Do You Think You're Clever? (14 page)

(Geography, Cambridge)

At first sight, this seems a rather pointless, uninteresting question that only a resident of Croydon or someone with a complete and detailed memory of the National Census could possibly answer.

But stop to think a second. You can actually make a guess. You might guess that the population of London is some 10 million. You might guess that there are some 30-odd boroughs in London. So, instantly, you might guess that the population of Croydon is 10 million divided by 30 – that is, about 333,333. In fact, if you did make a guess this way, you would be astonishingly close; the population of Croydon in 2007 was 336,600! So with a simple guess that took no more than a few seconds, you have got within about 1 per cent of the true figure. There was an element of luck in getting quite this close, since London’s population is actually less than 10 million and it happens to have 32 boroughs, not 30. But the point is that you can make a pretty good stab quickly and without access to any figures whatsoever.

In fact, making a rough, commonsense estimate from a few basic facts is a surprisingly useful skill not just in everyday life but even in high-level science, and that’s what makes this apparently routine question so fascinating. What you might call a ‘guesstimate’ or a ‘back-of-an-envelope’ calculation, physicists call a ‘Fermi problem’,
after the great nuclear physicist Enrico Fermi, who took a legendary delight in posing and solving such problems, such as ‘How many piano tuners are there in Chicago?’

During one of the first atom bomb tests at Trinity in New Mexico in 1945, Fermi famously estimated the power of the bomb by dropping a few scraps of paper as the shockwave passed and seeing how far they travelled as they fell. The scraps fell some 2.5 metres away, so Fermi guessed the blast was about 10 megatons. In fact, Fermi’s estimate was too small, since the blast turned out to be over 18 megatons. However, he had got within the right order of magnitude with just an incredibly simple, instant calculation. This is what makes guesstimates so valuable.

Making a guesstimate of the answer you expect before you embark on a long, complex scientific calculation, for instance, can reduce the chances of making a massive error simply through a wrongly inputted figure or miscalculation. Alternatively, a guesstimate can help you get a useful ‘ballpark’ figure even where numbers are huge and real figures are effectively unobtainable. That’s the basis of the famous Drake equation, devised in 1960 by Dr Frank Drake to estimate the likely number of intelligent civilisations in our galaxy. The fact that we haven’t actually encountered any of these civilisations is known as the Fermi paradox – to which the somewhat nihilistic answer is often that these civilisations lasted just a short while before self-destructing …

Beyond the academic world, guesstimates can provide valuable hints of possible policy flaws even without long
and extensive research. In their book on guesstimation, Lawrence Weinstein and John Adam show, for instance, how you can make an instant estimate of how much cropland would be needed to replace petrol with corn-based ethanol as motor fuel – an estimate which suggests instantly how ultimately unworkable the idea might be. Many management consultants and financial businesses also now use estimation questions, such as ‘What is the market for toilet rolls in China?’, to test the intelligence of job candidates and their ability to think on their feet.

Interestingly, Croydon’s population has been in the news recently because Croydon council challenged the calculation of its population by the Office of National Statistics. According to ONS figures, Croydon’s population has increased by barely 0.5 per cent since 2001, whereas Croydon council found that the local need for housing and schooling suggested a larger increase. Apparently, the ONS count was affected by changing the way it counted international migrants. The discrepancy was not just a matter of statistics, since Croydon’s general government grant, like that of all local councils in the UK, is given per head of its population. So an underestimate of population would mean a smaller grant.

Finally, the question, ‘What is the population of Croydon?’ does not necessarily require an answer in numbers. If you interpret it as meaning, ‘What is the
nature
of Croydon’s population?’ for instance, you open up a whole new range of possible answers. It might be that you talk about the population’s racial background, which in some areas of the borough is increasingly mixed. Or you could be talking about the age structure. A philosopher might even answer the question ‘What is the population of Croydon?’ existentially …

(Biological Sciences, Oxford)

This deceptively simple question gets right to the nub of the intricate, interdependent interrelationship between all the world’s living organisms. Big, fierce animals are large predators like lions, tigers and polar bears that are big and fierce because they need the strength and ferocity to kill and eat other fairly big creatures to survive. Polar bears prey on smaller animals such as seals. Lions prey on grazing animals such as zebras and antelopes.

Big animals like these need to eat a lot of meat, and must have plentiful prey. So large predators must inevitably be fewer in number than the creatures that they prey on. Indeed, nature ensures a fairly constant ratio between predators and prey. If the prey numbers ever expand, there is more food to sustain predators and so predator numbers expand – ultimately limiting the number of prey. If prey numbers shrink, predator numbers shrink too because there is less available food, until thgde ratio settles down again.

Of course, the large predators’ prey need to eat, too, and large predators are often at the top of a long chain of animals that feed upon other living things – or rather a pyramid, because the numbers get bigger and bigger the further down you go. So for every polar bear, for instance, there needs to be at least, say, ten seals. And for every seal there needs to be about 40 of the herring that they eat. Then for every herring, there needs to be 800 or so of the zooplankton called copepods that they feed on, while for every copepod there needs to be about 24,000 of their phytoplankton dinners. That means that to feed just a single polar bear you need a vast pyramid of organisms supported by nearly 8 billion phytoplankton! It’s hardly surprising, then, that big, fierce creatures are few in number.

In fact, they are even fewer in number than this simple numerical relationship might imply. Biologists refer to the different steps of the food pyramid as ‘trophic levels’ (from the Greek
trophe
, meaning food). Feeding and eating are essentially energy exchanges, and the fundamental laws of thermodynamics mean that each time energy is exchanged some is lost in the form of heat. So as you move up from one trophic level to the next, there is always a loss of energy.

The initial energy input usually comes from sunlight, which is used by ‘autotrophs’ (self-feeders) – essentially plants – to convert chemicals in the environment into food. All other living things are heterotrophs, which means that they depend on this initial energy input, either by eating the plants directly, or by eating other living things that eat
the plants and so on.
^*
No wonder, then, that big, fierce creatures are few in number.

Being at the top of the food pyramid also makes large predators particularly vulnerable to environmental shocks. Whenever there is any disruption of the habitat, the problems reverberate up through the pyramid and the top predators are usually first to suffer. As human activity has had more and more impact on the natural environment in the last century, for instance, large predators have become not just few in numbers but genuinely rare, as their habitats, and so their food supplies, dwindle. The human inclination to hunt and kill big, fierce creatures has reduced numbers still further. Sabre-tooth tigers are believed to have been driven to extinction 10,000 years ago by human hunters in North America. Today, the combination of environmental threats and hunting means that there are very few big, fierce creatures that are not just rare but actually in severe danger of extinction.

(Human Sciences, Oxford)

This is a loaded question which divides opinion sharply. The world’s population is certainly bigger than it has ever been before. There are now (in July 2009) some
6.77 billion people in the world – and three or four new ones are joining us every second. With such a gigantic, and rapidly growing, population, it’s easy to see why some prophets of doom predict that it will all end calamitously when the number of people simply becomes too great for the finite resources of the earth.

The idea of ‘overpopulation’ dates back to Thomas Malthus in the early nineteenth century. Malthus argued that it was easy for human population growth to outstrip the earth’s capacity to sustain it, and people began to talk of a ‘Malthusian catastrophe’ – the dramatic crash in population that would inevitably follow once the limits to growth had been reached. At the time Malthus was writing, the world’s population was under a billion, but the onset of the Industrial Revolution set in train a remarkable swelling of human numbers to more than 3 billion by the 1960s – with no sign of any global Malthusian catastrophe.

That, though, was when some economists began to ring the alarm bells. Paul Ehrlich wrote a bestseller called
The Population Bomb
, which predicted imminent doom, while in the early 1970s a group going by the name of the ‘Club of Rome’ produced a report called
The Limits to Growth
full of tables with equally dire forecasts. Yet the outcome in the decades since has confounded their pessimism. There are now more than twice as many people crowded onto the planet as there were when Ehrlich was writing – far, far more than his predicted catastrophic limits.

One reason why the calamity has not yet arrived is a revolution in agriculture which has dramatically boosted the world’s food output. So although over a billion people suffer from lack of food, the problem is how the food is shared, not the total quantity. And yet the arguments of the over-population doom-mongers seem in some ways to be just too much like plain common sense to ignore. Surely there must come a time when there are just too many people in the world for its resources?

Scientists and economists have now begun to argue about just what the earth’s ‘carrying capacity’ for humans is – and most suggest a maximum of between 10 and 20 billion. Current population forecasts by the US census predict that we’ll begin to reach those ultimate limits in just 40 years’ time. So if there are not too many people in the world now, there will be soon. Some scientists, however, argue that the notion of human carrying capacity is false and that human innovation will find ways to sustain an ever greater number of people. The repeated failure of dire predictions in the past seems to give that argument some sustenance.

And yet, the world is already – right now – facing manifold serious, and potentially disastrous, problems which can be directly attributed to pressure on the earth’s resources. The spectre of global warming, for instance, is now quite clearly attributable to the growing impact of human activity on the planet, while the pressure on water and food resources is at crisis point in many places around the world. Moreover, the natural world is going through a
sharp phase of mass extinctions as animals are muscled out of their environmental niches by humans. It’s unarguable that these problems are real, and serious, and happening now. Does this mean, then, that there are actually too many people in the world already? Well, not necessarily.

The problems are as much to do with the way the world’s resources are used as they are with a simple equation between population numbers and resource capacity. Global warming, for instance, has been driven by the massive growth in energy use which has gone hand-in-hand with the rise in human population over the last half-century in particular. Yet it’s the way energy is used that is a problem, not the sheer number of people. In fact, quite a small proportion of people in the developed world are responsible for the massive energy consumption that has started the global warming ball rolling. Most of the world’s population has played very little part as yet. So even a dramatic fall in the world’s population would not necessarily ease the problem of global warming – unless the remaining few changed their consumption patterns. And a rise in the world population does not necessarily have to bring further global warming.

Of course, it’s easy to imagine that a quiet, unpressured world in which there was plenty of space and resources for all would be a kind of nirvana. People often look back wistfully on the days when England had a population of just a few million and dream of how blissful that might be if we had all the comforts of modern living to go with that rural
expanse. There would be no need for green belts to stop city development, and each of us could have large houses with larger gardens to expand in. And yet most of the great things we associate with human progress – science, technology, democracy, the arts, living standards and so much more – have grown with the world’s population. They are the fruits of civilisation – of the growth of cities, of a dynamic urban milieu, of the bustling, booming, growing mess of humanity crowding together in ever greater numbers.

It is, perhaps, attractive to imagine more space for oneself, a bigger, more gently divided share of the world’s scarce resources. But just who is ‘too many’, then? Who is to say? How many of us would ever say, I am one of the thousand, the million, the billion, too many? Most of us, rightly, consider ourselves infinitely precious – and none of us, however disadvantaged, however ill-starred, is ‘too many’. What matters, of course, is how we treat each other and the world.