Introduction to Sociology/Demography
Demography is the study of human population dynamics. It encompasses the study of the size, structure and distribution of populations, and how populations change over time due to births, deaths, migration, and aging. Demographic analysis can relate to whole societies or to smaller groups defined by criteria such as education, religion, or ethnicity.
Why study demography? 
Before proposing complex theories to explain sociological phenomena (e.g., World Systems Theory), especially at the macro and/or societal levels, sociologists should first turn to demographic indicators for possible explanations. Demographic analysis is a powerful tool that can explain a number of sociological phenomena.
For instance, in examining the elements that led to the first World War, most people turn to political and diplomatic conflicts but fail to consider the implications of expanding populations in the European countries involved. Expanding populations will result in increased competition for resources (i.e., food, land, access to trade routes and ports, etc.). Expanding populations may not be the primary cause of World War I, but it may have played a role in the increased hostilities leading up to the war. In this fashion, demographic indicators are often informative in explaining world events and should be turned to first as explanations.
The study of human populations has its roots, like sociology generally, in the societal changes that accompanied both the scientific and industrial revolutions. Some early mathematicians developed primitive forms of life tables, which are tables of life expectancies, for life insurance and actuarial purposes. Censuses, another demographic tool, were institued for primarily political purposes:
- as a basis for taxation
- as a basis for political representation
The development of demographic calculations started in the 18th century. Census taking, on the other hand, has a long history dating back close to 2,000 years among the Chinese and the Romans and even further back in history among some groups in the Middle East. Most modern censuses began in the late 18th century.
Data and Methods 
Demography relies on large data sets that are primarily derived from censuses and registration statistics (i.e., birth, death, marriage registrations). Large data sets over long periods of time (e.g., the U.S. census is conducted every 10 years) are required to develop trends in demographic indicators, like birth and death rates.
In many countries, particularly in developing nations, reliable demographic data are still difficult to obtain. In some locales this may be due to the association of census with taxation.
Demographic Indicators 
Because demography is interested in changes in human populations, demographers focus on specific indicators of change. Two of the most important indicators are birth and death rates, which are also referred to as fertility (see also fecundity) and mortality. Additionally, demographers are interested in migration trends or the movement of people from one location to another. Some of the specific measures used to explore these elements of population change are discussed below.
Fertility and Fecundity 
Fertility, in demography, refers to the ability of females to produce healthy offspring in abundance. Fecundity is the potential reproductive capacity of a female. Some of the more common demographic measures used in relation to fertility and/or fecundity include:
- crude birth rate: the annual number of live births per thousand people
- general fertility rate: the annual number of live births per 1000 women of childbearing age (often taken to be from 15 to 49 years old, but sometimes from 15 to 44).
- age-specific fertility rate: the annual number of live births per 1000 women in particular age groups (usually age 15-19, 20-24 etc.)
- total fertility rate: the number of live births per woman completing her reproductive life if her childbearing at each age reflected current age-specific fertility rates
- gross reproduction rate: the number of daughters who would be born to a woman completing her reproductive life at current age-specific fertility rates
- net reproduction rate: the number of daughters who would be born to a woman according to current age-specific fertility and mortality rates
Another important demographic concept relating to fertility is replacement level. Replacement level fertility refers to the number of children that a woman (or monogamous couple) must have in order to replace the existing population. Sub-replacement fertility is a fertility rate that is not high enough to replace an existing population. Replacement level fertility is generally set at 2.1 children in a woman's lifetime (this number varies by geographic region given different mortality rates). Sub-replacement fertility is below approximately 2.1 children in a woman's life time. The reason the number is set to 2.1 children per woman is because two children are needed to replace the parents and an additional one-tenth of a child is needed to make up for the mortality of children and women who do not reach the end of their reproductive years. Of course, women don't have one-tenth of a child; this results from statistical averaging between women who have more than two children and those who have two or fewer children.
The chart below illustrates trends in childbearing by region of the world. Fertility rates dropped earlier in the more developed regions of the world, followed by Asia and Latin America. Fertility rates are just starting to decline in Africa.
The chart below highlights the varied fertility rates of specific countries as some have very low fertility rates, many have moderate rates, and some have very high rates.
The following chart illustrates the relationship between contraceptive use and the total fertility rate by regions of the world. Increased contraceptive use is associated with lower numbers of children per woman.
One of the strongest predictors of fertility rates is women's educational attainment. Almost universally, higher levels of educational attainment result in lower fertility rates. It is not, however, education itself that causes declines in fertility but rather its association with other factors that reduce fertility: women with higher levels of education delay marriage, have improved labor market opportunities, are more likely to use contraception during intercourse, and are less likely to adopt traditional childbearing roles.
Fertility rates are also closely related to a country's level of development, which influences other factors. For instance, women who have kids in developed countries have increased opportunity costs, meaning they will make less money because of time spent outside the workforce raising kids. This is true in developed countries because women are more likely to be highly skilled and well-paid (relative to women in developing countries). Additionally, delayed childbearing, probability of a child reaching adulthood, norms about ideal family sizes, and pervasiveness of contraceptives will all reduce fertility rates. But one of the biggest factors is the cost of children. In undeveloped and developing countries, children are often an economic asset to parents as they serve as cheap labor on the farm; they don't require pay, just food and shelter. That is not the case in developed countries, where very few people work in agriculture (roughly 2% in the US). Instead, children are an economic liability, meaning they cost money while not generating money for the parents. The cost of raising a child from birth to 17 in a middle-income home in 2005 was $191,000. That cost goes up if parents pay for a child's college education, which averages between $12,000 and $30,000. Thus, the cost of raising children in developed countries reduces fertility rates in those countries.
Mortality refers to the finite nature of humanity: people die. Mortality in demography is interested in the number of deaths in a given time or place or the proportion of deaths in relation to a population. Some of the more common demographic measures of mortality include:
- crude death rate: the annual number of deaths per 1000 people
- infant mortality rate: the annual number of deaths of children less than 1 year old per thousand live births
- life expectancy: the number of years which an individual at a given age can expect to live at present mortality rates
Note that the crude death rate as defined above and applied to a whole population can give a misleading impression. For example, the number of deaths per 1000 people can be higher for developed nations than in less-developed countries, despite standards of health being better in developed countries. This is because developed countries have relatively more older people, who are more likely to die in a given year, so that the overall mortality rate can be higher even if the mortality rate at any given age is lower. A more complete picture of mortality is given by a life table which summarizes mortality separately at each age.
This chart depicts infant mortality by region of the world. The less developed regions of the world have higher infant mortality rates than the more developed regions.
This chart depicts life expectancy by region of the world. Similar to infant mortality, life expectancies are higher in more developed regions of the world.
According to recent research, one of the best predictors of longevity (i.e., a long life) is education, even when other factors are controlled: the more educated you are, the longer you can expect to live. A few additional years of schooling can add several additional years to your life and vastly improve your health in old age. The mechanism through which this works is not the schooling itself, but schooling's influence on other health-related behaviors. The more education someone has, the lower his/her likelihood of smoking and engaging in unhealthy and high risk behaviors. Education also increases the probability of people engaging in healthy behaviors, like frequently exercising.
Other factors associated with greater longevity include:
- wealth: money increases access to good healthcare, which improves health and increases longevity
- race: whites live longer than blacks, though this is due to other social disparities, like income and education, and not to race itself
- ability to delay gratification: with the ability to delay gratification people live healthier lives and engage in healthier behaviors (e.g., exercise)
- larger social networks: having a large group of friends and close relationships with relatives increases your social support, which positively influences health
- job satisfaction: people in more powerful and more satisfying jobs tend to be healthier than people in less satisfying jobs
The Demographic Transition 
The demographic transition is a model and theory describing the transition from high birth rates and death rates to low birth and death rates that occurs as part of the economic development of a country. In pre-industrial societies, population growth is relatively slow because both birth and death rates are high. In most post-industrial societies, birth and death rates are both low. The transition from high rates to low rates is referred to as the demographic transition. This understanding of societal changes is based on the work of Thompson, Blacker, and Notestein, who derived the model based on changes in demographics over the preceding two hundred years or so.
The beginning of the demographic transition in a society is indicated when death rates drop without a corresponding fall in birth rates (usually the result of improved sanitation and advances in healthcare). Countries in the second stage of the demographic transition (see diagram) experience a large increase in population. This is depicted in the diagram when death rates fall in stage two but birth rates do not fall until stage three. The red line begins its rapid upward growth in stage two and begins to level off at the end of stage three.
By the end of stage three, birth rates drop to fall in line with the lower death rates. While there are several theories that attempt to explain why this occurs (e.g., Becker and Caldwell, who view children as economic commodities), why birth rates decline in post-industrial societies is still being evaluated. Many developed countries now have a population that is static or, in some cases, shrinking.
As with all models, this is an idealized, composite picture of population change in these countries. The model is a generalization that applies to these countries as a group and may not accurately describe all individual cases. Whether or not it will accurately depict changes in developing societies today remains to be seen. For more information on the demographic transition, see here.
Population Growth and Overpopulation 
Overpopulation indicates a scenario in which the population of a living species exceeds the carrying capacity of its ecological niche. Overpopulation is not a function of the number or density of the individuals, but rather the number of individuals compared to the resources they need to survive. In other words, it is a ratio: population over resources. If a given environment has a population of 10, but there is food and drinking water enough for only 9 people, then that environment is overpopulated, while if the population is 100 individuals but there are food and water enough for 200, then it is not overpopulated. Resources to be taken into account when estimating if an ecological niche is overpopulated include clean water, food, shelter, warmth, etc. In the case of human beings, there are others such as arable land and, for all but tribes with primitive lifestyles, lesser resources such as jobs, money, education, fuel, electricity, medicine, proper sewage and garbage management, and transportation.
Presently, every year the world's human population grows by approximately 80 million. About half the world lives in nations with sub-replacement fertility and population growth in those countries is due to immigration. The United Nations projects that the world human population will stabilize in 2075 at nine billion due to declining fertility rates. All the nations of East Asia, with the exceptions of Mongolia, the Philippines, and Laos, are below replacement level. Russia and Eastern Europe are dramatically below replacement fertility. Western Europe also is below replacement. In the Middle East Iran, Tunisia, Algeria, Turkey, and Lebanon are below replacement. Canada, Australia, and New Zealand are similar to Western Europe, while the United States is just barely below replacement with about 2.0 births per woman. All four of these nations still have growing populations due to high rates of immigration.
Much of the projected growth is expected to come from African countries where birth rates remain high. While birth rates in most countries have fallen since 1990, in some parts of Africa birth rates have actually increased and the average woman has more than five children, well above the replacement rate.
Early Projections of Overpopulation 
Early in the 19th century, Thomas Malthus argued in An Essay on the Principle of Population that, if left unrestricted, human populations would continue to grow until they would become too large to be supported by the food grown on available agricultural land. He proposed that, while resources tend to grow arithmetically, population grows exponentially. At that point, the population would be restrained through mass famine and starvation. Malthus argued for population control, through moral restraint, to avoid this happening.
The alternative to moral restraint, according to Malthus, is biological and natural population limitation. As the population exceeds the amount of available resources the population decreases through famine, disease, or war, since the lack of resources causes mortality to increase. This process keeps the population in check and ensures it does not exceed the amount of resources.
Over the two hundred years following Malthus's projections, famine has overtaken numerous individual regions. Proponents of this theory, Neo-Malthusians state that these famines were examples of Malthusian catastrophes. On a global scale, however, food production has grown faster than population. It has often been argued that future pressures on food production, combined with threats to other aspects of the earth's habitat such as global warming, make overpopulation a still more serious threat in the future.
Population as a function of food availability 
There are some scholars who argue that human populations predictably grow and shrink according to their available food supply - populations grow when there is an abundance of food and shrink in times of scarcity. This idea is only slightly less problematic than the idea that human population growth is not guided by food production, as it suggestions that that every time food production is intensified to feed a growing population, the population responds by increasing even more. Some human populations throughout history support this theory, as consistent population growth began with the agricultural revolution, when food supplies consistently increased.
Critics of this idea point out that birth rates are voluntarily the lowest in developed nations, which also have the highest access to food. In fact, the population is decreasing in some countries with abundant food supply. Thus, human populations do not always grow to match the available food supply. Critics cite other factors that contribute to declining birth rates in developed nations, including: increased access to contraception, later ages of marriage, the growing desire of many women in such settings to seek careers outside of childrearing and domestic work, and the decreased economic 'utility' of children in industrialized settings. The latter explanation stems from the fact that children perform a great deal of work in small-scale agricultural societies, and work less in industrial ones; this interpretation may seem callous, but it has been cited to explain the drop-off in birthrates worldwide in all industrializing regions.
For some, the concept that human populations behave in the same way as do populations of bears and fish is hard to believe; for others it indicates a feasible solution to population issues. In either case, since populations are tied to the food they consume, discussions of populations should not take place without considering the role played by food supply. There is a substantial body of research that has considered the ability of the planet to provide sufficient food for the world's growing population. This research suggests that the planet can potentially provide sufficient food for the projected peak population of humans of 9 billion people, but only if agriculture is carefully managed. Factors that must be considered include: genetically modified crops, employing agricultural tools in correct, context-specific ways, aquaculture, and simultaneously working to limit harm to the environment.
Effects of overpopulation 
In any case, many proponents of population control have averred that famine is far from being the only problem attendant to overpopulation. These critics point out ultimate shortages of energy sources and other natural resources, as well as the importance of serious communicable diseases in dense populations and war over scarce resources such as land area. A shortage of arable land (where food crops will grow) is also a problem.
The world's current agricultural production, if it were distributed evenly, would be sufficient to feed everyone living on the Earth today. However, many critics hold that, in the absence of other measures, simply feeding the world's population well would only make matters worse, natural growth will cause the population to grow to unsustainable levels, and will directly result in famines and deforestation and indirectly in pandemic disease and war.
Some of the other characteristics of overpopulation include:
- Child poverty
- High birth rates
- Lower life expectancies
- Lower levels of literacy
- Higher rates of unemployment, especially in urban
- Insufficient arable land
- Little surplus food
- Poor diet with ill health and diet-deficiency diseases (e.g. rickets)
- Low per capita GDP
- Increasingly unhygienic conditions
- Government is stretched economically
- Increased crime rates resulting from people stealing resources to survive
- Mass extinctions of plants and animals as habitat is used for farming and human settlements
Another point of view on population growth and how it effects the standard of living is that of Virginia Abernethy. In Population Politics she shows evidence that declining fertility following industrialization only holds true in nations where women enjoy a relatively high status. In strongly patriarchal nations, where women enjoy few rights, a higher standard of living tends to result in population growth. Abernathy argues that foreign aid to poor countries must include significant components designed to improve the education, human rights, political rights, political power, and economic status and power of women.
Possible Solutions to Overpopulation 
Some approach overpopulation with a survival of the fittest, laissez-faire attitude, arguing that if the Earth's ecosystem becomes overtaxed, it will naturally regulate itself. In this mode of thought, disease or starvation are "natural" means of lessening population. Objections to this argument are:
- in the meantime, a huge number of plant and animal species become extinct
- this would result in terrible pollution in some areas that would be difficult to abate
- it obviously creates certain moral problems, as this approach would result in great suffering in the people who die
Others argue that economic development is the best way to reduce population growth as economic development can spur demographic transitions that seem to naturally lead to reductions in fertility rates.
In either case, it is often held that the most productive approach is to provide a combination of help targeted towards population control and self-sufficiency. One of the most important measures proposed for this effort is the empowerment of women educationally, economically, politically, and in the family. The value of this philosophy has been substantially borne out in cases where great strides have been taken toward this goal. Where women's status has dramatically improved, there has generally been a drastic reduction in the birthrate to more sustainable levels. Other measures include effective family planning programs, local renewable energy systems, sustainable agriculture methods and supplies, reforestation, and measures to protect the local environment.
David Pimentel, a Cornell University professor of ecology and agricultural sciences, sees several possible scenarios for the 22nd century:
- a planet with 2 billion people thriving in harmony with the environment
- or, at the other extreme, 12 billion miserable humans suffering a difficult life with limited resources and widespread famine
Spreading awareness of the issues is an important first step in addressing it.
Once countries pass through the demographic transition, some experience fertility rate decreases so substantial that they fall well below replacement level and their populations begin to shrink (as has Russia's in recent years, though emigration has also played a role in Russia's population decline). A new fear for many governments, particularly those in countries with very low fertility rates, is that a declining population will reduce the GDP and economic growth of the country, as population growth is often a driving force of economic expansion. To combat extremely low fertility rates, some of these governments have introduced pro-family policies, that include things like payments to parents for having children and extensive parental leave for parents. Such policies may reverse the low fertility rates, but they also seem to be shortsighted in light of the concerns associated with overall world population growth.
The likelihood of a given individual in the U.S. moving to another place in the U.S. in any given year has declined over the last 40 years. Only about 1 in 10 Americans have moved in the last year, which is about half the proportion that changed residences annually in the 1960s. The reduction in moves is attributable to aging populations (older people are less likely to move) and an increase in dual-career couples. Those who do move are generally driven by jobs.
Close to 37% of Americans have never moved from the community in which they were born. There are wide variations in native inhabitants, however: 76% of Texans were born in-state while only 14% of Nevadans were born in-state. Some states lose a large number of people who were born in the state as well, like Alaska, where only 28% of the people born in that state have remained there. Immigration is often a controversial topic, for a variety of reasons, though many have to do with competition between those already living in the destination location and those arriving in that location. One recent study finds that one type of competition between immigrants and non-immigrants may be overstated. Some people have suggested that natives' opportunities to attend college are negatively impacted through competition with immigrants. Neymotin (2009) finds that competition with immigrants does not harm the educational outcomes of U.S. natives and may in fact facilitate college attending.
Urbanization is the physical growth of urban areas as a result of global change. Urbanization is also defined by the United Nations as movement of people from rural to urban areas with population growth equating to urban migration. The United Nations projected that half of the world's population would live in urban areas at the end of 2008. Urbanization is closely linked to modernization, industrialization, and the sociological process of rationalization.
As more and more people leave villages and farms to live in cities, urban growth results. The rapid growth of cities like Chicago in the late 19th century and Mumbai a century later can be attributed largely to rural-urban migration and the demographic transition. This kind of growth is especially commonplace in developing countries.
The rapid urbanisation of the world’s population over the twentieth century is described in the 2005 Revision of the UN World Urbanization Prospects report. The global proportion of urban population rose dramatically from 13% (220 million) in 1900, to 29% (732 million) in 1950, to 49% (3.2 billion) in 2005. The same report projected that the figure is likely to rise to 60% (4.9 billion) by 2030.. Urbanization rates vary between countries. The United States and United Kingdom have a far higher urbanization level than China, India, Swaziland or Niger, but a far slower annual urbanization rate, since much less of the population is living in a rural area.
People move into cities to seek economic opportunities. A major contributing factor is known as "rural flight". In rural areas, often on small family farms, it is difficult to improve one's standard of living beyond basic sustenance. Farm living is dependent on unpredictable environmental conditions, and in times of drought, flood or pestilence, survival becomes extremely problematic. In modern times, industrialization of agriculture has negatively affected the economy of small and middle-sized farms and strongly reduced the size of the rural labour market. Cities, in contrast, are known to be places where money, services and wealth are centralized. Cities are where fortunes are made and where social mobility is possible. Businesses, which generate jobs and capital, are usually located in urban areas. Whether the source is trade or tourism, it is also through the cities that foreign money flows into a country. Thus, as with immigration generally, there are factors that push people out of rural areas and pull them into urban areas.
There are also better basic services as well as other specialist services in urban areas that aren't found in rural areas. There are more job opportunities and a greater variety of jobs. Health is another major factor. People, especially the elderly are often forced to move to cities where there are doctors and hospitals that can address their health needs. Other factors include a greater variety of entertainment (e.g., restaurants, movie theaters, theme parks, etc.) and better quality of education in the form of universities. Due to their high populations, urban areas can also have much more diverse social communities allowing others to find people like them when they might not be able to in rural areas. These conditions are heightened during times of change from a pre-industrial society to an industrial one.
Economic effects 
As cities develop, effects can include a dramatic increase in costs, often pricing the local working class out of the real estate market. For example, Eric Hobsbawm's book The age of the revolution: 1789–1848 (published 1962 and 2005) chapter 11, stated "Urban development in our period [1789–1848] was a gigantic process of class segregation, which pushed the new labouring poor into great morasses of misery outside the centres of government and business and the newly specialised residential areas of the bourgeoisie. The almost universal European division into a 'good' west end and a 'poor' east end of large cities developed in this period." This is likely due the prevailing south-west wind which carries coal smoke and other airborne pollutants downwind, making the western edges of towns preferable to the eastern ones. Similar problems now affect the developing world; rising inequality results from rapid urbanization. The drive for growth and efficiency can lead to less equitable urban development.
Urbanization is often viewed as a negative trend, but can in fact, be perceived simply as a natural occurrence from individual and corporate efforts to reduce expense in commuting and transportation while improving opportunities for jobs, education, housing, and transportation. Living in cities permits individuals and families to take advantage of the opportunities of proximity, diversity, and marketplace competition.
Environmental effects 
One environmental concern associated with urbanization is the urban heat island. The urban heat island is formed when industrial and urban areas are developed and heat becomes more abundant. In rural areas, a large part of the incoming solar energy is used to evaporate water from vegetation and soil. In cities, where less vegetation and exposed soil exists, the majority of the sun’s energy is absorbed by urban structures and asphalt. Hence, during warm daylight hours, less evaporative cooling in cities allows surface temperatures to rise higher than in rural areas. Additional city heat is given off by vehicles and factories, as well as by industrial and domestic heating and cooling units. This effect causes the city to become 2 to 10o F (1 to 6o C) warmer than surrounding landscapes.. Impacts also include reducing soil moisture and intensification of carbon dioxide emissions.
The effects of urbanization may be an overall positive for the environment. Birth rates of new urban dwellers fall immediately to the replacement rate (2.1), and keep falling. This can prevent overpopulation (see discussion below). Additionally, it puts a stop to destructive subsistence farming techniques, like slash and burn agriculture. Finally, it minimizes land use by humans, leaving more for nature.
Changing forms of urbanization 
Different forms of urbanization can be classified depending on the style of architecture and planning methods as well as historic growth of areas. In cities of the developed world urbanization traditionally exhibited a concentration of human activities and settlements around the downtown area. Recent developments, such as inner-city redevelopment schemes, mean that new arrivals in cities no longer necessarily settle in the centre. In some developed regions, the reverse effect, originally called counter urbanisation has occurred, with cities losing population to rural areas, and is particularly common for richer families. This has been possible because of improved communications and means of transportation, and has been caused by factors such as the fear of crime and poor urban environments. Later termed "white flight", the effect is not restricted to cities with a high ethnic minority population. When the residential area shifts outward, this is called suburbanization. Some research suggests that suburbanization has gone so far to form new points of concentration outside the downtown both in developed and developing countries such as India .
Urbanization can be planned or organic. Planned urbanization, (e.g., planned communities), is based on an advanced plan, which can be prepared for military, aesthetic, economic or urban design reasons. Organic urbanization is not organized and happens haphazardly. Landscape planners are responsible for landscape infrastructure (e.g., public parks, sustainable urban drainage systems, greenways, etc.) which can be planned before urbanization takes place, or afterward to revitalize an area and create greater livability within a region. Planned urbanization and development is the aim of the American Institute of Planners.
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This chapter also draws on the following Wikipedia articles: