A When Pierre de Coubertin gathered delegates at the Sorbonne in Paris in June 1894 to found the International Olympic Committee, he was not simply reviving an ancient festival. He was also importing a moral code. The Games he imagined were to be contested by amateurs — men who competed for the love of sport rather than for money — and for most of the following century that principle, more than any other rule, determined who could take part. Its slow collapse reveals a great deal about how the modern Games came to be what they are.

B Coubertin and his contemporaries liked to believe that the athletes of ancient Olympia had been amateurs too. The historical record suggests otherwise. Although the official prize at Olympia was only a crown of wild olive, a victor could expect substantial rewards on returning home. According to Plutarch, the Athenian lawmaker Solon fixed a payment of 500 drachmas for any citizen of Athens who won at Olympia. Victors might also be granted free meals at public expense for the rest of their lives. Other festivals offered prizes of obvious market value, such as the large jars of olive oil presented at the Panathenaic Games. Even the word 'athlete' derives from a Greek term for a prize. The notion of the pure, unrewarded sportsman of antiquity was largely a nineteenth-century invention.

C Its real roots lay in Victorian Britain. As organised sport spread in the 1860s and 1870s, clubs run by the professional and upper classes drew up definitions of who counted as an amateur, and some went far beyond the question of prize money. A widely copied rule adopted by the Amateur Athletic Club in 1866 excluded anyone who was 'a mechanic, artisan or labourer', on the grounds that men who worked with their hands enjoyed an unfair physical advantage. In practice, such clauses kept working men out of competitions that the wealthy wished to reserve for themselves, and the ideal of playing purely for its own sake was, from the beginning, bound up with social exclusion.

D The Olympic version of the rule claimed its most famous casualty in 1912. At the Stockholm Games, the American Jim Thorpe, a member of the Sac and Fox Nation, won both the pentathlon and the decathlon by commanding margins. Months later, a newspaper revealed that he had received modest wages for playing minor-league baseball in 1909 and 1910. Thorpe protested that he had not realised he was breaking any regulation. Many college athletes of the period spent their summers playing baseball for money under false names to avoid detection; he had simply used his own. The authorities were unmoved, and in 1913 he was stripped of his titles. The International Olympic Committee restored his status in 1982, nearly three decades after his death, and only in 2022 did it formally recognise him as the sole champion in both events.

E By the middle of the twentieth century the rule was becoming difficult to defend, yet it found a determined guardian in Avery Brundage, an American who presided over the committee from 1952 to 1972. Brundage regarded commercial influence as a corruption of the Olympic spirit and enforced the amateur code with almost religious zeal. Shortly before the 1972 Winter Games in Sapporo, he had the Austrian skier Karl Schranz expelled for having profited from commercial deals, although many other leading skiers were widely believed to do the same. To his critics, the decision demonstrated that the rule was being applied selectively, and largely at the discretion of officials.

F The deeper problem was that the rule no longer matched the realities of international sport. Governments in the Soviet Union and its allies supported leading competitors as nominal soldiers, students or factory employees, which allowed them to train full-time while remaining technically unpaid. Athletes in the West, meanwhile, increasingly relied on university scholarships, discreet payments from equipment manufacturers and the generosity of private patrons. Each side accused the other of hypocrisy, and both had a point. A regulation intended to place everyone on equal terms was now producing the opposite result, favouring those whose countries or family backgrounds allowed them to train without the need for a conventional job.

G Reform, when it came, was gradual. In 1974 the committee rewrote its eligibility rule so that competitors could be compensated for earnings lost while training. In 1986 it voted to let each international sports federation decide whether professionals could take part. Tennis, which had disappeared from the programme after 1924, returned as a full medal sport at Seoul in 1988, and in 1992 the United States sent a basketball team made up of professional stars to Barcelona. Whether the abandonment of the old principle has made the Games fairer or merely more commercial remains a matter of lively debate, but the Olympics of the twenty-first century bear little resemblance to the gentlemanly contest that Coubertin envisaged.

A Few natural materials have attracted as much scientific envy as spider silk. Weight for weight, the dragline that a spider uses as its safety line and as the frame of its web is stronger than high-grade steel, and it is tougher — able to absorb more energy before breaking — than Kevlar, the synthetic fibre used in body armour. Unlike either of those materials, it is produced at room temperature, from water-based ingredients, by an animal that may weigh less than a gram. For more than half a century, researchers have tried to discover how spiders achieve this and, with considerably less success, to imitate them.

B Part of the difficulty is that 'spider silk' is not a single substance. A typical orb-weaving spider possesses up to seven distinct types of silk gland, each producing a fibre with its own properties. The major ampullate glands supply the dragline; the flagelliform glands make the highly elastic thread of the capture spiral, which can stretch to well over twice its resting length without snapping; the aggregate glands coat that spiral with sticky droplets; and other glands provide silk for wrapping prey, anchoring threads to surfaces and protecting eggs. A single web therefore combines several materials, each tailored to a particular mechanical task. Remarkably, many orb weavers eat their webs every day and reuse much of the protein to spin a fresh one.

C At the molecular level, silk consists of large proteins known as spidroins, and their architecture helps to explain the dragline's unusual combination of strength and stretch. Short sequences rich in the amino acid alanine stack together into tightly bonded crystals, which resist being pulled apart. These are embedded in a looser, disordered matrix rich in glycine, which allows the fibre to extend and to dissipate the energy of an insect striking the web. Alter the balance between the two regions and the behaviour of the thread alters too — one reason why the silks of different species, and even of different glands in the same spider, vary so widely.

D The process by which a liquid becomes a solid fibre is, if anything, more impressive than the material itself. Inside the gland, spidroins are kept at extremely high concentration in a viscous fluid that researchers call 'spinning dope'. This passes into a long, slender duct that tapers as it approaches the spinneret, the nozzle-like organ at the rear of the abdomen. Along this channel, water is steadily drawn out of the fluid. The narrowing of the passage, meanwhile, stretches the proteins and aligns them along the direction of flow. Near the exit, a valve helps to regulate the thread before it emerges. Crucially, the spider does not push silk out; it pulls it, using its legs or the weight of its own body as it drops. Fritz Vollrath, whose group at the University of Oxford has studied spinning for decades, has argued that the whole operation requires far less energy than the industrial manufacture of synthetic fibres such as nylon.

E Natural variation offers further clues. In 2010, a team including Ingi Agnarsson, Matjaž Kuntner and Todd Blackledge described Darwin's bark spider, a species from Madagascar that suspends its webs across rivers and lakes, with anchor lines up to 25 metres long. Laboratory tests showed that its dragline was roughly twice as tough as any spider silk measured before, making it the toughest biological material then known. Silk also serves purposes beyond trapping. Young spiders of many species disperse by 'ballooning', releasing threads that carry them into the air; in 2018 Erica Morley and Daniel Robert at the University of Bristol showed that spiders can sense the atmosphere's natural electric field, and that such a field alone can trigger take-off, even in still air.

F Why not simply farm spiders, as silkworms have been farmed for thousands of years? The obstacle is behavioural: most spiders are territorial and cannibalistic, and kept together in large numbers they tend to eat one another. The sheer labour involved in using wild spiders instead was demonstrated by the textile designers Simon Peers and Nicholas Godley, who, working in Madagascar, collected silk from more than a million golden orb-weavers to weave a cape that went on display at the Victoria and Albert Museum in London in 2012. Each spider was gently 'milked' of its thread and then released. The result was spectacular, but the project took years and was never intended as a model for industry.

G Instead, researchers have turned to genetic engineering. In the early 2000s, a Canadian company bred goats that secreted spider-silk proteins in their milk, and Randy Lewis, first at the University of Wyoming and later at Utah State University, continued similar work; bacteria, yeast and silkworms have also been modified to produce spidroins. Several firms now sell goods made from such proteins, from cosmetics to experimental sports clothing, yet none has matched the performance of natural dragline. The engineered proteins are generally much shorter than the enormous molecules spiders make. Moreover, reproducing the subtle chemistry and mechanics of the spinning duct has proved far harder than producing the raw ingredients. Medical researchers, for whom quantity matters less than compatibility with living tissue, may be the first to benefit: silk's low tendency to provoke an immune reaction has made it a candidate for wound dressings and for guiding the regrowth of damaged nerves.

A Few areas of public-health policy generate as much heat, and as little agreement, as the regulation of food marketing aimed at children. Campaigners point to the vast sums spent promoting products high in fat, sugar and salt, and to the rising prevalence of childhood obesity, and conclude that the two must be connected. Manufacturers and advertisers reply that the link is unproven and that restrictions infringe on legitimate commercial expression. Both sides tend to argue as though the question were straightforward. It is not, and the evidence accumulated over the past four decades suggests that each camp has been right about something and mistaken about rather more.

B The case for intervention rests on a substantial body of research into how children respond to persuasion. Younger children, in particular, struggle to distinguish commercials from programmes, and until around the age of eight most do not grasp that an advertisement is designed to influence rather than inform. Experimental studies have repeatedly found that children shown food advertisements subsequently eat more than those shown advertisements for toys, and systematic reviews, including one commissioned by the World Health Organization, have concluded that marketing shapes children's preferences, their requests to parents and their consumption. Sceptics are entitled to point out that such experiments capture short-term reactions in artificial settings. Yet it would be odd to suppose that an industry spending billions every year is buying nothing at all.

C The industry's most sophisticated counter-argument is that advertising chiefly redistributes sales between competing brands rather than enlarging total consumption. A cereal commercial, on this view, persuades a family to switch from one sugary breakfast to another, not to eat more of it. There is something in this, and it may explain why certain early restrictions produced disappointing results. Nevertheless, the argument proves less than its proponents imagine. Much food advertising promotes not a brand but a habit — the after-school snack, the sweetened drink with every meal — and habits, once established, benefit every seller in the category. If marketing merely shuffled market share, it would be difficult to account for the enthusiasm with which rival firms fund campaigns that celebrate eating occasions rather than products.

D What, then, does experience of actual restrictions show? The longest-running example is in Quebec, which has prohibited commercial advertising directed at children under thirteen since 1980. An analysis by the economists Tirtha Dhar and Kathy Baylis, published in 2011, estimated that the ban had reduced fast-food expenditure among French-speaking households — the group most exposed to Quebec's own media rather than to English-language broadcasts from elsewhere — by roughly 13 per cent. More recently, Transport for London restricted advertisements for less healthy foods across its network in 2019, and researchers later calculated that households in the capital bought around 1,000 fewer calories' worth of such products each week than a comparison group in the north of England. Chile's sweeping law, which took effect in 2016 and combined marketing limits for under-fourteens with prominent warning labels and the removal of cartoon characters from packaging, was followed by a marked fall in purchases of sugary drinks.

E These findings are encouraging, but they require careful interpretation. None of these measures has yet been shown to reduce obesity itself, a condition shaped by income, sleep, physical activity, the price of fresh produce and much else; a decline in purchases of one category may be partly offset by increases elsewhere. Measuring their impact is itself awkward, since children's exposure to advertising is rarely recorded directly and must usually be inferred from viewing figures or household purchases. Restrictions also leak. As television audiences have fragmented, marketing has migrated to social media, games and content sponsored by online personalities, where it is considerably harder to identify and police. In the United Kingdom, proposed limits on online and early-evening television advertising were postponed several times after first being announced. By the time such rules are drafted, the media landscape they address may already have moved on.

F My own view is that restrictions are worth having, but for reasons somewhat different from those usually advanced. Their principal value lies less in any direct effect on children's waistlines than in two indirect consequences. First, they give manufacturers an incentive to reformulate: when only products meeting a nutritional standard can be advertised, cutting the sugar or salt in a popular brand becomes commercially worthwhile, and the benefit extends to every consumer, not only to the young. Second, they shift social norms, signalling that certain foods are occasional treats rather than everyday staples. Neither effect will register in next year's statistics, and politicians who promise rapid results risk discrediting a sensible policy when those results fail to materialise. Advertising restrictions are not a cure for childhood obesity; they are one modest component of an environment that, taken as a whole, makes healthier choices easier. Judged on those terms, they deserve support. Judged as a solution in themselves, they will always disappoint.