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The Cultural Landscape Chapter 2: Population
Population
The typical family in a more developed country (MDC) today contains fewer people than in the past, and the number of children is declining.
In other regions of the world, the number of children per household tends to be much higher than in the MDCs
The ability of less developed countries (LDCs) to provide food, clothing, and shelter for their people is severely hampered by the continued rapid growth of their population.
The scientific study of population characteristics is demography.
Demographers look statistically at how people are distributed spatially and by age, gender, occupation fertility, health, and so on.
A study of population is the basis for understanding a wide variety of issues in human geography.
The study of population is critically important for three reasons:
More people are alive at this time—nearly 7 billion—than at any point in Earth’s long history.
The world’s population increased at a faster rate during the second half of the twentieth century than ever before in history.
Virtually all global population growth is concentrated in LDCs.
These facts lend urgency to the task of understanding the diversity of population problems in the world today.
The first two key issues ask “where” questions and the second two ask “why” questions.
Geographers study population problems by first describing where people are found across Earth’s space.
The chapter then turns to explaining why the population is growing at different rates in different places.
From the perspective of globalization, geographers argue that the world’s so-called overpopulation problem is not simply a matter of the total number of people on Earth but also includes the relationship between the number of people and the availability of resources.
At a local scale, geographers find that overpopulation is a threat in some regions of the world but not in others.
The final key issue explains why geographers consider local diversity in growth rates to be important.
Geographers who specialize in demography cannot offer a simple “yes” or “no” answer, but they recognize the connection between regions of high and low population growth, discussed in more detail in Chapter 3.
KEY ISSUE 1 - Where Is the World’s Population Distributed?
People Concentrations
Two-thirds of the world’s inhabitants are clustered in four regions—East Asia, South Asia, Southeast Asia, and Europe.
The clustering of the world’s population can be displayed on a cartogram, which depicts the size of countries according to population rather than land area, as is the case with most maps.
When compared to a more typical equal-area map, the population cartogram displays the major population cloisters of Europe and East, South, and Southeast Asia as much larger, and Africa and the Western Hemisphere as much smaller.
As you look at maps of population growth and other topics in this and subsequent chapters, pay special attention to Asia and Europe, because global patterns are heavily influenced by conditions in these regions, where two-thirds of the world’s people live.
The four regions display some similarities. Most people in these regions live near an ocean or near a river with easy access to an ocean, rather than in the interior of major landmasses.
The four population clusters occupy generally low-lying areas, with fertile soil and temperate climate.
Despite these similarities, we can see significant differences in the pattern of occupancy of the land in the five concentrations.
East Asia
Nearly one-fourth of the world’s people live in East Asia.
The region, bordering the Pacific Ocean, includes eastern China, the islands of Japan, the Korean peninsula, and the island of Taiwan.
Five-sixths of the people in this concentration live in the People’s Republic of China, the world’s most populous country.
China is the world’s fourth-largest country in land area.
The Chinese population is clustered near the Pacific Coast and in several fertile river valleys that extend inland.
More than one-half of the people live in rural areas where they work as farmers.
In Japan and South Korea, the population is not distributed uniformly either.
Forty percent of the people live in three large metropolitan areas—Tokyo and Osaka in Japan, and Seoul in South Korea—that cover less than 3 percent of the two countries’ land area.
In sharp contrast to China, more than three-fourths of all Japanese and Koreans live in urban areas and work in industrial or service jobs.
South Asia
Nearly one-fourth of the world’s people also live in South Asia, which includes India, Pakistan, Bangladesh, and the island of Sri Lanka.
The largest concentration of people within South Asia lives along a 1,500-kilometer corridor from Lahore, Pakistan through India and Bangladesh to the Bay of Bengal.
Like the Chinese, most people in South Asia are farmers living in rural areas.
The region contains 18 urban areas with more than 2 million inhabitants and 46 with more than 1 million, but only one-fourth of the total population lives in an urban area.
Southeast Asia
A third important Asian population cluster, and the world’s fourth-largest (after Europe), is in Southeast Asia.
Around 600 million people live in Southeast Asia, mostly on a series of islands that lie between the Indian and Pacific oceans.
These islands include Java, Sumatra, Borneo, Papua, New Guinea, and the Philippines.
The largest concentration is on the island of Java, inhabited by more than 100 million people.
Indonesia, which consists of 13,677 islands, including Java, is the world’s fourth most populous country.
Several islands that belong to the Philippines contain high population concentrations, and the population is also clustered along several river valleys and deltas at the southeastern tip of the Asian mainland, known as Indochina.
Like China, and South Asia, the Southeast Asia concentration is characterized by a high percentage of people working as farmers in rural areas.
The three Asian population concentrations together compromise more than half of the world’s toad population,m but together they live on less than 10 percent of Earth’s land area.
The same held true 2000 years ago.
Europe
Europe, including the European portion of Russia, forms the world’s third-largest population cluster, one-ninth of the world’s people.
The region includes four dozen countries.
In contrast to the three Asian concentrations, three-fourths of Europe's inhabitants live in cities, and less than 10 percent are farmers.
Although the region’s temperate climate permits the cultivation of a variety of crops, Europeans do not produce enough food for themselves.
Instead, they import food and other resources from elsewhere in the world.
Other Population Clusters
The largest population concentration in the Western Hemisphere is in the northeastern United States and southeastern Canada.
About 2 percent of the world’s people live in this area.
Like the Europeans, most Americans are urban dwellers; less than 2 percent are farmers.
Another 2 percent of the world’s population is clustered in West Africa, especially along the south-facing Atlantic coast.
Sparsely Populated Regions
Human beings avoid clustering in certain physical environments.
The portion of Earth’s surface occupied by permanent human settlements is called the ecumene.
The areas of Earth that humans consider too harsh for occupancy have diminished over time, whereas the ecumene has increased.
Still, approximately three-fourths of the world’s population live on only 5 percent of Earth’s surface.
Dry Lands
Areas too dry for farming cover approximately 20 percent of the Earth’s land surface.
The largest desert region, extending from North Africa to Southwest and Central Asia, is known by several names including the Sahara, Arabian, Thar, Takla Makan, and Gobi deserts.
Deserts generally lack sufficient water to grow crops that could feed a large population, although some people survive thereby raising animals, such as camels, that are adapted to the climate.
Wet Lands
Lands that receive very high levels of precipitation may also be inhospitable for human occupation.
Precipitation may be concentrated at specific times of the year or spread throughout the year.
Cold Lands
Much of the land near the North and South poles are perpetually covered with ice or the ground is permanently frozen (permafrost).
The polar regions are unsuitable for planting crops; few animals can survive the extreme cold, and few human beings live there.
High Lands
Relatively few people live at high elevations.
The highest mountains in the world are steep, snow-covered, and sparsely settled.
We can find some significant exceptions, especially in Latin America and Africa.
Population Density
Density, defined in Chapter 1 as the number of people occupying an area of land, can be computed in several ways, including arithmetic density, physiological density, and agricultural density.
These measures of density help geographers describe the distribution of people in comparison to available resources.
Arithmetic density
Geographers most frequently use arithmetic density, which was defined in Chapter 1 as the total number of objects in an area.
In population geography, arithmetic density refers to the total number of people divided by total land area.
For example, to compute the arithmetic or population density for the United States, we can divide the population (approximately 310 million people) by the land area (approximately 9.6 million square kilometers, or 3.7 million square miles).
The result is that the US has an arithmetic density of 32 persons per square kilometer (84 persons per square mile).
By comparison, the arithmetic density is much higher in South Asia.
Arithmetic dentistry varies even more within individual countries.
Arithmetic density enables geographers to compare the number of people trying to live on a given piece of land in different regions of the world.
Physiological Density
A more meaningful population measure is afforded by looking at the number of people per area of a certain type of land in a region.
Land suited for agriculture is called arable land.
In a region, the number of people supported by a unit area of arable land is called the physiological density.
The United States has a physiological density of 175 persons per square kilometer of arable land.
Physiological density provides insights into the relationship between the size of a population and the availability of resources in a region.
Comparing physiological and arithmetic densities help geographers to understand the capacity of the land to yield enough food for the needs of the people.
Agricultural Density
Two countries can have similar physiological densities, but they may produce significantly different amounts of food because of economic conditions.
Agricultural density is the ratio of the number of farmers to the amount of arable land, which is land suitable for agriculture.
This density helps account for economic differences.
The United States has an extremely low agricultural density (1.6 farmers per square kilometer of arable land), whereas Egypt has a very high density (2511 farmers per square kilometer of arable land).
MDCs have lower agricultural densities because technology and finance allow a few people to farm extensive land areas and feed many people.
To understand the relationship between population and resources in a country, geographers examine a country’s physiological and agricultural densities together.
KEY ISSUE 2 - Where Has the World’s Population Increased?
Natural Increase
Geographers most frequently measure population change in a country or the world as a whole through three measures—crude birth rate, crude death rate, and natural increase rate.
Crude birth rate (CBR) is the total number of live births in a year for every 1,000 people alive in society.
Crude death rate (CDR) is the total number of deaths in a year for every 1,000 people alive in society.
Natural increase rate (NIR) is the percentage by which a population grows in a year.
It is computed by subtracting CDR from CBR, after first converting the two measures from numbers per 1,000 to percentages (numbers per 100).
The world NIR during the early twenty-first century has been 1.2, meaning that the population of the world has been growing each year by 1.2 percent.
About 80 million people are being added to the population of the world annually.
The world population increased from 3 to 4 billion in 14 years, from 4 to 5 billion in 13 years, and from 5 to 6 billion in 12 years.
The rate of natural increase affects the doubling time, which is the number of years needed to double a population, assuming a constant rate of natural increase.
More than 95 percent of the natural increase is clustered in LDCs.
Regional differences in NIRs mean that most of the world’s additional people live in the countries that are least able to maintain them.
To explain these differences in growth rates, geographers point to regional differences in fertility and mortality rates.
Fertility
The world map of crude birth rates mirrors the distribution of NIRs.
The word crude birth rate and crude death rate means that we are concerned with society as a whole rather than a refined look at particular individuals or groups.
Geographers also use the total fertility rate (TER) to measure the number of births in a society.
The TFR is the average number of children a woman will have throughout her childbearing years (roughly 15 through 49).
The TFR for the world as a whole is 2.6, and, again, the figures vary between MDCs and LDCs.
The TFR
Mortality
Two useful measures of mortality in addition to the CDR already defined are the infant mortality rate and life expectancy.
The infant mortality rate (IMR) is the annual number of deaths of infants under 1 year of age, compared with total live births.
As was the case with the CBR and CDR, the IMR is usually expressed as the number of deaths among infants per 1,000 births rather than as a percentage (per 100).
The global distribution of IMRs follows the pattern that by now has become familiar.
The highest rates are in the LDCs of sub-Saharan Africa, whereas the lowest rates are in Europe.
Although the United States is well endowed with medical facilities, it suffers from a higher IMR than Canada and every country in Western Europe.
Life expectancy at birth measures the average number of years a newborn infant can expect to live at current mortality levels.
Natural increase, crude birth, total fertility, infant mortality, life expectancy—the descriptions follow similar patterns.
Higher natural increase, crude birth, total fertility rates, and IMRs, and lower average life expectancy are found in LDCs.
The final world map of demographic variables—CDR—does not follow the familiar pattern.
The combined CDR for all LDCs is actually lower than the combined rate for all MDCs.
KEY ISSUE 3 - Why Is Population Increasing at Different Rates in Different Countries?
The Demographic Transition
The demographic transition is a process with several stages, and every country is in one of them.
The process has a beginning, middle, and end.
Historically one country has moved from one stage of the process to the next, it has not reverted to an earlier.
Stage 1: Low Growth
Most of humanity’s several-hundred-thousand-year occupancy of Earth was characterized by stage 1 of the demographic transition.
During most of this period, people depended on hunting and gathering for food.
About the year 8000, the world’s population began to grow by several thousand per year.
Between 8000 BC and AD 1750, Earth’s human population began to grow by several thousand per year.
The burst of population growth around 8000 BC was caused by the agricultural revolution, which was the time when human beings first domesticated plants and animals and no longer relied entirely on hunting and gathering.
Despite the agricultural revolution, the human population remained in stage 1 of the demographic transition because food supplies were still unpredictable.
Farmers prospered in regions with abundant harvests, and the population expanded, but when unfavorable climatic conditions resulted in low food production, the CDR would soar.
War and disease also took their toll in stage 1 societies.
Stage 2: High Growth
For nearly 10,000 years after the agricultural revolution, the world population grew at a modest pace.
The sudden burst of population growth occurred in the late eighteenth and early nineteenth centuries because several countries moved on to stage 2 of the demographic transition.
In stage 2 of the demographic transition, the CDR suddenly plummets while the CBR remains roughly the same as in stage 1.
The NIR is very high, and the population grows rapidly.
Countries entered stage 21 of the demographic transition after 1750 as a result of the Industrial Revolution, which began in England in the late eighteenth century and spread to the European continent and North America during the nineteenth century.
New machines helped farmers increase agricultural production and feed the rapidly growing population.
Countries in Europe and North America entered stage 2 of the demographic transition about 1800, but stage 2 did not diffuse to most countries in Africa, Asia, and Latin America until around 1950.
Countries in Africa, Asia, and Latin America moved on to stage 2 of the demographic transition during the second half of the twentieth century for a different reason that was the case for Europe and North America 200 years earlier.
The late-twentieth-century push of countries into stage 2 was caused by the medical revolution
Stage 3: Moderate Growth
A country moves from stage 2 to stage 3 of the demographic transition when the CBR begins to drop sharply.
The CDR continues to fall in stage 3 but at a much slower rate than in stage 2.
The sudden drop in the CBR during stage 3 occurs for different reasons than the rapid decline of the CDR during stage 2.
CBR declines in stage 3 because of changes in social customs.
A society enters stage 3 of the demographic transition when people have fewer children.
Economic changes in stage 3 societies also induce people to have fewer offspring.
Stage 4: Low Growth
A country reaches stage 4 of the demographic transition when the CBR declines to the point where it equals the CDR, and the NIR approaches zero.
This condition is called zero population growth (ZPG), a term often applied to stage 4 countries.
ZPG may occur when the CBR is still slightly higher than the CDR, because some females die before reaching childbearing years, and the number of females in their childbearing years can vary.
Countries in stage 4 of the demographic transition can be identified on the map of total fertility rate.
Most European countries have reached stage 4 of the demographic transition because they have TFRs well below the ZPG replacement level of 2.1.
Social customs again explain the movement from one stage of the demographic transition to the next.
Changes in lifestyle also encourage smaller families.
Several Eastern European countries, most notably Russia have negative NIRs, meaning that the number of deaths exceeds the number of births.
Higher death rates may be a result of inadequate pollution controls and inaccurate reporting by the Communists.
Lower death rates may stem from very strong family-planning programs and deep-seated pessimism about having children.
A country that has passed through all four stages of the demographic transition has in some ways completed a cycle—from little or no natural increase in stage 1, to little or no natural increase in stage 4.
Two crucial demographic differences underlie this process, however. First, at the beginning of the demographic transition, the CBRs and CDRs are high—35 to 40 per 1,000—whereas at the end of the process the rates are very low, approximately 10 per 1,000. Second, the total populauon of the country is much higher in stage 4 than in stage 1.
Population Pyramids
A country’s stage of demographic transition gives it a distinctive population structure.
Population in a country is influenced by the demographic transition in two principal ways—the percentage of the population in each age group and the distribution of males and females.
A country's population can be displayed by age and gender groups on a bar graph called a population pyramid.
A population pyramid normally shows the percentage of the total population in 5-year age groups, with the youngest group (0 to 4 years old) at the base of the pyramid and the oldest group at the top.
The length of the bar represents the percentage of the total population contained in the group.
The shape of a pyramid is determined primarily by the CBR in the community.
Age Distribution
The age structure of a population is extremely important in understanding similarities and differences among countries.
The most important factor is the dependency ratio, which is the number of people who are too young or too old to work, compared to the number of people in their productive years.
To compare the dependency ratios of different countries, we can divide the population into three age groups—0 to 14, 15 to 64, and 65 and older.
The dependency ratio is nearly 1:1 in stage 2 counties, whereas in stage 4 countries the ratio is 1:2 (one dependent for every two workers).
Young dependents outnumber the elderly ones by 10:1 in stage 2 countries, but the number of young and elderly dependents are roughly equal in stage 4 countries.
As countries pass through the stages of the demographic transition, the percentage of elderly people increases.
Older people must receive adequate levels of income and medical care after they retire from their jobs.
Sex Ratio
The number of males per hundred females in the population is sex ratio.
In general, slightly more males than females are born, but males have higher death rates.
In the United States, males under age of 15 exceed females 105:100.
In stage 2 countries, the high mortality rate during childbirth partly explain the lower percentage of women.
The shape of a community population pyramid tells a lot about its distinctive character, especially compared with other places.
Countries in Different Stages of Demographic Transition
Countries display distinctive population characteristics depending on their stage in the demographic transition.
No country today remains in stage 1 of the demographic transition, but it is instructive to compare countries in each of the other three stages.
Cape Verde: Stage 2 (High Growth)
Cape Verde, a collection of ten small islands in the Atlantic Ocean off the coast of West Africa, moved from stage 1 to stage 2 in about 1950.
During the first half of the twentieth century, Cape Verde’s population declined, from 147,000 in 1900 to 137,000 in 1949.
This long-term pattern of demographic uncertainty suddenly ended in 1950, and Cape Verde quickly moved to stage 2 of the demographic transition.
Since entering stage 2 a half-century ago, the population of Cape Verde has surged to 427,000, and natural increase has averaged more than 2.0 percent per year.
The wild fluctuations in Cape Verdes CBR are a legacy of severe famines during the 1940s.
The population pyramid shows that Cape Verde has a large number of females aged 5-14 who will soon start moving into their prime childbearing years.
Chile: Stage 3 (Moderate Growth)
Chile provides an example of a country outside Europe and North America that has reached stage 3 of the demographic transition but is likely to take some time before continuing to stage 4.
Chile has changed from a predominantly rural society based on agriculture to an urban society in which most people now work in factories, offices, and shops. However, many Chileans still have large families.
Like many countries outside Europe and North America, Chile entered the twentieth century still in stage 1 of the demographic transition.
Chile's CDR declined sharply in the 1930s, moving the country into stage 2 of the demographic transition.
Chile has been in stage 3 of the demographic transition since the 1960s.
Although Chile’s NIR is lower today than in the 1950s, the country is unlikely to move into stage 4 of the demographic transition in the near future.
Denmark: Stage 4 (Low Growth)
Denmark, like most European countries, has reached stage 4 of the demographic transition.
The country entered stage 2 in the nineteenth century when the CDR began its permanent decline.
The country has reached ZPG, and the population is increasing almost entirely because of immigration
Denmark's population pyramid shows the impact of the demographic transition.
Instead of a classic pyramid shape Denmark has a column, demonstrating that the percentages of young and elderly people are nearly the same.
Denmark’s CDR has actually increased somewhat in recent years because of the increasing number of elderly people.
Demographic Transition and World Population Growth
The worldwide population increased rapidly during the second half of the twentieth century because few countries were in the two stages of demographic transition that have low population growth—no country remains in stage 1, and few have reached stage 4.
The overwhelming majority of countries are in either stage 2 or 3 of the demographic transition—stages with rapid population growth—and only a few are likely to reach stage 4 in the near future.
The four-stage demographic transition is characterized by two big breaks from the past
The first break—the sudden drop in the death rate that comes from technological innovation—has been accomplished everywhere.
The second break—the sudden drop in the birth rate that comes from changing social customs—has yet to be achieved in many countries
If most countries in Europe and North America have reached—or at least are approaching—stage 4 of the demographic transition, why arent countries elsewhere in the world?
The answer is that fundamental problems prevent other countries from replicating the experience in Europe and North America.
The first demographic change—the sudden decline in CDR—occurred for different reasons in the past.
In contrast, the sudden drop in the CDR in Africa, Asia, and Latin America in the twentieth century was accomplished by different means and with less internal effort by local citizens.
Sri Lanka: CDR was reduced by nearly one-half in a single year with no change in the country’s s economy or culture.
Having caused the first break with the past through diffusion of medical technology. European and North American countries now urge other countries to complete the second break with the past—the reduction in the birth rate.
In the past, stage 2 of the demographic transition lasted for approximately 100 years in Europe and North America, but today’s stage 2 countries are being asked to move through to stage 3 in much Jess time in order to curtail population growth.
When European and North American countries were in stage 2, the global population was increasing but only about 6 million per year, compared to 80 million per year now.
KEY ISSUE 4 - Why Might the World Face an Overpopulation Problem?
Malthus on Overpopulation
English economist Thomas Malthus (1766-1834) was one of the first to argue that the world’s rate of population increase was far outrunning the development of food supplies.
In An Essay on the Principle of Population, published in 1798, Malthus claimed that The population was growing much more rapidly than Earth's food supply because population increased geometrically, whereas food supply increased arithmetically.
According to Malthus, these growth rates would produce the following relationships between people and food in the future:
Today - 1 person, 1 unit of food
100 years from now - 16 persons, 5 units of food
Malthus made these conclusions several decades after England had become the first country to enter stage 2 of the demographic transition, in association with the Industrial Revolution.
He concluded that population growth would press against available resources in every country; unless “moral restraint” produced lower CBRs or unless disease, famine, war, or other disasters produced higher CDRs.
Contemporary Neo-Malthusians
Malthus’s views remain influential today.
Contemporary geographers and other analysts are taking another look at Malthus’s theory because of Earth’s unprecedented rate of natural increase during the late twentieth century.
Neo-Malthusians argue that two characteristics of recent population growth make Malthus’s thesis more frightening than when it was written more than 200 years ago.
First, in Malthus’s time only a few relatively wealthy countries had entered stage 2 of the demographic transition characterized by rapid population increase. Malthus failed to anticipate that relatively poor countries would have the most rapid population growth because of the transfer of medical technology (but not wealth) from MDCs.
The second argument made by neo-Malthusians is that world population growth is outstripping a wide variety of resources, not just food production.
Malthus's Critics
Mathus’s theory has been severely criticized from a variety of perspectives.
Many geographers consider Malthusian beliefs unrealistically pessimistic because they are based on a belief that the world’s supply of resources is fixed rather than expanding.
Contemporary analysts such as Esther Boserup and Simon Kuznets criticize Malthus’s theory that population growth produces problems.
Julian Simon argued that population growth stimulated economic growth.
Marxists maintain that no cause-and-effect relationship exists between population growth and economic development.
Poverty, hunger, and other social welfare problems associated with lack of economic development are a result of unjust social and economic institutions, not population growth.
Marxist theorist Friedrich Engels (1820-1895) dismissed Malthus’s arithmetic as an artifact of capitalism.
The world is much better off economically with 7 billion people than it was with 1 billion, argue Malthus's critics, because too few people can retard economic development as surely as can too many people.
Some political leaders, especially in Africa, argue that high population growth is good for a country because more people will result in greater power.
Malthus’s Theory and Reality
On a global scale, conditions during the past half-century have not supported Malthus's Theory
World food production has consistently grown at a faster rate than the NIR since 1950.
Overall food production has increased during the last half century somewhat more rapidly than Malthus predicted.
It is on the population side of the equation, though, that Malthus has proved to be inaccurate.
However, neo-Malthusians point out that production of both wheat and rice has slowed in India in recent years.
Declining Birth Rates
The Malthus theory seems unduly pessimistic on a global scale, but geographers recognize the diversity of conditions among regions of the world.
The NIR can decline for only reasons—lower birth rates or higher death rates.
The CBR has declined rapidly since 1990 from 27 to 21 in the world as a whole and from 31 to 23 in LDCs.
Two strategies have been successful in reducing birth rates.
One alternative emphasizes reliance on economic development, the other on the distribution of contraceptives.
Reasons for Declining Birth Rates
One approach to lowering birth rates emphasizes the importance of improving local economic conditions.
With better education, women would better understand their reproductive rights, make more informed reproductive choices, and select more effective methods of contraception.
Reducing Births Through Contraception
The other approach to lowering birth rates emphasizes the importance of rapidly diffusing modern contraceptive methods.
Bangladesh is an example of a country that has had little improvement in the wealth and literacy of its people, but 56 percent of the women in the country used contraceptives in 2009 compared to 6 percent three decades earlier.
The percentage of women using contraceptives is especially low in sub-Saharan Africa, so the alternative of distributing contraceptives could have an especially strong impact there.
Methods of family planning also vary among countries.
The reason for this is partly economics, religion, and education.
Regardless of which alternative is more successful, many oppose birth-control programs for religious and political reasons.
Analysts agree that the most effective means of reducing births would employ both alternatives.
World Health Threats
Lower CBRs have been responsible for declining NIRs in most countries.
Medical researchers have identified an epidemiologic transition that focuses on distinctive causes of death in each stage of the demographic transition.
The term epidemiologic transition comes from epidemiology, which is the branch of medical science concerned with the incidence, distribution, and control of diseases that are prevalent among a population at a special time and are produced by some special causes not generally present in the affected locality.
Epidemiologic Transition Stages 1 and 2
Stage 1 of the epidemiologic transition, as originally formulated by epidemiologist Abdel Omran in 1971, has been called the stage of pestilence and famine.
BLACK PLAGUE
Well documented is the origin and diffusion of history's most violent stage 1 epidemic—the Black Plague, or bubonic plague, which was probably transmitted to humans by fleas from migrating infected rats.
The plague spread across the coast to inland towns and then to rural areas.
The plague wiped out entire villages and families, leaving farms with no workers and estates with no heirs.
Stage 2 of the epidemiologic transition has been called the stage of receding pandemics. A pandemic is a disease that occurs over a wide geographic area and affects a very high proportion of the population.
Death rates did not decline immediately and universally during the early years of the Industrial Revolution.
Geographic methods played a key role in understanding the cause of cholera during the early nineteenth century.
Many in the nineteenth century believed that epidemic victims were being punished for sinful behavior and that most victims were poor because poverty was considered a sin.
Dr. Snow found that a large percentage of cholera victims were clustered around one water pump, on Broad Street.
Construction of water and sewer systems eradicated cholera by the nineteenth century.
Epidemiologic Transition Stages 3 and 4
Stage 3 of the epidemiological transition, is the stage of degenerative increase in deaths from infectious diseases and an increase in chronic disorders associated with aging.
A decline in infectious diseases has sharpened stage 3 countries.
As LDCs moved recently from stage 2 to stage 3, infectious diseases also declined.
Omran’s epidemiological transition was extended by S.
Epidemiologic Transition Possible Stage 5
Some medical analysts argue that the world is moving into stage 5 of the epidemiologic transition, the stage of reemergence of infectious and parasitic diseases.
Three reasons help to explain the possible emergence of stage 5 of the epidemiologic transition:
Evolution. Infectious disease microbes have continuously evolved in response to environmental pressures by developing resistance to drugs and insecticides.
Malaria was nearly eradicated in the mid-twentieth century by spraying DDT in areas infested with the mosquito that carries a parasite.
Poverty. Tuberculosis (TB) is an example of an infectious disease that has been largely controlled and remains a major cause of death in LDCs.
TB was one of the principal causes of death among the urban poor in the nineteenth century during the Industrial Revolution.
Improved travel. A pandemic is a disease that occurs over a wide geographic area and affects an exceptionally high proportion of the population.
Several dozen “new” infectious diseases have emerged over the past three decades and have spread through travel.
The Bio. Diaspora Project, based at St. Michael’s hospital in Toronto, matched the global diffusion of H1N1 to airline travel patterns.
AIDS
The most lethal epidemic in recent years has been AIDS (acquired immunodeficiency syndrome).
The impact of AIDS has been felt most strongly in sub-Saharan Africa.
CDRs In many sub-Saharan African countries rose sharply during the 1990s as a result of AIDS, from the mid-teens to the low twenties.