IELTS Academic Reading Practice Test 4

Chocolate is today one of the most widely consumed luxury foods in the world, yet for most of its long history it was neither sweet nor solid. Its source is the cacao tree, Theobroma cacao, a small evergreen that grows only in hot, humid regions within about twenty degrees of the equator. The tree produces large, ridged pods directly from its trunk and main branches, and each pod contains several dozen seeds surrounded by a sweet white pulp. It is these seeds, commonly known as cocoa beans, that are transformed – through a surprisingly lengthy series of processes – into the chocolate sold in shops.

For many years, archaeologists assumed that cacao had first been used in Central America, where the Olmec, Maya and later Aztec civilisations all valued it highly. A study published in 2018, however, changed that view. Researchers analysing pottery from a site called Santa Ana-La Florida, in the upper Amazon region of south-eastern Ecuador, detected cacao residues, starch grains and ancient DNA dating back around 5,300 years. This suggests that people in South America were using cacao roughly 1,500 years before there is any evidence of it in Central America, and that the plant was probably first domesticated there.

In Mesoamerica, cacao was consumed mainly as a drink. The beans were fermented, roasted and ground into a paste, which was mixed with water and often flavoured with chilli, vanilla or maize. The liquid was then poured repeatedly from one vessel to another from a height in order to produce a layer of foam, which was regarded as the most desirable part of the drink. Cacao was closely associated with ritual and social status: it was served at feasts and ceremonies, and among the Aztecs the beans were so valuable that they functioned as a form of currency with which people could buy everyday goods.

Spanish explorers encountered the drink in the early sixteenth century, and by the end of that century cacao was being shipped to Spain, where it was sweetened with sugar and sometimes spiced with cinnamon. Over the following decades the fashion for drinking chocolate spread to Italy, France and England. It remained expensive, however, and was consumed mainly by the wealthy, often in specialised chocolate houses; the first of these in London opened in 1657. At this stage chocolate was still a coarse, oily drink, since the cocoa butter – the natural fat that makes up roughly half of the weight of the bean – could not easily be removed.

The technological changes that created modern chocolate came in the nineteenth century. In 1828 a press developed by the Van Houten family in the Netherlands made it possible to squeeze out much of the cocoa butter, leaving a dry cake that could be ground into cocoa powder. The powder mixed far more easily with water, and treating it with alkaline salts reduced its bitterness. In 1847 the English firm J. S.

Fry & Sons discovered that by adding cocoa butter back to a mixture of cocoa powder and sugar, it could produce a paste that could be poured into a mould – the first chocolate bar intended for eating rather than drinking. In Switzerland, Daniel Peter combined chocolate with condensed milk in 1875 to create the first successful milk chocolate, and in 1879 Rodolphe Lindt invented the conche, a machine that stirs liquid chocolate for many hours, giving it a smoothness that earlier products had lacked.

Although the factory stages have since been refined, the first steps still take place on the farm and have changed relatively little. Once the pods are harvested, they are split open and the beans and pulp are piled in heaps or placed in wooden boxes, usually covered with banana leaves, and left to ferment for between five and seven days.

Fermentation is essential: it kills the seed, reduces bitterness and initiates the chemical reactions that later produce the characteristic chocolate flavour. The beans are then spread out and dried in the sun for about a week before being sold. At the factory they are roasted, after which the thin outer shells are cracked and removed in a process known as winnowing, leaving fragments called nibs. These are ground into a thick liquid known as cocoa liquor, the basic ingredient of all chocolate.

Today, around 60 per cent of the world's cocoa is grown in just two West African countries, Côte d'Ivoire and Ghana, mostly by smallholders cultivating a few hectares each. Many of these farmers receive very low incomes, and the industry has been widely criticised for its reliance on child labour. Production is also threatened by plant diseases, such as the swollen shoot virus, and by changes in rainfall associated with climate change, which may make some current growing areas unsuitable in future.

Coral reefs occupy less than one per cent of the ocean floor, yet they are thought to support around a quarter of all known marine species. They also provide food and income for hundreds of millions of people, attract tourists, and protect coastlines by absorbing much of the energy of incoming waves. Despite their appearance, the structures that make up a reef are built by animals: tiny creatures called polyps, related to jellyfish, which secrete skeletons of calcium carbonate. Over thousands of years, the accumulated skeletons of countless generations of polyps can form reefs hundreds of kilometres long. The reefs of the so-called Coral Triangle in South-East Asia alone are estimated to contain around three-quarters of the world's reef-building coral species.

The success of reef-building corals depends on a remarkable partnership. Living inside the tissues of the polyps are microscopic algae, which use sunlight to produce sugars through photosynthesis. The algae pass most of these sugars to their host, supplying up to 90 per cent of the coral's energy, and in return they receive shelter and the nutrients contained in the coral's waste. The algae are also responsible for the vivid colours of healthy coral. This relationship allows corals to thrive in clear tropical waters that are otherwise poor in nutrients, but it also makes them vulnerable, because the partnership functions only within a narrow range of temperatures. Different coral species host different types of algae, and some of these partners tolerate heat better than others, a variation that researchers believe may partly explain why bleaching affects neighbouring colonies so unevenly.

When the water becomes too warm – often by only one or two degrees Celsius above the usual summer maximum, sustained for several weeks – the relationship breaks down. The heat-stressed algae begin to produce harmful chemicals, and the coral expels them from its tissues. Without the algae, the coral's translucent tissue reveals the white skeleton beneath, a phenomenon known as bleaching. A bleached coral is not dead, and if temperatures return to normal quickly enough, it can regain its algae and recover. If the heat persists, however, the coral gradually starves, becomes more susceptible to disease and may eventually die. The transformation can be strikingly rapid: divers have described reefs changing from brown, green and purple to a uniform, ghostly white within a few weeks of a marine heatwave.

Bleaching was rarely recorded before the 1980s, but it has since become increasingly frequent and widespread as ocean temperatures have risen. The first global bleaching event, in 1998, affected reefs in every major ocean basin. Further global events have followed, and in 2024 scientists at the United States' National Oceanic and Atmospheric Administration confirmed a fourth. On Australia's Great Barrier Reef, the world's largest reef system, severe bleaching in consecutive years in 2016 and 2017 killed a large proportion of the corals in its northern section. To assess the risk, scientists combine satellite measurements of sea-surface temperature into a measure called 'degree heating weeks', which reflects both how far and for how long temperatures exceed normal levels. Long-term monitoring also suggests that the interval between severe bleaching events, once measured in decades, has shrunk to a few years in many regions, leaving too little time for slow-growing corals to recover fully before the next episode.

Heat is not the only threat. As the oceans absorb carbon dioxide from the atmosphere, seawater becomes more acidic, which makes it harder for corals to build their skeletons. Local pressures add to the damage: pollution and sediment washed from farmland reduce water quality, and fertiliser runoff can encourage outbreaks of coral-eating crown-of-thorns starfish, while overfishing removes the plant-eating fish that prevent seaweed from smothering young corals. Reefs exposed to several of these stresses at once tend to recover more slowly after bleaching than those that are well protected, which is why many scientists argue that reducing local pressures can improve a reef's chances of surviving periods of extreme heat.

Scientists and conservationists are exploring a range of responses. In some places, fragments of coral are grown in underwater nurseries and transplanted onto damaged reefs, an approach that can restore small areas but is difficult to apply at the scale of entire reef systems. Other researchers are investigating why certain corals survive heatwaves that kill their neighbours, in the hope of breeding more heat-tolerant varieties – a field sometimes described as assisted evolution. Still more experimental proposals include shading reefs or spraying fine droplets of seawater into the air to brighten low clouds, thereby reducing the amount of sunlight that reaches the water during the hottest weeks. Most experts emphasise, however, that such interventions can only buy time. Unless global greenhouse gas emissions are substantially reduced, they argue, warming will eventually outpace any attempt to help reefs adapt, and the ecosystems that coastal communities have depended on for generations will be transformed beyond recognition.

In 2008 the economist Richard Thaler and the legal scholar Cass Sunstein published Nudge, a book that would influence policymakers around the world. Its central argument was that people's choices are shaped by the way options are presented – what the authors called the 'choice architecture' – and that governments and organisations could therefore encourage better decisions without restricting anyone's freedom. A nudge, in their definition, is any aspect of the choice architecture that alters people's behaviour in a predictable way without forbidding any options or significantly changing their financial incentives. Placing fruit at eye level in a canteen counts as a nudge; banning unhealthy food does not.

The intellectual foundations of the approach lay in earlier research by the psychologists Daniel Kahneman and Amos Tversky, who from the 1970s onwards documented the many ways in which human judgement departs from the model of the perfectly rational decision-maker assumed in traditional economics. People, they showed, rely on mental shortcuts that are usually useful but lead to predictable errors; they also feel losses more strongly than equivalent gains. Kahneman was awarded the Nobel Prize in economics in 2002 for this work, and Thaler received the same prize in 2017.

One of the most influential findings concerned the power of defaults – the option that applies if a person does nothing. In a widely cited study published in 2003, Eric Johnson and Daniel Goldstein compared European countries in which citizens had to opt in to become organ donors with those in which they were registered automatically unless they opted out. Consent rates were dramatically higher in the opt-out countries.

Similar reasoning lay behind pension reforms in several countries, including the United Kingdom, where employers have been required since 2012 to enrol workers automatically in a workplace pension scheme; the proportion of eligible employees saving for retirement rose substantially as a result. Opt-out organ donation has since been adopted in several further countries, including England in 2020, although researchers caution that the default is only one of many factors, such as hospital capacity and the views of families, that determine how many organs are eventually donated.

Governments soon began to create specialist teams to apply these ideas. The first, the United Kingdom's Behavioural Insights Team, was established in 2010 and quickly became known as the 'nudge unit'. One of its early projects involved letters sent to people who had not paid their taxes on time. Simply adding a sentence stating that most people in the recipient's area paid on time increased the number of payments, at almost no extra cost. Such low-cost interventions, which could be evaluated in randomised trials before being adopted, proved highly attractive to governments under financial pressure, and similar units were soon established in many other countries. In 2014 the British team itself was spun out of government into a separate company, and it has since advised public bodies on several continents.

As the approach spread, however, questions arose about how large its effects really were. A study published in 2022 by the economists Stefano DellaVigna and Elizabeth Linos compared the results of nudges reported in academic journals with those of every trial conducted by two large nudge units in the United States. The published studies suggested an average effect of 8.7 percentage points; the nudge units' own trials, many of which were never published, showed an average of just 1.4 points. The researchers concluded that much of the difference could be explained by the tendency of journals to publish striking results, and that the more modest figure was probably a more realistic guide to what nudges could achieve in practice.

Other critics have raised ethical objections. Because nudges work partly by exploiting habits and biases of which people are not fully aware, some argue that they are manipulative, even when the intended outcome is beneficial. Others worry that enthusiasm for nudging has distracted governments from more demanding policies: encouraging individuals to recycle or save energy, they argue, is no substitute for regulating the industries responsible for most pollution.

Thaler and Sunstein have responded that choice architecture is unavoidable – every form and menu must present options in some order – so the real question is not whether to influence choices, but how to do so transparently. A further concern is durability: some studies suggest that a reminder which is effective when first introduced may gradually lose its influence once people become accustomed to it.

Both sides have a point. The early claims made for nudging were undoubtedly exaggerated, and a small average effect is a poor foundation for solving problems as complex as climate change or obesity. Yet a change of one or two percentage points, achieved at almost no cost across millions of people, is far from trivial. The most sensible conclusion is that nudges are a useful addition to the policymaker's toolkit, best suited to situations in which people already intend to act but fail to follow through – and that they should complement, rather than replace, traditional instruments such as taxation and regulation.