IELTS Academic Reading Practice Test 35

A The black surface that covers most of the world's paved roads is among the most familiar materials of modern life, yet its origins reach back several thousand years. The Sumerians of Mesopotamia were collecting natural asphalt, a sticky residue of seeping crude oil, by the fourth millennium BCE. They used it as mortar for brick walls, as caulking for reed boats navigating the marshes of the Tigris and Euphrates, and as a waterproofing layer beneath the bathing pools of palace complexes at Mari and Ur. The Babylonians paved a ceremonial avenue known as the Procession Way of Marduk with stone slabs set in an asphalt bed around 615 BCE, producing what may well have been the first deliberately surfaced thoroughfare anywhere on earth.

B The roads of the Roman world were extraordinary by virtually any measure, although they were not made of asphalt. The viae publicae, built between the third century BCE and the third century CE, used carefully layered foundations of large stones, rubble, sand, and gravel, topped with closely fitted basalt or limestone paving blocks. A surveyed Roman road was crowned in the centre to shed rainwater and bordered by drainage ditches; its construction was robust enough that several stretches, including the Appian Way and portions of Hadrian's Wall, still bear pedestrian traffic today. The collapse of the Western Roman Empire, however, dragged road maintenance into a long decline. By the late medieval period, even main highways across much of Europe had degenerated into the rutted dirt tracks of which travellers complained well into the eighteenth century.

C Two Scottish engineers are widely held to have largely transformed the discipline of road-building in the early nineteenth century. John Loudon McAdam argued that a thick base of broken stone was unnecessary; a comparatively thin layer of small, angular fragments of consistent size, well compacted, would bear heavy loads as the traffic itself drove the stones together. His method, dubbed macadamisation, was adopted in Britain, France, and the United States within decades. Thomas Telford, working at much the same time, devised a heavier system with a foundation of large stones laid by hand below a macadam surface. Telford roads cost more but tended to last longer, and the principles of both engineers underpinned the great majority of nineteenth-century highway construction.

D The dust kicked up by a macadam road was the chief complaint of its users. As bicycles became popular in the 1870s and motor cars a generation later, the demand for a smoother, harder, less dusty surface intensified accordingly. Coatings of tar — the black, sticky byproduct of coal-gas manufacture — had been used since the 1830s for waterproofing pavements, and the term "tarmacadam," usually abbreviated to tarmac, came into use around 1900 to describe a macadam surface sealed with tar. Tar, however, became brittle in cold weather and softened in extreme heat, which limited its usefulness considerably. The arrival of petroleum-derived bitumen as a road binder, pioneered by the Belgian engineer Edward de Smedt in late-nineteenth-century New York, produced a far more durable material. Bitumen-bound asphalt was first laid on Pennsylvania Avenue in Washington in 1876 and quickly became the standard surfacing for urban streets.

E The expansion of motorised traffic during the twentieth century turned road-building into a major industry. The German Autobahn network, initiated in the 1930s, was the first sustained system of high-speed, limited-access highways designed entirely around the requirements of the automobile. The American Interstate Highway System, authorised by Congress in 1956 and largely completed by the 1990s, ultimately covered seventy-eight thousand kilometres at a total construction cost exceeding $530 billion in present-day terms. Both systems relied on layered asphalt pavements engineered to withstand specific loads under specific climates; both helped to transform patterns of work, leisure, and settlement across two continents.

F Modern asphalt mixtures bear little resemblance to the natural deposits the Sumerians once scraped from the surface of pitch pools. Engineers typically blend petroleum bitumen with carefully graded aggregates, with additives such as polymers or recycled rubber to enhance elasticity, and with mineral fillers to fine-tune density. Increasing attention is being paid to the environmental costs of road surfacing. Conventional hot-mix asphalt requires temperatures around 160 degrees Celsius and is a significant source of carbon emissions; warm-mix and cold-mix technologies developed since the 2000s reportedly reduce energy consumption by up to thirty percent. Pavements containing pulverised waste tyres and reclaimed asphalt pavement, or RAP, now apparently account for a substantial share of new road material in several countries. Whether such innovations can keep pace with rising global vehicle traffic — and with the longer-term need to maintain road networks in a warming climate — remains arguably one of the central questions facing twenty-first-century transport engineering.

A The grey wolf was deliberately exterminated from the Greater Yellowstone Ecosystem during the early decades of the twentieth century. United States Park Service rangers, acting under predator-control policies inherited from livestock-protection laws, reportedly shot, trapped, and poisoned the last identified pack within the park in 1926. For sixty-nine years thereafter Yellowstone was a wolf-free landscape, an outcome regarded at the time as a triumph of wildlife stewardship and only much later as the source of a slowly unfolding ecological problem. In January 1995, a single van crossed the boundary of the park carrying fourteen wolves trapped in Alberta, Canada. The reintroduction, which was the outcome of a twenty-year political battle, has since become arguably the most-cited example of what ecologists term a trophic cascade.

B A trophic cascade is understood as a chain of effects in which a change at one trophic level of an ecosystem propagates downward, or occasionally upward, to influence species at other levels. In Yellowstone, the relevant predator-prey relationship is between wolves and elk. During the wolf-free decades, the park's elk population had grown to historically unusual densities — peaking at over twenty thousand animals in the late 1980s — and the herd appears to have altered its behaviour. With no large predator to fear, elk grazed for long, stationary periods in valley bottoms and along streamsides, suppressing the regeneration of willow, cottonwood, and aspen saplings on which they preferentially fed.

C The returning wolves did not merely reduce elk numbers; according to many ecologists, they appear to have reorganised elk behaviour. By rendering certain valleys and gulches risky places to linger, wolves induced what the ecologist Joel Berger has largely termed a "landscape of fear," in which prey animals trade off feeding opportunities against the perceived danger of attack. Researchers using GPS collars and remote cameras documented that elk now spent less time in open river bottoms and more time on slopes affording good sightlines. The riparian woody vegetation gradually began, after decades of suppression, to return.

D The consequences are said to have rippled outward. Beavers, which had been almost entirely absent from the park's northern range since the 1950s because they typically require willow for both food and dam material, reappeared along several creeks within ten years of the wolves' return. Beaver dams generally largely created shallow ponds, and ponds in turn raised water tables, stabilised stream temperatures, and provided habitat for amphibians and fish. Songbirds nesting in the recovering riparian thickets appear to have largely increased in both species richness and density. Coyote populations, which had expanded in the absence of wolves, declined as wolves killed competitors and displaced them from prime hunting territory, and this in turn allegedly allowed a partial recovery of the small mammals on which coyotes had heavily preyed. Pronghorn antelope, whose fawns are highly vulnerable to coyote predation, are reported to have recorded improved juvenile survival.

E The scientific case for the cascade is not without dissent. Critics including the ecologist Arthur Middleton have argued that the recovery of riparian vegetation in some valleys has been less dramatic than popular accounts tend to suggest, and that other factors — climate-driven changes in snowpack, recovery of bison herds, varying levels of human hunting outside park boundaries, and even the lingering effects of drought — may also influence elk distribution. Long-term studies suggest that vegetation responses have been patchy, with some watersheds rebounding markedly and others scarcely at all. The relative weight of behavioural versus numerical effects on the elk herd, too, remains the subject of active debate.

F Even granting these qualifications, the cumulative weight of evidence has reshaped conservation thinking far beyond Yellowstone. The reintroduction of large predators is now actively considered, and in several cases pursued, in landscapes from Romania's Carpathians to Argentina's Iberá wetlands. The dingo's role as an apex predator in Australia, jaguar recovery in Latin America, and the slow expansion of European wolf populations into Germany, France, and Belgium have all reportedly been analysed in terms borrowed from the Yellowstone cascade. Even in marine ecosystems, the recovery of sharks and sea otters has been examined as a possible cascade trigger, with sea-otter predation of urchins permitting kelp-forest regrowth along the Pacific coast of North America.

G There are, of course, limits to how far the model can be stretched. Cascades are easier to demonstrate in relatively simple food webs than in complex ones, and the absence of a predator is not the only — or always the principal — driver of ecological change. Nonetheless, the Yellowstone story has supplied environmental policy with both a vivid case study and a useful conceptual framework. It has also, it seems, shifted public sentiment in ways few biologists could have predicted. Polling within the Greater Yellowstone Ecosystem in 2018 found majorities in favour of continued wolf presence even in states where livestock-loss compensation remains contentious. The wolf-free landscape, once defended as the ideal, is now widely regarded as the historical aberration; the return of an old predator is treated, increasingly, as the restoration of an absent function on which an entire ecosystem had depended without anyone fully noticing.

A The classical economic model of charitable behaviour is austere. A rational donor contemplating a contribution to a humanitarian cause is assumed to compare the marginal increase in well-being produced by the gift with the cost of forgoing the same resources elsewhere. Under this account, generosity ought to scale roughly with both income and the magnitude of need. In practice, decades of empirical work have shown that almost none of these predictions appears to hold. Donations do not increase neatly with income, do not respond proportionally to the size of a tragedy, and seem to be surprisingly insensitive to whether a gift will reach one beneficiary or one hundred. The systematic gap between the rational model and observed behaviour has provided behavioural economists with one of their richest fields of study.

B The most-cited single finding in the literature is widely held to be the identifiable victim effect. In an influential 2007 experiment by Paul Slovic and his collaborators, participants were shown one of three appeals from the charity Save the Children. The first described a single, named seven-year-old girl in Mali. The second presented anonymous statistics on African food insecurity, including that more than three million children faced famine. The third combined both. Donations were highest for the individual story, lowest for the statistical appeal, and intermediate for the combined version. Strikingly, adding the statistics to the personal story actually reduced giving relative to the personal story alone — a result Slovic attributed to a process he called "psychic numbing." Beyond a single identifiable face, additional victims appear to diminish, rather than augment, the impulse to help.

C Closely related is what economists generally call scope insensitivity. In a series of contingent-valuation studies in the 1990s, Daniel Kahneman and his colleagues asked respondents how much they would pay to save migratory birds from being trapped in uncovered oil ponds. The mean willingness to pay was about eighty dollars for two thousand birds, eighty-two for twenty thousand, and eighty-eight for two hundred thousand. The hundredfold increase in scale produced essentially no change in giving. Donors broadly react to the emotional category of an issue rather than to its quantitative magnitude.

D The framing of the request also tends to matter in ways the rational model cannot easily accommodate. People generally give more when asked for a "small amount of two dollars" than when asked simply to give "two dollars." Field experiments by Jen Shang and Rachel Croson have largely shown that telling potential donors at a public radio fundraising drive that "another donor just contributed $300" can raise both the rate of donation and the average size of subsequent gifts, an effect known as social information. Defaults seem to play an even larger role. Eric Johnson and Daniel Goldstein famously demonstrated that organ-donor registration rates depend overwhelmingly on whether citizens are enrolled by default or must actively opt in. In Austria, where the default is enrolment, registration exceeds ninety-nine percent; in neighbouring Germany, where one must opt in, it stands closer to twelve.

E A second body of work asks why people give at all. The economist James Andreoni proposed in 1990 that donors derive a private satisfaction from the act of giving itself, independent of any consequence for the recipient — a phenomenon he called "warm glow." The warm-glow model neatly explains why charitable behaviour persists in situations where a rational donor would conclude that an additional individual contribution makes no difference at the margin. It also predicts something uncomfortable: that a donor who gives chiefly for warm glow may be largely insensitive to whether a charity actually delivers benefits to its beneficiaries, since the satisfaction is generated by the act of giving rather than by its outcome.

F The "effective altruism" movement, articulated most prominently by the philosopher Peter Singer and the writer William MacAskill, has argued explicitly against warm-glow giving. Effective altruists typically encourage donors to evaluate charities by impact per dollar — using metrics such as the cost of saving a statistical life from preventable disease — and to direct funds toward the most cost-effective intervention rather than the one that feels most rewarding. Critics counter that this framework underweights local commitments, the dignity of beneficiaries, and the value of the emotional engagement that motivates much charitable behaviour. The debate has had real consequences: GiveWell, which evaluates global-health charities for cost-effectiveness, channelled more than $400 million in donor money during 2022 alone.

G Several behavioural-economic findings have been applied directly by fundraisers. The wording of appeals has been redesigned around the identifiable victim effect, with charities preferring narratives about specific named recipients to abstract statistics. Matching gifts, in which an external donor agrees to double or triple a contribution, exploit reciprocity and have been shown by John List and his collaborators to increase donation rates substantially, though the increase is driven by the framing rather than by the mathematical attractiveness of the match. Even the trivial-seeming detail of donation defaults — pre-selecting a higher or lower amount on a webpage — appears to produce large changes in average gifts. Some of these techniques skirt ethical questions. If a donor's giving can be reliably increased by a personal photograph and a familiar name, has the donor been informed or merely manipulated?

H The discipline has also begun to engage seriously with cultural variation. Studies in India, China, and the Middle East suggest that religious motivations and kin-network obligations play larger roles in giving than the secular, individualised model assumed by much Western research. The fundamental insight of behavioural economics — that charitable behaviour is not a precise function of need and resource but a deeply contextual mixture of emotion, identity, and design — has nevertheless held up across cultures. Whether public policy should accommodate these tendencies, or attempt to correct them, remains contested. For now, the gap between how people actually give and how a strictly utilitarian calculus says they should give appears, if anything, to be widening.