Editing Demographic transition (section)

==Stages==

=== Stage one ===
In pre-industrial society, death rates and birth rates were both high, fluctuating rapidly according to natural events, such as drought and disease, to produce a relatively constant and young population.<ref name=":2" /> [[Family planning]] and contraception were virtually nonexistent; therefore, birth rates were essentially only limited by the ability of women to bear children. Emigration depressed death rates in some special cases (for example, Europe and particularly the Eastern United States during the 19th century), but, overall, death rates tended to match birth rates, often exceeding 40 per 1000 per year. Children contributed to the economy of the household from an early age by carrying water, firewood, and messages, caring for younger siblings, sweeping, washing dishes, preparing food, and working in the fields.<ref>{{cite web|url=http://geographyfieldwork.com/DemographicTransition.htm|title=Demographic Transition Model| website=geographyfieldwork.com}}</ref> Raising a child cost little more than feeding him or her; there were no education or entertainment expenses. Thus, the total [[Cost of raising a child|cost of raising children]] barely exceeded their contribution to the household. In addition, as they became adults they became a major input to the family business, mainly farming, and were the primary form of insurance for adults in old age. In India, an adult son was all that prevented a widow from falling into destitution. While death rates remained high there was no question as to the need for children, even if the means to prevent them had existed.<ref name=Caldwell5>Caldwell (2006), Chapter 5</ref>

During this stage, the society evolves in accordance with [[Malthusian growth model|Malthusian]] paradigm, with population essentially determined by the food supply. Any fluctuations in food supply (either positive, for example, due to technology improvements, or negative, due to droughts and pest invasions) tend to translate directly into population fluctuations. [[Famine]]s resulting in significant mortality are frequent. Overall, [[population dynamics]] during stage one are comparable to those of animals living in the wild. This is the earlier stage of demographic transition in the world and also characterized by primary activities such as small fishing activities, farming practices, pastoralism, and petty businesses.

===Stage two===
[[File:Population curve.svg|thumb|upright=1.7|right|World population 10,000 BC-2017 AD]]
This stage leads to a fall in death rates and an increase in population.<ref>{{Cite web|url=http://www.bbc.co.uk/schools/gcsebitesize/geography/population/popchangestructurerev5.shtml|archiveurl=https://web.archive.org/web/20071023172810/http://www.bbc.co.uk/schools/gcsebitesize/geography/population/popchangestructurerev5.shtml|url-status=dead|title=BBC bitesize|archivedate=October 23, 2007}}</ref> The changes leading to this stage in Europe were initiated in the [[British Agricultural Revolution|Agricultural Revolution]] of the eighteenth century and were initially quite slow. In the twentieth century, the falls in death rates in developing countries tended to be substantially faster. Countries in this stage include [[Yemen]], [[Afghanistan]], and [[Iraq]] and much of [[Sub-Saharan Africa]] (but this does not include [[South Africa]], [[Botswana]], [[Eswatini]], [[Lesotho]], [[Namibia]], [[Gabon]] and [[Ghana]], which have begun to move into stage 3).<ref name=Caldwell10>Caldwell (2006), Chapter 10</ref>{{update inline|date=January 2020}}

The decline in the death rate is due initially to two factors:
* First, improvements in the food supply brought about by higher yields in agricultural practices and better transportation reduce death due to starvation and lack of water. Agricultural improvements included [[crop rotation]], [[selective breeding]], and [[seed drill]] technology.
* Second, significant improvements in public health reduce mortality, particularly in childhood. These are not so much medical breakthroughs (Europe passed through stage two before the advances of the mid-twentieth century, although there was significant medical progress in the nineteenth century, such as the development of [[vaccination]]) as they are improvements in water supply, [[sanitary sewer|sewerage]], food handling, and general personal [[hygiene]] following from growing scientific knowledge of the causes of disease and the improved education and social status of mothers.

A consequence of the decline in mortality in Stage Two is an increasingly rapid growth in population growth (a.k.a. "[[population explosion]]") as the gap between deaths and births grows wider and wider. Note that this growth is not due to an increase in fertility (or birth rates) but to a decline in deaths. This change in population occurred in north-western Europe during the nineteenth century due to the [[Industrial Revolution]]. During the second half of the twentieth century less-developed countries entered Stage Two, creating the worldwide rapid growth of number of living people that has demographers concerned today. In this stage of DT, countries are vulnerable to become [[Failed States Index|failed states]] in the absence of progressive governments.

[[File:Angola population pyramid 2005.svg|right|upright=1.7|thumb| [[Population pyramid]] of [[Angola]] 2005]]
Another characteristic of Stage Two of the demographic transition is a change in the [[population pyramid|age structure]] of the population. In Stage One, the majority of deaths are concentrated in the first 5–10 years of life. Therefore, the decline in death rates in Stage Two entails the increasing survival of children and a growing population. Hence, the age structure of the population becomes increasingly youthful and start to have big families and more of these children enter the reproductive cycle of their lives while maintaining the high fertility rates of their parents. The bottom of the "[[population pyramid|age pyramid]]" widens first where children, teenagers and infants are here, accelerating population growth rate. The age structure of such a population is illustrated by using an example from the [[Third World]] today.

===Stage three===
[[File:Uzbekistan population pyramid.svg|thumb|Population pyramid of [[Demographics of Uzbekistan|Uzbekistan]] in 2023 (Stage three).]]
[[File:Israel_2023_Population_Pyramid.svg|thumb|Population pyramid of [[Demographics of Israel|Israel]] in 2023 (Stage three).]]

In Stage 3 of the Demographic Transition Model (DTM), death rates are low and birth rates diminish, as a rule accordingly of enhanced economic conditions, an expansion in women's status and education, and access to contraception. The decrease in birth rate fluctuates from nation to nation, as does the time span in which it is experienced.<ref>{{cite web|url=https://www.populationeducation.org/content/stage-3-demographic-transition-model|title=Stage 3 of the Demographic Transition Model - Population Education|date=16 October 2014}}</ref> Stage Three moves the population towards stability through a decline in the birth rate.<ref>{{Citation | publisher = UWC | url = http://pages.uwc.edu/keith.montgomery/Demotrans/demtran.htm | series = Marathon | title = Geography | contribution = Demographic transition | access-date = 2014-04-25 | archive-date = 2019-06-05 | archive-url = https://web.archive.org/web/20190605095831/http://pages.uwc.edu/keith.montgomery/demotrans/demtran.htm | url-status = dead }}.</ref> Several [[fertility factor (demography)|fertility factor]]s contribute to this eventual decline, and are generally similar to [[Sub-replacement fertility#Causes|those associated with sub-replacement fertility]], although some are speculative:
* In rural areas continued decline in childhood death meant that at some point parents realized that they did not need as many children to ensure a comfortable old age. As childhood death continues to fall and incomes increase, parents can become increasingly confident that fewer children will suffice to help in family business and care for them at old age.
* Increasing [[urbanization]] changes the traditional values placed upon fertility and the value of children in rural society. Urban living also raises the cost of dependent children to a family. A recent theory suggests that urbanization also contributes to reducing the birth rate because it disrupts optimal mating patterns. A 2008 study in Iceland found that the most fecund marriages are between distant cousins. Genetic incompatibilities inherent in more distant out breeding makes reproduction harder.<ref>{{Citation | title= Third Cousins Have Greatest Number Of Offspring, Data From Iceland Shows | url= https://www.sciencedaily.com/releases/2008/02/080207140855.htm | archive-url= https://web.archive.org/web/20210102112300/https://www.sciencedaily.com/releases/2008/02/080207140855.htm | url-status= dead | archive-date= 2 January 2021 | journal= ScienceDaily | date = 8 February 2008}}.</ref>
* In both rural and urban areas, the cost of children to parents is exacerbated by the introduction of compulsory education acts and the increased need to educate children so they can take up a respected position in society. Children are increasingly prohibited under law from working outside the household and make an increasingly limited contribution to the household, as school children are increasingly exempted from the expectation of making a significant contribution to domestic work. Even in equatorial Africa, children (under the age of 5) are now required to have clothes and shoes, and may even need school uniforms. Parents begin to consider it a duty to buy children's books and toys. Partly due to education and access to family planning, people begin to reassess their need for children and their ability to raise them.<ref name=Caldwell5/>
[[File:Familyplanningmalaysia.jpg|thumb|right|upright=1.15|A major factor in reducing birth rates in stage&nbsp;3 countries such as Malaysia is the availability of family planning facilities, like this one in Kuala Terengganu, Terengganu, Malaysia.]]
* Increasing literacy and employment lowers the uncritical acceptance of childbearing and motherhood as measures of the status of women. Working women have less time to raise children; this is particularly an issue where fathers traditionally make little or no contribution to child-raising, such as [[southern Europe]] or [[Japan]]. Valuation of women beyond childbearing and motherhood becomes important.
* Improvements in contraceptive technology are now a major factor in fertility decline. Changes in values regarding children and gender play as significant a role as the availability of contraceptives and knowledge of how to use them.

The resulting changes in the age structure of the population include a decline in the youth [[dependency ratio]] and eventually [[population aging]]. The population structure becomes less triangular and more like an elongated balloon. During the period between the decline in youth dependency and rise in old age dependency there is a [[demographic window]] of opportunity that can potentially produce economic growth through an increase in the ratio of working age to dependent population; the [[demographic dividend]].

However, unless factors such as those listed above are allowed to work, a society's birth rates may not drop to a low level in due time, which means that the society cannot proceed to stage three and is locked in what is called a [[demographic trap]].

Countries that have witnessed a fertility decline of over 50% from their pre-transition levels include: [[Costa Rica]], [[El Salvador]], [[Panama]], [[Jamaica]], [[Mexico]], [[Colombia]], [[Ecuador]], [[Guyana]], [[Philippines]], [[Indonesia]], [[Malaysia]], [[Sri Lanka]], [[Turkey]], [[Azerbaijan]], [[Turkmenistan]], [[Uzbekistan]], [[Tunisia]], [[Algeria]], [[Morocco]], [[Lebanon]], [[South Africa]], [[India]], [[Saudi Arabia]], and many [[Pacific islands]].

Countries that have experienced a fertility decline of 25–50% include: [[Demographics of Guatemala|Guatemala]], [[Demographics of Tajikistan|Tajikistan]], [[Demographics of Egypt|Egypt]] and [[Demographics of Zimbabwe|Zimbabwe]].

Countries that have experienced a fertility decline of less than 25% include: [[Demographics of Sudan|Sudan]], [[Demographics of Niger|Niger]], [[Demographics of Afghanistan|Afghanistan]].

===Stage four===
[[File:Argentina_2022_population_pyramid.svg|thumb|Population pyramid of [[Demographics of Argentina|Argentina]] in 2022 (Stage four).]]

This occurs where birth and death rates are both low, leading to total population stability. Death rates are low for a number of reasons, primarily due to lower rates of diseases and increased food production. The birth rate is low because people have more opportunities to choose if they want children. This is made possible by improvements in contraception or women gaining more independence and work opportunities.<ref>{{Citation | url = http://www.main-vision.com/richard/demographic.htm | title = Main vision |contribution = Demographic}}.</ref> The DTM (Demographic Transition model) is only a suggestion about the future population levels of a country, not a prediction.

Countries that were at this stage ([[total fertility rate]] between 2.0 and 2.5) in 2015 include: Antigua and Barbuda, Argentina, Bahrain, Bangladesh, Bhutan, Cabo Verde, El Salvador, Faroe Islands, Grenada, Guam, India, Indonesia, Kosovo, Libya, Malaysia, Maldives, Mexico, Myanmar, Nepal, New Caledonia, Nicaragua, Palau, Peru, Seychelles, Sri Lanka, Suriname, Tunisia, Turkey, and Venezuela.<ref>{{cite web|url=https://data.worldbank.org/indicator/SP.DYN.TFRT.IN|title=Fertility rate, total (births per woman) - Data|website=data.worldbank.org}}</ref>

===Stage five===
{{See also|Population aging|Aging of Europe|Aging of Japan|Evolutionary psychology}}
[[File:Portugal population pyramid.svg|thumb|Population pyramid of [[Demographics of Portugal|Portugal]] in 2023 (Stage five).]]
[[File:Belarus_2023_population_pyramid.svg|thumb|Population pyramid of [[Demographics of Belarus|Belarus]] in 2023 (Stage five).]]

[[File:World population (UN).svg|thumb|right|upright=1.35|United Nation's population projections by location.<br />
Note the vertical axis is [[Logarithmic scale|logarithmic]] and represents millions of people.]]
The original Demographic Transition model has just four stages, but additional stages have been proposed. Both more-fertile and less-fertile futures have been claimed as a Stage Five.

Some countries have [[sub-replacement fertility]] (that is, below 2.1–2.2 children per woman). Replacement fertility is generally slightly higher than 2 (the level which replaces the two parents, achieving equilibrium) both because boys are born more often than girls (about 1.05–1.1 to 1), and to compensate for deaths prior to full reproduction. Many European and East Asian countries now have higher death rates than birth rates. [[Population aging]] and [[population decline]] may eventually occur, assuming that the fertility rate does not change and sustained mass immigration does not occur.

Using data through 2005, researchers have suggested that the negative relationship between development, as measured by the [[Human Development Index]] (HDI), and birth rates had reversed at very high levels of development. In many countries with very high levels of development, fertility rates were approaching two children per woman in the early 2000s.<ref name="Nature" /><ref>{{Citation | title= The best of all possible worlds? | url = https://www.economist.com/science-and-technology/2009/08/06/the-best-of-all-possible-worlds | newspaper = The Economist | date = 6 August 2009}}.</ref> However, fertility rates declined significantly in many very high development countries between 2010 and 2018, including in countries with high levels of [[gender parity]]. The global data no longer support the suggestion that fertility rates tend to broadly rise at very high levels of national development.<ref name=":1">{{Cite journal|last=Gaddy|first=Hampton Gray|date=2021-01-20|title=A decade of TFR declines suggests no relationship between development and sub-replacement fertility rebounds|url=https://www.demographic-research.org/volumes/vol44/5/|journal=Demographic Research|language=en|volume=44|pages=125–142|doi=10.4054/DemRes.2021.44.5|issn=1435-9871|doi-access=free}}</ref>

From the point of view of [[evolutionary biology]], wealthier people having fewer children is unexpected, as [[natural selection]] would be expected to favor individuals who are willing and able to convert plentiful resources into plentiful fertile descendants. This may be the result of a departure from the [[Evolutionary psychology#Environment of evolutionary adaptedness|environment of evolutionary adaptedness]].<ref name=bbc_sure /><ref>{{cite journal | last1 = Clarke | first1 = Alice L. | last2 = Low | first2 = Bobbi S. | year = 2001 | title = Testing evolutionary hypotheses with demographic data |journal = Population and Development Review | volume = 27 | issue = 4| pages = 633–660 | doi=10.1111/j.1728-4457.2001.00633.x| url = https://deepblue.lib.umich.edu/bitstream/2027.42/74296/1/j.1728-4457.2001.00633.x.pdf | hdl = 2027.42/74296| hdl-access = free }}</ref><ref>{{cite journal |last1=Daly |first1= Martin |last2=Wilson |first2=Margo I |title=Human evolutionary psychology and animal behaviour |journal= Animal Behaviour |url= http://courses.washington.edu/evpsych/Daly%26Wilson-HEP-AB1999.pdf |publisher= Department of Psychology, McMaster University |access-date=14 November 2018 |date=26 June 1998|volume= 57 |issue= 3 |pages= 509–519 |doi= 10.1006/anbe.1998.1027 |pmid= 10196040 |s2cid= 4007382 }}</ref>

Most models posit that the birth rate will stabilize at a low level indefinitely. Some dissenting scholars note that the modern environment is exerting [[evolutionary pressure]] for higher fertility, and that eventually due to individual natural selection or cultural selection, birth rates may rise again. Part of the "cultural selection" hypothesis is that the variance in birth rate between cultures is significant; for example, some religious cultures have a higher birth rate that is not accounted for by differences in income.<ref>{{cite journal|last1=Kolk|first1=M.|last2= Cownden |first2=D.|last3=Enquist|first3=M. |title=Correlations in fertility across generations: can low fertility persist?|journal=Proceedings of the Royal Society B: Biological Sciences|date=29 January 2014|volume=281|issue=1779|page = 20132561 |doi=10.1098/rspb.2013.2561|pmid= 24478294 |pmc=3924067}}</ref><ref>{{cite journal|last1=Burger|first1=Oskar|last2= DeLong|first2=John P.|title= What if fertility decline is not permanent? The need for an evolutionarily informed approach to understanding low fertility|journal= Philosophical Transactions of the Royal Society B: Biological Sciences|date=28 March 2016|volume=371|issue=1692|page = 20150157|doi= 10.1098/rstb.2015.0157 |pmid= 27022084|pmc= 4822437}}</ref><ref>{{cite news |title= Population paradox: Europe's time bomb |url= https://www.independent.co.uk/news/world/europe/population-paradox-europes-time-bomb-888030.html |access-date=31 March 2019 |work=The Independent |date=9 August 2008}}</ref> In his book ''Shall the Religious Inherit the Earth?'', [[Eric Kaufmann]] argues that demographic trends point to religious fundamentalists greatly increasing as a share of the population over the next century.<ref>{{Cite web|title=Shall the religious inherit the earth?|url=https://www.mercatornet.com/articles/view/shall_the_religious_inherit_the_earth/|date=April 6, 2010|website=Mercator Net|access-date=February 27, 2020|archive-date=June 23, 2019|archive-url=https://web.archive.org/web/20190623040350/https://www.mercatornet.com/articles/view/shall_the_religious_inherit_the_earth/|url-status=dead}}</ref><ref>{{Cite journal|last=McClendon|first=David|date=Autumn 2013|title=Shall the Religious Inherit the Earth? Demography and Politics in the Twenty-First Century, by ERIC KAUFMANN|url=https://academic.oup.com/socrel/article-abstract/74/3/417/1640161|journal=Sociology of Religion|volume=74|issue=3|pages=417–9|doi=10.1093/socrel/srt026}}</ref>

[[Jane Falkingham]] of [[Southampton University]] has noted that "We've actually got population projections wrong consistently over the last 50 years... we've underestimated the improvements in mortality... but also we've not been very good at spotting the trends in fertility."<ref name= bbc_sure /> In 2004 a United Nations office published its guesses for global population in the year 2300; estimates ranged from a "low estimate" of 2.3 billion (tending to −0.32% per year) to a "high estimate" of 36.4 billion (tending to +0.54% per year), which were contrasted with a deliberately "unrealistic" illustrative "constant fertility" scenario of 134 trillion (obtained if 1995–2000 fertility rates stay constant into the far future).<ref name= bbc_sure /><ref>{{cite web|title= World Population to 2300|url= https://www.un.org/esa/population/publications/longrange2/WorldPop2300final.pdf |publisher=United Nations Department of Economic and Social Affairs |access-date= 24 May 2016|date= 2004}}</ref>