Reading — 2026 Jan–Apr Recall Set 51

A. Scientists have succeeded in copying the silk-producing gene of the Golden Orb Weaver spider and are using them to create a synthetic material which they believe is the model for a new generation of advanced bio-materials. The new material, bio-silk, which has been spun for the first time by researchers at DuPont, has an enormous range of potential uses in construction and manufacturing. B. The attraction of the silk spun by the spider is a combination of great strength and enormous elasticity, which man-made fibres have been unable to replicate. On an equal-weight basis, spider silk is far stronger than steel and it is estimated that if a single strand could be made about 10m in diameter, it would be strong enough to stop a jumbo jet in flight. A third important factor is that it is extremely light. Army scientists are already looking at the possibilities of using it for lightweight, bullet-proof vests and parachutes. C. For some time, biochemists have been trying to synthesise the drag-line silk of the Golden Orb Weaver. The drag-line silk, which forms the radial arms of the web, is stronger than the other parts of the web and some biochemists believe a synthetic version could prove to be as important a material as nylon, which has been around for 50 years, since the discoveries of Wallace Carothers and his team ushered in the age of polymers. D. To recreate the material, scientists, including Randolph Lewis at the University of Wyoming, first examined the silk-producing gland of the spider. "We took out the glands that produce the silk and looked at the coding for the protein material they make, which is spun into a web. We then went looking for clones with the right DNA," he says. E. At DuPont, researchers have used both yeast and bacteria as hosts to grow the raw material, which they have spun into fibres. Robert Dorsch, DuPont’s director of biochemical development, says the globules of protein, comparable with marbles in an egg, are harvested and processed. "We break open the bacteria, separate out the globules of protein and use them as the raw starting material. With yeast, the gene system can be designed so that the material excretes the protein outside the yeast for better access," he says. F. "The bacteria and the yeast produce the same protein, equivalent to that which the spider uses in the drag lines of the web. The spider mixes the protein into a water-based solution and then spins it into a solid fibre in one go. Since we are not as clever as the spider and we are not using such sophisticated organisms, we substituted man-made approaches and dissolved the protein in chemical solvents, which are then spun to push the material through small holes to form the solid fibre." G. Researchers at DuPont say they envisage many possible uses for a new biosilk material. They say that earthquake-resistant suspension bridges hung from cables of synthetic spider silk fibres may become a reality. Stronger ropes, safer seat belts, shoe soles that do not wear out so quickly and tough new clothing are among the other applications. Biochemists such as Lewis see the potential range of uses of biosilk as almost limitless. "It is very strong and retains elasticity; there are no man-made materials that can mimic both these properties. It is also a biological material with all the advantages that has over petrochemicals," he says. H. At DuPond’s laboratories, Dorsch is excited by the prospect of new super-strong materials but he warns they are many years away. "We are at an early stage but theoretical predictions are that we will wind up with a very strong, tough material, with an ability to absorb shock, which is stronger and tougher than the man-made materials that are conventionally available to us," he says. I. The spider is not the only creature that has aroused the interest of material scientists. They have also become envious of the natural adhesive secreted by the sea mussel. It produces a protein adhesive to attach itself to rocks. It is tedious and expensive to extract the protein from the mussel, so researchers have already produced a synthetic gene for use in surrogate bacteria.

AS AN EAST WIND blasts through a gap in the Cordillera de Tilaran, a rugged mountain range that splits northern Costa Rica in half, a female mantled howler monkey moves through the swaying trees of the forest canopy. A. Ken Glander, a primatologist from Duke University, gazes into the canopy, tracking the female’s movements. Holding a dart gun, he waits with infinite patience for the right moment to shoot. With great care, Glander aims and fires. Hit in the rump, the monkey wobbles. This howler belongs to a population that has lived for decades at Hacienda La Pacifica, a working cattle ranch in Guanacaste province. Other native primates — white-faced capuchin monkeys and spider monkeys — once were common in this area, too, but vanished after the Pan-American Highway was built nearby in the 1950s. Most of the surrounding land was clear-cut for pasture. B. Howlers persist at La Pacifica, Glander explains, because they are leaf-eaters. They eat fruit, when it’s available but, unlike capuchin and spider monkeys, do not depend on large areas of fruiting trees. “Howlers can survive anyplace you have half a dozen trees because their eating habits are so flexible” he says. In forests, life is an arms race between trees and the myriad creatures that feed on leaves. Plants have evolved a variety of chemical defences, ranging from bad-tasting tannins, which bind with plant-produced nutrients, rendering them indigestible, to deadly poisons, such as alkaloids and cyanide. C. All primates, including humans, have some ability to handle plant toxins. “We can detoxify a dangerous poison known as caffeine, which is deadly to a lot of animals,” Glander says. For leaf-eaters, long-term exposure to a specific plant toxin can increase their ability to defuse the poison and absorb the leaf nutrients. The leaves that grow in regenerating forests, like those at La Pacifica, are actually more howler friendly than those produced by the undisturbed, centuries-old trees that survive farther south, in the Amazon Basin. In younger forests, trees put most of their limited energy into growing wood, leaves and fruit, so they produce much lower levels of toxin than do well-established, old-growth trees. D. The value of maturing forests to primates is a subject of study at Santa Rosa National Park, about 35 miles northwest of Hacienda La Pacifica. The park hosts populations not only of mantled howlers but also of white-faced capuchins and spider monkeys. Yet the forests there are young, most of them less than 50 years old. Capuchins were the first to begin using the reborn forests when the trees were as young as 14 years. Howlers, larger and heavier than capuchins, need somewhat older trees, with limbs that can support their greater body weight. A working ranch at Hacienda La Pacifica also explains their population boom in Santa Rosa. “Howlers are more resilient than capuchins and spider monkeys for several reasons,” Fedigan explains. “They can live within a small home range, as long as the trees have the right food for them. Spider monkeys, on the other hand, occupy a huge home range, so they can’t make it in fragmented habitat.” E. Howlers also reproduce faster than do other monkey species in the area. Capuchins don’t bear their first young until about 7 years old, and spider monkeys do so even later, but howlers give birth for the first time at about 3.5 years of age. Also, while a female spider monkey will have a baby about once every four years, well-fed howlers can produce an infant every two years. F. The leaves howlers eat hold plenty of water, so the monkeys can survive away from open streams and water holes. This ability gives them a real advantage over capuchin and spider monkeys, which have suffered during the long, ongoing drought in Guanacaste. G. Growing human population pressures in Central and South America have led to the persistent destruction of forests. During the 1990s, about 1.1 million acres of Central American forest were felled yearly. Alejandro Estrada, an ecologist at Estacion de Biologia Los Tuxtlas in Veracruz, Mexico, has been exploring how monkeys survive in a landscape increasingly shaped by humans. He and his colleagues recently studied the ecology of a group of mantled howler monkeys that thrive in a habitat completely altered by humans: a cacao plantation in Tabasco, Mexico. Like many varieties of coffee, cacao plants need shade to grow, so 40 years ago the landowners planted fig, monkey pod and other tall trees to form a protective canopy over their crop. The howlers moved in about 25 years ago after nearby forests were cut. This strange habitat, a hodgepodge of cultivated native and exotic plants, seems to support about as many monkeys as would a same-sized patch of wild forest. The howlers eat the leaves and fruit of the shade trees, leaving the valuable cacao pods alone, so the farmers tolerate them. H. Estrada believes the monkeys bring underappreciated benefits to such farms, dispersing the seeds of fig and other shade trees and fertilizing the soil with feces. He points out that howler monkeys live in shade coffee and cacao plantations in Nicaragua and Costa Rica as well as in Mexico. Spider monkeys also forage in such plantations, though they need nearby areas of forest to survive in the long term. He hopes that farmers will begin to see the advantages of associating with wild monkeys, which includes potential ecotourism projects. “Conservation is usually viewed as a conflict between agricultural practices and the need to preserve nature,” Estrada says. “We’re moving away from that vision and beginning to consider ways in which agricultural activities may become a tool for the conservation of primates in human-modified landscapes.”

A Londoner with a sudden urge for giant African snails could do worse than head to the bustling marketplace in Brixton, a part of south London that is home to many people from Africa. Markets like Brixton Market that cater to migrants are a testament to the fact that people often retain very strong preferences for the kinds of food they grew up eating. Just ask the expatriate Britons who flock to ‘Tea and Sympathy’ in New York’s Greenwich Village for pots of Marmite, a yeast-based spread whose delights baffle other nationalities (and many of their own compatriots). Past research has shown that people are often willing to pay much more for a favoured brand than for seemingly identical alternatives. It is not always obvious why. However, there is ample evidence to support the theory that certain food preferences form in childhood. Children have a predisposition to fear new foods, which is only overcome when they are repeatedly presented with, and encouraged to consume, a particular food. Evidence shows that children’s instinctive wariness of new foods dates back to the times when humans had to forage for food, and it was important that they learnt which foods were safe to eat. In the modern world, people routinely express a strong liking for a brand even though they are unable to tell the brand apart from rival brands in blind tests, and many studies have found that advertising alone cannot explain the strength of brand loyalty. A new study by economists from the universities of Tilburg and Chicago tracks the consumption patterns of 38,000 US households over two years, and confirms the theory that such brand loyalty is widespread, deep and long-lasting. There were clear local patterns in consumption, although the same brands were available everywhere. But 16% of people studied were migrants: they had grown up in one state and moved to another. These migrants had the same options, in terms of what was on offer and at what price, as everyone else in their adopted home, but although they consumed local favourites, they bought fewer than longtime residents. This gap between purchases of migrants and those of the locally born was quite stubborn: although it faded the longer a person lived in their new state, it still took 20 years to halve in magnitude. Even 50 years on, it was still large enough to show up in the data. This could mean that the benefits of being the first brand into a market could last longer than might be assumed. David Atkin of Yale University has identified some important implications of local food favourites. He suggests in a recent paper that the effects of people being loyal to known brands may also lead economists to rethink the way they calculate the benefits resulting from trade. This is because opening up to trade is in some ways very similar to migrating, as it changes the composition and prices of the foods that are available to a person. In particular, trade can cause local foods to become relatively more expensive. Atkin’s data show something many economists do not take into account: when a traditional food has to compete with imported foods, it may no longer be the cheapest food available for people to choose to eat. Atkin decided to look at this situation in the context of developing countries. To illustrate his point, Atkin uses detailed data about people’s food choices in India. India is a good choice because it covers a large number of climatic zones where different specialised crops are grown. Despite being part of the same country, the prevalence of internal barriers to trade means that its regions are best thought of as being only partially open to trade. Atkin’s data show that the foods a region specialises in producing are instead cheaper in that region. However, there has been some opening up of internal trade in India in recent years, and this has revealed that for every rupee spent on food, people’s intake of calories declined most in regions where prices of local favourite foods had risen. In theory, when there is a greater choice of types of food, people should adjust their food habits and purchase the cheapest option so that they boost their calorie intake. However, in practice, food habits mean that consumers keep buying the things they know and like even though these foods have become relatively expensive. Atkin calculates that if all barriers to internal trade in India were abolished, the average Indian household would have to generate a rise of 3.3 percent in income to maintain their calorie intake. In developing countries where there is a high prevalence of undernutrition, such as in sub-Saharan Africa, the habit of continuing to eat favourite foods could have a serious effect on development. There is clear evidence that nutritional shortfalls in children can affect their ability to work and earn as adults, and also have detrimental effects on their long-term health. Consequently, the nutritional declines that can occur as a result of the opening up of trade are of serious concern, because an entire generation that is malnourished as children will continue to suffer irreversible consequences for the rest of their lives, which could hinder the development of their country due to a lack of a quality workforce.