Alice Reid & Romola Davenport

The world’s population has exploded since the 18th century, from perhaps 1 billion in 1800 to over 8 billion today. The usual story is that this extraordinary growth was caused by dramatic falls in mortality. But research at Campop has shown that, at least in England, fertility has actually played a larger role than mortality in regulating population growth. 

The Demographic Transition Model 

The ‘Demographic Transition Model’ describes societal transitions from high birth and death rates to low birth and death rates. In the orthodox model, pre-transitional populations are kept in check by high death rates that roughly balanced high birth rates. The model goes on to say that transitions are triggered by falls in mortality, but because fertility initially stays high, births exceed deaths, and populations grow rapidly. As modernization proceeds and population pressures grow, couples finally begin to reduce their family sizes, and eventually birth and death rates come into balance again.  

For a long time, those considering the period before the Demographic Transition also assumed that fluctuations in mortality were the main drivers of population change, with population pressure leading to Malthusian increases in death rates, which reduced population to more manageable levels.  

But how good are these models at explaining actual population growth in England, and what about the role played by migration?  

English population growth over the long run 

As a result of work at Campop, England is the only national population for which we have good estimates of population size over the long run (spanning nearly half a millennium). For England, we not only have a clear view of the whole demographic transition, but also of population dynamics before the transition.  

As figure 1 shows, the population of England grew slowly until the 1750s, much as Malthus would have expected. However, after 1750 the population grew in an historically unprecedented fashion, increasing rapidly for two centuries without reversals (except as a result of mass conscription during the world wars). Growth rates exceeded 1 percent per annum across the 19th century, and the population increased from under 6 million in the 1750s to 30 million by 1900 and nearly 60 million in 2023. 

Fertility didn’t fall decisively in England until the 1870s (the period marked ‘Demographic transition’ on the graph above), and so the classic demographic transition model would seem to apply particularly clearly to the English case, where the population experienced over a century of relatively rapid growth before fertility fell.  

This implies that population growth between 1750 and 1870s was the product of reduced mortality, but was this true? 

Fertility, mortality, and population growth 

Populations grow when there are more new people entering the population through birth and in-migration than leaving it through death and out-migration. The population growth rate is determined by the difference between the rates of population increase (births and in-migrants per 1,000 people) and decrease (deaths and out-migrants per 1,000 people).  

Figure 2 shows these birth and death rates for England over the long term. Because migration is difficult to measure, the figure does not show in- and out-migration rates separately, just the difference between them: ‘net migration’. When there were more in-migrants than out-migrants, there is net in-migration, and this is shown with birth rates as part of inflows. When there were more out-migrants than in-migrants, this is shown with death rates as part of outflows.  

The yellowish areas of the graph indicate times when rates of inflow were greater than rates of outflow, and therefore population was growing. The larger the distance between the inflow and outflow lines, the faster the population was growing.  

Population growth before 1750 

The birth rates shown in Figure 2 depend on a combination of the number of children each woman had, the proportions of women who ever married, and the ages at which they wed. Before about 1750, average age at marriage was high for both men and women (27–28 for men and 25–26 for women), and a high and variable proportion of women (a tenth to a quarter) never married. The proportion marrying had a very strong effect on the average number of children that women had – the number they bore within marriage remained fairly constant and high (around 7 children per married woman), but because many women never married, the average for all women varied between less than 4 to nearly 6.

The proportions marrying depended on economic conditions (the Malthusian ‘preventive check’), and possibly also on the availability of work for women (as an alternative to marriage). This means that the birth rates shown in Figure 2 predominantly reflect marriage patterns, and therefore economic conditions. 

Mortality crises occasionally caused short periods of population loss (e.g. 1556-60 and 1726-30), and in the period 1650 to 1740 death rates were high enough to suppress and sometimes to reverse population growth. But mortality bore a complex relationship to economic conditions. England was free of famines after the 1620s, and food prices played only a very minor role in mortality patterns.  

However, while economic growth and food security reduced mortality crises associated with harvest failures, the overall relationship between economic growth and mortality was positive – urbanisation and trade seem to have driven the death rate up, because they favoured the circulation of infectious diseases. Occasional epidemics of plague, typhus and other diseases caused soaring mortality. But it was the increasing circulation of smallpox and other ‘crowd’ diseases that contributed to the protracted period of high mortality and population decline in the second half of the 17th century, even after the disappearance of plague in the 1670s.  

Critically, high death rates should not be viewed as a Malthusian mechanism that operated to keep the population in balance with resources in this period. The economy was growing, and the population was urbanizing, indicating a society that was not under high Malthusian pressure. Instead, a combination of high infectious disease rates (associated with urbanisation and economic development) and late marriage checked population growth, while also allowing per capita incomes to grow.   

Population growth 1750-1870 

After 1750, fertility rose as a result of marked changes in marriage patterns. Between 1750 and 1870, roughly 90 percent of English women married, and age at marriage was lower during this period than in the previous two centuries. This produced the high birth rates seen in Figure 2. This upsurge in nuptiality (marriage) probably reflected the growing economy, as well as the disappearance of some work for single women.      

What about mortality? Death rates fell after 1750, especially in cities, and especially for infants and young adults. These falls contributed to population growth in two ways – deaths were reduced, and improvements in maternal health and survival contributed to higher fertility within marriage. Although most of the rise in birth rates was driven by falling age at marriage and higher proportions of women marrying, fertility within marriage also contributed.  

So both mortality and fertility trends pulled in the same direction to cause growth of the English population between 1750 and the 1870s. In his final reworking, Tony Wrigley estimated that rising fertility accounted for roughly 64 percent of population growth in this period, and falling mortality for 36 percent. Migration played a negligible role (see below). 

This rapid population growth was largely balanced by economic growth. Real wages did not grow during the classic Industrial Revolution period, and GDP/capita only really pulled ahead of population growth after the 1830s.   

The Demographic Transition 

After 1870, both mortality and fertility fell rapidly. These falls represented a decisive break with previous trends. Before the 1870s, swings in the birth rate depended mainly on changes in age at marriage or in the proportions marrying – marital fertility was fairly stable. After 1870, the main driver of fertility was the reduction of births within marriage – married couples began to control their fertility (initially using traditional techniques such as withdrawal and abstinence), and overall birth rates dropped dramatically.  

Classic demographic transition theory suggests that couples reduced their fertility because it was no longer economically rational to have large families. While this is supported by restrictions on child labour and the introduction of compulsory education, which reduced the earning potential of children and increased the costs of raising them, it has also been suggested that large families have never been economically rational, particularly in the British context where children left home early and did not routinely take in their elderly parents.  

An alternative theory suggests that fertility fell because of cultural changes in the acceptability of birth control within marriage, allowing couples to achieve smaller families. These theories are still debated, but both may have elements of truth. 

In the case of mortality, a combination of public health improvements in towns, improved nutrition and housing, and medical advances progressively reduced exposure and improved population resistance to common infectious diseases. By the 1930s the ‘urban penalty’ had disappeared, and life expectancy in towns was as high as in rural areas.   

These simultaneous falls in fertility and mortality contradict the classic Demographic Transition model (where population growth is driven by falling mortality in the presence of high and stable fertility). Since fertility fell even faster than mortality, population growth finally began to slow after World War I. The population had grown nearly seven–fold between 1750 and the 1930s. Life expectancy had risen from around 40 years to 60 years, and fertility had fallen from 4-6 children per woman to around replacement level (just over 2 children per woman).  

The baby boom and its aftermaths

Mortality rates within each age group continued to fall across the 20th century, but population ageing meant that increasing proportions of the population were in the older, higher mortality, age groups. This meant that the overall number of deaths as a proportion of the population, as shown in Figure 2, stayed fairly constant between 1930 and 1980.

Births, on the other hand, fluctuated wildly. A big upswing in the number of births started during the Second World War and continued after it, peaking in 1947, followed by another peak in the early 1960s. The first of these was fuelled by a catch-up in marriages which had been postponed by the Depression and by those who married on the eve of war, and it was added to by post-war births. The second peak was linked to a reduction in the age of marriage, an increase in the proportion of women ever marrying, and a small increase in the numbers of children each woman had.  

Birth rates in the late 20th and early 21st centuries are highly influenced by changes in the timing of births in successive generations. Very low birth rates in the 1970s were due to the facts that those who married young in the 1960s had already their children, while younger women were starting to delay both partnership formation and childbearing. A continued trend towards delaying births has been linked to increases in higher education and women’s desire to establish a career before starting a family. Economic insecurity and the difficulty of combining a work and childbearing may create further postponement, while for some women not having children is a positive choice.  

There are some groups in the population, however, that have higher average fertility rates than others, and among these are women born outside the UK. In 2021, the Total Fertility Rate for women born outside the UK was just over 2, compared to just over 1.5 for UK-born women. In the last few decades, net in-migration has also started to make a significant contribution to population growth.  

What about migration?

For the long sweep of British history, net migration had very little impact on population growth, but this does not imply that migration levels were low in the past. It is estimated that during the 19th century around 10 million British people emigrated, but this was offset by a considerable number of immigrants. During the 1850s and 1860s the arrival of many Irish people fleeing the potato famine almost completely balanced the numbers of emigrants. In the 1880s – the decade of peak emigration – there were around six emigrants and three immigrants per 1000 people, so the net emigration rate was also around three per 1000.  

For most of the last half millennium, England has been a net exporter of people, mostly to the colonies of north America in the 17th and 18th centuries, and to Australia and New Zealand in the 19th and early 20th centuries. Immigration has only made a sustained positive contribution to population growth since the 1920s. In the last five years immigration has become almost the sole source of population growth, and its contribution is in fact larger than net fluxes of people would suggest, because women born outside the UK now contribute nearly a third of all births. 

Where does this leave the Demographic Transition Model? 

The statistician George Box said: ‘all models are wrong, but some are useful’. All models are wrong because they are simplified, but it is this simplification which makes them useful. In this case, is there anything useful left of the Demographic Transition model?  

It is clear that the classic description of economic growth to mortality decline to population pressure to fertility decline does not work for the English case. Instead, England appears to have followed a trajectory in common with a number of low-income countries in the 20th century, where very rapid population growth was fuelled by rises in fertility as well as mortality improvements. These patterns hint at the dynamism of fertility responses, and the importance of understanding the interplay between social and economic changes on the one hand, and norms and decision-making with respect to family formation on the other.

It would therefore be unwise to suggest that there is a universal trajectory between economic growth, mortality and fertility changes. Most demographers agree that the Demographic Transition remains useful as a description of changes in mortality and fertility rates, but not as an explanatory model.   

Further reading

• Alter, G., ‘Theories of fertility decline: A non-specialist’s guide to the current debate on European fertility decline’, in D. Levine, J. R. Gillis, and Tilly (eds.), The European experience of declining fertility, 1850-1970: The quiet revolution (Blackwell Cambridge MA, 1992), pp. 13–27. 
• Jaadla, H., Reid, A., Garrett, E., Schürer, K. and Day, J., ‘Revisiting the Fertility Transition in England and Wales: The Role of Social Class and Migration.’ Demography 57:4 (2020), 1543-1569.  
• Kirk, D., ‘Demographic Transition Theory.’ Population Studies 50:3 (1996), 361–387.  
• Wrigley, E. A., ‘British Population during the ‘Long’ Eighteenth Century, 1680–1840’, in R. Floud and P. Johnson (eds.), The Cambridge Economic History of Modern Britain, (Cambridge: Cambridge University Press, 2004), pp. 57–95. 

Tags: age at marriage, demographic transition, demography, fertility, historical demography, migration, mortality, population growth

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