IELTS Academic Reading Practice Test 28

A The Fertile Crescent, an arc of land stretching from the eastern Mediterranean coast through southern Turkey and down the valleys of the Tigris and Euphrates to the Persian Gulf, is widely regarded by archaeologists as the cradle of farming. It was here, between roughly 12,000 and 8,000 years ago, that small communities of hunter-gatherers gradually transformed themselves into the first villages of settled cultivators, domesticating eight founder crops and four founder livestock species in the process.

B The story is said to begin not with farming but with sedentism. From roughly 14,500 years ago a culture known as the Natufian flourished in present-day Israel, Jordan, Lebanon, and Syria. The Natufians built solid, round stone-walled houses, buried their dead with carved bone ornaments, and constructed deep storage pits. They did not yet plant crops, but they harvested wild stands of cereals such as wild barley and wild emmer wheat with sickles whose flint blades, when examined under the microscope by archaeologist Daniel Zohary in the 1990s, are reported to show the characteristic gloss produced by cutting grass-stems.

C The transition to farming itself appears to have been triggered, at least in part, by a sudden climatic deterioration. Around 12,900 years ago, the Younger Dryas, a thousand-year cold snap of glacial intensity, abruptly returned to the Levant after several centuries of warming. Stable isotope analyses from cave speleothems published by researchers at the University of Reading in 2014 reportedly confirm that average annual rainfall fell by between 250 and 400 millimetres. Wild cereal stands shrank, and the well-fed Natufian villages came under pressure. The archaeological record shows shifts toward smaller dwellings, more diverse and lower-status diets, and the first signs of deliberate planting at sites such as Tell Abu Hureyra in northern Syria.

D By the end of the Younger Dryas, around 11,700 years ago, communities across the Levant had begun systematic cultivation. Initially, the plants they sowed were morphologically indistinguishable from their wild ancestors. Domestication proper — the appearance of genetic changes such as larger grains, simultaneous ripening, and seeds that remain on the stalk rather than scattering on the wind — required several thousand years of selective harvesting. A celebrated 2006 paper by Manfred Heun reconstructed the domestication of einkorn wheat using DNA from modern wild and cultivated populations and concluded that all modern einkorn descends from a single wild population in the Karaca Dağ mountains of southeastern Turkey. Similar work has since localised the domestication of emmer wheat, barley, lentils, peas, chickpeas, and bitter vetch to relatively small areas within the Fertile Crescent, suggesting the founder crop package emerged not from a single site but from a network of contemporaneous experiments.

E Animal domestication followed a parallel trajectory. Sheep and goats appear to have been brought under human control in the Zagros mountains of present-day Iran and eastern Turkey from about 11,000 years ago. Cattle were domesticated separately, probably from a wild aurochs population in southeastern Turkey, by 10,500 years ago. Pigs were domesticated, perhaps more than once, by 10,000 years ago. Each process can now be traced through changes in skeletal morphology — smaller bones, shorter horns, reduced sexual dimorphism — and in the genetic signatures preserved in modern domestic populations.

F The consequences were enormous. Settled agricultural communities supported far denser populations than hunting and gathering could, with archaeological estimates suggesting density increases of between ten and a hundred fold. The earliest towns, such as Çatalhöyük in central Turkey at 9,000 years ago, housed thousands of people in tightly packed mud-brick dwellings. Yet the transition came with significant costs. Skeletal evidence from early Neolithic populations shows reduced stature, increased rates of tooth decay, and evidence of infectious diseases that thrive in dense settlements. The American physiologist Jared Diamond once famously described the adoption of agriculture as "the worst mistake in the history of the human race," a deliberately provocative judgement that nevertheless captured something real about the trade-offs involved.

G What seems clear is that the agricultural package developed in the Fertile Crescent did not stay there. Crops, animals, and the people who tended them apparently spread westward into Europe at a measurable rate of roughly one kilometre per year, eastward across the Iranian plateau and into the Indian subcontinent, and southward into the Nile valley. By 5,000 years ago, the descendants of the first Fertile Crescent farmers, or their cultural and genetic legacies, could be found from Britain to the Indus.

A For roughly a decade, vertical farming was widely promised to be the future of food production. Indoor facilities, growing crops in stacked trays under tightly controlled light, temperature, and humidity, were said to use only a fraction of the water of conventional agriculture, eliminate the need for pesticides, and bring fresh produce within walking distance of urban consumers. Between 2014 and 2022, venture capital pouring into the sector exceeded 4 billion US dollars. By 2024, however, the picture had become considerably more complicated. Several of the industry's largest players had filed for bankruptcy, surviving operators had scaled back expansion plans, and analysts were openly questioning whether the technology could ever compete on cost with field agriculture for most crops.

B The economic case for vertical farming is said to begin with land. A vertical farm can produce as much usable food per square metre of footprint as 300 times the same area of conventional field. Water use is also dramatically lower: a well-designed hydroponic facility recirculates 95 percent or more of its water, compared with the 30 to 60 percent typical of open-field irrigation. Pesticide use approaches zero. Crops can be harvested year-round, eliminating the seasonal gluts and shortages that drive much of the volatility in conventional fresh-produce pricing.

C Against these advantages sit costs that have proved harder to control. The largest is energy. Even the most efficient horticultural LED lighting consumes roughly 350 to 500 kilowatt-hours of electricity per square metre of cropping area per year, far more than greenhouses. Climate control adds another large block of consumption: dehumidification in particular is energy-intensive because the air inside a sealed grow room must be continuously stripped of moisture released by transpiring plants. A 2023 study by researchers at Wageningen University estimated that energy and climate control account for 35 to 50 percent of total operating costs in a typical commercial vertical farm, leaving the business model highly exposed to electricity prices.

D Labour costs are widely considered the second major item. Although early proponents emphasised automation, the reality is that planting, transplanting, harvesting, and packaging leafy greens still generally depend heavily on human hands. Robotic harvesters reportedly exist but, as of 2024, are commercially viable only for a narrow range of crops in tightly standardised tray systems. Capital costs round out the picture: a 1,000 square metre vertical farm requires investment of between 10 and 15 million US dollars before producing a single salad leaf.

E The result is that the unit cost of produce from a typical urban vertical farm is several times that of imported field-grown alternatives. For leafy greens, where premium consumers are willing to pay for freshness and provenance, the difference can be absorbed. For most other crops it generally cannot. Tomatoes can already be grown profitably in glasshouses on a far larger scale than is feasible in stacked indoor facilities. Staple crops such as wheat, rice, and potatoes simply cannot be produced indoors at anything resembling economic prices, because their light requirements, growth cycles, and energy density are largely incompatible with the cost structure of artificial illumination. The economic core of vertical farming, in short, appears much narrower than it first seemed, concentrated on salad leaves, herbs, microgreens, and high-value specialty plants.

F The collapse of several high-profile operators has driven a sober recalibration. AeroFarms, once a $1.2 billion company, filed for bankruptcy in 2023 before being acquired by new investors and restructured around a smaller footprint. Infarm, a German operator that once supplied modular growing cabinets to supermarkets across Europe, withdrew from most of its markets in 2022. Fifth Season, a US start-up, closed in 2022 with most of its 100 employees losing their jobs. Each closure reflected high electricity costs, slow uptake by retailers, and reluctance among consumers to pay a premium for indoor-grown leaves.

G Despite these setbacks, several niches continue to look viable. Cold-climate cities and isolated communities can support vertical farms at a premium. The Norwegian operator Avisomo, for instance, supplies herbs and leafy greens year-round to remote Arctic settlements where the alternative is week-old produce flown from the south. Specialty pharmaceutical applications, particularly the production of plant-based medicinal compounds under sterile conditions, offer margins entirely different from those of supermarket lettuce. Researchers at Cornell University have argued that the long-term role of vertical farming may be as a complement to, rather than a replacement for, field agriculture: meeting the demand for the most perishable and highest-value urban crops while leaving the bulk of human nutrition to be produced under the sun.

H The longer-term outlook depends on two trends. The first is the cost of clean electricity. If solar and wind continue to drive down wholesale electricity prices, the dominant component of vertical farming's cost structure should weaken correspondingly. The second is the development of more efficient lighting and climate-control technology. Recent advances in far-red LED supplementation, in dehumidification using novel desiccants, and in machine-learning-driven climate optimisation suggest that energy intensity could plausibly be reduced by 30 to 40 percent over the next decade.

A Human beings see the world in a way that is unusual, even among mammals. We perceive blues, greens, yellows and reds in vivid contrast, distinguish subtle pastel shades, and can pick out a ripe fruit from a tangle of leaves at considerable distance. Most other mammals, including dogs and cats, possess at most two functioning colour-receptor types and apparently see only a dichromatic version of the world. Our trichromatic vision is widely regarded as a striking biological inheritance, the result of a sequence of evolutionary events stretching back tens of millions of years.

B Vertebrate colour vision depends on retinal cells called cone photoreceptors, each carrying a pigment most sensitive to a particular range of wavelengths. The earliest vertebrates appear to have possessed four cone classes, sensitive to red, green, blue and ultraviolet light respectively, a system known as tetrachromacy. Most fish, birds, and reptiles reportedly retain tetrachromacy to this day. Mammals are the exception. During the early Mesozoic, around 200 million years ago, the ancestors of modern mammals took up a largely nocturnal lifestyle in the shadow of the dinosaurs. Two of the four ancestral cone pigments were lost, leaving most mammals as dichromats sensitive only to blue and yellow-green wavelengths.

C The story takes a sharp turn in the lineage that led to monkeys, apes, and humans. Around 30 to 40 million years ago, in a primate ancestor living in tropical Africa, a duplication occurred of the gene coding for the surviving green-yellow cone pigment. The two copies subsequently mutated independently, one shifting toward longer wavelengths to produce a "red" receptor while the other remained tuned to slightly shorter "green" wavelengths. Combined with the unchanged blue receptor, the result was a fully trichromatic visual system. Genetic evidence published in 1999 by molecular biologist Shozo Yokoyama is reported to have shown that this duplication occurred in the common ancestor of Old World monkeys, apes, and humans.

D New World monkeys, the catarrhine primates that diverged from the Old World line about 40 million years ago, present an instructive partial case. In most species, the red and green pigment genes are carried not on different chromosomes but as alternative versions of a single gene on the X chromosome. Female monkeys, who carry two X chromosomes, may therefore inherit different versions and end up trichromatic; males, with only one X, are essentially always dichromatic. The result is that within a single troop of marmosets or capuchins, some individuals see colour as humans do, while others apparently do not. Behavioural studies by Nathaniel Dominy and Peter Lucas, published in Nature in 2001, are reported to have shown that trichromatic individuals find ripe red fruit against green foliage substantially faster than their dichromatic group-mates.

E The advantage that trichromacy conferred on the human lineage has long been debated. The most influential hypothesis, advanced by John Mollon at Cambridge University in the 1980s, is the "ripe fruit hypothesis," which holds that the duplication was favoured because it improved foragers' ability to detect ripe fruit against tropical foliage. Subsequent work has identified other plausible advantages, including better detection of young, edible leaves and improved social signalling through skin colour changes. A 2020 review by Amanda Melin at the University of Calgary argued that no single explanation suffices: trichromacy probably conferred small advantages on several fronts simultaneously.

F Human trichromacy comes with intriguing variations. About one in twelve men of European descent is colour-blind to varying degrees, almost always because of mutations on the X chromosome affecting the red or green pigment gene. Because males inherit only one X, a single defective copy is sufficient; females, with two X chromosomes, are usually buffered. Much rarer is the case of "tetrachromat" women. Around two percent of women may inherit, on their two X chromosomes, two slightly different versions of the red or green pigment gene, producing four functioning cone types rather than three. Most tetrachromat women appear to see the world as their trichromat sisters do, but the British psychologist Gabriele Jordan reported in 2010 a single carefully tested participant who could reliably distinguish colour patches that ordinary trichromats experienced as identical.

G Comparative work has continued to throw up surprises. Mantis shrimps, marine crustaceans far removed from any vertebrate, possess up to sixteen different cone-equivalent receptors but, contrary to early speculation, do not appear to use them for fine colour discrimination. Birds, which retain tetrachromacy and can also see ultraviolet, perceive plumage patterns essentially invisible to humans, including the otherwise drab-looking blue tit whose males display vivid ultraviolet crown patches. Each of these systems is a reminder that "colour" is not a property of the world but a construction of the visual system that perceives it.

H Studying these systems has practical consequences. Designers of colour displays, traffic signals, and pharmaceutical packaging now routinely use simulations that reproduce dichromatic vision, so that important distinctions remain accessible to colour-blind users. Veterinarians typically choose toys for dogs with their dichromatic vision in mind. Conservation biologists planning bird-friendly windows take into account avian tetrachromacy, since markings invisible to humans can deter birds from colliding with glass.