can be drawn across the eye without blinding the animal.

The feet are not hooves. Each foot ends in two toes resting on a broad elastic pad, which spreads the animal's weight over soft ground and is the reason camels cross sand that would defeat a horse. The same pad serves the vicuna on loose mountain scree. Camelids are also commonly called ruminants, which is not quite right: they chew the cud and ferment their food in a chambered stomach, but the stomach has three chambers rather than the four of cattle and sheep, and the two groups arrived at the arrangement independently.

The family's economic importance has shifted rather than declined. Camels are no longer the freight system of the Sahara, but camel milk — lower in fat and higher in vitamin C than cow's milk — has found an export market, and racing has made breeding stock valuable. Alpaca fleece supports thousands of small Andean producers. The wild species have fared less well: the guanaco has lost most of its range to sheep, and the wild Bactrian camel now competes for water with mining operations in a desert that, until recently, almost nobody else wanted.

Wind comes back to cargo shipping — Why merchant ships are growing sails again, and what the sails can and cannot do

A. Merchant sailing ships did not disappear because they stopped working. They disappeared because coal, and then oil, made schedules predictable, and predictability was worth more to a shipping line than free propulsion. For most of the twentieth century that trade-off was not seriously questioned. It is being questioned now, for two reasons that have nothing to do with nostalgia: fuel is the largest single operating cost of a merchant ship, and shipping produces close to three per cent of the world's carbon dioxide emissions, a share that climate agreements drawn up country by country left unaccounted for.

B. The regulatory position changed in stages. The International Maritime Organization, which sets rules for shipping worldwide, adopted a target of net zero greenhouse gas emissions from international shipping by or around the middle of the century, and from 2023 began rating vessels already in service on their carbon intensity. A ship that rates badly for three years in a row must submit a corrective plan. None of this requires sails. What it does is put a price on every tonne of fuel burnt, and that is enough to turn a device saving eight per cent of fuel into something worth installing.

C. The oldest of the devices on offer is also the strangest. A Flettner rotor is not a sail but a tall spinning cylinder, turned by a small motor, which generates sideways thrust when wind passes it — an effect named after the nineteenth-century German physicist who described it. The engineer Anton Flettner fitted rotors to a converted schooner in 1924 and sent the vessel across the Atlantic two years later. The idea then lay unused for some sixty years. Modern versions, up to thirty metres tall, have been installed on tankers and ferries, and independent monitoring has reported fuel savings of roughly eight to twelve per cent on favourable routes.

D. A second approach abandons the cylinder and returns to something recognisably a sail, but built as a rigid wing rather than a sheet of cloth. Wings of this kind, developed for racing yachts, are more efficient than soft sails and can be trimmed automatically; the largest proposals are for wings that telescope down flat so that the ship can pass under bridges and load cargo. The drawback is deck space. A container ship earns money by filling its deck, and a wing standing over a hold hatch has to save a great deal of fuel to pay for the boxes it displaces. For that reason the concept has advanced furthest on car carriers and bulk carriers, whose decks are otherwise idle.

E. Kites avoid the deck problem altogether by working far above the ship. A towing kite flown at two or three hundred metres reaches air that is both stronger and steadier than the wind at deck level, and the pull is carried down a single line to a mast at the bow. Because the kite flies in figures of eight rather than sitting still, it develops far more force than its area alone would suggest. Handling it is the difficulty: launch and recovery have to be automatic, and a system that sends crew onto an open deck in bad weather will not be used. A fourth device, the suction wing, is a fixed hollow aerofoil that draws air through slots in its surface to keep the airflow attached; it is short, needs no rigging and produces useful thrust from a compact structure, though rather less of it.

F. None of these devices propels a modern cargo ship on its own, and no serious proposal claims otherwise. What they do is reduce the load on the engine, and how much they reduce it depends less on the technology than on the route. Wind assistance pays on long ocean crossings with steady beam winds and pays very little on short coastal runs through crowded water. The most valuable change may therefore be one that involves no hardware at all: routing software that treats wind as an asset to be sought rather than an obstacle to be endured, and a willingness to accept a slower and less rigid schedule. That last condition is the one the industry gave up a century ago, and the one it finds hardest to take back.

Wind comes back to cargo shipping — Why merchant ships are growing sails again, and what the sails can and cannot do

A. Merchant sailing ships did not disappear because they stopped working. They disappeared because coal, and then oil, made schedules predictable, and predictability was worth more to a shipping line than free propulsion. For most of the twentieth century that trade-off was not seriously questioned. It is being questioned now, for two reasons that have nothing to do with nostalgia: fuel is the largest single operating cost of a merchant ship, and shipping produces close to three per cent of the world's carbon dioxide emissions, a share that climate agreements drawn up country by country left unaccounted for.

B. The regulatory position changed in stages. The International Maritime Organization, which sets rules for shipping worldwide, adopted a target of net zero greenhouse gas emissions from international shipping by or around the middle of the century, and from 2023 began rating vessels already in service on their carbon intensity. A ship that rates badly for three years in a row must submit a corrective plan. None of this requires sails. What it does is put a price on every tonne of fuel burnt, and that is enough to turn a device saving eight per cent of fuel into something worth installing.

C. The oldest of the devices on offer is also the strangest. A Flettner rotor is not a sail but a tall spinning cylinder, turned by a small motor, which generates sideways thrust when wind passes it — an effect named after the nineteenth-century German physicist who described it. The engineer Anton Flettner fitted rotors to a converted schooner in 1924 and sent the vessel across the Atlantic two years later. The idea then lay unused for some sixty years. Modern versions, up to thirty metres tall, have been installed on tankers and ferries, and independent monitoring has reported fuel savings of roughly eight to twelve per cent on favourable routes.

D. A second approach abandons the cylinder and returns to something recognisably a sail, but built as a rigid wing rather than a sheet of cloth. Wings of this kind, developed for racing yachts, are more efficient than soft sails and can be trimmed automatically; the largest proposals are for wings that telescope down flat so that the ship can pass under bridges and load cargo. The drawback is deck space. A container ship earns money by filling its deck, and a wing standing over a hold hatch has to save a great deal of fuel to pay for the boxes it displaces. For that reason the concept has advanced furthest on car carriers and bulk carriers, whose decks are otherwise idle.

E. Kites avoid the deck problem altogether by working far above the ship. A towing kite flown at two or three hundred metres reaches air that is both stronger and steadier than the wind at deck level, and the pull is carried down a single line to a mast at the bow. Because the kite flies in figures of eight rather than sitting still, it develops far more force than its area alone would suggest. Handling it is the difficulty: launch and recovery have to be automatic, and a system that sends crew onto an open deck in bad weather will not be used. A fourth device, the suction wing, is a fixed hollow aerofoil that draws air through slots in its surface to keep the airflow attached; it is short, needs no rigging and produces useful thrust from a compact structure, though rather less of it.

F. None of these devices propels a modern cargo ship on its own, and no serious proposal claims otherwise. What they do is reduce the load on the engine, and how much they reduce it depends less on the technology than on the route. Wind assistance pays on long ocean crossings with steady beam winds and pays very little on short coastal runs through crowded water. The most valuable change may therefore be one that involves no hardware at all: routing software that treats wind as an asset to be sought rather than an obstacle to be endured, and a willingness to accept a slower and less rigid schedule. That last condition is the one the industry gave up a century ago, and the one it finds hardest to take back.

Wind comes back to cargo shipping — Why merchant ships are growing sails again, and what the sails can and cannot do

A. Merchant sailing ships did not disappear because they stopped working. They disappeared because coal, and then oil, made schedules predictable, and predictability was worth more to a shipping line than free propulsion. For most of the twentieth century that trade-off was not seriously questioned. It is being questioned now, for two reasons that have nothing to do with nostalgia: fuel is the largest single operating cost of a merchant ship, and shipping produces close to three per cent of the world's carbon dioxide emissions, a share that climate agreements drawn up country by country left unaccounted for.

B. The regulatory position changed in stages. The International Maritime Organization, which sets rules for shipping worldwide, adopted a target of net zero greenhouse gas emissions from international shipping by or around the middle of the century, and from 2023 began rating vessels already in service on their carbon intensity. A ship that rates badly for three years in a row must submit a corrective plan. None of this requires sails. What it does is put a price on every tonne of fuel burnt, and that is enough to turn a device saving eight per cent of fuel into something worth installing.

C. The oldest of the devices on offer is also the strangest. A Flettner rotor is not a sail but a tall spinning cylinder, turned by a small motor, which generates sideways thrust when wind passes it — an effect named after the nineteenth-century German physicist who described it. The engineer Anton Flettner fitted rotors to a converted schooner in 1924 and sent the vessel across the Atlantic two years later. The idea then lay unused for some sixty years. Modern versions, up to thirty metres tall, have been installed on tankers and ferries, and independent monitoring has reported fuel savings of roughly eight to twelve per cent on favourable routes.

D. A second approach abandons the cylinder and returns to something recognisably a sail, but built as a rigid wing rather than a sheet of cloth. Wings of this kind, developed for racing yachts, are more efficient than soft sails and can be trimmed automatically; the largest proposals are for wings that telescope down flat so that the ship can pass under bridges and load cargo. The drawback is deck space. A container ship earns money by filling its deck, and a wing standing over a hold hatch has to save a great deal of fuel to pay for the boxes it displaces. For that reason the concept has advanced furthest on car carriers and bulk carriers, whose decks are otherwise idle.

E. Kites avoid the deck problem altogether by working far above the ship. A towing kite flown at two or three hundred metres reaches air that is both stronger and steadier than the wind at deck level, and the pull is carried down a single line to a mast at the bow. Because the kite flies in figures of eight rather than sitting still, it develops far more force than its area alone would suggest. Handling it is the difficulty: launch and recovery have to be automatic, and a system that sends crew onto an open deck in bad weather will not be used. A fourth device, the suction wing, is a fixed hollow aerofoil that draws air through slots in its surface to keep the airflow attached; it is short, needs no rigging and produces useful thrust from a compact structure, though rather less of it.

F. None of these devices propels a modern cargo ship on its own, and no serious proposal claims otherwise. What they do is reduce the load on the engine, and how much they reduce it depends less on the technology than on the route. Wind assistance pays on long ocean crossings with steady beam winds and pays very little on short coastal runs through crowded water. The most valuable change may therefore be one that involves no hardware at all: routing software that treats wind as an asset to be sought rather than an obstacle to be endured, and a willingness to accept a slower and less rigid schedule. That last condition is the one the industry gave up a century ago, and the one it finds hardest to take back.

Rewilding: letting go of the plan

A. For most of the last century, conservation in Europe meant management. A nature reserve was a place where scrub was cut, water levels were held steady and grazing was controlled, all in order to keep a particular assemblage of species — usually the one recorded when the reserve was designated — in place. Rewilding proposes something close to the opposite: restore the large animals and the natural processes, then step back and accept whatever emerges. It is an appealing idea, and it has spread faster than the evidence supporting it. That is not an argument against it, but it is a reason to be careful about what is claimed on its behalf.

B. The best-known experiment is also the most contested. At Oostvaardersplassen, a tract of reclaimed seabed east of Amsterdam, cattle, horses and red deer were introduced as substitutes for the wild grazers of prehistoric Europe, and their numbers were left to find their own level. For two decades the site was celebrated. Then, in a hard winter, more than half the large animals starved, and the reserve had to be entered and the survivors shot. The scientific case had always been that starvation is what regulates wild populations; the public case collapsed the moment starvation became visible. The lesson was not that the ecology was wrong. It was that a fenced site of six thousand hectares, from which animals cannot disperse, is not a wilderness and cannot be defended as though it were.

C. A different model has worked better. At Knepp, a former dairy and arable estate in southern England, farming was given up in stages from 2001 and replaced with free-roaming pigs, cattle, ponies and deer at low densities. The land was poor, the farm had been losing money, and nobody expected much. Within fifteen years the estate held breeding turtle doves and nightingales, both in steep national decline, and the largest population of purple emperor butterflies in Britain. What made the difference was not the animals in themselves but the untidy vegetation they produced: thorny scrub that sheltered young trees, and a patchwork of open ground, thicket and mature timber that the older, neater reserves had spent decades removing.

D. Rewilding's public appeal, however, rests heavily on a story that its own scientists treat with caution. The return of wolves to Yellowstone in 1995 is widely retold as a chain of consequences running from predator to prey to vegetation and finally to the shape of the rivers themselves. It makes a superb short film. It is also, at best, an oversimplification: elk numbers were falling for several reasons at once, willow recovery has been patchy and appears to depend as much on water and beavers as on wolves, and the researchers who work on the system have spent years publishing corrections that reach a fraction of the audience of the original story. Overstating a case is not a harmless enthusiasm. When a project is sold on a claim that does not hold, the failure of the claim is taken as the failure of the whole approach.

E. Part of the difficulty is that nobody can say precisely what is being restored. Ecological memory is short: a coastline that a fisherman remembers as rich may already have been stripped in his grandfather's time, and each generation takes the depleted state it inherits as normal. This shifting of the baseline means that the word natural describes a moving target, and proposals differ enormously in how far back they aim. Some would be satisfied with the wood pasture of medieval Europe. Others have argued for introducing elephants and lions to North America as stand-ins for the great mammals that vanished there some thirteen thousand years ago — a proposal that, whatever its ecological merits, asks a great deal of the people who would live alongside them.

F. For all that, the practical record is better than the arguments suggest. Beavers, returned to British rivers first without permission and later under licence, have been shown to hold back water in ways that reduce flooding downstream and to improve water quality, and they now have legal protection. European bison, extinct in the wild a century ago, graze again in Poland and Romania. What these successes have in common is modesty: a single species, a defined catchment, a measurable outcome. The grander versions of rewilding may yet be vindicated, but they will be vindicated by results of that kind, accumulated slowly, rather than by the appeal of the idea itself. In the meantime the movement would lose nothing by claiming less.

Rewilding: letting go of the plan

A. For most of the last century, conservation in Europe meant management. A nature reserve was a place where scrub was cut, water levels were held steady and grazing was controlled, all in order to keep a particular assemblage of species — usually the one recorded when the reserve was designated — in place. Rewilding proposes something close to the opposite: restore the large animals and the natural processes, then step back and accept whatever emerges. It is an appealing idea, and it has spread faster than the evidence supporting it. That is not an argument against it, but it is a reason to be careful about what is claimed on its behalf.

B. The best-known experiment is also the most contested. At Oostvaardersplassen, a tract of reclaimed seabed east of Amsterdam, cattle, horses and red deer were introduced as substitutes for the wild grazers of prehistoric Europe, and their numbers were left to find their own level. For two decades the site was celebrated. Then, in a hard winter, more than half the large animals starved, and the reserve had to be entered and the survivors shot. The scientific case had always been that starvation is what regulates wild populations; the public case collapsed the moment starvation became visible. The lesson was not that the ecology was wrong. It was that a fenced site of six thousand hectares, from which animals cannot disperse, is not a wilderness and cannot be defended as though it were.

C. A different model has worked better. At Knepp, a former dairy and arable estate in southern England, farming was given up in stages from 2001 and replaced with free-roaming pigs, cattle, ponies and deer at low densities. The land was poor, the farm had been losing money, and nobody expected much. Within fifteen years the estate held breeding turtle doves and nightingales, both in steep national decline, and the largest population of purple emperor butterflies in Britain. What made the difference was not the animals in themselves but the untidy vegetation they produced: thorny scrub that sheltered young trees, and a patchwork of open ground, thicket and mature timber that the older, neater reserves had spent decades removing.

D. Rewilding's public appeal, however, rests heavily on a story that its own scientists treat with caution. The return of wolves to Yellowstone in 1995 is widely retold as a chain of consequences running from predator to prey to vegetation and finally to the shape of the rivers themselves. It makes a superb short film. It is also, at best, an oversimplification: elk numbers were falling for several reasons at once, willow recovery has been patchy and appears to depend as much on water and beavers as on wolves, and the researchers who work on the system have spent years publishing corrections that reach a fraction of the audience of the original story. Overstating a case is not a harmless enthusiasm. When a project is sold on a claim that does not hold, the failure of the claim is taken as the failure of the whole approach.

E. Part of the difficulty is that nobody can say precisely what is being restored. Ecological memory is short: a coastline that a fisherman remembers as rich may already have been stripped in his grandfather's time, and each generation takes the depleted state it inherits as normal. This shifting of the baseline means that the word natural describes a moving target, and proposals differ enormously in how far back they aim. Some would be satisfied with the wood pasture of medieval Europe. Others have argued for introducing elephants and lions to North America as stand-ins for the great mammals that vanished there some thirteen thousand years ago — a proposal that, whatever its ecological merits, asks a great deal of the people who would live alongside them.

F. For all that, the practical record is better than the arguments suggest. Beavers, returned to British rivers first without permission and later under licence, have been shown to hold back water in ways that reduce flooding downstream and to improve water quality, and they now have legal protection. European bison, extinct in the wild a century ago, graze again in Poland and Romania. What these successes have in common is modesty: a single species, a defined catchment, a measurable outcome. The grander versions of rewilding may yet be vindicated, but they will be vindicated by results of that kind, accumulated slowly, rather than by the appeal of the idea itself. In the meantime the movement would lose nothing by claiming less.

Rewilding: letting go of the plan

A. For most of the last century, conservation in Europe meant management. A nature reserve was a place where scrub was cut, water levels were held steady and grazing was controlled, all in order to keep a particular assemblage of species — usually the one recorded when the reserve was designated — in place. Rewilding proposes something close to the opposite: restore the large animals and the natural processes, then step back and accept whatever emerges. It is an appealing idea, and it has spread faster than the evidence supporting it. That is not an argument against it, but it is a reason to be careful about what is claimed on its behalf.

B. The best-known experiment is also the most contested. At Oostvaardersplassen, a tract of reclaimed seabed east of Amsterdam, cattle, horses and red deer were introduced as substitutes for the wild grazers of prehistoric Europe, and their numbers were left to find their own level. For two decades the site was celebrated. Then, in a hard winter, more than half the large animals starved, and the reserve had to be entered and the survivors shot. The scientific case had always been that starvation is what regulates wild populations; the public case collapsed the moment starvation became visible. The lesson was not that the ecology was wrong. It was that a fenced site of six thousand hectares, from which animals cannot disperse, is not a wilderness and cannot be defended as though it were.

C. A different model has worked better. At Knepp, a former dairy and arable estate in southern England, farming was given up in stages from 2001 and replaced with free-roaming pigs, cattle, ponies and deer at low densities. The land was poor, the farm had been losing money, and nobody expected much. Within fifteen years the estate held breeding turtle doves and nightingales, both in steep national decline, and the largest population of purple emperor butterflies in Britain. What made the difference was not the animals in themselves but the untidy vegetation they produced: thorny scrub that sheltered young trees, and a patchwork of open ground, thicket and mature timber that the older, neater reserves had spent decades removing.

D. Rewilding's public appeal, however, rests heavily on a story that its own scientists treat with caution. The return of wolves to Yellowstone in 1995 is widely retold as a chain of consequences running from predator to prey to vegetation and finally to the shape of the rivers themselves. It makes a superb short film. It is also, at best, an oversimplification: elk numbers were falling for several reasons at once, willow recovery has been patchy and appears to depend as much on water and beavers as on wolves, and the researchers who work on the system have spent years publishing corrections that reach a fraction of the audience of the original story. Overstating a case is not a harmless enthusiasm. When a project is sold on a claim that does not hold, the failure of the claim is taken as the failure of the whole approach.

E. Part of the difficulty is that nobody can say precisely what is being restored. Ecological memory is short: a coastline that a fisherman remembers as rich may already have been stripped in his grandfather's time, and each generation takes the depleted state it inherits as normal. This shifting of the baseline means that the word natural describes a moving target, and proposals differ enormously in how far back they aim. Some would be satisfied with the wood pasture of medieval Europe. Others have argued for introducing elephants and lions to North America as stand-ins for the great mammals that vanished there some thirteen thousand years ago — a proposal that, whatever its ecological merits, asks a great deal of the people who would live alongside them.

F. For all that, the practical record is better than the arguments suggest. Beavers, returned to British rivers first without permission and later under licence, have been shown to hold back water in ways that reduce flooding downstream and to improve water quality, and they now have legal protection. European bison, extinct in the wild a century ago, graze again in Poland and Romania. What these successes have in common is modesty: a single species, a defined catchment, a measurable outcome. The grander versions of rewilding may yet be vindicated, but they will be vindicated by results of that kind, accumulated slowly, rather than by the appeal of the idea itself. In the meantime the movement would lose nothing by claiming less.