IELTS Academic Reading Practice Test 20

For most of the history of ocean navigation, sailors could determine how far north or south they were with reasonable accuracy, but not how far east or west. Latitude could be calculated by measuring the height of the sun at midday, or of the Pole Star at night, above the horizon. Longitude was a different matter. Because the Earth turns through 360 degrees in twenty-four hours, every hour of difference between local time and the time at a fixed reference point corresponds to fifteen degrees of longitude. Local time could be established from the sun, but a navigator also needed to know the time at his home port, and no clock of the period could keep accurate time on a rolling ship exposed to changes in temperature and humidity.

Instead, sailors relied on dead reckoning, estimating their position from their speed, their direction and the time that had passed since they last knew where they were. In practice, currents and leeway, the sideways drift caused by wind, made such estimates even less reliable. Errors accumulated quickly, and the consequences could be catastrophic. In October 1707, a British fleet returning from the Mediterranean misjudged its position in bad weather and struck rocks off the Isles of Scilly, south-west of Cornwall. Four warships were lost, and estimates of the number of sailors who drowned range from around 1,400 to 2,000. The disaster added to pressure on the government, and in 1714 Parliament passed the Longitude Act, which offered a prize of £20,000 – an enormous sum at the time – for a method of finding longitude at sea to within half a degree.

Many leading scientists believed that the answer lay in the sky. The so-called lunar distance method involved measuring the angle between the moon and certain stars and comparing the result with tables predicting where the moon would appear at given times, as seen from a reference point. The method was sound in theory, but it required precise instruments, reliable tables and lengthy calculations that few ordinary navigators were trained to perform. Observations also had to be made from a moving deck, and cloud could prevent them altogether for days at a time.

The man who solved the problem by mechanical means was John Harrison, a carpenter from Lincolnshire with no formal scientific education. Harrison had already built remarkably accurate clocks made largely of wood, and he set out to construct one that could cope with the motion of a ship. His first marine timekeeper, now known as H1, was tested on a voyage to Lisbon in 1736 and performed well enough to persuade the Board of Longitude, which judged proposals for the prize, to fund further work.

Over the next two decades he built two more large clocks, introducing a series of innovations, including a strip made of two different metals bonded together, which bent as the temperature changed and so compensated for its effects. Then Harrison changed direction entirely. His fourth timekeeper, H4, completed in 1759, was not a clock at all but a large pocket watch about thirteen centimetres across.

In 1761 Harrison's son William took H4 on a voyage to Jamaica. On arrival, after more than two months at sea, the watch had lost only about five seconds, well within the accuracy required for the prize, and a second trial, to Barbados in 1764, confirmed the result. The Board, however, was reluctant to pay. Some of its members, including the astronomer Nevil Maskelyne, favoured the lunar method, and the Board argued that a single watch might have succeeded by chance and that a method was useful only if others could reproduce it. Harrison was required to hand over his timekeepers and explain their construction in detail, and he received only part of the prize. Eventually, after he appealed to King George III, Parliament awarded him a further £8,750 in 1773, three years before his death.

The question of reproduction was a real one. H4 had taken years to build, and a navy could not depend on a device that only one man could make. The watchmaker Larcum Kendall was commissioned to produce a copy, known as K1, and James Cook took it on his second great voyage to the Pacific between 1772 and 1775, during which he spoke highly of its reliability.

In the following decades, makers such as John Arnold and Thomas Earnshaw simplified the design so that chronometers could be manufactured in larger numbers and at lower cost, and by the middle of the nineteenth century they had become standard equipment on ocean-going ships. Greenwich itself gained a new importance: in 1884 an international conference in Washington adopted the meridian passing through the Royal Observatory as the prime meridian, the zero line from which longitude is measured.

Even so, the two approaches were never as opposed as the rivalry suggested. Maskelyne's Nautical Almanac, first published for the year 1767, made lunar calculations far quicker, and for decades many navigators used lunar observations to check their chronometers, which could stop or drift on long voyages. Satellite navigation has since made both methods largely obsolete, but Harrison's four timekeepers survive. Restored in the twentieth century, they are displayed at the Royal Observatory in Greenwich, where the three large clocks can still be seen running.

When penicillin came into widespread use in the 1940s, it seemed that some of humanity's oldest enemies had at last been defeated. Infections that had routinely killed, such as pneumonia, blood poisoning and infected wounds, could suddenly be cured within days. Before antibiotics, even a minor scratch could lead to a fatal infection, and surgery and childbirth carried far greater risks than they do today. Yet in his Nobel Prize lecture in 1945, Alexander Fleming himself warned that bacteria given doses insufficient to destroy them could develop resistance to the drug. His warning proved accurate. Resistant strains of bacteria have appeared within a few years of the introduction of almost every new antibiotic, and the World Health Organization now regards resistance as one of the most serious threats to global public health.

Resistance is an example of evolution by natural selection operating at remarkable speed. Bacteria reproduce rapidly, in some cases dividing every twenty minutes or so, and random mutations in their DNA occasionally make an individual less vulnerable to a particular drug. Because a single bacterium can give rise to millions of descendants within a day, even an extremely rare mutation is likely to appear somewhere in a large population. When an antibiotic is used, susceptible bacteria die, while resistant ones survive and multiply. The mechanisms involved vary. Some bacteria produce enzymes that break the antibiotic down before it can act; others alter the structure that the drug normally attacks, so that it no longer fits; still others use molecular pumps to expel the drug from the cell before it reaches a harmful concentration.

What makes resistance particularly difficult to contain is that bacteria do not depend on inheritance alone. They can also exchange genetic material directly, even between different species, often by passing on small circular pieces of DNA called plasmids, and a single plasmid may carry genes for resistance to several antibiotics at once. Bacteria can also take up fragments of DNA released by dead cells, or receive genes carried by viruses that infect them. In 2015 researchers in China identified a gene called mcr-1, carried on a plasmid, that made bacteria resistant to colistin, an old antibiotic kept as a last resort for infections that no other drug can treat. The gene was found in bacteria from pigs, from meat on sale in shops and, less commonly, from hospital patients, and it has since been detected in many other countries.

Resistance is not, in itself, a modern phenomenon. Many antibiotics are derived from compounds that soil microbes have produced for millions of years in their competition with one another, and resistance genes evolved alongside them. In 2011 a team analysing DNA from permafrost in the Yukon, in northern Canada, found genes conferring resistance to several classes of antibiotic in sediments about 30,000 years old. What has changed is the scale of exposure. By using antibiotics in enormous quantities, people have created conditions in which resistant strains enjoy a constant advantage over their competitors.

Much of that use takes place outside human medicine. In many countries, a large share of all antibiotics is given to farm animals, sometimes not to treat illness but to prevent it in crowded conditions or to make the animals grow faster. The European Union banned the use of antibiotics as growth promoters in 2006, and following the discovery of mcr-1, China prohibited colistin as an additive to animal feed. In human medicine, antibiotics are frequently prescribed for colds and influenza, which are caused by viruses and do not respond to them, and in some countries the drugs can be bought without a prescription at all. Antibiotic residues and resistant bacteria then reach the wider environment through manure and waste water.

Estimating the human toll is difficult, but the most comprehensive study so far, published in The Lancet in 2022, calculated that infections resistant to antibiotics were directly responsible for about 1.27 million deaths in 2019 and played a part in nearly five million. The burden falls most heavily on low- and middle-income countries, where infections are more common and access to newer drugs is limited. A follow-up analysis published in 2024 forecast that, without further action, more than 39 million people could die directly from resistant infections between 2025 and 2050. Resistance also threatens much of modern medicine indirectly, since procedures such as hip replacements, caesarean sections and cancer chemotherapy depend on effective antibiotics to prevent or treat infection.

The obvious response would be to develop new drugs, but few genuinely new classes of antibiotic have reached patients since the 1980s, and the main obstacle is economic. A new antibiotic is likely to be held in reserve and used only when older drugs fail, so its sales are small, and a course of treatment lasts days rather than years. In 2019 the American company Achaogen filed for bankruptcy less than a year after one of its antibiotics was approved, largely because sales had been so low. Governments have begun to experiment with alternatives. Since 2022 the National Health Service in England has paid manufacturers fixed annual fees for access to certain antibiotics, regardless of how much is used, an arrangement often compared to a subscription. Researchers, meanwhile, are exploring new sources of drugs, including the use of artificial intelligence to screen millions of molecules for antibacterial activity. In 2020 a team at the Massachusetts Institute of Technology used this approach to identify a compound, later named halicin, that killed a range of resistant bacteria in laboratory tests.

A generation ago, it was common for children in many Western countries to spend long afternoons outdoors without adult supervision, climbing trees, building dens and roaming their neighbourhoods. Today such freedom is much rarer. In Britain, a study led by Mayer Hillman found that in 1971 around 80 per cent of seven- and eight-year-olds travelled to school without an adult; by 1990 the figure had fallen to 9 per cent. Playgrounds have been redesigned with soft surfaces and low equipment, and some schools restrict games such as tag or climbing. These changes were made with the best of intentions. There is growing evidence, however, that in protecting children from minor injuries, adults may be depriving them of experiences that are essential to their development.

Researchers use the term 'risky play' to describe thrilling and exciting forms of play that involve the possibility of physical injury. The Norwegian researcher Ellen Sandseter, who observed children in preschools, identified six broad categories: play at great heights, play at high speed, play with dangerous tools such as knives or saws, play near dangerous elements such as water or fire, rough-and-tumble play such as wrestling, and play in which children can wander out of sight of adults. What these activities have in common is that children choose them freely and find them exhilarating precisely because they contain an element of fear. Crucially, children typically regulate the level of risk themselves, retreating when they feel out of their depth and returning later to try again.

The benefits appear to be substantial. A systematic review published in 2015 by Mariana Brussoni and colleagues, which examined 21 studies, found that risky outdoor play was associated with higher levels of physical activity and with better social health and behaviour, and the authors concluded that the evidence supported promoting it. As they acknowledged, however, the quality of much of the available evidence was low, and most of it came from observational studies rather than controlled experiments. Nevertheless, the findings are consistent with a long tradition of research suggesting that children learn to judge their own abilities by testing them. A Canadian position statement on active outdoor play, published in the same year and drawing on this review, encouraged parents and educators to give children more opportunities for self-directed play outdoors.

Some psychologists go further, arguing that risky play protects against anxiety. Sandseter and the evolutionary psychologist Leif Kennair have proposed that it acts as a natural form of exposure therapy. Fear of heights, for example, is common in young children; by gradually climbing higher and discovering that they can cope, children may overcome it, whereas if they are prevented from doing so, the fear may persist. This 'anti-phobic' hypothesis has not yet been tested directly in controlled studies, but it fits the observation that reported anxiety among children and adolescents has increased in several countries during the same decades in which their independent play has declined. The developmental psychologist Peter Gray has argued that the two trends are connected, although an association of this kind does not in itself prove that one caused the other.

Critics of risky play understandably point to injuries. Children do break arms falling from climbing frames, and occasionally far more serious accidents occur. Yet such risks need to be kept in perspective. Most injuries in play are minor, the impact-absorbing surfaces now installed under playground equipment have not prevented all injuries, and some researchers have suggested that children who believe a surface is safe may take less care. By contrast, the dangers associated with inactivity, such as obesity and poor mental health, are less visible but affect far more children. A policy that minimises one type of harm while increasing another is not necessarily a safe one.

Attitudes among policymakers have begun to change. In the United Kingdom, the Health and Safety Executive issued a statement in 2012 emphasising that play is important for children's well-being and development and that the aim is not to eliminate risk but to weigh it against benefits. Many play providers now carry out a risk-benefit assessment, considering what children gain from an activity as well as what might go wrong. Adventure playgrounds, which originated in Denmark in 1943 when the landscape architect Carl Theodor Sørensen helped to create a junk playground at Emdrup, near Copenhagen, offer children materials, tools and space to build their own structures under the eye of trained staff. In 2018 the American state of Utah passed a law stating that allowing children to engage in independent activities, such as walking to school alone, does not in itself amount to neglect.

None of this means that children should be left to face any danger whatever. There is a clear difference between risks that children can perceive and judge for themselves, such as a high branch, and hazards that they cannot, such as fast traffic or a rotten structure that looks sound. The task of adults is to remove the second while tolerating the first. That requires parents, teachers and designers to accept that some injuries will occur, and courts and insurers to support them when they do. Children, after all, will eventually have to cross busy roads, travel alone and make their own judgements about danger. It is a difficult balance to strike, but the alternative – a childhood so carefully managed that children never learn to manage themselves – carries serious risks of its own.