In demography, demographic transition theory was introduced in the 1940s to provide a description and explanation of the main lines of European and American population history. It is the theory that societies progress from a premodern regime of high fertility and high mortality to a postmodern regime of low fertility and low mortality. The cause of the transition has been sought in the reduction of the death rate by controlling epidemic and contagious diseases. Then, with modernization, children become more costly. Cultural changes weaken the importance of children. The increasing empowerment of women to make their own reproductive decisions leads to smaller families. Thus there is a change in values, emphasizing the quality of children rather than their quantity. In short, the fertility transition is becoming a universal phenomenon, in which every country may be placed on a continuum of progress in transition.
The demographic transition involves three stages:
- Stage 1: In the first stage, birth rates are high and death rates are high. The population grows slowly.
- Stage 2: In the second stage modernization begins—especially industrialization (factories and railroads) and urbanization (movement off the farms). Medicine improves, as do personal hygiene and public health. This leads to a sharp fall in the death rate. Everyone lives longer, and infants are much more likely to survive. In the second stage, birth rates remain high so (with fewer deaths) the population increases rapidly.
- Stage 3: In the third stage, the death rate continues to fall and now the birth rate falls as well. Families become smaller. Instead of the rapid growth of stage two, population growth slows down; indeed, the population may start to shrink.
The United Nations in 1989 defined the four phases of demographic transition. In the first, high mortality and high fertility corresponded to a life expectancy at birth lower than 45 years and a fertility index of more than six children. In an overall decrease of mortality and fertility, life expectancy was between 45 and 55 and the fertility index between 4.5 and 6 in the second phase, between 55 and 65 and between 3 and 4.5 in the third, and higher than 65 and lower than 3 in the fourth. In 1992 Europe, North America, Australia, and New Zealand were in the fourth phase of transition. In 1993 Africa belonged to the first phase for fertility and to the second for life expectancy, Asia to the third, and Latin America to the fourth. Japan had a life expectancy of 79, the highest in the world, and a fertility index of 1.5, one of the lowest. China had a life expectancy of 70 and a fertility index of 1.9.
Modernization and the demographic transition
The modernization model was quite popular in the decades after World War II in many disciplines, and still is the dominant theory of population. The modernization model sees Stage One as an era of traditionalism, with everyone following traditional beliefs and behavior. The modernization model explains the fall in the death rate (stage two) as a consequence of industrialization, urbanization, and individual modernity in terms of better personal hygiene and more attention to public health. Since 1945, better medicine has played a key role. Birth rates are still high in Stage Two because most people are still traditional in terms of fertility, and do not realize the advantages of small families.
Modernization theory explains the third stage of the demographic transition (falling birth rates) in terms of the needs and plans of the modernized parents. The traditional reasons for having large families have faded away. (These traditional reasons included the prestige of having many children, their usefulness in working on the farm, and the need for adult children to care for aged parents before the days of social security.) Children are much less productive in urban industrial society than they had been on the farm, so the economic advantage for the large family disappears. The decline in infant mortality means that more babies grow to adulthood, and so fewer births are needed to produce the desired number of adult children. Because of psychological modernization parents desire smaller families, and because of their better education they can plan their family size.
Until the 1970s transition theory focused on urbanization and industrialization as causes. More recently the emphasis has focused on the motivations of the parents, with special reference to cultural values and the economic and social advantages of having smaller families. Thus, education is now seen as the single most important indicator of modernity; in survey after survey around the world, women with more education are much more likely to control their fertility.
Recent historical research on Europe and America before 1900 has refined the demographic transition theory. Historians point out the importance of the nuclear family (husband, wife and children living together, with no one else in the house) in contrast to the extended family (with various grandparents, in-laws and other relatives sharing the same house.) Different religious, ethnic and cultural groups went through the demographic transition at different speeds. Roman Catholics, for example, had a group preference for larger families and an aversion to birth control techniques until the 1960s. Some historians argue the European Fertility Project failed to substantiate demographic transition theory. Therefore their accounts of the decline of fertility in Europe have tended to emphasize cultural or social explanations that are grounded in communication and social interaction.
It is generally recognized that life expectancy has doubled in Western industrialized countries since the 19th century, despite a temporary rise in mortality in the second third of the 19th century (due primarily to dramatic urbanization rates). A more precise view of the course and causes of this dramatic rise in longevity is obtained by utilizing the concept of an epidemiological transition, analogous to the well-known demographic transition and generally divided into three stages. Quantitative assessment or morbidity and mortality trends in Germany in the 19th-20th centuries illustrates the methodology, which depends on specific consideration of causes of death, types of morbidity, age, and gender. The results indicate that reductions in infant and child morbidity and mortality were the main contributors to increased longevity, and that these reductions were until the mid-20th century due more to improvements in hygiene, nutrition, and maternal care than medical progress.
Fertility control methods and the Pill
Nevin and Oris contrast the fertility of a Catholic rural area (Pays de Herve) and a working center, secularized and with left-wing tendencies (Tilleur), paying attention both to the pre-transitional period and to the beginning of the so-called demographic transition. Located in eastern Belgium, these communities are analyzed from three points of view: their economic and social history; rates of marriage, illegitimacy, and premarital conception, measures regarded as indicators of social control and religiosity; and fertility patterns. Results indicate important contrasts: traditional social controls persisted in Pays de Herve but not in Tilleur. Yet, the beginning of the transition did not appear as a revolution. In these very different populations, fertility strategies centered on the number of desired children and on their sex composition both before and after the transition. When birth control appeared, such cultural decisionmaking was enhanced; thus the fertility decline was in keeping with the family culture and was not, at least initially, a radical change.
Szreter et al (2003) show that despite the advent of improved methods of contraception, especially after the invention of synthetic prophylactics, traditional methods of birth control, such as coitus interruptus and abortion, continued to be used in 19th- and 20th-century France, Canada, Great Britain, the Netherlands, Norway, and Finland. Fertility fell during this period at different times in different countries. Preference for one method over another was determined by ideologies of sexual and gender relations
Between 1750 and 1975 England experienced the demographic transition from high levels of both mortality and fertility, to low levels. A major factor was the sharp decline in the death rate for infectious diseases has fallen from about 11 per 1,000 to less than 1 per 1,000. By contrast the death rate from other causes, was 12 per 1,000 in 1850 and has not declined markedly. The agricultural revolution and the development of transport, initiated by the construction of canals, led to the greater availability of food and coal, and enabled the Industrial Revolution to improve the standard of living of the people. Scientific discoveries and medical breakthroughs did not in general, contribute importantly to the early major decline in infectious disease mortality and the decline in fertility occurred before efficient contraception became available.
Greenwood and Seshadri (2002) show that from 1800 to 1940 there was a demographic shift from a mostly rural US population with high fertility, with an average of seven children born per white woman, to a minority (43%) rural population with low fertility, with an average of two births per white woman. This shift resulted from technological progress. A sixfold increase in real wages made children more expensive in terms of forgone opportunities to work and increases in agricultural productivity reduced rural demand for labor, a substantial portion of which traditionally had been performed by children in farm families.
In the 1980s and the early 1990s the Irish demographic regime converged to the European norm. Mortality rose above the European Community average, and in 1991 Irish fertility fell to replacement level. The peculiarities of Ireland's past demography and its recent rapid changes challenge established theory. The recent changes have mirrored inward changes in society itself concerning family planning, women in the workforce, the sharply declining power of the Catholic Church, and the emigration factor. 
France displays real divergences from the standard model of Western demographic evolution. The uniqueness of the French case arises from its specific demographic history, its historic cultural values, and its internal regional dynamics. France's demographic profile is similar to its European neighbors and to developed countries in general, yet it seems to be staving off the population decline of Western countries. With 62.9 million inhabitants in 2006, it is the second most populous country in the European Union, and it displays a certain demographic dynamism thanks to a growth rate of 2.4% between 2000 and 2005, above the European average. More than two-thirds of that growth can be ascribed to a natural increase due to high fertility and birthrates. In contrast, France is one of the developed nations whose migratory balance is rather weak, which is an original feature at the European level. Several interrelated reasons account for such singularities, in particular the impact of pro-family policies accompanied by greater unmarried households and out-of-wedlock births. These general demographic trends parallel equally important changes in regional demographics. Since 1982 the same significant tendencies have occurred throughout mainland France: demographic stagnation in the least-populated rural regions and industrial regions in the northwest, with strong growth in the southwest and along the Atlantic coast, plus dynamism in metropolitan areas. Shifts in population between regions account for most of the differences in growth. The varying demographic evolution regions can be analyzed though the filter of several parameters, including residential facilities, economic growth, and urban dynamism, which yield several distinct regional profiles. The distribution of the French population therefore seems increasingly defined not only by interregional mobility but also by the residential preferences of individual households. These challenges, linked to configurations of population and the dynamics of distribution, inevitably raise the issue of town and country planning. The most recent census figures show that an outpouring of the urban population means that fewer rural areas are continuing to register a negative migratory flow - two-thirds of rural communities have shown some since 2000. The spatial demographic expansion of large cities amplifies the process of peri-urbanization yet is also accompanied by movement of selective residential flow, social selection, and sociospatial segregation based on income.
McNicoll (2006) examines the common features behind the striking changes in health and fertility in East and Southeast Asia in the 1960s-1990s, focusing on seven countries: Taiwan and South Korea ("tiger" economies), Thailand, Malaysia, and Indonesia ("second wave" countries), and China and Vietnam ("market-Leninist" economies). Demographic change can be seen as a byproduct of social and economic development together with, in some cases, strong governmental pressures. The transition sequence entailed the establishment of an effective, typically authoritarian, system of local administration, providing a framework for promotion and service delivery in health, education, and family planning. Subsequent economic liberalization offered new opportunities for upward mobility - and greater risks of backsliding - but these opportunities were accompanied by the erosion of social capital and the breakdown or privatization of service programs.
Cha (2007) analyzes a panel dataset to explore how industrial revolution, demographic transition, and human capital accumulation interacted in Korea from 1916-38. Income growth and public investment in health caused mortality to fall, which suppressed fertility and promoted education. Industrialization, skill premium, and closing gender wage gap further induced parents to opt for child quality. Expanding demand for education was accommodated by an active public school building program. The interwar agricultural depression aggravated traditional income inequality, raising fertility and impeding the spread of mass schooling. Landlordism collapsed in the wake of de-colonization, and the consequent reduction in inequality accelerated human and physical capital accumulation, hence growth in South Korea.
Campbell has studied the demography of 19th-century Madagascar in the light of demographic transition theory. Both supporters and critics of the theory hold to an intrinsic opposition between human and "natural" factors, such as climate, famine, and disease, influencing demography. They also suppose a sharp chronological divide between the precolonial and colonial eras, arguing that whereas "natural" demographic influences were of greater importance in the former period, human factors predominated thereafter. Campbell argues that in 19th-century Madagascar the human factor, in the form of the Merina state, was the predominant demographic influence. However, the impact of the state was felt through natural forces, and it varied over time. In the late 18th and early 19th centuries Merina state policies stimulated agricultural production, which helped to create a larger and healthier population and laid the foundation for Merina military and economic expansion within Madagascar. From 1820, the cost of such expansionism led the state to increase its exploitation of forced labor at the expense of agricultural production and thus transformed it into a negative demographic force. Infertility and infant mortality, which were probably more significant influences on overall population levels than the adult mortality rate, increased from 1820 due to disease, malnutrition, and stress, all of which stemmed from state forced labor policies. Available estimates indicate little if any population growth for Madagascar between 1820 and 1895. The demographic "crisis" in Africa, ascribed by critics of the demographic transition theory to the colonial era, stemmed in Madagascar from the policies of the imperial Merina regime, which in this sense formed a link to the French regime of the colonial era. Campbell thus questions the underlying assumptions governing the debate about historical demography in Africa and suggests that the demographic impact of political forces be reevaluated in terms of their changing interaction with "natural" demographic influences.
Russia has been undergoing a unique demographic transition since the 1980s; observers call it a "demographic catastrophe": the number of deaths exceeds the number of births, life expectancy is drastically decreasing, the number of suicides has increased, and there are 240 abortions per 100 live births.
Second demographic transition
Since the 1980s demographers have begun to speak of a "second demographic transition" in Europe in an effort to describe a situation that includes an increasing number of partnerships instead of marriages, a higher average age at marriage, later births, and an increasing share of children born out of wedlock.
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