But there is a wide range of possible world population scenarios. Three plausible projections published by the United Nations in lead to outcomes ranging from 7. The average number of children a women would have assuming that current age-specific birth rates remain constant throughout her childbearing years usually considered to be ages 15 to Population change affects all our lives in a much more immediate way today than it has throughout most of human history.
For the first one-half million years of human existence, the population growth rate was about zero. The population stayed about the same size from year to year.
It was not until the s that the modern era of population growth began. Between and , the annual growth rate reached 0. The rate surged to 2. Why has world population grown at such different rates throughout history?
Population change results from the interaction of three variables: births, deaths, and migration. This relationship is summarized by a formula known as the balancing equation. The difference between births and deaths in a population produces the natural increase or decrease of a population. Net migration is the difference between the number of persons entering a geographic area immigrants and those leaving emigrants.
Natural increase usually accounts for the greatest amount of growth in a population, especially within a short period of time. For the world, growth occurs only when there are more births than deaths; for individual countries, migration is also a factor. Human population grew rapidly during the Industrial Revolution, not because the birth rate increased, but because the death rate began to fall.
This mortality revolution began in the s in Europe and spread to North America by the mids. Death rates fell as new farming and transportation technology expanded the food supply and lessened the danger of famine.
New technologies and increasing industrialization improved public health and living standards. Late in the 19th century, birth rates also began to fall in Europe and North America, slowing the population growth that had resulted from continued moderately higher birth rates than death rates. Since , both birth and death rates in the more developed countries have continued to fall in tandem, with a few interruptions. A worldwide influenza pandemic in caused the death of between 20 million and 40 million people and produced a temporary increase in the death rate.
Since the s, birth rates have continued their decline, while death rates declined into the s but have been slowly increasing since. In some European countries, declining birth rates and an increase in death rates are contributing to declining population size. The total fertility rate TFR in many more-developed countries is well below replacement levels of two children per couple. Demographers have attempted to explain the experience of these more developed countries as a demographic transition from high birth rates and death rates to the current low levels.
This process tends to occur in three stages. First, birth and death rates are both high, so little growth occurs. Second, death rates fall due to improved living conditions, while birth rates remain high. During this period population grows rapidly.
The third stage of the transition is reached when fertility falls and closes the gap between birth and death rates, resulting again in a slower pace of population growth.
All the more developed countries have entered this third stage of the demographic transition, and some have gone on to a fourth stage in which death rates are higher than birth rates, and the population declines. In contrast to the more developed countries, the less developed countries—in Asia, Africa, and Latin America—had both higher birth and death rates in the s than Europe and North America had in the s, and these higher rates have continued throughout the 20th century.
In most less developed countries, the mortality revolution did not begin in earnest until after World War II, and it followed a different pattern than that in European countries. Birth and death rates were higher at the start of the demographic transition than they had been in Europe or North America.
Death rates fell rapidly in less developed countries through the introduction of medical and public health technology; antibiotics and immunization reduced deaths from infectious diseases; and insecticides helped control malaria. In the second stage of the demographic transition of these regions, mortality declines led to continued population growth. With declining mortality and high fertility rates, the population growth of the less developed countries achieved an unparalleled 2.
Overall, mortality rates in the less developed countries fell much faster than during the demographic transition in the more developed countries. As a result, there was a large gap in the percentage of growth between these two regions.
Since , birth rates have fallen in less developed countries, but the death rate has fallen faster. The population growth rate is still high, about 1. While the patterns of fertility decline have varied dramatically throughout the less developed world, many countries are well into the transition process. Even in sub-Saharan Africa, where birth rates remained high through much of the s and s, fertility rates in most countries are declining.
But we can make educated guesses by looking at past and present trends in two of the components of population growth: births and deaths. The third component, migration, can affect the growth of individual countries, but not world population. World population is projected to increase to 8 billion by and to reach 9. The population of these regions would almost double by according to moderate projections. In , close to 90 percent of world population could live in countries currently considered less developed, compared with about 80 percent today.
The historical shift of birth and death rates from high to low levels in a population. The decline of mortality usually precedes the decline in fertility, thus producing rapid population growth during the transition period. The process of entering one country from another to take up permanent or semipermanent residence. The birth rate minus the death rate, implying the annual rate of population growth without regard for migration.
Expressed as a percentage. The high degree of HIV prevalence worldwide has had an impact on population growth rates. In fact, many believed that AIDS would have little or no impact on population growth. At that time, it was difficult to predict or imagine that there would be any country with 25 percent of the population between the ages of 15 to 49 living with HIV.
The plague, or Black Death, killed an estimated 25 million to 35 million people in Europe alone, a number that represented approximately one-third of its population. In some regions, the impact of AIDS has been more pronounced.
In nine countries in Africa, at least one out of every 10 adults is HIV positive. For some countries, the AIDS epidemic has nearly erased improvements in life expectancy achieved in the last 20 years.
In southern Africa, one of the worst affected regions, life expectancy has declined from 61 to 49 years over the last two decades. The most direct impact has been the increase in the overall number of deaths. Mortality patterns of adults are much higher than they would have been if AIDS were not so prevalent.
Additionally, infant and child mortality rates in some countries are higher than they would have been in the absence of AIDS. As AIDS reshapes the distribution of deaths by age, it is affecting the population composition of many places.
Between and , deaths in eastern Africa were concentrated among young children and older adults, while adults ages 20 to 49 accounted for a smaller share of deaths: 16 percent. However, by the year , it is expected that deaths among adults ages 20 to 49 will double, accounting for almost 30 percent of AIDS deaths. Deaths of large numbers of women in their reproductive years and the lower survival prospects of infected children will also reduce the size of the younger population.
The new age and sex structure for some populations will result in lower growth rates. Still, the overall population size of affected countries is projected to increase due to relatively high fertility levels. Additionally, deaths from HIV have seen a decline in recent years due to the scale-up of antiretroviral treatment.
The greatest impact of the epidemic on population growth is that the rate of growth is now slower. Information on age-sex composition is essential for the description and analysis of many types of demographic data.
The average number of years a newborn infant can expect to live under current mortality levels. Declining mortality, not rising fertility, has been the cause of the accelerating pace of world population growth. By attacking the causes of death that have kept population growth low for most of human existence, we have extended life expectancies and multiplied our numbers.
Life expectancy has increased steadily through history. During the Roman Empire, average life expectancy at birth was a brief 22 years. By the Middle Ages it had risen to about 33 years in England, and increased to 43 years by the middle of the 19th century. In the early s, life expectancies in more developed countries ranged from 35 to They have climbed to about 77 years today, and continue to improve. Meanwhile, life expectancy in less developed countries has gradually climbed, rising to about 65 years today.
Initial declines in mortality can be attributed to improvements in public health and living standards that accompanied the Industrial Revolution. Greater declines in the early 20th century were attributable to improvements in medical technology, which led to the control of such infectious diseases as smallpox and cholera.
Further improvements in life expectancy are anticipated in most countries. In countries where death from infectious diseases is minimal, the improvements will come from the decline in mortality from degenerative diseases such as heart disease and cancer. However, in some countries, the spread of AIDS and other infectious ailments is a potential threat to further gains in life expectancy. In parts of Africa, where the spread of HIV infection is disproportionately high, life expectancy has been declining.
It shows the major causes of death for the United States in and , and for Peru in Each column accounts for all causes of death with the top causes specified. Some causes are combined because of their similarities. Data on cause of death should be interpreted cautiously because some causes are more easily identified than others and are reported more completely.
In the United States in , pneumonia and influenza, tuberculosis, and diarrhea accounted for almost one-third of all deaths. Since then, mortality rates from these diseases have declined sharply. For example, pneumonia and influenza, which accounted for 12 percent of deaths in in the United States, accounted for 3percent in Heart disease and cancer, which account for half of all deaths today, caused only about 12 percent of deaths in In Peru today, the causes of death are broadly dispersed.
About half are attributable to the top four causes: cancer, respiratory infections, heart disease, and accidents. As Peru and other countries continue to develop, their causes of death may more closely resemble those of the United States today.
As life expectancy improves and the role of infectious, parasitic, and respiratory infections further diminishes, more people will survive to older ages and chronic degenerative diseases such as stroke, cancer, and heart disease will make up a larger proportion of deaths. In less developed countries, the chances of dying are greatest at infancy and remain high during the first few years of childhood.
A newborn child is fragile and has not developed immunities to common ailments. When a country has a high rate of infant death, it usually signals high mortality risk from infectious, parasitic, communicable, and other diseases associated with poor sanitary conditions and undernutrition.
Worldwide, over 10 million children die annually before their fifth birthday. Neonatal causes include deaths from tetanus, severe infections, and premature births. Following neonatal causes, two of the primary causes of infant and child deaths are acute respiratory infections such as pneumonia and diarrhea.
Other infectious diseases, such as malaria and measles, are also major causes of deaths to infants and children. Death from these conditions is almost unheard of for infants in more developed countries. However, in less developed countries where undernutrition is prevalent, medical facilities are scarce, and living areas may be unsanitary, infant deaths are common.
In , world IMRs ranged from 2. Many countries have even lower rates, with Iceland, Singapore, Japan, and Sweden heading the list. How has the proportion of Asian immigrants changed during the 20th century?
The proportion of Latin Americans? World population grows as a result of births and declines as a result of deaths. Net migration is the difference between the number of people entering a geographic area immigrants and those leaving emigrants.
Over time, migration contributes more than just the initial number of people moving into an area, because the children and grandchildren born to the immigrant population add several times the original number to the population base.
There is also an increase in the number of deaths as a result of in-migration. Most Americans are immigrants or descendants of immigrants who arrived here over the past years.
Only a small fraction of the population is related to the American Indians who were here when the first European settlers arrived in the s. Australia and Brazil are other countries whose current populations consist primarily of descendants of persons who immigrated there during the past two centuries. In absolute numbers, international migration is at an all-time high. About million people lived outside their native countries in the mids, and that number increased to roughly million in The Middle East draws migrants from Africa and Asia and hosts millions of refugees from within the region.
There is considerable migration within Asia, Africa, and Latin America. Most people move for economic reasons, but some migrate to escape political or religious persecution or simply to fulfill a personal dream. Some experts divide the many reasons people leave their homes for a new one into push and pull factors. Push factors might be widespread unemployment, lack of farmland, famine, or war at home. The Great Depression — is a good example of a push factor, as hard times encouraged more residents to leave the United States than move in.
In the s and s, hundreds of thousands of Africans were pushed out of their homelands to neighboring countries because of famine and civil war. Factors that attract migrants are called pull factors. These include a booming economy, favorable immigration laws, or free agricultural land in the area to which the migrant is moving.
For example, the labor shortage in Japan is pulling record numbers of legal and illegal immigrants to fill the low-status, low-paying, or dangerous jobs that Japanese natives reject. In order to keep a working population that can support its elderly, Japan would need 17 million new immigrants by , according to a recent United Nations report.
Other estimates have said Japan would need , new immigrants each year; however the idea of increased immigration is not favorable to most Japanese. The majority of migrants to the United States in the past years were European. By mid-century, just half of the migrants were from Europe. The total number of immigrants fell to around 1 million in the s.
In the s the number of migrants increased to levels similar to those at the turn of the century. But 84 percent of these migrants were from Latin America and Asia, and just 10 percent were from Europe. The volume of legal immigration and the prevalence of migrants from Asia and Latin America will continue in the new century. The origins of immigrants change over time, as do their numbers and the effect that they have on U.
According to one estimate, about 42 percent of the U. Immigration was an even greater factor in growth between and , when 20 million people entered the country. Natural increase added an average of 1 percent of the population increase per year during that period. At that rate the population would have doubled in about 70 years, but it took only 50 years to double.
Many immigrants have children once they arrive in the United States, creating further momentum for population growth. Currently, fertility rates of immigrants are higher than those of the U. The volume of legal migration has fluctuated since the s. Immigration has accounted for an increasing portion of population growth as American women began having fewer children.
If current patterns continue, the population of the United States could rise to million in , from million in According to a recent report by the Pew Research Center, 82 percent of U.
Of the three components of population change, migration is the most difficult component to predict and is most affected by government policies.
Because nations can control their borders, they may regulate the flow of legal immigrants. The oil-producing countries in the Middle East offered financial incentives to attract immigrants, just as the United States and Australia once offered free land.
In , Japan permitted employment rights and residence for ethnic Japanese from Latin America. An estimated 12 million were unauthorized. A migration theory that suggests that circumstances at the place of origin such as poverty and unemployment repel or push people out of that place to other places that exert a positive attraction or pull such as a high standard of living or job opportunities.
How does this compare to population growth in more developed countries? For the last 50 years, world population multiplied more rapidly than ever before, and more rapidly than it is projected to grow in the future. In , the world had 2. Anthropologists believe the human species dates back at least 3 million years. For most of our history, these distant ancestors lived a precarious existence as hunters and gatherers. This way of life kept their total numbers small, probably less than 10 million.
However, as agriculture was introduced, communities evolved that could support more people. World population expanded to about million by A. But after the start of the Industrial Revolution in the 18th century, living standards rose and widespread famines and epidemics diminished in some regions. Population growth accelerated. The population climbed to about million in and reached 1 billion around Since rates of population growth are currently highest in the less developed regions , their share of world population will increase.
Over time, the distribution of population changes because of variations in the rate of natural increase and net migration. In the United States between 60 percent and 70 percent of annual population growth is from natural increase and the rest is driven by international migration. Rural-to-urban migration, combined with natural increase, is leading to a disproportionate increase in urban population, especially in less developed countries.
By , the urban share had risen to 29 percent, and today it is 49 percent. Urban areas are getting larger. In , only the Tokyo and New York urban areas had over 10 million people. By , there could be more than 25 urban areas with over 10 million people.
Eight of these urban areas would hold over 20 million people each. Percentage of the total population living in areas termed urban by that country. Typically, the population living in towns of 2, or more or in national and provincial capitals is classified as urban. Some of this growth spilled over to the Americas, increasing their share of the world total.
World population growth accelerated after World War II, when the population of less developed countries began to increase dramatically. After millions of years of extremely slow growth, the human population indeed grew explosively, doubling again and again; a billion people were added between and ; another billion were added between and Throughout the 20th century each additional billion has been achieved in a shorter period of time. Human population entered the 20th century with 1.
The growth of the last years appears explosive on the historical timeline. The overall effects of this growth on living standards, resource use, and the environment will continue to change the world landscape long after. As long ago as , Thomas Malthus studied the nature of population growth in Europe. He claimed that population was increasing faster than food production, and he feared eventual global starvation.
Of course he could not foresee how modern technology would expand food production, but his observations about how populations increase were important. Population grows geometrically 1, 2, 4, 8 … , rather than arithmetically 1, 2, 3, 4 … , which is why the numbers can increase so quickly.
A story said to have originated in Persia offers a classic example of exponential growth. It tells of a clever courtier who presented a beautiful chess set to his king and in return asked only that the king give him one grain of rice for the first square, two grains, or double the amount, for the second square, four grains or double again for the third, and so forth.
The king, not being mathematically inclined, agreed and ordered the rice to be brought from storage. The eighth square required grains, the 12th took more than one pound. Long before reaching the 64th square, every grain of rice in the kingdom had been used. Even today, the total world rice production would not be enough to meet the amount required for the final square of the chessboard.
The secret to understanding the arithmetic is that the rate of growth doubling for each square applies to an ever-expanding amount of rice, so the number of grains added with each doubling goes up, even though the rate of growth is constant. At a 3 percent growth rate, its doubling time — or the number of years to double in size — is 23 years. The growth rate of 1. On a global scale, however, food production has grown faster than population due to transformational advances in agricultural technology.
Overpopulated Urban Slums : Malthusians would cite epidemics and starvation in overpopulated urban slums, like this one in Cairo, as natural checks on growing populations that have exceeded the carrying capacities of their local environments. Demographic transition theory outlines five stages of change in birth and death rates to predict the growth of populations. Whether you believe that we are headed for environmental disaster and the end of human existence as we know it, or you think people will always adapt to changing circumstances, we can see clear patterns in population growth.
Societies develop along a predictable continuum as they evolve from unindustrialized to postindustrial. Demographic transition theory Caldwell and Caldwell suggests that future population growth will develop along a predictable four- or five-stage model. In stage one, pre-industrial society, death rates and birth rates are high and roughly in balance. An example of this stage is the United States in the s.
All human populations are believed to have had this balance until the late 18th century, when this balance ended in Western Europe. In fact, growth rates were less than 0. 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.
In stage two, that of a developing country, the death rates drop rapidly due to improvements in food supply and sanitation, which increase life spans and reduce disease. Afghanistan is currently in this stage. The improvements specific to food supply typically include selective breeding and crop rotation and farming techniques. Other improvements generally include access to technology, basic healthcare, and education. For example, numerous improvements in public health reduce mortality, especially childhood mortality.
Prior to the midth century, these improvements in public health were primarily in the areas of food handling, water supply, sewage, and personal hygiene. Another variable often cited is the increase in female literacy combined with public health education programs which emerged in the late 19th and early 20th centuries. 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 years.
Without a corresponding fall in birth rates this produces an imbalance, and the countries in this stage experience a large increase in population. In stage three, birth rates fall. Population growth begins to level off. The birth rate decline in developed countries started in the late 19th century in northern Europe. While improvements in contraception do play a role in birth rate decline, it should be noted that 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.
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. During 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 shrinking population, a threat to many industries that rely on population growth. Sweden is considered to currently be in Stage 4. 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 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. Some scholars delineate a separate fifth stage of below-replacement fertility levels. Others hypothesize a different stage five involving an increase in fertility.
The United Nations Population Fund categorizes nations as high-fertility, intermediate-fertility, or low-fertility. The United Nations UN anticipates the population growth will triple between and in high-fertility countries, which are currently concentrated in sub-Saharan Africa. For countries with intermediate fertility rates the United States, India, and Mexico all fall into this category , growth is expected to be about 26 percent.
And low-fertility countries like China, Australia, and most of Europe will actually see population declines of approximately 20 percent.
As with all models, this is an idealized 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. The extent to which it applies to less-developed societies today remains to be seen.
Some countries, particularly African countries, appear to be stalled in the second stage due to stagnant development and the effect of AIDS. Privacy Policy. Skip to main content. Population and Urbanization. Search for:. Population Growth. Implications of Different Rates of Growth Different rates of growth can lead to overpopulation or underpopulation, both of which have potential consequences.
Learning Objectives Discuss the implications both overpopulation and underpopulation can have for society. Key Takeaways Key Points When the fertility rate is at the replacement level, a population will remain stable, neither growing nor shrinking. Overpopulation is judged relative to carrying capacity and can have deleterious effects. When the population is too large for the available resources, famine, energy shortages, war, and disease can result.
Recently, in some countries, sub-replacement fertility rates have led to underpopulation. This can lead to economic decline, the aging of the population, and poverty. Key Terms fertility rate : The average number of children that would be born to a woman over her lifetime if she followed the current average pattern of fertility among a given group of women and survived through her reproductive years; used as an indicator of strength of population growth.
Replacement level : Regarding fertility, refers to the number of children that a woman must have in order to replace the existing population. Three Demographic Variables The basics of demographic population growth depend on the rate of natural increase births versus deaths and net migration. The main causes of a change in population size. Topic Home. Population Policies. Population and Settlement.
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