IELTS Academic Reading Practice Test 21

For more than two centuries, one of the most vexing problems in seafaring was the accurate determination of longitude. While latitude could be calculated with relative ease by measuring the angle of the sun at noon or the elevation of the North Star, longitude largely depended on knowing the exact time at a reference port while simultaneously observing local time at sea. A difference of just four minutes in time translated into a positional error of one degree of longitude, which at the equator amounted to roughly 111 kilometres. The pendulum clocks generally available in the seventeenth century were widely regarded as utterly unsuitable for shipboard use, since the pitching and rolling of vessels rendered them inaccurate within hours, and changes in temperature, humidity, and barometric pressure compounded the problem. The result was that ships frequently grounded on coasts they believed lay safely beyond the horizon, with appalling losses of life and cargo.

The catastrophic loss of four British naval vessels off the Isles of Scilly in October 1707, in which more than 1,400 sailors perished, finally is said to have prompted decisive action. The British Parliament passed the Longitude Act in 1714, offering a prize of £20,000 — equivalent to several million pounds in modern currency — to anyone who could devise a practical method for determining longitude to within half a degree on an ocean voyage. A specially convened Board of Longitude was established to evaluate submissions. Astronomers and natural philosophers across Europe proposed various solutions, most based on celestial observations, but these methods demanded clear skies, complicated calculations, and trained observers, conditions rarely met aboard a working ship.

The eventual solution came not from the scientific establishment but from a self-taught Yorkshire carpenter and clockmaker named John Harrison. Beginning in the 1720s, Harrison devoted himself to the construction of a series of increasingly refined timepieces, each designed to keep accurate time despite the violent motion and changing climate of a sea voyage. His first marine timekeeper, designated H1, was completed in 1735. Weighing over thirty kilograms, it used opposed brass bars connected by springs to compensate for the rolling of a ship. On a trial voyage to Lisbon, H1 performed remarkably well, but Harrison himself was dissatisfied and refused to submit it for the prize, requesting further funds to develop an improved version.

Over the following decades, Harrison produced H2 and H3, each incorporating successive innovations. H3 alone took him seventeen years to complete and introduced the bimetallic strip — two strips of different metals fused together — which compensated automatically for changes in temperature. However, it was H4, finished in 1759, that finally satisfied his ambitions. Resembling an oversized pocket watch rather than a piece of furniture, H4 measured only 13 centimetres across and weighed just 1.45 kilograms. On its trial voyage to Jamaica in 1761, H4 lost only 5.1 seconds over the eighty-one-day passage, a level of accuracy that comfortably exceeded the requirements of the Longitude Act.

The Board of Longitude, however, proved reluctant to award the full prize. Members suspected that Harrison's success had been the result of fortunate circumstances and demanded a second sea trial as well as the construction of additional copies to demonstrate that the design could be reproduced by other craftsmen. Harrison, by then in his seventies, complained bitterly of unfair treatment, and the dispute dragged on for years. He ultimately received the full reward in 1773, following a personal intervention by King George III, only three years before his death at the age of eighty-three.

Although Harrison's chronometers represented a triumph of individual genius, their widespread adoption depended upon making such instruments affordable and reproducible. The English clockmaker Larcum Kendall constructed three copies of H4 between 1769 and 1774, the second of which, K2, was carried by Captain William Bligh on HMS Bounty in 1787 and famously remained with the mutineers on Pitcairn Island. Meanwhile, the watchmaker John Arnold simplified Harrison's design and pioneered methods of mass production. By 1815, a competent marine chronometer could be purchased for around £80, and by the middle of the nineteenth century the Royal Navy alone owned more than eight hundred such instruments. The chronometer remained the principal means of determining longitude at sea until the introduction of radio time signals in the 1920s, and continued in regular use as a backup well into the era of satellite navigation.

A Each autumn, hundreds of millions of monarch butterflies (Danaus plexippus) typically embark on one of the most remarkable journeys in the animal kingdom. Departing from breeding grounds across the eastern United States and southern Canada, they travel up to 4,500 kilometres south to a cluster of high-altitude oyamel fir forests in central Mexico, where they generally overwinter in massive aggregations on tree trunks and branches. The migration is widely regarded as staggering not only for its distance but for the fact that no individual butterfly makes the journey twice. The generation that arrives in Mexico is the great-grandchild — or even the great-great-grandchild — of the generation that left Mexico the previous spring. How a creature with a brain weighing less than a milligram can navigate accurately to a destination it has never seen has fascinated biologists for decades.

B The phenomenon was unknown to Western science until 1976, when Canadian zoologist Fred Urquhart and his colleagues, after nearly four decades of tagging butterflies, finally tracked them to their wintering sites in the mountains of Michoacán. Local people in the region had largely long been aware of the dense, fluttering colonies that appeared each November, but the precise locations had remained obscure to outsiders. Urquhart's discovery galvanised scientific interest and prompted the creation of the Monarch Butterfly Biosphere Reserve in 1980, which now covers more than 56,000 hectares of forest and is recognised as a UNESCO World Heritage Site.

C Subsequent research has largely revealed that monarchs employ a sophisticated suite of navigational mechanisms. The most important is a time-compensated sun compass, which allows the butterflies to maintain a southerly heading regardless of the hour of day. Because the sun moves across the sky from east to west, a simple solar reference would lead an animal travelling at noon to head in a quite different direction than one travelling at dawn. To correct for this, monarchs typically rely on a circadian clock located in their antennae, not in their brains, as biologists had previously assumed. Experiments by neurobiologist Steven Reppert at the University of Massachusetts demonstrated this by surgically removing antennae from tagged butterflies and observing that their navigational ability was severely disrupted, even though they remained otherwise healthy.

D A secondary mechanism appears to involve sensitivity to the Earth's magnetic field. In 2014, researchers at Worcester Polytechnic Institute showed that monarchs possess magnetoreceptive cells, possibly involving the photoreceptive protein cryptochrome, which respond to inclination angles in the geomagnetic field. When the butterflies were placed in artificial magnetic fields that simulated those of the equator, they lost their southerly orientation and circled directionlessly. This magnetic sense reportedly likely serves as a backup system on cloudy days, when the sun compass becomes unreliable, although its precise role under natural conditions is still broadly under investigation.

E The destination itself is uniquely suited to the butterflies' physiological needs. The oyamel fir forests are situated between 2,400 and 3,600 metres above sea level, where temperatures generally remain cold enough to keep the butterflies in a state of near-torpor — slowing their metabolism and conserving the lipid reserves they accumulated during the autumn migration — but rarely cold enough to kill them. The dense canopy of fir branches creates a microclimate that buffers the colonies from wind, rain, and frost. In a typical winter, a single tree may bear several hundred thousand butterflies, transforming forest groves into shimmering rust-coloured cathedrals.

F The migration is undertaken by a special generation of monarchs known as the Methuselah generation. While summer monarchs typically live only two to six weeks, individuals that emerge in late August or September enter a state of reproductive diapause that suspends their sexual development and dramatically extends their lifespan to as long as eight months. This diapause is triggered by a combination of shortening day length, falling temperatures, and the ageing of the milkweed plants on which monarch caterpillars exclusively feed. Only when the Methuselah generation begins to fly north in late February or March does its reproductive system mature, enabling it to lay the eggs that would become the next year's first generation.

G In recent decades, the eastern monarch population has declined precipitously, falling by an estimated 80 percent since the 1990s. Several factors contribute to this decline. Illegal logging within the biosphere reserve has reduced the area of overwintering habitat, and agricultural intensification across the United States, particularly the widespread use of herbicide-resistant crops, has dramatically reduced the abundance of milkweed in the butterflies' summer range. Climate change has further disrupted the delicate seasonal cues that govern the migration. Conservation organisations are now collaborating with farmers, schools, and homeowners along the migratory corridor to plant milkweed and nectar-producing flowers, in an effort to restore habitat at a continental scale.

A Classical economic theory has long assumed that individuals are rational agents who allocate their income across present consumption and future savings to maximise lifetime wellbeing. The American economist Franco Modigliani's Life Cycle Hypothesis, formulated in the 1950s, held that people generally save during their working years in order to maintain a stable level of consumption in retirement. Yet decades of empirical evidence reveal that actual savings behaviour bears only a passing resemblance to this elegant model. Across countries with very different cultural and institutional contexts, large fractions of working adults report saving nothing at all in a typical month, and most are unable to meet a moderate unexpected expense from accumulated reserves. The discrepancy between what classical theory predicts and what people actually do has become the central puzzle of a relatively new discipline known as behavioural economics.

B The intellectual origins of behavioural economics can be traced to the collaborative work of two Israeli psychologists, Daniel Kahneman and Amos Tversky, beginning in the late 1960s. Through ingeniously designed experiments, they demonstrated that human judgement systematically departs from the predictions of rational choice theory. People typically weight prospective losses more heavily than equivalent gains, anchor unrelated decisions to whatever number happens to be salient, and apparently overestimate the probability of vivid or recent events. Kahneman's 2002 Nobel Prize in Economic Sciences, awarded for work he had largely conducted with Tversky before the latter's death in 1996, marked the formal acceptance of these ideas into the economic mainstream.

C Among the most consequential cognitive biases identified by behavioural economists is present bias, also known as hyperbolic discounting. Whereas standard economic models generally assume people discount future rewards at a constant rate, real human beings typically exhibit a strong preference for immediate gratification that diminishes sharply once the alternative is also in the future. Asked whether they would prefer £100 today or £110 next week, most people choose the smaller, sooner sum. Asked, however, whether they would prefer £100 in a year or £110 in a year and a week, most choose the larger amount. This inconsistency means that intentions to save largely formed today are routinely overridden by competing impulses when the moment to act actually arrives.

D A second important factor is cognitive overload. Choosing how much to save, in what type of account, with which provider, and under which tax regime requires substantial mental effort. Faced with such complexity, many individuals reportedly choose the path of least resistance, which is inaction. This default effect was illustrated by a celebrated study of US firms conducted by economists Brigitte Madrian and Dennis Shea in 2001. When new employees had to actively opt in to a workplace pension scheme, participation rates hovered around 40 percent in the first months of employment. When the same firms switched to automatic enrolment, with employees having to actively opt out if they did not wish to participate, enrolment leapt to 90 percent within a year. Few opted out, even though the underlying decision was financially identical.

E Mental accounting also plays a powerful role. Although a unit of currency is technically fungible — interchangeable regardless of its source — people frequently treat money differently depending on how they receive it or have largely categorised it. Research by Richard Thaler, who won the Nobel Prize for his contributions to behavioural economics in 2017, has shown that windfalls such as tax refunds and bonuses are far more likely to be spent on luxury items than equivalent sums earned through regular wages. Conversely, households often save aggressively in dedicated accounts labelled for goals such as a holiday or a child's education while simultaneously carrying high-interest credit card debt, a pattern that violates the predictions of a rational allocation model.

F Social influences typically further complicate savings decisions. The economist James Duesenberry observed in the 1940s that households tend to benchmark their consumption against that of their neighbours, peers, and colleagues — a phenomenon he called the relative income hypothesis. More recent research using social media data has confirmed that visible spending by reference groups, such as friends posting photographs of holidays, restaurant meals, and new purchases, exerts a measurable pull on individual expenditure. The corresponding effect on savings is consistently negative, since the desire to keep pace with observed peer consumption competes directly with the willingness to set income aside.

G The practical insights generated by behavioural economics have been adopted enthusiastically by governments seeking to improve household financial outcomes. In 2010, the British government established the Behavioural Insights Team, popularly known as the Nudge Unit, which has subsequently designed dozens of interventions to encourage saving. The United Kingdom's 2012 automatic enrolment legislation, modelled on the Madrian and Shea findings, has resulted in an additional ten million workers contributing to workplace pensions. In the United States, the Save More Tomorrow programme, devised by Richard Thaler and Shlomo Benartzi, invites employees to commit in advance to increase their pension contributions whenever they receive a future pay rise. Because the increase is scheduled rather than immediate, present bias works in favour of saving rather than against it, and trials have shown average contribution rates rising from 3.5 percent to 13.6 percent of salary within four years of participation.

H Critics of behavioural economics generally argue that nudges, however well designed, address only the symptoms rather than the underlying causes of inadequate saving. They point out that real wages have stagnated in many developed economies for several decades, while housing, childcare, and education costs have risen sharply, leaving little discretionary income to allocate to long-term goals. From this perspective, even the most sophisticated psychological intervention cannot substitute for structural reforms to wages, taxation, and public services. Proponents of behavioural economics generally accept the force of these criticisms but maintain that nudges represent a relatively inexpensive complement to, not a replacement for, broader policy. The growing body of evidence from real-world trials suggests that the most effective approach to encouraging household saving combines structural support with carefully designed behavioural interventions.