IELTS CAM Inspired 10 - Reading Test 4 with Practice Test, Answers And Explanation
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IELTS CAM Inspired 10 - Reading Test 4 With Practice Test, Answers And Explanation
Passage
❓ Câu hỏi passage 1
Question 1 - 6
Complete the notes below.
Choose ONE WORD AND/OR A NUMBER from the passage for each answer.
Wildfires
• Ways in which today's fires differ from those of the past:
– they break out more often
– they reach higher temperatures
– they move at greater speed
– the direction the fires take is much less
1.
– in area, one megafire can match about
2.
average fires from an earlier generation
• Why today's fires cause more harm than they used to:
– in a number of the last few years,
3.
has stayed well below normal
– because fires are put out so fast,
4.
is no longer removed naturally and now feeds the worst blazes
– the average yearly temperature has climbed
– the yearly fire period has lengthened by roughly
5.
days since earlier decades
– ever more homes are springing up in
6.
areas
Question 7 - 13
Do the following statements agree with the information given in the Reading Passage?
TRUE if the statement agrees with the information
FALSE if the statement contradicts the information
NOT GIVEN if it is impossible to say what the writer thinks about this
7
The amount of undeveloped land in California has increased over the past ten years.
8
Most of the new houses in California are bought by people moving in from other states.
9
Observers say fire crews now deal with erratic, fast-spreading fires more effectively than they once did.
10
The modern engines and aircraft the state had promised never materialised.
11
The money spent on fighting fires increased, even as many other public schemes had their funding sharply reduced.
12
Other states have asked California to pay for improvements to their own emergency communication systems.
13
Curtis Ballard believes wildfire deaths will remain as high as they were in the past.
Passage
❓ Câu hỏi passage 2
Question 14 - 18
Complete the summary below.
Choose NO MORE THAN TWO WORDS from the passage for each answer.
For many years, psychologists assumed that the key that make up someone's personality are laid down early in life and stay fixed. Positive psychologists take a different view. They regard the qualities people prize not as inborn gifts but as a form of that governs how we react to the world, and they hold that these can be trained. Whatever the quality, its development calls for an unexpectedly varied set of . The effort pays off, since it can help a person fulfil their whole . It may even call for discomfort: to feel greater and passion in daily life, for example, you must be ready to accept unpleasant emotions.
Question 19 - 22
Look at the following statements and the list of people below.
Match each statement with the correct person, A-G.
Write the correct letter, A-G.
List of Findings
A
Marisa Delgado
B
Emil Feld
C
Anders Holt
D
Bram Kessler
E
Petra Nowak
F
Devon Rask
G
Ingrid Solheim
19
A person's optimism is better built by acting than by trying to think positively.
20
Someone came to see that the real limit on their ability lay far beyond what they had feared.
21
A newcomer to any activity has to be willing to look foolish.
22
Bravery is something that can be developed rather than simply possessed.
Question 23 - 26
Reading Passage 2 has eight sections, A-H.
Which section contains the following information?
Write the correct letter, A-H.
23
a claim that demanding pursuits are rewarding precisely because they are hard
24
the recommendation to keep a daily record of things that go well
25
an example of someone whose changed social manner eventually became automatic
26
an account of someone who turned a personal misfortune into assistance for people caught in a comparable plight
Passage
❓ Câu hỏi passage 3
Question 27 - 31
Choose the correct letter, A, B, C or D.
Write the correct letter in boxes on your answer sheet.
27
When the writer discusses the theory put forward by Anton Reuvers, he indicates that
A
early twentieth-century biologists altered it.
B
it lent weight to the idea of throwbacks.
C
it was named after him straight away.
D
it rested on decades of fieldwork.
28
The fin whale landed off southern Chile is brought up because of
A
the remarkable size of the creature.
B
the explanation offered for its strange anatomy.
C
the dispute it stirred up locally.
D
the way it bore out Reuvers's rule.
29
What does the writer say about 'silent genes'?
A
Their number differs from one species to another.
B
Krause took issue with the term.
C
They remain viable without limit.
D
They can restore characteristics that had been lost.
30
The writer refers to the 'lake-child' salamander in order to show that
A
it develops in the way typical of most amphibians.
B
its ancestors are now studied intensively.
C
it lends support to Krause's account.
D
it has repeatedly shed and recovered a single ability.
31
Which of these is a claim made by Brandt?
A
His conclusions extend to other groups of lizards.
B
On more than one occasion, the reed lizards have lost a feature and then grown it back.
C
His work confirms what Krause proposed.
D
Their evolution was driven by environmental conditions.
Question 32 - 36
Complete each of the following statements with the best ending A-G from the box below.
List of Endings
A
the emergence of one and the same feature in species that are not related.
B
the contrasting conclusions of Reuvers and Halász.
C
the puzzle of how vanished traits can return.
D
comparisons made between conduct and physical form.
E
the idea that evolution can run in reverse.
F
the lasting survival of the biological instructions needed to build a trait.
G
the scepticism surrounding evolutionary throwbacks.
Biologists spent decades refusing to accept
32
Two conflicting positions on throwbacks can be seen in
33
The discovery of throwback cases gave rise to
34
Birds and bats are cited as an instance of
35
Brandt's results might be accounted for by
36
Question 37 - 40
Do the following statements agree with the information given in Reading Passage?
In following statements below, choose
YES if the statement agrees with the information
NO if the statement contradicts the information
NOT GIVEN if it is impossible to say what the writer thinks about this
37
In appearance, some of the reed lizards are closer to snakes than to other lizards.
38
Brandt's investigation of the reed lizards took several years to complete.
39
In many species, traits belonging to distant ancestors appear in the early embryo and are removed only later.
40
The writer holds that inactive genes remain usable well beyond a ten-million-year limit.
DOL IELTS Đình Lực
21/10/2026
📖 Bài đọc passage 1
The megafires of California
Drought, the spread of housing and a surplus of dry tinder are producing bigger, hotter fires across the western United States
Across the western United States, wildfires have become a mounting danger, and nowhere suffers more than Southern California. Why do the crews tackling the region's ever more frequent blazes find them so hard to contain, when they are better prepared than ever and have decades of experience with fires driven by the 'Santa Ana Winds'? The reason, specialists say, lies in the fires themselves: compared with those of the past, today's burn hotter, move faster and follow far less predictable routes.
Megafires, or 'siege fires', are blazes that consume 400,000 acres or more — about eight times the area a typical forest fire destroyed two decades ago. In terms of acreage reduced to ash, several recent fires rank among the largest California has ever known, according to state data and news reports.
One reason for these unusually fierce fires is climatic: a region with naturally dry summers has, over many of the past years, had far less rain than normal. Another, experts say, goes back to a century-long US Forest Service policy of putting wildfires out as quickly as possible.
The unintended result was that underbrush was no longer cleared away by nature — and it is this underbrush that now gives megafires most of their fuel.
Experts add three more drivers. The first is a warming climate, seen in a two-degree Fahrenheit rise in mean annual temperature across the western states. The second is the fire season, now on average sixty days longer than twenty years ago. The third is a growing tendency to build houses in heavily wooded country.
'More and more, the homes we build sit inside fire-prone ecosystems,' says Dr Ivan Petrescu, a fire ecologist at the Cascade Institute for Environmental Research in Boulder, Colorado. 'In much of the western forests, doing that is like putting a house on the side of an active volcano.'
For at least a decade, California has been adding more than 500,000 residents a year, and new housing has spread to keep pace. Where open ground once lay, houses now stand, and each of them, according to Frank Delgado of the state firefighters' union, gives the flames more to burn and greater intensity. So much dry land, so many settlements that could catch alight and so many separate fronts to fight, he adds, turn the work into a nearly impossible task.
Still, the state earns high praise from many specialists for the readiness it has built up recently — a shift that followed several of the largest blazes on record, which scorched thousands of acres, reduced thousands of homes to ruins and claimed many lives. Crews had once been blamed for mishandling that let fires spread when they could have been checked; now, observers report, those same crews cope with the strange demands of fires hopping between neighbourhoods and canyons far more capably than in the past.
What the state pledged — newer engines, planes and helicopters for the fire lines — has duly been delivered. Where unions once complained about decrepit equipment, ageing engines and inadequate fire-safety plans, they now commend the state's resolve, observing that firefighting budgets have climbed even as many other programmes suffered deep cuts. 'We're glad the present administration has stood firmly behind us and found the money for the infrastructure we long asked for,' says Delgado.
Money has gone not only into upgrading the engines — which must travel across a huge state and negotiate its winding canyon roads — but also into stronger command-and-control centres and the methods for running them. During the sieges of earlier years, recalls Lorna Whitfield, head of the state's Emergency Response and Rescue Bureau, other states and agencies were willing to send mutual aid, yet her teams found it impossible to communicate with them adequately.
Communication procedures were later examined and rebuilt by a commission, after which, she says, the state's overall response grew markedly more professional and quicker to respond. Government officials and ordinary residents alike now feel that firefighters drawn from many states and agencies work with a speed, commitment and coordination that deliver greater efficiency than earlier 'siege fire' episodes ever managed.
Southern California has also tightened its building codes of late, revised how evacuations are run, and bought in new technology. 'What we've witnessed has left me deeply impressed,' says Curtis Ballard, a lawyer based in the region who twice had to abandon his house and his practice as wildfires bore down. 'Whatever destruction fires may still bring, the loss of life we once suffered will not happen again, because of the prevention and firefighting measures now established,' he says.
Character need not be permanent. A little experimentation, it turns out, lets people remake their temperaments and pour fresh courage, optimism, passion and joy into how they live.
A
A. For a long time the profession assumed the opposite: that no one's character truly shifts, and that the key traits of a personality are fixed in early childhood. Lately, though, how we might change has drawn closer scrutiny. Positive psychologists have drawn up two dozen admired qualities — loyalty and kindness among them — and asked why a lucky few possess them effortlessly. Their finding is that many such qualities are really habitual behaviour, and this behaviour shapes how we answer the world. Encouragingly, all of it can be learned. Optimism is among the handful that come more readily than the rest. Building any quality, though, means picking up a range of skills — wide-ranging and, now and then, unexpected. Greater joy and passion in your days, for example, are within reach only if you are willing to sit with negative emotions instead of dodging them. Tend to your qualities like this, and your full potential comes closer.
B
Anders Holt, a psychology professor at Rennwick University, points to his own case. Most personality traits, he argues, really can be altered — "the case for that is strong," he says. Shy by nature, Holt recognised early in academic life that reticence would be fatal at the lecture podium, so he trained himself into someone more outgoing, able to hold a room. What began as effort is now automatic: "my outgoing manner these days is entirely spontaneous."
C
Bram Kessler went through much the same shift. While getting ready for university, he was injured in an accident that ended his sporting career. Once there, he found that, beyond routine counselling, his university offered nothing for students who were recovering physically while battling depression. So he set up a support group for others in the same predicament. That he acted at all while still in pain is just how an optimist responds.
D
Optimism, in the view of Marisa Delgado — a psychology professor at the University of Haldane — is a product of optimistic conduct, not of positive thought. Her advice: train yourself to notice good fortune by setting down, day by day, three things that turned out well. Keep it up, and the belief slowly takes hold that favourable outcomes are simply how life runs — at which point acting becomes much easier.
E
The mark of a real passion is how deeply its owner is drawn into it. Freediving is Ingrid Solheim's — a sport whose competitors sink far beneath the surface with no tanks or breathing gear at all. Seven world records have fallen to her since 2002, and a single breath lasts her five minutes. Hard as the sport is on the body, it presses harder still on the mind. Her breakthrough was to prise apart two things — her fears, and a truthful reckoning of what body and mind could manage. "There was a ceiling on my freediving," she says, "but it stood nowhere near where I'd pictured it."
F
Discovering a pursuit that fires you up can enrich any life. The snag with an all-consuming passion, observes Brenmark University psychologist Lorcan Vey, is that "it takes discipline, effort and skill — which is exactly why it repays you so well." And for the raw beginner, Devon Rask, another psychologist, has a caution: "Your own ignorance is something you will have to tolerate, even laugh at. Brace yourself, too, to welcome feelings you would rather not have."
G
Niko Varga, a physician-scientist, was deeply unhappy when he took up his PhD at Kestrel Medical School in 2003: the research he was doing pulled against his curiosity about healing. So he broke off, and a seven-month stay in Taos introduced him to healing approaches Kestrel had never covered. Back on campus, he changed laboratories, turning to the way cerebrospinal fluid feeds a developing nervous system; and he made himself a promise to seek joy in everything, failure among it, since even that might teach him about his work and his character. What can hold joy back, more than anything, is a mind trained on dodging failure instead of on the satisfaction of a job done well. As Rask puts it, "the path to your goals can be blocked by an obsession with playing safe." At a business lunch, say: are you simply praying to escape without embarrassment, or savouring in advance how absorbing the conversation could be?
H
We tend to picture courage as physical, yet everyday life asks for a different sort. For Emil Feld, a marketing executive, it meant objecting to conduct he judged unethical. A newly appointed manager had taken to intimidating the staff, so Feld kept a careful log of every act of bullying and, aware his own position might suffer for it, in time carried the record to a senior director. In the end it was the manager who left. To Petra Nowak, a psychologist at Calderon University, what Feld did bears out a claim: that courage springs not from an absence of fear but from a sense of moral duty. Nowak holds, too, that courage can be acquired. Many of her students have told her that, faced with a risky moment, they first calmed themselves and then looked for a way to lessen the danger, just as Feld did in setting down his allegations. Adopt a fresh character trait and, over time, you edge nearer to the self you hope to be. Even briefly, though, the attempt can repay you in ways you would not expect — an adventure that runs inward rather than out.
Running in reverse is not something evolution is meant to do; yet the cases pointing the other way keep multiplying, and in certain species that backward step may actually be where their future lies.
To label any creature an 'evolutionary throwback' still provokes argument. Wary of a long-standing rule holding that evolution simply cannot reverse itself, most biologists have shied away from the phrase for close to a hundred years. That rule, however, is now being rewritten, as fresh cases accumulate and genetics sheds new light on them. Throwbacks, it turns out, are not merely possible; on occasion they even help drive evolution forwards.
Scientists call such a throwback an 'atavism', a word borrowed from the Latin atavus, or forefather. Much of its unpleasant flavour can be traced to Viktor Halász, a nineteenth-century Hungarian physician. Criminality, Halász maintained, was inborn rather than acquired, and a wrongdoer could be picked out by particular bodily traits — features he read as reversions to a primitive, less-than-human condition.
As Halász took his measurements, a Dutch palaeontologist, Anton Reuvers, was poring over fossils and arriving at the reverse view. Evolution, he suggested in 1893, could not be undone: no organism, he wrote, can go back — even in part — to a condition its ancestors had already passed through. Biologists of the early twentieth century reached much the same verdict, but softened it into a matter of odds, allowing that nothing forbids evolution from running backwards; it is merely most improbable. In this form the notion of irreversibility took hold, and it became known as 'Reuvers's rule'.
Were Reuvers's rule correct, atavisms ought to be vanishingly rare, if they happened at all. Almost from the moment the idea gained ground, though, awkward exceptions began to surface. A fin whale hauled up off the coast of southern Chile in 1923, for instance, carried a pair of leg-like projections more than a metre long, each with a complete set of limb bones. For the naturalist Halvard Sørensen, only one reading made sense: the animal was a throwback to an ancestor that had lived on land. 'I can see no other explanation,' he wrote in 1925.
So many further cases have turned up since then that calling evolution all but irreversible no longer holds water. A riddle follows from this: how can features lost to a lineage millions of years earlier abruptly return?
In 1996, Milena Krause and her team at Ashford University set out to attach an actual figure to the odds of evolution reversing, and they turned to genetics to do it. Some evolutionary shifts, they noted, destroy genes outright and cannot be undone; others, though, may amount to no more than genes being switched off. Should those dormant — or 'silent' — genes ever be switched on again, the team argued, traits long since lost might resurface.
Krause's group then tried to pin down how probable such an event was. Left unused, they reasoned, a gene steadily gathers random mutations until it is good for nothing; so how long can one persist in a species once it has fallen idle? Their figures suggested that silent genes stand a fair chance of lasting as long as five million years in at least a handful of a population's members, with a few possibly enduring for eight million. Throwbacks, in short, can happen — but only reaching back into the fairly recent evolutionary past.
By way of illustration, the team turned to a group of salamanders living across Guatemala and Arizona. Most amphibians open life as juvenile 'tadpoles' before transforming into adults, and these salamanders are no exception — save for a single species, known to locals as the 'lake-child', which famously stays a juvenile all its life. The obvious reading is that this one lineage, and no other, gave up the capacity to transform. Trace the group's family tree, however, and a different picture emerges: the remaining lineages sprang from an ancestor that had itself already lost that capacity. Transformation in these salamanders is, then, an atavism — one that sits comfortably within Krause's eight-million-year window.
Lately, though, reports have appeared of cases that overshoot this limit, hinting that silent genes are not the whole account. In a paper released last year, the biologist Tomasz Brandt of Valmont University described his study of the evolutionary past of the reed lizards, a group native to the grasslands of eastern Africa. Tiny limbs are common among them; a number could easily be mistaken for snakes, and in a few the toes of the hind limbs have vanished altogether, while other species carry as many as four toes behind. That the toed kinds simply never mislaid their toes is the tidy explanation — but Brandt takes a different line. His reading of the reed lizards' family tree has the toed species growing their toes afresh from toeless forebears; more striking still, toes have been lost and regained not once but repeatedly across tens of millions of years.
What, then, lies behind this? One account holds that such traits vanish and later crop up again, no differently from the way matching structures can arise on their own in wholly unrelated animals — the wings of birds and of bats being a case in point. A second, more arresting account is that the genetic instructions for building toes lingered somehow inside the lizards for tens, even hundreds, of millions of years before being switched back on. Once revived, these atavistic traits conferred an advantage and worked their way through the population, in effect turning evolution around.
Yet if silent genes fall apart within five to eight million years, how could traits lost far earlier be switched on again? Perhaps the answer lies before birth. In many species the early embryo passes through ancestral features on its way to its final form; snake embryos, for instance, put out buds for hind limbs. Ordinarily a developmental programme telling the body to 'lose the leg' erases these as growth proceeds. Where it fails to run, the ancestral feature can stay put, and an atavism results.
Across the western United States, wildfires have become a mounting danger, and nowhere suffers more than Southern California. Why do the crews tackling the region's ever more frequent blazes find them so hard to contain, when they are better prepared than ever and have decades of experience with fires driven by the 'Santa Ana Winds'? The reason, specialists say, lies in the fires themselves: compared with those of the past, today's burn hotter, move faster and follow far less predictable routes.
Megafires, or 'siege fires', are blazes that consume 400,000 acres or more — about eight times the area a typical forest fire destroyed two decades ago. In terms of acreage reduced to ash, several recent fires rank among the largest California has ever known, according to state data and news reports.
One reason for these unusually fierce fires is climatic: a region with naturally dry summers has, over many of the past years, had far less rain than normal. Another, experts say, goes back to a century-long US Forest Service policy of putting wildfires out as quickly as possible.
The unintended result was that underbrush was no longer cleared away by nature — and it is this underbrush that now gives megafires most of their fuel.
Experts add three more drivers. The first is a warming climate, seen in a two-degree Fahrenheit rise in mean annual temperature across the western states. The second is the fire season, now on average sixty days longer than twenty years ago. The third is a growing tendency to build houses in heavily wooded country.
'More and more, the homes we build sit inside fire-prone ecosystems,' says Dr Ivan Petrescu, a fire ecologist at the Cascade Institute for Environmental Research in Boulder, Colorado. 'In much of the western forests, doing that is like putting a house on the side of an active volcano.'
For at least a decade, California has been adding more than 500,000 residents a year, and new housing has spread to keep pace. Where open ground once lay, houses now stand, and each of them, according to Frank Delgado of the state firefighters' union, gives the flames more to burn and greater intensity. So much dry land, so many settlements that could catch alight and so many separate fronts to fight, he adds, turn the work into a nearly impossible task.
Still, the state earns high praise from many specialists for the readiness it has built up recently — a shift that followed several of the largest blazes on record, which scorched thousands of acres, reduced thousands of homes to ruins and claimed many lives. Crews had once been blamed for mishandling that let fires spread when they could have been checked; now, observers report, those same crews cope with the strange demands of fires hopping between neighbourhoods and canyons far more capably than in the past.
What the state pledged — newer engines, planes and helicopters for the fire lines — has duly been delivered. Where unions once complained about decrepit equipment, ageing engines and inadequate fire-safety plans, they now commend the state's resolve, observing that firefighting budgets have climbed even as many other programmes suffered deep cuts. 'We're glad the present administration has stood firmly behind us and found the money for the infrastructure we long asked for,' says Delgado.
Money has gone not only into upgrading the engines — which must travel across a huge state and negotiate its winding canyon roads — but also into stronger command-and-control centres and the methods for running them. During the sieges of earlier years, recalls Lorna Whitfield, head of the state's Emergency Response and Rescue Bureau, other states and agencies were willing to send mutual aid, yet her teams found it impossible to communicate with them adequately.
Communication procedures were later examined and rebuilt by a commission, after which, she says, the state's overall response grew markedly more professional and quicker to respond. Government officials and ordinary residents alike now feel that firefighters drawn from many states and agencies work with a speed, commitment and coordination that deliver greater efficiency than earlier 'siege fire' episodes ever managed.
Southern California has also tightened its building codes of late, revised how evacuations are run, and bought in new technology. 'What we've witnessed has left me deeply impressed,' says Curtis Ballard, a lawyer based in the region who twice had to abandon his house and his practice as wildfires bore down. 'Whatever destruction fires may still bring, the loss of life we once suffered will not happen again, because of the prevention and firefighting measures now established,' he says.
B. Anders Holt, a psychology professor at Rennwick University, points to his own case. Most personality traits, he argues, really can be altered — "the case for that is strong," he says. Shy by nature, Holt recognised early in academic life that reticence would be fatal at the lecture podium, so he trained himself into someone more outgoing, able to hold a room. What began as effort is now automatic: "my outgoing manner these days is entirely spontaneous."
C. Bram Kessler went through much the same shift. While getting ready for university, he was injured in an accident that ended his sporting career. Once there, he found that, beyond routine counselling, his university offered nothing for students who were recovering physically while battling depression. So he set up a support group for others in the same predicament. That he acted at all while still in pain is just how an optimist responds.
D. Optimism, in the view of Marisa Delgado — a psychology professor at the University of Haldane — is a product of optimistic conduct, not of positive thought. Her advice: train yourself to notice good fortune by setting down, day by day, three things that turned out well. Keep it up, and the belief slowly takes hold that favourable outcomes are simply how life runs — at which point acting becomes much easier.
E. The mark of a real passion is how deeply its owner is drawn into it. Freediving is Ingrid Solheim's — a sport whose competitors sink far beneath the surface with no tanks or breathing gear at all. Seven world records have fallen to her since 2002, and a single breath lasts her five minutes. Hard as the sport is on the body, it presses harder still on the mind. Her breakthrough was to prise apart two things — her fears, and a truthful reckoning of what body and mind could manage. "There was a ceiling on my freediving," she says, "but it stood nowhere near where I'd pictured it."
F. Discovering a pursuit that fires you up can enrich any life. The snag with an all-consuming passion, observes Brenmark University psychologist Lorcan Vey, is that "it takes discipline, effort and skill — which is exactly why it repays you so well." And for the raw beginner, Devon Rask, another psychologist, has a caution: "Your own ignorance is something you will have to tolerate, even laugh at. Brace yourself, too, to welcome feelings you would rather not have."
G. Niko Varga, a physician-scientist, was deeply unhappy when he took up his PhD at Kestrel Medical School in 2003: the research he was doing pulled against his curiosity about healing. So he broke off, and a seven-month stay in Taos introduced him to healing approaches Kestrel had never covered. Back on campus, he changed laboratories, turning to the way cerebrospinal fluid feeds a developing nervous system; and he made himself a promise to seek joy in everything, failure among it, since even that might teach him about his work and his character. What can hold joy back, more than anything, is a mind trained on dodging failure instead of on the satisfaction of a job done well. As Rask puts it, "the path to your goals can be blocked by an obsession with playing safe." At a business lunch, say: are you simply praying to escape without embarrassment, or savouring in advance how absorbing the conversation could be?
H. We tend to picture courage as physical, yet everyday life asks for a different sort. For Emil Feld, a marketing executive, it meant objecting to conduct he judged unethical. A newly appointed manager had taken to intimidating the staff, so Feld kept a careful log of every act of bullying and, aware his own position might suffer for it, in time carried the record to a senior director. In the end it was the manager who left. To Petra Nowak, a psychologist at Calderon University, what Feld did bears out a claim: that courage springs not from an absence of fear but from a sense of moral duty. Nowak holds, too, that courage can be acquired. Many of her students have told her that, faced with a risky moment, they first calmed themselves and then looked for a way to lessen the danger, just as Feld did in setting down his allegations. Adopt a fresh character trait and, over time, you edge nearer to the self you hope to be. Even briefly, though, the attempt can repay you in ways you would not expect — an adventure that runs inward rather than out.
To label any creature an 'evolutionary throwback' still provokes argument. Wary of a long-standing rule holding that evolution simply cannot reverse itself, most biologists have shied away from the phrase for close to a hundred years. That rule, however, is now being rewritten, as fresh cases accumulate and genetics sheds new light on them. Throwbacks, it turns out, are not merely possible; on occasion they even help drive evolution forwards.
Scientists call such a throwback an 'atavism', a word borrowed from the Latin atavus, or forefather. Much of its unpleasant flavour can be traced to Viktor Halász, a nineteenth-century Hungarian physician. Criminality, Halász maintained, was inborn rather than acquired, and a wrongdoer could be picked out by particular bodily traits — features he read as reversions to a primitive, less-than-human condition.
As Halász took his measurements, a Dutch palaeontologist, Anton Reuvers, was poring over fossils and arriving at the reverse view. Evolution, he suggested in 1893, could not be undone: no organism, he wrote, can go back — even in part — to a condition its ancestors had already passed through. Biologists of the early twentieth century reached much the same verdict, but softened it into a matter of odds, allowing that nothing forbids evolution from running backwards; it is merely most improbable. In this form the notion of irreversibility took hold, and it became known as 'Reuvers's rule'.
Were Reuvers's rule correct, atavisms ought to be vanishingly rare, if they happened at all. Almost from the moment the idea gained ground, though, awkward exceptions began to surface. A fin whale hauled up off the coast of southern Chile in 1923, for instance, carried a pair of leg-like projections more than a metre long, each with a complete set of limb bones. For the naturalist Halvard Sørensen, only one reading made sense: the animal was a throwback to an ancestor that had lived on land. 'I can see no other explanation,' he wrote in 1925.
So many further cases have turned up since then that calling evolution all but irreversible no longer holds water. A riddle follows from this: how can features lost to a lineage millions of years earlier abruptly return?
In 1996, Milena Krause and her team at Ashford University set out to attach an actual figure to the odds of evolution reversing, and they turned to genetics to do it. Some evolutionary shifts, they noted, destroy genes outright and cannot be undone; others, though, may amount to no more than genes being switched off. Should those dormant — or 'silent' — genes ever be switched on again, the team argued, traits long since lost might resurface.
Krause's group then tried to pin down how probable such an event was. Left unused, they reasoned, a gene steadily gathers random mutations until it is good for nothing; so how long can one persist in a species once it has fallen idle? Their figures suggested that silent genes stand a fair chance of lasting as long as five million years in at least a handful of a population's members, with a few possibly enduring for eight million. Throwbacks, in short, can happen — but only reaching back into the fairly recent evolutionary past.
By way of illustration, the team turned to a group of salamanders living across Guatemala and Arizona. Most amphibians open life as juvenile 'tadpoles' before transforming into adults, and these salamanders are no exception — save for a single species, known to locals as the 'lake-child', which famously stays a juvenile all its life. The obvious reading is that this one lineage, and no other, gave up the capacity to transform. Trace the group's family tree, however, and a different picture emerges: the remaining lineages sprang from an ancestor that had itself already lost that capacity. Transformation in these salamanders is, then, an atavism — one that sits comfortably within Krause's eight-million-year window.
Lately, though, reports have appeared of cases that overshoot this limit, hinting that silent genes are not the whole account. In a paper released last year, the biologist Tomasz Brandt of Valmont University described his study of the evolutionary past of the reed lizards, a group native to the grasslands of eastern Africa. Tiny limbs are common among them; a number could easily be mistaken for snakes, and in a few the toes of the hind limbs have vanished altogether, while other species carry as many as four toes behind. That the toed kinds simply never mislaid their toes is the tidy explanation — but Brandt takes a different line. His reading of the reed lizards' family tree has the toed species growing their toes afresh from toeless forebears; more striking still, toes have been lost and regained not once but repeatedly across tens of millions of years.
What, then, lies behind this? One account holds that such traits vanish and later crop up again, no differently from the way matching structures can arise on their own in wholly unrelated animals — the wings of birds and of bats being a case in point. A second, more arresting account is that the genetic instructions for building toes lingered somehow inside the lizards for tens, even hundreds, of millions of years before being switched back on. Once revived, these atavistic traits conferred an advantage and worked their way through the population, in effect turning evolution around.
Yet if silent genes fall apart within five to eight million years, how could traits lost far earlier be switched on again? Perhaps the answer lies before birth. In many species the early embryo passes through ancestral features on its way to its final form; snake embryos, for instance, put out buds for hind limbs. Ordinarily a developmental programme telling the body to 'lose the leg' erases these as growth proceeds. Where it fails to run, the ancestral feature can stay put, and an atavism results.
To label any creature an 'evolutionary throwback' still provokes argument. Wary of a long-standing rule holding that evolution simply cannot reverse itself, most biologists have shied away from the phrase for close to a hundred years. That rule, however, is now being rewritten, as fresh cases accumulate and genetics sheds new light on them. Throwbacks, it turns out, are not merely possible; on occasion they even help drive evolution forwards.
Scientists call such a throwback an 'atavism', a word borrowed from the Latin atavus, or forefather. Much of its unpleasant flavour can be traced to Viktor Halász, a nineteenth-century Hungarian physician. Criminality, Halász maintained, was inborn rather than acquired, and a wrongdoer could be picked out by particular bodily traits — features he read as reversions to a primitive, less-than-human condition.
As Halász took his measurements, a Dutch palaeontologist, Anton Reuvers, was poring over fossils and arriving at the reverse view. Evolution, he suggested in 1893, could not be undone: no organism, he wrote, can go back — even in part — to a condition its ancestors had already passed through. Biologists of the early twentieth century reached much the same verdict, but softened it into a matter of odds, allowing that nothing forbids evolution from running backwards; it is merely most improbable. In this form the notion of irreversibility took hold, and it became known as 'Reuvers's rule'.
Were Reuvers's rule correct, atavisms ought to be vanishingly rare, if they happened at all. Almost from the moment the idea gained ground, though, awkward exceptions began to surface. A fin whale hauled up off the coast of southern Chile in 1923, for instance, carried a pair of leg-like projections more than a metre long, each with a complete set of limb bones. For the naturalist Halvard Sørensen, only one reading made sense: the animal was a throwback to an ancestor that had lived on land. 'I can see no other explanation,' he wrote in 1925.
So many further cases have turned up since then that calling evolution all but irreversible no longer holds water. A riddle follows from this: how can features lost to a lineage millions of years earlier abruptly return?
In 1996, Milena Krause and her team at Ashford University set out to attach an actual figure to the odds of evolution reversing, and they turned to genetics to do it. Some evolutionary shifts, they noted, destroy genes outright and cannot be undone; others, though, may amount to no more than genes being switched off. Should those dormant — or 'silent' — genes ever be switched on again, the team argued, traits long since lost might resurface.
Krause's group then tried to pin down how probable such an event was. Left unused, they reasoned, a gene steadily gathers random mutations until it is good for nothing; so how long can one persist in a species once it has fallen idle? Their figures suggested that silent genes stand a fair chance of lasting as long as five million years in at least a handful of a population's members, with a few possibly enduring for eight million. Throwbacks, in short, can happen — but only reaching back into the fairly recent evolutionary past.
By way of illustration, the team turned to a group of salamanders living across Guatemala and Arizona. Most amphibians open life as juvenile 'tadpoles' before transforming into adults, and these salamanders are no exception — save for a single species, known to locals as the 'lake-child', which famously stays a juvenile all its life. The obvious reading is that this one lineage, and no other, gave up the capacity to transform. Trace the group's family tree, however, and a different picture emerges: the remaining lineages sprang from an ancestor that had itself already lost that capacity. Transformation in these salamanders is, then, an atavism — one that sits comfortably within Krause's eight-million-year window.
Lately, though, reports have appeared of cases that overshoot this limit, hinting that silent genes are not the whole account. In a paper released last year, the biologist Tomasz Brandt of Valmont University described his study of the evolutionary past of the reed lizards, a group native to the grasslands of eastern Africa. Tiny limbs are common among them; a number could easily be mistaken for snakes, and in a few the toes of the hind limbs have vanished altogether, while other species carry as many as four toes behind. That the toed kinds simply never mislaid their toes is the tidy explanation — but Brandt takes a different line. His reading of the reed lizards' family tree has the toed species growing their toes afresh from toeless forebears; more striking still, toes have been lost and regained not once but repeatedly across tens of millions of years.
What, then, lies behind this? One account holds that such traits vanish and later crop up again, no differently from the way matching structures can arise on their own in wholly unrelated animals — the wings of birds and of bats being a case in point. A second, more arresting account is that the genetic instructions for building toes lingered somehow inside the lizards for tens, even hundreds, of millions of years before being switched back on. Once revived, these atavistic traits conferred an advantage and worked their way through the population, in effect turning evolution around.
Yet if silent genes fall apart within five to eight million years, how could traits lost far earlier be switched on again? Perhaps the answer lies before birth. In many species the early embryo passes through ancestral features on its way to its final form; snake embryos, for instance, put out buds for hind limbs. Ordinarily a developmental programme telling the body to 'lose the leg' erases these as growth proceeds. Where it fails to run, the ancestral feature can stay put, and an atavism results.
