Sub-replacement fertility

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Sub-replacement fertility is a total fertility rate (TFR) that (if sustained) leads to each new generation being less populous than the older, previous one in a given area. In developed countries sub-replacement fertility is any rate below approximately 2.1 children born per woman, but the threshold can be as high as 3.4 in some developing countries because of higher mortality rates.[1] Taken globally, the total fertility rate at replacement was 2.33 children per woman in 2003.[1] This can be "translated" as 2 children per woman to replace the parents, plus a "third of a child" to make up for the higher probability of boys being born and early mortality prior to the end of their fertile life.[2]

Replacement level fertility in terms of the net reproduction rate (NRR) is exactly one, because the NRR takes both mortality rates and sex ratios at birth into account.

Map of countries by fertility rate (2015)
  7–8 Children
  6–7 Children
  5–6 Children
  4–5 Children
  3–4 Children
  2–3 Children
  1–2 Children

As of 2010, about 48% (3.3 billion people) of the world population lives in nations with sub-replacement fertility.[3] Nonetheless most of these countries still have growing populations due to immigration, population momentum and increase of the life expectancy. This includes most nations of Europe, Canada, Australia, Brazil, Russia, Iran, Tunisia, China, the United States and many others. The countries or areas that have the lowest fertility are Hong Kong, Macau, Singapore, Taiwan, Ukraine and Lithuania. Only a few countries have had, for the time being, sufficiently sustained sub-replacement fertility (sometimes combined with other population factors like higher emigration than immigration) to have population decline, such as Japan, Germany, Lithuania, and Ukraine.


Further information: Fertility factor (demography)

There have been a number of explanations for the general decline in fertility rates in much of the world, and the true explanation is almost certainly a combination of different factors.

Higher education[edit]

The fact that more people are going to colleges and universities, and are working to obtain more post-graduate degrees there, along with the soaring costs of education, have contributed greatly to postponing marriage in many cases, and bearing children at all, or fewer numbers of children. And the fact that the number of women getting higher education has increased has contributed to fewer of them getting married younger, if at all. In the US, for example, females make up more than half of all college students, which is a reversal from a few decades back.[6]

Economic development[edit]

Further information: Income and fertility

The growth of wealth and human development are related to sub-replacement fertility. High costs of living and job insecurity can make it difficult for young people to marry and start families.


The increase of urbanization around the world is considered by some a central cause. In recent times, residents of urban areas tend to have fewer children than people in rural areas.[7][8] The need for extra labour from children on farms does not apply to urban-dwellers. Cities tend to have higher property prices, making a large family more expensive, especially in those societies where each child is now expected to have their own bedroom, rather than sharing with siblings as was the case until recently. Rural areas also tend to be more conservative with less contraception and abortion than urban areas.


Changes in contraception are also an important cause, and one that has seen dramatic changes in the last few generations. Legalization, and widespread acceptance, of contraception in the developed world is a large factor in decreased fertility levels. However, for instance in a European context where its prevalence has always been very high in the modern era, the fertility rates do not seem to be influenced significantly by availability of contraception.[9]

Assisted reproductive technology[edit]

The availability of assisted reproductive technology (ART) may foster delay of childbearing because many couples are inclined to think that it will solve any fertility problems they might encounter in the future.[9] Its effect on total fertility rate is extremely small but government support for it is beneficial for families.[9]

Government policies[edit]

Some governments have launched programmes to reduce fertility rates and curb population growth. Notably, China implemented a one-child policy for 35 years.


It has been shown, both historically and in the present day, that societies engaged in a prolonged state of war experience a substantial lag in fertility rate. The most notable examples of this phenomenon are widely accredited to the First and Second World Wars. Modeled by these examples, "total war" subjects individuals to intense social upheavals and a heavy psychological impact that forcefully prioritizes survival and economic stability over the need to reproduce for the duration of the conflict. Events like these subsequently pave way for an active effort to repopulate, such as the "baby boom" after the Second World War.[10]

Tempo effect[edit]

The conventionally reported measure of TFR, the period TFR (based on the level of fertility or number of births in a given year), is affected by a statistical effect called the tempo effect which makes it a misleading measure of overall (life cycle) fertility.

Specifically, if the age of childbearing increases – assuming that the total number of births over a life cycle remains unchanged – the measured TFR is lower (the births happen in a later year), but when the age of childbearing stops increasing the TFR increase, due to these births catching up. For illustration, if women in the past always had 1 child at the age of 20 (TFR of 1), and all women born in 1980 or later postponed having children until age 30 in the year 2000, there would be no births for 10 years (TFR of 0). After 10 years (assuming flat population structure, no deaths, etc.), in 2010, it would suddenly jump back up (TFR of 1), even though the life cycle TFR was always 1.

Thus, period TFR reflects not only life cycle TFR, but also timing effects, and these effects are conflated in a simple period TFR number. Life cycle TFR is unambiguous, and strict measure of life cycle fertility are not affected by this effect (e.g., counting the average children that have been born to all women who cease child-bearing in a given year via menopause, sterilization, death, etc.), but are lagging statistics because they require women to cease child-bearing before they are counted. Thus, adjusted measures of TFR – period TFR, adjusted for timing – are proposed instead to give a more accurate measure of life cycle fertility, without needing to wait until women have definitively ceased bearing children.

Thus, if age of childbearing is increasing and life cycle fertility is decreasing, period TFR will initially overstate the decline, and then may have a spurious increase even if life cycle fertility is actually still declining. For instance, this is computed to be the case in Spain in the period 1980–2002.[11]

John Bongaarts and Griffith Feeney have suggested that this tempo effect is driving the decline of measured fertility rate in the developed world.[12] Taking tempo changes into account, adjusted birth rates for a number of European countries are higher than the conventional TFR.[13] A particularly strong example is the Czech Republic in the period 1992–2002, which witnessed a steady rise in childbearing age. Hence, the period TFR dropped sharply, overstating the decline in life cycle fertility.[11]

Partnership instability[edit]

Also, a number of sociologists and demographers have pointed out that among those who co-habit, without marrying, are now usually likely to have fewer children than those who are married, due to the lack of commitment in the male/female relationship. This uncertainty induces a 'wait and see' approach in many cases, especially on the part of the female.[14] A study came to the result that individual decisions arising from the instability of modern partnerships are a major cause of European sub-replacement fertility.[9]

Frequency of sex[edit]

Another explanation for falling fertility could be a reduction in the frequency of sex. For example, according to a survey published by the Japanese Family Planning Association in March 2007, a record 39.7 per cent of Japanese citizens aged 16–49 had not had sex for more than a month.[15]

Historical effects[edit]

The Greek historian Polybius largely blamed the decline of the Hellenistic world on low fertility rates,[16] writing his work The Histories that:

In a speech to Roman nobles, the Emperor Augustus commented on the low birthrates of the Roman elite:[18]

Upon the establishment of the Roman Empire, Emperor Augustus would introduce legislation to increase the birthrates of the Roman nobility.[20]

Some believe that not only the Great Recession, but the Great Depression, may have been the result of a decline in birthrates overall. Clarence L. Barber, an economist at the University of Manitoba, pointed out how demand for housing in the US, for example, began to decline in 1926, due to a decline in 'household formation' (marriage), due, he believed, to the effects of World War I upon society. In early 1929, US housing demand declined precipitously. And, of course, the stock market crash followed in October of that same year.[21]

Even though the overall world population continues to increase, it is more at the 'back end' than the 'front end' that this is occurring. That is, more people are kept alive than in the past due to improved nutrition, more refrigeration and better sanitation worldwide, as well as health care advances, from vaccines to antibiotics, and many other advances in medications and in different improvements in health care. Certainly, in advanced nations, few groups would be considered to be "breeding like rabbits". The 'baby boom' (1946–1964) in the US, was likely, if Barber's contentions are correct, more of a return to birthrates closer to historical norms, like those of the first decade of the 20th century (but the 'baby boom' of 1946–1964 were still lower than the 1900–1910 period), with birth dearths both before and since making the so-called "baby boom" appear so big.

Current effects[edit]

Population aging may pose an economic challenge to governments as the number of retired citizens drawing public pensions rises in relation to the number of workers. This has been raised as a political issue in France, Germany, and the United States where many people have advocated policy changes to encourage higher birth and immigration rates.

Analysing data for 40 countries, Lee et al. show that fertility well above replacement and population growth would typically be most beneficial for government budgets. However, fertility near replacement and population stability would be most beneficial for standards of living when the analysis includes the effects of age structure on families as well as governments. And fertility moderately below replacement and population decline would maximize standards of living when the cost of providing capital for a growing labour force is taken into account.[22]


United Nation's population projections by location.
Note the vertical axis is logarithmic and represents millions of people.

Sub-replacement fertility does not immediately translate into a population decline because of population momentum: recently high fertility rates produce a disproportionately young population, and younger populations have higher birth rates. This is why some nations with sub-replacement fertility still have a growing population, because a relatively large fraction of their population are still of child-bearing age. But if the fertility trend is sustained (and not compensated by immigration), it results in population ageing and population decline. This is already happening and impacts first most of the countries of Europe and East Asia.

Current estimates expect the world's total fertility rate to fall below replacement levels by 2050,[23] although population momentum will continue to increase global population for several generations beyond that. The development of the world population is linked with concerns of overpopulation, sustainability and exceeding Earth's carrying capacity.

Some governments, fearful of a future pensions crisis, have developed natalist policies to attempt to encourage more women to have children. Measures include increasing tax allowances for working parents, improving child-care provision, reducing working hours/weekend working in female-dominated professions such as healthcare and a stricter enforcement of anti-discrimination measures to prevent professional women's promotion prospects being hindered when they take time off work to care for children. Over recent years, the fertility rate has increased to around 2.0 in France and 1.9 in Britain and some other northern European countries, but the role of population policies in these trends is debated.[24]

European analysts hope, with the help of government incentives and large-scale change towards family-friendly policies, to stall the population decline and reverse it by around 2030, expecting that most of Europe will have a slight natural increase by then. C. D. Howe Institute, for example, tries to demonstrate that immigration can not be used to effectively counter population ageing.[25]

Cases of fertility rate increases in individual countries[edit]

United States[edit]

While much of the world has experienced declining fertility rates over the last twenty years, the total fertility rate in the United States has remained relatively stable in comparison.[26] This is largely due to the high fertility rate among communities such as Hispanics, but it is also because the fertility rate among non-Hispanic whites in the US, after falling to about 1.6 in the 1970s and early 1980s, had increased and is now around 1.89 rather than lower to the 1.6 level common in Europe. It can also be explained by a substantial immigration.

New England has a rate similar to most Western European countries, while the South, Midwest, and border states have fertility rates considerably higher than replacement. States where The Church of Jesus Christ of Latter-day Saints has a strong presence, most notably Utah, also have higher-than-replacement fertility rates, especially among the LDS population. Heaton and Goodman (1985) found that LDS women average about one child more than women in other religious groups.[27]

Other developed countries[edit]

Some other developed countries are experiencing an increase in their birth rate, including France, which recorded a TFR of over 2.00 in 2008;[28] the United Kingdom where TFR increased from 1.64 in 2000 to 1.98 in 2010;[29][30] Australia, where the birth rate rose from 1.73 in 2001[31] to 1.93 in 2007[32] and New Zealand, where the TFR was 2.2 in 2008.[33]

Israel is the only developed country that has never had sub-replacement fertility; a declining Arab and Bedouin fertility rate is countered by religious Jewish groups (mostly Haredim) with higher than average fertility rates. In addition, the (mostly non-religious)[citation needed] aliyah Jews from the former USSR shifted from a 1 child per woman fertility rate to an average fertility rate close to 2.2 children per woman. As of 2008, Israel's Jewish fertility rate is the highest among the industrial nations.[34]

See also[edit]

Economic dynamics


  1. ^ a b Espenshade TJ, Guzman JC, Westoff CF (2003). "The surprising global variation in replacement fertility". Population Research and Policy Review 22 (5/6): 575. doi:10.1023/B:POPU.0000020882.29684.8e. , Introduction and Table 1, p. 580
  2. ^ For example in the United Kingdom in 2001 304,635 boys were born as opposed to 289,999 girls, and some of these girls will not survive to the end of their child bearing years. In future, therefore, the girls born in this year would have to have more than two children each to replace the total population. For a full explanation see 'Replacement Fertility, What has it been and What does it mean?' (PDF)
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  27. ^ Goodman, Kristen L.; Heaton, Tim B. (1985). "Religion and Family Formation". Review of Religious Research 26 (4): 343–359. JSTOR 3511049. 
  28. ^ Tabc3 Tableau complémentaire 3 : Taux de fécondité par groupe d'âges.
  29. ^ Doughty, Steve (17 September 2012) British birth rate has soared to one of highest in Europe thanks to increase in migrants. Daily Mail
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  32. ^ "3301.0 – Births, Australia, 2007, Australian Bureau of Statistics". Australian Bureau of Statistics. 
  33. ^ Collins, Simon (19 February 2009). "Baby boom goes against mothers' advice". The New Zealand Herald. Retrieved 14 November 2011. 
  34. ^ "Demographic Optimism, Not Pessimism -Yoram Ettinger". January 2013. 

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