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Lichens: the great survivors

They are easy to overlook, but these small organisms have a remarkable story to tell

Look closely at almost any old stone wall, gravestone or tree trunk in Britain and you are likely to find patches of colour: flat grey-green circles, bright orange crusts, or small leafy growths that look a little like dried seaweed. Most people who notice them at all assume that they are some kind of moss or small plant. In fact, they are lichens, and they are among the most unusual living things on Earth. Lichens are found on every continent, from the edges of hot deserts to the frozen rocks of Antarctica, and Britain alone is home to well over a thousand different species.

What makes lichens so unusual is that a lichen is not a single organism at all. Each one is a partnership between a fungus and a partner that can make its own food from sunlight – usually a green alga, or a type of bacterium known as a cyanobacterium. The fungus forms the body of the lichen and provides shelter, protecting its partner from strong light and from drying out. In return, the partner uses the energy of sunlight to produce sugars, which feed the fungus. In many of the places where lichens grow, neither partner could survive on its own. Scientists first suggested this explanation in the 1860s, and the idea was so surprising that many experts at the time refused to accept it. More recently, researchers have found that many lichens also contain a third partner, a kind of yeast, which suggests that the relationship is even more complicated than was once believed.

This cooperation allows lichens to live in conditions that would kill most plants. Lichens have no roots and do not need soil, so they can grow on bare rock, metal and even glass. They take in water directly through their surface, and when there is no rain they can dry out almost completely, remaining in a resting state for long periods. When water returns, they quickly become active again. The price of this toughness is extremely slow growth. Many of the flat, crusty lichens found on rocks spread by only a millimetre or so each year, and some individual patches are thought to be hundreds or even thousands of years old.

Because they grow at a slow and fairly steady rate, lichens can be used as a kind of natural clock. When glaciers melt and retreat, for example, they leave behind areas of bare rock that lichens begin to colonise. By measuring the largest lichens on these rocks, geologists can estimate how long ago the ice disappeared, and so build up a picture of the movement of glaciers over time. This technique, known as lichenometry, has also been used to estimate the age of stone monuments and old buildings, although it works best when the results can be checked against dates from other sources.

Lichens are also extremely sensitive to the quality of the air. Because they absorb most of what they need from rain and the air, they also take in whatever pollution the air contains. During the nineteenth and twentieth centuries, smoke from factories and household coal fires filled the air of British cities with sulphur dioxide, a gas that is harmful to many lichens. As a result, large areas in and around industrial towns became so-called ‘lichen deserts’, where only a handful of tolerant species could grow. After laws were introduced in the 1950s to reduce smoke, the air slowly became cleaner, and many lichens have since returned to towns and cities.

Today, scientists are paying closer attention to a different kind of pollution. Nitrogen compounds from vehicle exhausts and from farming encourage the growth of certain lichens, often bright yellow or orange species, while other types become less common. By recording which species are present on the trees in a particular area, it is possible to build up a picture of local air quality without the need for expensive equipment. Several surveys in the UK have invited schoolchildren and other members of the public to take part, using simple identification charts.

People have made use of lichens for thousands of years. In the far north, reindeer depend on them for food through the long winter, when little else is available. Lichens have also been used to make dyes: in parts of Scotland, a reddish-brown dye produced from rock lichens was traditionally used to colour wool. Litmus, the substance that turns red in acid and blue in alkali, was originally obtained from lichens. In some regions, certain species have even been eaten by people at times when other food was scarce.

Despite this long history, lichens are still not fully understood. New species are described every year, and scientists believe that many more are waiting to be discovered, particularly in tropical forests. The next old wall you walk past may be home to a community of lichens that has been growing quietly there since long before you were born.

Railway time

How the coming of the railways persuaded Britain – and eventually the world – to agree on what time it was

AUntil the middle of the nineteenth century, few people in Britain had any reason to know the exact time in another town. Each community kept its own time, based on the position of the sun. When the sun reached its highest point in the sky, it was midday, and church and town-hall clocks were set accordingly. Because the Earth turns from west to east, midday arrives slightly later the further west you go – about four minutes later for every degree of longitude. Bristol therefore ran roughly ten minutes behind London. For people travelling on horseback or by stagecoach, these differences hardly mattered. A journey between two cities could take a day or more, and no traveller was in a position to notice that a few minutes had been gained or lost on the way.

BThe arrival of the railways changed this. By the 1840s, trains were covering in a few hours journeys that had once taken days, and railway companies needed to publish timetables that passengers could trust. But a timetable is of little use if the stations along a line do not agree on the time. A train might leave London at noon by the London clock and reach a town where the local clock showed a different time altogether, leaving passengers unsure whether they had missed their connection. For railway staff, the problem was more serious than inconvenience. On lines where trains shared a single track, safety depended on knowing precisely when other trains would pass, and any confusion about the time could end in a collision.

CThe solution the railway companies adopted was simple: they would ignore local time altogether. In 1840, one of the largest companies began running all its services on London time, and others gradually followed. By the end of the decade, most of Britain’s railways were working to the time kept at the Royal Observatory in Greenwich, which came to be known as Greenwich Mean Time, or GMT. Because many towns still used their own time for everything else, some public clocks were given two minute hands, one showing local time and the other railway time. A clock of this kind can still be seen on the front of an old trading hall in Bristol.

DKeeping clocks across the country in step was itself a technical challenge. Before the 1850s, the most reliable way of obtaining the correct time was to observe it directly. From 1833, a large ball on a mast above the observatory at Greenwich was dropped at exactly one o’clock every afternoon, so that the officers of ships on the River Thames could check the instruments they would rely on at sea. In London, one family even made a living for around a century by carrying a carefully adjusted watch to Greenwich, having it checked, and then visiting customers who paid to set their own clocks by it. The real breakthrough, however, came with the electric telegraph, whose wires often ran beside the railway lines. From the early 1850s, signals sent from Greenwich allowed clocks in distant towns to be checked, and in some cases corrected automatically.

ENot everyone welcomed the change. To some, railway time seemed like an attempt by London to dictate to the rest of the country, and a number of towns kept their clocks on local time for years. In Oxford, one college still rings its great bell each evening at five past nine rather than on the hour, a reminder of the days when the city kept its own time. There was also a legal difficulty. Although the railways and most public clocks had switched to Greenwich time by the mid-1850s, the law continued to recognise local time, and courts were occasionally asked to decide which of the two counted. This situation lasted until 1880, when Parliament finally passed an act making Greenwich time the legal standard throughout Great Britain.

FOther countries faced the same difficulty on a much larger scale. In the United States, railway companies were at one stage using dozens of different times. On 18 November 1883, the railways of the United States and Canada introduced a system of standard time zones, each one hour apart. The occasion became known as ‘the day of two noons’, because in many places the clocks were put back at midday and twelve o’clock came round twice. The following year, delegates from twenty-five countries met in Washington to choose a single line from which longitude, and ultimately time, would be measured around the globe. They chose the line passing through Greenwich, largely because most of the world’s shipping already used sea charts based on it.

GAgreement in principle did not lead to immediate change. Several countries took decades to adopt time based on Greenwich; France, for instance, continued to use the time of Paris until 1911. Nor did governments regard the new system as fixed. During the First World War, a number of countries, including Britain, began moving their clocks forward in summer to make better use of daylight and save fuel. Today, when phones adjust themselves automatically as their owners cross a border, it is easy to forget that the idea of a whole country sharing a single time is less than two centuries old – and that it was the railway timetable, rather than the movement of the sun, that first made it necessary.

The puzzle of the tip

Why do so many people pay extra for a service they have already received? The answer reveals as much about social pressure as about economics.

Every day, millions of people leave restaurants, taxis and hairdressers having handed over more money than they were obliged to pay. Viewed through the lens of conventional economics, this is a curious act. The meal has been eaten and the journey completed; nothing the customer does at this point can improve either. In the textbook account of human behaviour, in which individuals act rationally to advance their own interests, the tip ought to be a rarity, confined perhaps to regular customers hoping to secure better treatment on their next visit. Yet tipping is commonplace even among travellers passing through a town they have no intention of returning to. For economists working within this traditional framework, the custom has long been something of an embarrassment: a widespread behaviour that their models suggest should barely exist.

The practice is, in any case, considerably older than the theories that struggle to account for it. Its precise origins are disputed, but tipping was well established in parts of Europe before it spread to the United States in the second half of the nineteenth century. There, it initially met with fierce hostility. Critics condemned it as an aristocratic import that had no place in a democracy, since it appeared to cast one citizen in the role of a servant waiting for the favour of another, and in the early twentieth century several states passed laws prohibiting it. None of these measures lasted. Within two decades every one had been repealed, and the United States went on to become the country where tipping is arguably more deeply entrenched than anywhere else.

The most intuitive defence of tipping is that it rewards good service. Since a manager cannot observe every exchange between staff and diners, the argument runs, it makes sense to hand the task of supervision to customers, who are ideally placed to judge whether they have been well treated. It is an elegant theory, but the evidence for it is surprisingly thin. Researchers in hospitality management who have analysed large numbers of restaurant bills have repeatedly found that the quality of service, as rated by the customers themselves, accounts for only a small part of the variation in the amounts they leave. Far more influential, it seems, are the size of the bill, the customer’s habitual practice and a range of minor gestures – a server introducing herself by name, say, or crouching beside the table to take an order – that have little bearing on the standard of the service itself. If tipping is a system of quality control, it is a remarkably imprecise one.

A more persuasive account is offered by social psychologists, who argue that the tip is motivated less by a desire to reward than by a wish to avoid discomfort. Leaving nothing, or too little, invites the disapproval of the server and perhaps of one’s companions, and even diners who will never see the server again seem to experience something close to guilt at the prospect of breaking a widely shared rule. On this view, the tip is not so much a payment for service as a fee for social ease. This also helps to explain why tipping norms are so resistant to change: once a particular percentage has become customary, falling below it feels like a deliberate statement, whatever the quality of the meal.

For employers, meanwhile, the custom has obvious attractions. It allows a restaurant to display menu prices that are lower than the real cost of a meal, and it shifts part of the wage bill onto customers in a form that rises and falls with demand. Labour campaigners point out that this flexibility is achieved at the expense of staff. On a quiet evening it is the worker, not the business, who absorbs the loss, and an income that varies unpredictably from week to week makes it hard to budget or to borrow. Campaigners also note that tips depend on customers’ judgements and can therefore reflect their prejudices. A further question is whether tips reach staff at all: in Britain, a law requiring employers to pass on tips to workers in full came into force only in 2024.

Why, then, do businesses not simply abolish tipping and raise their prices to fund higher wages? Over the past decade, a number of restaurants in the United States have tried exactly that, and their experience has been instructive. Many owners reported that customers compared menus as though no tip would be added elsewhere, and therefore concluded that the restaurant without tipping was expensive, even when the final bill came to much the same. Some employees were also unenthusiastic, particularly those in the most visible roles, who had earned more from tips than they did under fixed wages. Several of the best-known experiments were quietly abandoned within a few years.

The persistence of tipping, then, says less about its merits than about the difficulty of escaping it. A single restaurant that gives up the custom bears the costs of change, while its competitors do not; the obstacle is one of coordination rather than of public preference. Where tipping has been successfully limited, it has usually been through rules applying to all businesses at once, or through long-established cultural norms, as in Japan, where tipping is not customary and an attempt to leave money may simply cause confusion. None of this means that the tip is about to disappear: a habit sustained by both guilt and convenience is not easily dislodged. It does suggest, however, that the familiar justification of tipping as a reward for good service deserves considerable scepticism.