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In [[demography]], '''demographic transition''' is a phenomenon and theory which refersreferring to the historical shift from high [[birth rate]]s and high [[Mortality rate|death rates]] to low birth rates and low death rates, as societies attain more technology, education (especially of [[female education|women]]), and [[economic development]].<ref name=":2">{{Cite web|title=Models of Demographic Transition [ Biz/ed Virtual Developing Country ]|url=https://web.csulb.edu/~gossette/classes/g460/DemTrans4.html|access-date=2021-06-16|website=web.csulb.edu}}</ref> The demographic transition has occurred in most of the world over the past two centuries, bringing the unprecedented population growth of the [[Malthusianism|post-Malthusian period]], then reducing birth rates and population growth significantly in all regions of the world. The demographic transition strengthens economic growth process by three changes: (i) reduced dilution of capital and land stock, (ii) increased investment in human capital, and (iii) increased size of the labor force relative to the total population and changed age population distribution.<ref name="Unified Growth Theory">{{cite book|title=Unified Growth Theory|last1=Galor|first1=Oded|date=2011|publisher=Princeton University Press|isbn=9781400838868|___location=Princeton}}</ref> Although this shift has occurred in many [[Developed country|industrialized countries]], the theory and model are frequently imprecise when applied to individual countries due to specific social, political, and economic factors affecting particular populations.<ref name=":2" />
However, the existence of some kind of demographic transition is widely accepted in the social sciences because of the well-established historical [[Correlation and dependence|correlation]] linking dropping [[fertility]] to social and economic development.<ref name="Nature">{{cite journal |doi=10.1038/nature08230 |pmid=19661915 |title=Advances in development reverse fertility declines |journal=Nature |volume=460 |issue=7256 |pages=741–3 |year=2009 |last1=Myrskylä |first1=Mikko |last2=Kohler |first2=Hans-Peter |last3=Billari |first3=Francesco C. |bibcode=2009Natur.460..741M|s2cid=4381880 }}</ref> Scholars debate whether [[Industrialisation|industrialization]] and higher incomes [[Causation (sociology)|lead to]] lower population, or whether lower populations lead to industrialization and higher incomes. Scholars also debate to what extent various proposed and sometimes inter-relatedinterrelated factors such as higher [[per capita]] income, lower [[Mortality rate|mortality]], old-age security, and rise of demand for [[human capital]] are involved.<ref name=":3">{{cite journal|last1=Galor|first1=Oded|title=The demographic transition: causes and consequences|journal=Cliometrica|date=17 February 2011|volume=6|issue=1|pages=1–28|doi=10.1007/s11698-011-0062-7|pmid=25089157|pmc=4116081}}</ref> Human capital gradually increased in the second stage of the industrial revolution, which coincided with the demographic transition. The increasing role of human capital in the production process led to the investment of human capital in children by families, which may be the beginning of the demographic transition.<ref name="jstor.org">{{cite journal | last1 = Galor | first1 = Oded | author-link = Oded Galor | year = 2005 | title = The Demographic Transition and the Emergence of Sustained Economic Growth |journal = Journal of the European Economic Association | volume = 3 | issue = 2–3| pages = 494–504 | doi=10.1162/jeea.2005.3.2-3.494| hdl = 10419/80187 | url = https://www.econstor.eu/bitstream/10419/80187/1/481895825.pdf }}</ref>
==History==
The transition involves four stages, or possibly five.
* In stage one, [[pre-industrial society]], [[Mortality rate|death rates]] and [[birth rate]]s are high and roughly in balance. All human [[population]]s are believed to have had this balance until the late 18th century, when this balance ended in Western Europe.<ref name=":5">{{Cite web |last=Montgomery |first=Keith |title=Demographic Transition |url=https://web.archive.org/web/20190605095831/http://pages.uwc.edu/keith.montgomery/demotrans/demtran.htm |website=WayBackMachine}}</ref> In fact, growth rates were less than 0.05% at least since the [[Neolithic Revolution|Agricultural Revolution]] over 10,000 years ago.<ref name=":5" /> [[Population growth]] is typically very slow in this stage, because the society is constrained by the available food supply; therefore, unless the society develops new technologies to increase food production (e.g. discovers new sources of food or achieves higher crop yields), any fluctuations in birth rates are soon matched by death rates.
* In stage two, that of a [[developing country]], the [[Mortality rate|death rates]] drop quickly due to improvements in food supply and [[sanitation]], which increase [[life expectancy]] and reduce [[disease]]. The improvements specific to food supply typically include selective breeding and crop rotation and farming techniques.<ref name=":5" /> Numerous improvements in public health reduce mortality, especially childhood mortality.<ref name=":5" /> Prior to the mid-20th century, these improvements in public health were primarily in the areas of food handling, water supply, sewage, and personal hygiene.<ref name=":5" /> One of the variables often cited is the increase in female literacy combined with public health education programs which emerged in the late 19th and early 20th centuries.<ref name=":5" /> In [[Europe]], the death rate decline started in the late 18th century in [[northwestern Europe]] and spread to the south and east over approximately the next 100 years.<ref name=":5" /> Without a corresponding fall in birth rates this produces an [[Demographic trap|imbalance]], and the countries in this stage experience a large increase in [[population]].
* In stage three, birth rates fall due to various [[Fertility factor (demography)|fertility factors]] such as access to [[contraception]], increases in wages, [[urbanization]], a reduction in [[subsistence agriculture]], an increase in the status and education of women, a reduction in the value of children's work, an increase in parental investment in the education of children, and other social changes. Population growth begins to level off. The birth rate decline in developed countries started in the late 19th century in northern Europe.<ref name=":5" /> While improvements in contraception do play a role in birth rate decline, contraceptives were not generally available nor widely used in the 19th century and as a result likely did not play a significant role in the decline then.<ref name=":5" /> It is important to note that birth rate decline is caused also by a transition in values;, not just because of the availability of contraceptives.<ref name=":5" />
* In stage four, there are both low birth rates and low death rates. Birth rates may drop to well below replacement level, as has happened in countries like [[Germany]], [[Italy]], and [[Japan]], leading to a [[population decline|shrinking population]], a threat to many industries that rely on population growth. As the large group born during stage two ages, it creates an economic burden on the shrinking working population. Death rates may remain consistently low or increase slightly due to increases in lifestyle diseases due to low exercise levels and high [[obesity]] rates and an aging population in [[developed countries]]. By the late 20th century, birth rates and death rates in developed countries leveled off at lower rates.<ref name="geography.about.com">{{Citation | publisher = About | title = Geography | url = http://geography.about.com/od/culturalgeography/a/demotransition.htm | contribution = Demographic transition | access-date = 2010-10-26 | archive-date = 2017-02-26 | archive-url = https://web.archive.org/web/20170226225454/http://geography.about.com/od/culturalgeography/a/demotransition.htm | url-status = dead }}.</ref>
* Some scholars break out, from stage four, a "stage five" of below-replacement fertility levels. Others hypothesize a different "stage five" involving an increase in fertility.<ref name=bbc_sure>[https://www.bbc.co.uk/news/technology-19923200 Can we be sure the world's population will stop rising?], BBC News, 13 October 2012</ref>
=== Stage one ===
In pre-industrial society, death rates and birth rates were both high, and fluctuatedfluctuating 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: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, more than anything else, 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===
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