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. Learning Objectives Explain how population growth is calculated.
Key Takeaways Key Points Demography is the statistical study of human populations. Population change depends on the rate of natural increase and net migration.
Natural increase is calculated by the fertility rate minus the mortality rate. Net migration depends on in-migration and out-migration. Key Terms Natural increase : Population growth that depends on the fertility rate and the mortality rate. Net migration : The difference of immigrants and emigrants of an area in a period of time, divided usually per 1, inhabitants considered on midterm population.
A positive value represents more people entering the country than leaving it, while a negative value mean more people leaving than entering it. Problems in Forecasting Population Growth Population growth is difficult to predict because unforeseen events can alter birth rates, death rates, migration, or resource limitations. Learning Objectives Explain the various ways sociologist try to estimate the rate of population growth, such as through fertility, birth and death rates.
Key Takeaways Key Points Population forecasts try to estimate the rate of population growth. However, unpredictable factors can change fertility rates, mortality rates, or migration rates, which can cause difficulty in forecasting.
Likewise, some countries are instituting pro-natalist policies to encourage fertility. Malthusian catastrophe refers to a scenario where overpopulation would compromise global food security, leading to mass starvation.
In the future, food production be increased by innovations such as genetically modified crops, more efficiently employing agricultural technology, and aquaculture. This would raise the limit on the number of people the world can support. Key Terms Green Revolution : Green Revolution refers to a series of research, development, and technology transfer initiatives, occurring between the s and the late s, that increased agriculture production around the world, beginning most markedly in the late s Birth rates : The birth rate is typically the rate of births in a population over time.
Vandermeer for a more detailed explanation of the equations that describe exponential and logistic growth. Figure 5: This curve describes logistic growth.
The population size grows exponentially for a while like the bison in Figure 1 , but then it slows down and levels off when as it approaches the carrying capacity K. Logistic growth is commonly observed in nature as well as in the laboratory Figure 6 , but ecologists have observed that the size of many populations fluctuates over time rather than remaining constant as logistic growth predicts.
Fluctuating populations generally exhibit a period of population growth followed a period of population decline, followed by another period of population growth, followed by Figure 6: Logistic growth curves as seen in real populations. Populations growing according to logistic growth are observed in laboratory populations Paramecium and Daphnia as well as in nature fur seals.
In the Daphnia example, it appears that the population size grew to more than individuals and then declined, leveling off at around — individuals. What factors might have caused this pattern? Populations can fluctuate because of seasonal or other regular environmental cycles e. For example, Elton observed that snowshoe hare and lynx populations in Canadian boreal forests fluctuated over time in a fairly regular cycle Figure 7. More importantly, they fluctuated, one after the other, in a predictable way: when the snowshoe hare population increased, the lynx population tended to rise plentiful food for the lynx!
Many populations, over time, exhibit periods of growth and decline. Cyclic changes in population growth can be caused by seasonal, or other environmental changes, or can be driven by density-dependent processes, such as predation, like the snowshoe hare and lynx example depicted here.
It is also possible for populations to decline to extinction if changing conditions cause death rates to exceed birth rates by a large enough margin or for a long enough period of time. Native species are currently declining at unprecedented rates — one important reason why scientists study population ecology. On the other hand, as seen in the YNP bison population, if new habitats or resources are made available, a population that has been declining or relatively stable over a long period of time can experience a new phase of rapid, long-term growth.
Figure 8: Does it surprise you that human population size is growing exponentially? This graph shows the explosion of human population over the last 10, years along with some relevant historical events.
Think about the ways that each of these events might have affected birth and death rates of the human population. Note that the x-axis represents years before the present i. The growth of the global human population shown in Figure 8 appears exponential, but viewing population growth in different geographic regions shows that the human population is not growing the same everywhere. Some countries, particularly those in the developing world, are growing rapidly, but in other countries the human population is growing very slowly, or even contracting Figure 9.
Studying the characteristics of populations experiencing different rates of growth helps provide scientists and demographers with insight into the factors important for predicting future human population growth, but it is a complicated task: in addition to the density dependent and independent factors we discussed for the northern Yellowstone National Park bison and other organisms, human population growth is affected by cultural, economic, and social factors that determine not only how the population grows, but also the potential carrying capacity of the Earth.
Human populations in Kenya are growing exponentially, but human populations in Japan have slowed, and may even be declining. What pattern do you expect for human population growth in the United States?
In China? Dary, D. Chicago, IL: Swallow Press, Elton, C. Periodic fluctuations in the numbers of animals: Their causes and effects. British Journal of Experimental Biology 2, Gates, C. Hornaday, W. Annual Report Washington, DC: Smithsonian Institution, Jones, J. Timing of parturition events in Yellowstone bison Bison bison : Implications for bison conservation and brucellosis transmission risk to cattle. Wildlife Biology 16, Livingston, M. Regulating agricultural imports to keep out foreign pests and disease.
Pearl, R. On the rate of growth of the population of the United States since and its mathematical representation. Plumb, G. Carrying capacity, migration, and dispersal in Yellowstone bison. The increased use of fossil fuels has a negative effect on the health of the environment in terms of air and water pollution. Air pollution from greater coal use and vehicle exhaust has led to acid rain, which is particularly damaging to forests, lakes, and streams.
Rising fossil fuel use also means a greater build-up of carbon dioxide in the atmosphere, higher greenhouse gas emissions, and global warming. The environmental costs of using fossil fuels have led to efforts to decrease their level of use. Alternative energy sources that are more efficient are being sought, such as renewable resources like hydropower and solar power.
Reducing the environmental costs from energy consumption and ensuring there will be an adequate supply of energy for the future involves the careful management of existing and potential resources. The loss of trees due to overcutting of forests. One consequence of deforestation is soil erosion, which results in the loss of protective soil cover and the water-holding capacity of the soil.
The process of grasslands being converted to desert mainly as a result of deforestation, overgrazing, and erosion due to poor land management. A situation that exists when people lack secure access to sufficient amounts of safe and nutritious food for normal growth and development and an active and healthy life.
Food insecurity may be chronic, seasonal, or transitory. A group of primary energy sources created from the incomplete biological decomposition of dead organic matter. The fossil fuels include oil, coal, and natural gas and account for about 90 percent of all the energy consumed in the world. The surface water runoff from local precipitation, the inflow from other regions, and the groundwater recharge that replenishes aquifers.
The rate of natural increase is the difference between birth and death rates. It measures the degree to which a population is growing. Since birth and death rates are measured as the number of births or deaths occurring per 1, population, the difference is divided by 10 to convert this rate into a percentage. World population will stop growing when the birth rate equals the death rate; no one knows whether this will happen.
The birth rate and the death rate would eventually reach equilibrium several decades after couples average two children each. This two-child average is called replacement level fertility, because each couple simply replaces themselves, not increasing the size of each generation.
The total fertility rate TFR refers to the average number of children women are having. When the total fertility rate is at replacement 2. The replacement level TFR is 2. When might it be possible for world population growth to come to an end? The United Nations has projected that growth could end in the latter part of this century if the use of family planning were essentially universal and couples limited themselves to fewer than two children.
Under such a scenario, world population would be about 9 billion by the end of the century and in slow decline. There is certainly no guarantee that this will happen. If couples average more than 2. We do know that world population growth is inevitable in the near term. 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.
It is 1. An astounding growth rate, even though the net reproductive rate is actually quite small. But growth is not evenly distributed around the world. Certain countries are growing faster than others, while some are actually losing growth deaths and emigration exceed births plus immigration - Albania is an example.
Remember, only two things affect population growth: births and deaths. So, have these changed? Liberia 3. Canada 0. Mexico 1. England 0. For example, if the world growth rate is 1.
When I was born, the population was about 2 Billion in It is now 50 years later, and the population is 6. That is nearly a tripling!! The world population growth rate was much higher in the past 50 years than it currently is.
If you have more young people, then you have more opportunity to make babies!! Developing countries have more young people than developed ones. In developed countries, couples wait longer to have babies, and, they tend to have fewer per couple.
In undeveloped countries, children are produced sooner, and couples have larger families than in developed countries. There are two simple ways to lower population growth: increase the number of deaths, or, decrease the number of births. I think for most of us, we would opt for the latter solution. How to do that?
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