Test 1 — The Silent Decline of the Honeybee

Across Europe and North America, beekeepers have reported losing between 30 and 45 per cent of their colonies each winter since the early 2000s. The phenomenon, popularly called Colony Collapse Disorder (CCD), is unusual not because bees die — colonies have always experienced some seasonal loss — but because adult workers vanish without leaving bodies near the hive. The queen, brood and food stores often remain untouched, yet the colony cannot sustain itself and ultimately fails.

Scientists no longer believe a single cause is responsible. Instead, most researchers now describe CCD as a "perfect storm" of overlapping stressors. The most consistent finding is that the parasitic mite Varroa destructor weakens bees by feeding on their fat reserves and by spreading at least twenty different viruses, including Deformed Wing Virus. Once a colony is infested, even moderate exposure to other pressures can prove fatal.

A second pressure is the agricultural use of neonicotinoid pesticides, a class of chemicals introduced in the 1990s and applied as seed coatings on crops such as maize and oilseed rape. Even at sub-lethal doses, neonicotinoids impair a forager's ability to navigate home. Three commonly used neonicotinoids were restricted in the European Union in 2018, though the substances remain widely used elsewhere.

Habitat loss completes the picture. The conversion of mixed meadows into single-crop fields means that for several weeks of the year bees have nothing to forage on. Urban gardens, ironically, often provide more continuous floral diversity than the surrounding countryside. Several cities, including Oslo, Utrecht and Paris, have responded by planting "bee corridors" along tram lines and rooftops.

The economic stakes are substantial. The United Nations Food and Agriculture Organisation estimates that 75 per cent of leading global food crops depend on animal pollination, with honeybees the single most important pollinator. Without them, the price of almonds, apples and many berries would rise sharply, and certain crops — such as Californian almonds, which require around two million colonies trucked in each spring — could not be produced commercially at all.

What can be done? Researchers at the University of Reading argue that the simplest measures are also the most effective: planting wildflower strips, leaving uncut grass margins around fields, and supporting small-scale beekeepers who breed mite-resistant queens. Technology helps too — sensor-equipped hives now warn beekeepers of temperature or weight anomalies within hours rather than weeks. Yet most specialists agree that no app will compensate for the loss of flowering land.

For most of human history, exchange did not depend on coins or banknotes. The economist Adam Smith popularised the idea that money emerged because barter was inefficient — if a fisherman wanted bread, he had to find a baker who also wanted fish. Yet anthropological evidence collected since the 1980s suggests that pure barter economies were rare. Instead, early communities relied on systems of credit: who owed what to whom was simply remembered, sometimes for years.

The first true money seems to have appeared not as a tool for trade but as a unit of account in temple economies. In Mesopotamia around 3000 BCE, priests recorded grain debts in cuneiform tablets. A standard "silver shekel" was defined as the equivalent of a fixed weight of barley. Crucially, no silver actually changed hands in most transactions; the metal was a yardstick, not a means of payment.

Coinage, by contrast, was a Mediterranean invention. The kingdom of Lydia, in modern Turkey, struck the earliest known coins around 600 BCE from electrum, a natural alloy of gold and silver. State stamping guaranteed weight and purity, which dramatically reduced the cost of trade between strangers. Within a century, coins had spread to Greek city-states, where they helped pay mercenary soldiers — a use that may explain their rapid adoption.

Paper money followed much later and developed independently in China during the Tang and Song dynasties. Merchants, weary of carrying heavy strings of bronze coins, deposited them with trusted houses and received receipts. By the eleventh century these receipts were being issued by the state itself. European travellers such as Marco Polo were astonished that subjects of the Mongol Khan accepted printed paper as readily as silver.

Modern banknotes, with their elaborate watermarks and serial numbers, descend from seventeenth-century European goldsmiths' notes. Goldsmiths who stored other people's gold soon noticed that depositors rarely withdrew everything at once. They began lending out portions of their reserves at interest — the birth of fractional reserve banking, and arguably of modern capitalism.

Today most money is neither metal nor paper but a series of digits on bank servers. The shift to electronic balances has been so complete that in Sweden cash now accounts for under two per cent of transactions. Yet the principles remain those identified by Mesopotamian scribes five thousand years ago: money is, above all, a record of who owes what to whom.

Why do humans, like almost every animal studied, need to sleep? For most of the twentieth century, the answer seemed obvious: the body rests so that it can recover energy. Yet measurements show that the energy saved by eight hours of sleep is no greater than that of quietly lying still — about a hundred kilocalories, roughly the energy contained in a slice of bread. The metabolic explanation, in other words, is far too weak to justify giving up a third of our lives.

A more promising framework, developed in the 1980s by the Swiss researcher Alexander Borbély, treats sleep as the product of two interacting processes. Process C is the circadian rhythm, an internal clock running on a cycle of roughly twenty-four hours. Process S is "sleep pressure", a homeostatic signal that builds up the longer one stays awake and dissipates only during sleep itself. The two processes pull in different directions: sleep pressure rises steadily through the day, while the circadian signal promotes alertness from late morning until early evening. Sleep occurs when the gap between them is widest.

Recent neuroscience has begun to identify the molecular basis of sleep pressure. The leading candidate is adenosine, a by-product of cellular energy metabolism that accumulates in the brain during waking hours. Caffeine works precisely because it blocks adenosine receptors, masking the signal of accumulated sleep debt without removing the debt itself. When the caffeine wears off, the underlying pressure remains — sometimes overwhelmingly so.

Sleep itself is not a single state but a sequence of stages. Most striking is rapid eye movement (REM) sleep, during which the brain is almost as active as in waking life but the body is paralysed. REM appears to play a specific role in consolidating emotional memories. Volunteers deprived of REM, but allowed equal total sleep, show more negative interpretations of ambiguous faces the following day.

Deep non-REM sleep, meanwhile, has been linked to a remarkable cleaning function. In 2013, researchers at the University of Rochester showed that during deep sleep the spaces between brain cells widen by roughly 60 per cent, allowing cerebrospinal fluid to wash away metabolic waste, including the protein fragments associated with Alzheimer's disease. The brain, it seems, takes itself offline in order to clean house.

The implications are sobering. Adults who routinely sleep fewer than six hours show higher rates of cardiovascular disease, depression and dementia. Yet sleep is uniquely vulnerable to modern life: artificial light delays the circadian signal, screen use suppresses melatonin, and shift work scrambles both Process S and Process C. Some experts argue that public-health campaigns should treat chronic short sleep with the same urgency once given to smoking.