The phrase ceteris paribus—other things being equal—is absurd, because other things are almost never equal. But it is useful. It is a way of identifying the one thing that matters in the midst of a lot of things that are beside the point.

In the case of population, the key point is this: the growth in the population of organisms develops a characteristic momentum. It is self-replicating. Ceteris paribus, more produces more, in a process of exponential growth, with each year’s population rising by multiples of the previous year’s. The growth of non-self-replicating things, on the other hand, is additive, and the additions come from outside interventions, not from any internal dynamic that gives them a life and growth momentum of their own.P47

Here is the story elegantly summarised by Thomas Malthus:

Population, when unchecked, increases in a geometrical ratio. Subsistence increases only in an arithmetical ratio. A slight acquaintance with numbers will shew the immensity of the first power in comparison of the second.

By that law of our nature which makes food necessary to the life of man, the effects of these two unequal powers must be kept equal.

This implies a strong and constantly operating check on population from the difficulty of subsistence.

This difficulty must fall somewhere and must necessarily be severely felt by a large proportion of mankind.P48

Now, since other things are not equal, it doesn’t work out like that. What we don’t get is a “strong and constantly operating check on population”. Instead, we get time-lags, during which, from the growing population’s point of view, things seem to be moving ahead just fine. But if the population takes advantage of this, and stops worrying about numbers, there will in due course be overshoot. The population will have to fall to get back into equilibrium with its environment. That fall may be abrupt and “severely felt”. Time-lags switch off the automatic nudges and corrections which would keep us sensible. They make it necessary to think. In the case of something that matters as much as population—and where errors are so hard to correct—it is necessary to think a lot.P49

The second thing to note is that, in the case of the human population (in common with virtually all other populations), there are things other than subsistence that can reduce or halt their growth; disease, for example. Human populations—before they invented civilisation—in fact had a long history of intentionally restricting their numbers rather than waiting for subsistence to do it for them. Other controls include changing social attitudes and priorities, prohibitions on marriage and coitus under certain conditions, advances in contraceptive medicine, wars and even infanticide. There are also many things which affect the match between the amount of food that the land can produce and the amount that people actually get. They include the presence or absence of cheap energy, the weather, distribution in the sense of being able to buy and transport food, crop diseases (such as potato blight), and shifts in agricultural ownership from local subsistence farming to large-scale enterprises producing food for distant cities.P50

It is during periods of sharp change and instability, especially when an economy intensifies, that humans tend to lose control of their numbers. There are more jobs to be done, so there is an incentive for having more people to do them. Insecurity encourages parents to have more children to increase the chances of some still being around to look after them in their own old age. At times of dislocation, the taboos and practices by which a settled population can limit its fertility (discussed later) are seen to be unacceptable, or forgotten. Migration, too, is associated with high fertility, as migrants do all they can to establish their presence. An illustration of this is supplied by a 2010 University of Leeds study, whose projections of the UK’s population (2001–2051) suggest that, while the population of the White British group can be expected to grow by 4% between 2001 and 2031, the growth of the Asian, Black African, Chinese and Other Ethnic groups over the same time period are estimated at 95–153%, 179%, 202% and 350%, respectively.P51

The arrival of new crops in a region can also lead to rapid population growth: for instance, the population of Ireland is estimated to have grown from 3 million in 1779 to over 8 million when the census was taken in 1841, and this is taken to be mainly due to the cultivation of potatoes which, along with milk or buttermilk, make a cheap and nutritious diet.

All these factors, and feedbacks between them, contribute to pulses of population growth, but, thanks to those time-lags, it may be some time before it becomes clear what the consequences are, and how and when the environment will bite back.P52


The ‘demographic transition’ to lower population growth

In nature, populations that grow out of equilibrium with their environments crash. In the case of the human population of the present, we are not, or not yet, seeing a crash, but we are seeing a reduction in the rate of growth. When urban society settles down, families realise that they are better off with a few children whom they can afford to feed and educate properly than with a large number of children that are beyond their means. And the range of choice changes: as domestic technology improves, and as service industries grow, opportunities for women outside family life, especially the ablest women, cause some to wonder whether they have better things to do with their time than to have children (in economists’ terms, child-rearing acquires a higher ‘opportunity cost’ for those women). This leads to the inverse of Darwinian selection: a pattern in which the fittest produce the fewest children, the survival of the unfittest. And, in growing market economies, labour-intensive forms of work that are least affected by technical advance—such as teaching and child-rearing—become increasingly expensive relative to other forms of work: child-rearing is priced out of the market (Composition).P53

All these effects, taken together, add up to the “demographic transition”, a reduction in the growth of—or actual reductions in the size of—populations in a mature market economy. At least, the demographer John Weeks broadens out the meaning of the demographic transition to include all these factors. In its more familiar usage, it refers to a fall in the fertility rate—the number of children per woman—but Weeks insists that it is more complex than that. His transition includes changes in health and mortality, fertility, age, migration, the growth of cities and changes in the family and household.P54 The net outcome of all these transitions, including the decline in fertility, is what we should have in mind when thinking about trends in future population, and the science writer Fred Pearce writes of this as a “peoplequake”, unfolding in the present century:

Once the trend has set in, it may prove very hard to break. As well as having ever fewer potential mothers, societies may get out of the habit of having babies. Children will be rare, exotic and unusual. We can see this already. Only a few years ago, going to a café in Italy would see you surrounded by noisy children. Now you will likely see only adults, including many young latte-sipping men and women who would once have been surrounded by kids.

And Pearce provides some startling estimates of populations in 2100, with Russia at some 20% of its present population and Italy as low as 14%. Undoubtedly, there has been a change in the trend, starting in the second half of the twentieth century.55

For example, China’s one-child policy, introduced in 1979 at a time when the fertility rate was already on the way down, contributed to a reduction in fertility from 7.5 children per woman in 1963 to 2.5 children per woman in 1983. And yet this is also an illustration of how weak the link is between reductions in fertility and reductions in population—for, as a result of its former rapid growth rate, there are so many young women of reproductive age that China is still adding 7.7 million people each year, with an increasing proportion of old people to be looked after by the young. In due course, low birth rates will work through to declining populations, but it will take time. Over the whole period 1950–2000, China’s population grew by 700 million; it is slowing, but between 2000 and 2050 it will still grow—by a further 150 million. In Japan, the fertility rate, at a mere 1.2 children per woman, is low enough to have relatively quick results: by 2050 its population is expected to have fallen from 127 million at the millennium to 100 million. Worldwide, the rate of growth is expected to slow from 76 million per year in 2010, to 34 million by 2050, but that will still take population up from a 2010 total of 6.8 billion to 9.1 billion in 2050.P56

Weeks summarises,

As the rate of population growth has slowed down over the past two decades, there has been talk of a population implosion, implying that “the world is in for some rapid downsizing”. . . . The demographics of the world are shifting, to be sure, and there are pockets of potential implosion, especially in Japan and Eastern Europe, but there is no global implosion in sight.P57


Difficulties severely felt

While acknowledging the uncertainties of forecasts about such systems, then, there is nothing in the demographics to suggest prospects of any significant decline in the population . . .

. . . so long as our economies can keep it fed through the climacteric, and supplied with its energy needs in a liveable climate, and in tolerable conditions of political and social order—aka peace—and . . .

The big driver of food production during the twentieth century was the abundant supply of oil, gas and coal. That abundance is over. This fact alone is on course to reduce the population on a scale that makes all demographic forecasts irrelevant unless they take into account the possibility of catastrophic impacts, of which famine is one. Here are some of the critics that do so:

• John Weeks puts food and the prospect of famine in context with environmental change as a whole, including climate change:

Can we increase the food supply enough to feed the nearly 80 million additional people on the planet every year while also improving everyone’s diet in the process? We do not know. Do we have enough fresh water to support all those people? We do not know that either. . . . Still, we always have to come back to the fact that in the long run the only solution is to halt population growth; at some point, the finite limit to resources will close the gate on population growth.P58

• Martin Rees considers the prospect of the end of civilisation, with a corresponding collapse in population, in the course of this century.P59

• James Lovelock writes, “. . . the evidence coming in from the watchers around the world brings news of an imminent shift in our climate towards one that could easily be described as Hell: so hot, so deadly, that only a handful of the teeming billions now alive will survive.”P60

• A study by William Stanton, based on a worldwide historical analysis, concludes that, after an initial period when energy conservation and renewable energy sources are diligently developed, the link between oil and food will prove too strong: as oil production declines, so will population. There will be competition for survival, and some of the conflict that will develop under the pressure of scarce resources will reflect ethnic divisions in multicultural populations. Stanton argues that, even if all the correct decisions in response to oil depletion and climate change were to be made, the current population would still be far (some 7–14 times) in excess of the level sustainable under the conditions of the coming energy-famine. By 2050, he writes, the falling world population may stabilise at between 0.5 and 1 billion.P61

• And it is now widely recognised that global transportation and identical hybrid crop strains provide conditions for both pandemics (such as bird flu) affecting the population and threats affecting crops; but there is no basis for an estimate of their effect on population numbers.P62

The last time there was a population collapse in Europe was in 1348–9, when between a third and a half of the population died in the Black Death; it was, as Joan Thirsk describes it, “a Malthusian crisis that had long been waiting to happen”.P63 One effect of this was to make much more land available per capita—and this meant both a better, more varied diet and the freedom to experiment which opened the way for a revolution in agriculture. A new generation of crops and agricultural techniques was introduced, and there was substantial redistribution of wealth.P64

The significance of this was recognised. Before the catastrophe, the need for bread had demanded desperate measures—felled forests, drained swamps, ploughed meadows; after it, as the historian George Huppert writes, the survivors became prudent: they built “an artfully balanced social organisation” capable of controlling its own population. “Grim lessons had been learned. . . . They bowed to constraints, but they also achieved a degree of autonomy.” It would be as wrong to deny the benefits that would be derived in our time from a reduced population as it would be to welcome them, but there is no need to do either. The Lean Economy is designed not only to prevent or mitigate a reduction in population, but to provide the basis for a stabilised society far into the future, whether such a population collapse occurs at the start of the period or not.P65

In fact, population has fallen out of the range of things which politicians think they can do anything about. On the presumption that population movements (shifting labour forces around according to demand) are good for the economy, and in tune with the fact that “good for growth” trumps all other arguments, the European Union has abolished controls on migration across its national boundaries—an engaging instance of the rule that the larger the consequences, the more infantile the decision. There is no substantial benefit to be derived from the economic growth produced by a growing population, whatever the source, and the belief that there is one arises from an elementary confusion between aggregate income (or growth) and per capita growth income (or growth). As the House of Lords economic affairs committee summarised in 2008:

GDP—which measures the total output created by immigrants and pre-existing residents in the UK—is an irrelevant and misleading measure for the economic impacts of immigration on the resident population. The total size of an economy is not an indicator of prosperity or of residents’ living standards.

GDP per capita is a better measure than GDP because it takes account of the fact that immigration increases not only GDP but also population. . . . Rather than referring to total GDP when discussing the economic impacts of immigration, the Government should focus on the per capita income (as a measure of the standard of living) of the resident population.

Although possible in theory, we found no systematic empirical evidence to suggest that net immigration creates significant dynamic effects for the resident population of the UK . . . , and it is possible that there are also negative dynamic and wider welfare effects.P66

In fact, there are benefits, but they are minor and temporary. In addition to those discussed in the entry on growth, topping up the workforce with immigration can absorb some of the inflation-potential in a chronically overheated economy; it allows the economy to import skills, briefly saving it the trouble of effectively educating its workforce and developing practice in the manual skills; and it gives employers and middle-income householders access to labour which, for a short period, is prepared to work for little money.P67

On the other hand, such minor, short-term opportunism is no good reason for irreversible change. Immigration requires big increases in infrastructure; it means less farmland and more people to feed in the event of food shortages; and it brings problems of increased water demand and waste disposal needs, a further reduction in the space available for local food and the natural environment, smaller per capita entitlements when energy rationing begins, ethnic divisions as a factor in law and order, and greater difficulty in sustaining the collective effort, the shared culture and the latent gift of trust between strangers needed for the fluid conditions of the near future. Only the wealth temporarily conferred on the market economy by oil, gas and coal removed population policy from the list of things we have needed to think about.


Intentional limits

How was population controlled in the past? There is debate about this. The conventional view is that death rates in hunter-gatherer societies were very high (all those wild animals), so that humans were lucky to live long enough to have children and keep their numbers up. No doubt that was the case in some places. But a species that was developing tools and intelligence, which had evolved a physiology capable of staying alive for up to a century and was engaged in taking over the world, is likely also to have been more successful than this. Humans during that long period, as the anthropologist Marvin Harris insists, were no bumbling amateurs.P68 For the stable clan and village societies that comprised (by far) the longest phase in human history, the need to maintain a steady population was non-negotiable. Their numbers were not kept down by predators, disease or starvation; rather, they had an accommodation with their environment, with food and materials in variety; they recognised that if they were to hold on to all that, they had to control their own population, and that in turn meant that, per woman, the number of children surviving long enough to have their own children could not be much more than two. Harris summarises,

Each woman must have had on average less than 2.1 children who survived to reproductive age.P69

Harris gives us a rough guide to how they did this, starting with the presumption that the fertile span for women would be from sixteen to forty-two, long enough in theory for twelve pregnancies. The principal way of reducing this was by prolonged lactations. It is not clear that this is still possible in our own day, when lactation does not appear to be so effective as a way of preventing menstruation, perhaps owing to high rates of exposure to oestrogen in the environment. But on the evidence of the past, a woman did not resume ovulation after giving birth until her body fat recovered to about 20–25 percent of her weight, which was difficult to achieve when she was nursing because the nursing infant needs 1,000 calories a day. Prolonged lactation (four years) would reduce the number of pregnancies from twelve to six.P70

Reduced coitus in older women might bring that down to five; spontaneous abortions, accidents and predation might take it to four. But that is two more than a village with a stable population can support. Abortions during this period were rarely performed, not least because the techniques available were as likely to lead to the death of the mother as of the foetus. And that left infanticide.P71

It was always a grief-drenched thing to do, and it was done with an array of denials, delusions and taboos to fog the truth. A common means was neglect: the mother might not feed the infant enough, or she might abandon it in the wild, or accidentally drop it. Another mother could be asked to “look after” it for a day, while the real mother went foraging, to learn the sad news of her child’s death when she returned. Feet-first (breech) births, or being born in the yard rather than in the house, were taken as signs that the child was not for this world. Even the foundling hospitals of the eighteenth and nineteenth centuries applied such principles of deception. An infant left at a hospital would be placed in a revolving box in the wall of the hospital, allowing the mother surrendering her infant to hope that it would get a better life than she could provide for it. There was just a chance she was right: between 10 and 20 percent of them survived.P72

For those groups and villages that kept the human race and its planet intact for so long, there was no alternative to maintaining stable numbers at a level at which food would be plentiful, or at an optimum where material affluence (in the terms of a traditional society) could be maximised. This stable society—as one eighteenth century missionary put it, this “rude image of the Golden Age”—would destroy itself if it destabilised its population.P73 The anthropologist Hugh Brody reports,

[Inuit] families do not desire more than two small children at any one time, and to this end they do what they can to space births by about three years. Thus the apparent paradox noted by so many observers of hunter-gatherer societies: intense love for children, yet occasional readiness, at times of shortage, to use infanticide if a child just born is perceived as one too many.P74

As for less drastic methods of birth control? Since pre-industrial contraception (e.g., beeswax, honey, pessaries, caps made of oiled paper and condoms made of animal intestines and herbal contraceptives) was unreliable and unpopular, the main alternative was abstinence, sustained by convents, monasteries, a celibate priesthood, and local rules such as those which did not permit a couple to get married until a house became available for them in the village. But those are methods suited to settled and comparatively rich states. For most of history, the urgent task of preventing death rates rising out of control demanded a sense of the gift of life being the intense, special outcome of getting a lot of things right at the same time.P75


In the end, we do not need to make predictions about the scale of future population. The Lean Economy has other business. Its aim is to explore how human society could sustain a mannerly and decent civilisation despite the shocks, and we should not be distracted from this by uncertainty about the size of the population. What we do know is that, in an economy with richly-developed reciprocities, social capital and culture, it is possible to support institutions and practices which limit the growth of populations. And one reason why the limits failed was that those structures of social order declined—slowly in the early medieval period, but gathering speed with the growth of towns whose long commercial reach enabled them to break free of the need to maintain a stable population. Then the larger population required an intensive, urban industry to meet the need not just for more goods, but for the increasing elaboration—the intensification and intermediate economy—that goes with large scale. And that triggered a classic positive (i.e., amplifying) feedback of further dislocation and further growth.

Exploding populations in nature are never sustainable. The Lean Economy may, or may not, start with a much smaller population than that of now, but—however population numbers eventually settle down—it will support cultural standards controlling population with the effectiveness with which it delivers all its other solutions from energy to agriculture to music. This will be neither a voluntary system nor an authoritarian one: it will be a culture that has learned from experience.

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David Fleming
Dr David Fleming (2 January 1940 – 29 November 2010) was an economist, historian and writer, based in London. He was among the first to reveal the possibility of peak oil's approach and invented the influential TEQs scheme, designed to address this and climate change. He was also a significant figure in the development of the UK Green Party, the Transition Towns movement and the New Economics Foundation, as well as a Chairman of the Soil Association. His wide-ranging independent analysis culminated in two critically acclaimed books, Lean Logic and Surviving the Future. A film about his perspective and legacy - The Sequel: What Will Follow Our Troubled Civilisation? - was released in 2019, directed by BAFTA-winning director Peter Armstrong. For more information, including on Lean Logic, click the little globe below!

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