PG4. The History of Human Population Growth


All living things have evolved with the capacity to reproduce at very high rates. What would happen if this were not so? What if a maple tree produced only one seed in a year? What are the chances that a single seed would find a hospitable patch of ground to land on and be able to take root and prosper? 

Rabbit drawing

What would happen to the population of rabbits, given the appetite of foxes, if only one baby rabbit was born each year? For any species where the reproductive rate cannot increase their number despite the ravages of the environment, extinction is inevitable. Nature has left alive only those species that reproduce enough to maintain or increase their numbers.

Remember what Darwin stated in his tenets: “populations tend to produce more offspring than can be supported by the environment, and only the fittest are selected to survive.” Human beings survived because they are part of the tendency of nature to select species that increase through multiple reproduction. Some human families have as many as fifteen children. 

The Book of Genesis in the King James Version of the Bible, which has had a profound effect on human history, especially in the west, exhorts its followers in the following verses: 

“And God blessed them, and God said unto them, be fruitful, and multiply, and replenish the earth, and subdue it: and have dominion over the fish of the sea, and over the fowl of the air, and over every living thing that moveth upon the earth. ” (001:028) 

After the great flood, Noah was told in verse 8 to: 

“Bring forth with thee every living thing that is with thee, of all flesh, both of fowl, and of cattle, and of every creeping thing that creepeth upon the earth; that they may breed abundantly in the earth, and be fruitful, and multiply upon the earth” (008:016)

Question 4.1
Have human beings followed these commands? If so, is it a good thing that they have? If not, should they have? Discuss your opinion with your classmates.

I. Population Surges in Earth History

We are living through a very special period in Earth’s history. In no other time in the 4.5 billion year history of our planet has one species inhabited all the regions of the Earth and made use of so much of the Earth’s resources. How did a few hundred thousand individuals whose ancestors lived in the trees and who survived by gathering fruits, nuts and berries, and perhaps even scavenging the bodies of dead animals, become the billions that populate the Earth today? 

It is only in the past two hundred years that population estimates have been available, and these are only estimates. Therefore, very little data is available regarding the ancient history of world human population. 

Even fixing a time when the human race actually came into existence is still hotly debated among scientists.

human skulls
Photo By Eloise Farmer.

Hominids walked the earth as early as several million years ago. 

Various ancestors of Homo sapiens seem to have appeared at least as early as 700,000 B.C. On average, our most recent hominid ancestors, Homo sapiens, are believed to have appeared about 200,000 to 100,000 years ago and migrated from Africa to Europe. According to the United Nations’ Determinants and Consequences of Population Trends, modern Homo sapiens may have appeared about 50,000 B.C. 

So human population growth may have started about a million years ago. It seems to have occurred in three surges that are related to the use of human brains and hands. 

Population Surge 1: Fire and Tools

The first surge in human population came as a result of increased ability to hunt—sharpened sticks, the bow and arrow, spears, stone knives and tools, together with the ability to communicate and cooperate, aided survival. The use of fire as protection against wild animals and the environment enabled our ancestors to increase their numbers. 

Realistic estimates of past population size depend on a review of the way people led their lives at the time and by figuring out how many people could be supported by various life styles. When humans lived in tribes with a nomadic lifestyle where they constantly followed the seasons and the game by moving from place to place, very few people could be supported, and the human population grew very slowly. 

Population Surge 2: Agriculture

The second surge in human population started with the dawn of agriculture, about 8,000 B.C., when the population of the world was somewhere on the order of 5 million—less than the population of New York City. The benefit of stone-age inventions gradually enabled human populations to expand. The initiation of agriculture and the domestication of animals kept the food supply in a local area, allowing humans to settle down and obtain more food by growing plants and taming animals than they could by searching for and chasing after their food. Humans could build villages and they had to protect their crops from marauding groups of those who were still nomadic. 

By 1 A.D., the world may have held about 300 million people. By 1650, world population rose to about 500 million, not a large increase over the 1 A.D. estimate. One reason for this slow growth was the Black Plague. This horrible disease which peaked in 14th century Europe may actually have begun about 542 A.D. in Western Asia and spread from there. As much as half the Byzantine Empire was destroyed in the 6th century, a total of 100 million deaths. Despite the decimation caused by the plague, by 1800 the world population had passed the 1 billion mark.

Population Surge 3: Industrial Revolution

The third surge in human population began with the scientific-industrial revolution, which is still in progress, and is responsible for the great population explosion that is now underway in the world. This accelerated growth in world population began in the eighteenth century and first swept over the countries that we now call “developed.” This population growth is now also affecting the developing nations.

World Human Population YearTime to increase population by 1 billion Percentage rate of increase 
 1 billion1850 (>1 million yrs)  0.05 % / year
 2 billion1930  80 years 1.25% / year
 3 billion1960 30 years 3.33% / year
 4 billion1976 16 years 6.25% / year
 5 billion1987 11 years 9% / year
Graph of world population 1-2000AD
Copyright 2001, Population Reference Bureau.
bar graph of World population in jumps of a billion
Data Source: U.S. Census Bureau

World population has been growing geometrically (or exponentially). 
Such growth, when graphed, yields a “J” shaped curve. 
Numbers double and double again, soon yielding enormous totals. 

The Population Reference Bureau predicts a slowing of the rate of increase in world population, to 

7 billion in 2013 (3.8% per year average increase since 1987),
8 billion in 2028 (6.7% per year), and
9 billion by 2054 (3.8% per year). 

Note that total numbers continue to increase dramatically, despite a decrease in the percentage rate of increase. 

Question 4.3. 
Look back in your book to the bacterial growth curve, and to the graph you made of the armadillo population. How does this graph compare? 

Question 4.4.
During what “age” of human history did the world’s population begin to grow rapidly? 

Question 4.5.
What is the world’s population in 2000? How many people were added to the world population in 2000? 

Research and answer the following questions: The Population Reference Bureau has an excellent web site with this information. Visit

Question 4.6.
Which world regions have the fastest rate of population growth? 

Question 4.7.
In which world region does the greatest share of the world’s population reside? 

Question 4.8.
Brainstorm some possible reasons for the tremendous growth rate of the human population in the past century. Using your brainstormed list, research to find the reasons. 

II. Why Does Human Population Grow?

In the simplest terms, the increase in population is the difference between the birth rate and the death rate. 

Birth Rate and Family Size

For much of human history having many children in a family was desirable. On a pre-industrial farm many hands are needed to care for the crops and tend the animals. Successful families were large families. Having many children became part of the growth psychology that has permeated human society for ages. More crops, more herds, more products, increase of every kind seems to be a shield against misfortune. High death rates made having many children a sensible course of action so that some of them would survive to help the family or support the parents in their old age. Trouble begins when old cultural patterns are carried over into times when they are no longer appropriate. 

Even today many people consider large families a blessing and more offspring, especially boys, mean more strength to the family, to the community, and to the nation. In some cultures, children as young as nine are expected to work to help the family, contributing to the family income rather than depleting it (as for developed countries). The more children a family has, the greater their income is. Numerous offspring also prove to be an advantageous strategy for later in life. With no national social security scheme to support the elderly, when the parents become too ill or old to work, their children are expected to support them—this is their only means of support. 

The modern population explosion is not because of an increase in birth rates. In older times the birth rates were much higher than they are now even in the developing nations. Today, a high birth rate would be about 45-50 per 1,000 population per year. This rate is found in only a few countries of Africa and in several Middle Eastern states. In some developed countries the birth rates per woman have been decreasing below the level necessary to replace the number of people who die. But the population in the United States and other industrialized countries continues to rise. 

Question 4.2.
How might the scientific-industrial revolution have produced a population increase with a lower birth rate?

Even though the birth rate per woman is lower, there are more healthy, fertile men and women than in previous decades and the population rise in developed countries continues today. The current population of the United States is expected to increase to 322,000,000 by 2025. A larger starting base will produce a larger number even if the percentage increase is small. Starting with a larger bunch can increase the numbers even if the growth rate is smaller. 

Lack of education is a key cause of high birth rates. Before the details of the human reproductive system were known, pregnancies were a matter of accident. This is still true in many parts of the world. Birth control requires a degree of control and foresight. Educational efforts in birth control are having notable success in many countries. For example, since 1972 the number of children born in Indonesia has fallen from 5.6 to 3.4 children per woman. Throughout the country every afternoon at five o’clock sirens are turned on to remind women to take their birth control pills. But birth control is a sensitive issue among some groups of people because it goes against some strongly held religious beliefs. There will be more about family planning later in this book.

III. Death Rate and Life Expectancy

Population growth depends critically on survival of females to childbearing age. Life was short for early humans, averaging only about 10 years for much of human history. Infant mortality in the human race’s earliest days is thought to have been very high perhaps 500 infant deaths per 1,000 births, or even higher. Children were probably not very useful to the tribes in hunter-gatherer societies, and this may even have led to infanticide, especially of infants who were less than perfect. This would have led to a true “survival of the fittest” group of humans. Birth rate had to have been at least 80 per 1,000 people per year just for the species to survive. 

The average lifetimes of humans increased from 29 years for the hunter-gatherers to 35 years for the bronze-age farmers. That 35-year average life span was the same for the citizens of ancient Greece and Rome and continued into the Middle Ages. Slow growth of population from an estimated 5 million in 8,000 B.C. to 300 million in 1 A.D., is still reflective of a very low growth rate: only 0.0512 percent per year. Human populations in different parts of the world still grew or declined as a result of famines, hunting conditions, tribal war, changing climate, and natural disasters. These were the same limiting factors we discussed earlier in the book as those limiting any population. 

By year 0, the average life expectancy of a woman was just twenty years. Only 30% of the female population lived to child bearing age; the vast majority of mortality was at five years old. If you were born in 1800 you could expect to live about 35 years, and by 1900 the average life span rose to about 50 years. 

The average life expectancy at the outset of the 21st century is 75 years for people in the developed countries. For women, the average life expectancy is 78 years, and 97% of all females born survive to child bearing age. 

No one doubts that, in the industrialized world, the standard of living, in general, is higher today than at any other time in human history. People are living longer and healthier compared to pre-industrial times. The greatest improvement in the human way of life was due to the invention of machines and the discovery of how to provide power for them by the release of chemical energy of fossil fuels. Machine power was substituted for muscle power. This led to increased productivity in agriculture and industry as well as the development of efficient trade and transportation. 

The major cause of human population increase is the recent success in preserving human life. Before the modern era, famine and disease periodically decimated the human population in certain areas. Shorter life spans reduced the number of childbearing women. Today technological innovations, such as food preservation and distribution and medical care keep many people alive who might have otherwise died. The vast rise in our numbers has produced some serious problems for the planet. We are becoming victims of our own success.z

IV. Exceptions to the Trends

While the general trend in the modern world is decreasing death rate, there still remains threat of disease and war. 


Sub-Saharan Africa is ravaged by HIV/AIDS, with more than 23 million adults infected with the disease. An astounding 36 percent of Botswana’s 15- to 49-year-olds live with the disease. In Lesotho, Swaziland, and Zimbabwe, approximately 25 percent of adults in these prime ages have HIV. Namibia, South Africa, and Zambia each have prevalence rates of 20 percent among adults ages 15 to 49. In another nine sub-Saharan African countries, more than 10 percent of adults ages 15 to 49 are infected. South Africa has the highest number of adults living with the virus, at about 4.1 million. Nearly 3 million Ethiopian adults live with HIV. 

Outside of sub-Saharan Africa, the largest numbers of people infected with HIV or living with AIDS are in India at 3.5 million. Globally, 15.7 million adults with AIDS are women and 1.3 million are children below the age of 15.

War and Genocide

Modern societies have not eradicated war and genocide. Most notable in the last century was the Nazi genocidal attempt to eradicate Jews via death camps in World War II. But there are other examples. In 1991 to 1995, Bosnia initiated a policy of “ethnic cleansing,” a practice where the members of a given ethnic group or groups are eliminated, the goal being that the territory would contain only members of a single ethnic group. There the Serbians, mostly associated with the Orthodox Church, attempted to ethnically cleanse their region of non-Serbs, including Croats, who by tradition were Catholics, and the Muslim Bosnians. There was also some ethnic cleansing attempted by Croats against Bosnian Muslims and vice versa, but the Serbs practised ethnic cleansing in a systematic manner. 

Genocide in Africa occurred in the countries of Rwanda and Burundi. In Burundi, 1973–1974, the government, run by the minority Tutsi tribe, tried to eliminate, in a chilling and systematic way, the entire elite class of the Hutu people—all those with some education, government jobs, or money. The death toll was perhaps one hundred thousand, perhaps as great as two hundred thousand


Over the next twenty years, the cycle of violence and counter-violence in Rwanda and neighboring Burundi resulted in the killing of between 300,000 and 600,000 people. Then in spring of 1994, carnage and violence happened on a massive scale in Rwanda. An organized campaign of violence, executions, and massacres was carried out, during which the Tutsi were referred to as “cockroaches” and “the enemy,” and Rwandan radio broadcasters exhorted every Hutu to kill Tutsi, complaining that “graves are still only half full.” In less than four months, between 500,000 and a million people were killed. Before 1994, Rwanda was the most densely populated country in continental Africa. Between April and August 1994, that statistic shifted radically, as Rwanda lost 20 percent to 40 percent of its population to slaughter or exile. 


Population Decline in Europe

While in most regions of the world population growth rate is decreasing, there is still population growth, just at a somewhat slower rate. But some European populations are experiencing more deaths than births annually, a phenomenon that is not occurring in any other world region. Ukraine and Russia have the largest gaps between birth rates and death rates. The population of Ukraine is losing about 340,000 people each year from having more deaths than births and the population of Russia is losing 950,000 people. In the absence of offsetting international migration, the population of these countries will decline in size. In addition to very low birth rates, a chief cause for surplus European deaths is the relatively high proportion of the region’s population in the older ages where death rates are higher. Fifteen percent of Europe’s population is age 65 or older, compared with 7 percent for the world. 

The Transition from Rural to Industrialized Society

Keeping in mind that the increase in population is the difference between the birth rate and the death rate, compare the beginning, middle, and end of the period shown on the graph. How fast is the population growing as each stage? How does the size of the population at the end of the curve compare with the size at the beginning? 

Graph of birth rate & death rate in the transition for rural to industrialized society
(From the World Resources 1994-1995 Guide to the Global Environment.)

The curves in the graph on this page are about life and death. Recent history of human population growth has shown similarities as countries move from rural agrarian cultures to industrial societies. 

The curves represent what is called the demographic transition that usually accompanies the modernization of nations. Before industrial development the birth rate is high and steady (the top line). The death rate is also high and it varies within high limits. As the country modernizes, modern health practices and increased food production reduce the death rate. For a while the birth rate stays high, but as time goes on and people recognize that all of their children are likely to survive, the birth rate declines and then fluctuates within lower limits. The reduced death rate remains fairly constant. 

This demographic transition began in Europe and in the U.S. late in the eighteenth century and early in the nineteenth. It is now complete in the developed countries. In the developing countries it began later and in some of them it is now underway. Therefore in much of the world only the death rates have been reduced and the birth rates remain high. The result is an explosive growth in population in the less developed countries of the world.

Population Growth in Less-Developed Countries

Most of the world’s population growth continues to occur in less developed countries. World population increases by about 83 million annually—99 percent of this increase occurs in the less developed countries of Africa, Asia, Latin America and the Caribbean, and Oceania. According to current population projections, only three of the more developed countrqies, the United States, Russia, and Japan, are expected to remain among the world’s most populous by 2025. The United States is expected to remain in third place, but Russia will drop from seventh to ninth, Japan will drop from ninth to eleventh, and Germany will no longer be in the top fifteen.

World's largest countries in 2001
For latest population data, check Population Reference Bureau’s World Population Data Sheet at

See also

V. The Malthusian Hypothesis

Why are there so many people around? That question was first systematically addressed by an English clergyman in 1798.

Thomas Malthus
Thomas Malthus

Thomas Malthus’ An Essay on the Principle of Population began a discussion that continues today. Malthus’ name is often brought up in discussions about population growth. People who predict that human starvation is around the corner as well as those who believe that living conditions will get better, not worse, begin with Malthus’ ideas. Malthus himself felt that the increase in human population would end in famine and misery for all. His reasons are stated in his own words. 

The following are excerpts from “An Essay on the Principle of Population” by Thomas Malthus written in 1798.

“I have read some of the speculations on the perfectibility of man and of society with great pleasure. I have been warmed and delighted with the enchanting picture which they hold forth. I ardently wish for such happy improvements. But I see great, and, to my understanding, unconquerable difficulties in the way to them… 

“I think I may fairly make two postulata. 

“First, That food is necessary to the existence of man. 

“Secondly, that the passion between the sexes is necessary and will remain nearly in its present state. 

“These two laws, ever since we have had any knowledge of mankind, appear to have been fixed laws of our nature, and … we have no right to conclude that they will ever cease to be what they are now… 

“I say that the power of population is infinitely greater than the power in the earth to produce subsistence [food] for man. 

“Population, when unchecked, increases in a geometrical ratio. Subsistence increases only in an arithmetical ratio… 

“In the United States, where the means of subsistence have been more than ample,… the population has been found to double itself in twenty-five years. 

This ratio of increase, we will take as our rule, and say, that population, when unchecked, goes on doubling itself every twenty five years or increases in a geometrical ratio. 

Let us now take any spot on earth, this Island [England] for instance… if I allow the produce of this Island to be doubled in the first twenty five years I think it will be allowing as much as any person can well demand … 

In the next twenty-five years, it is impossible to suppose that the produce could be quadrupled… The very utmost that we can conceive, is, that the increase in produce in the next twenty-five years might equal the previous increase. 

“By great exertion the whole produce of the Island might be increased each twenty-five years [by similar amounts.] This ratio of increase is evidently arithmetical… 

“Let us take the whole earth, instead of one spot, and suppose that the restraints to population were universally removed… Taking the population of the world at any number, a thousand millions, for instance, the human species would increase in the ratio of: 1, 2, 4, 8, 16, 32, 64, 128, 256, 512, etc. and subsistence as: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, etc. 

“The power of population is so superior to the power in the earth to produce subsistence for man, that premature death must in some shape or other visit the human race… Gigantic inevitable famine stalks in the rear, and with one mighty blow, levels the population with the food of the world.” 

Was Malthus Right?

In the early 1800s, the years that followed the publication of Malthus’ essay, England experienced both a period of population growth and a general increase in the health of its people. There was no shortage of food. For the remaining thirty-six years of his life Malthus witnessed a population and prosperity increase that was in opposition to his expectations. Although many scoffed at his ideas, Malthus never abandoned his theory. 

What Malthus did not know, because he was living through it, was that England was moving through an unusual period in its history. The agricultural and industrial revolutions were in full swing. New methods and tools were appearing on the farms and the food supply was increasing. At the same time new inventions, like the steam engine and cloth manufacturing machinery, were opening new opportunities for jobs. As people moved from the farms to the cities they often found their living conditions improved. 

Today, as industrialization spreads to the developing countries, will the living conditions of people continue to improve? Or was Malthus right in believing that the world is headed for catastrophic famine? 

Charles Darwin read what Malthus had written, and adopted some of his ideas when writing his tenets. Do you see a relationship between Malthus’ writings and Darwin’s tenets? Go back and look at Darwin’s tenets (p. 26) to help you answer this question. 

Question 4.9. 
What must happen to prevent Malthus gloomy predictions from coming true? 

Question 4.10. 
What factors worked to show that Malthus’ idea was untrue during his lifetime? 

Question 4.11.  
What factors today would support Malthus’ hypothesis? 

Question 4.12.  
What factors today would refute Malthus’ hypothesis?


PG4.1. Investigation: What Do You Think About Malthus’ Argument?

After the investigations you have done in earlier sections of this book, what do you think about the prophecies of Thomas Malthus? Malthus believed that the mathematics of growth is of great importance if we are to avoid needless human suffering. On the other hand, many people believe Malthus was wrong, and that people will overcome any limitations to population growth through new methods of farming or other new technologies. What is your opinion? Decide whether or not you agree with what he has written and be prepared to defend your opinion.

VI. Doubling Times

Malthus brought up the subject of doubling time of population growth. This is a much-used way of comparing the rate of growth of populations in different countries and at different times. For example, between A.D. 1 and 1750 the world population doubled every 1200 years. At present the present rate of growth the world population will double in 41 years. That is, if the growth rate continues the way things are going now. When you are in your late 50’s the world will have twice as many people as it does now. 

The Value of “Doubling Time”

The doubling time of a population is simply the number of years it would take for a population to double in size if the present rate of growth remained unchanged. Used for many years, its primary purpose has been to emphasize just how quickly populations can grow, doubling their numbers geometrically. 

Graph of doubling time
If a country’s population continues to grow at a constant rate of 2%, it will double in size every 35 years. [70÷2=35.]

If a country’s population continues to grow at a constant rate of 2%, it will double in size every 35 years. [70÷2=35.]

The power of a growth rate such as 3 percent (giving a doubling time of only 23 years) can be dramatically illustrated. In addition, it serves to remind us that populations do double in size if their growth rates remain constant. Thus, a population of 20 million could grow to 40 million, then 80 million, then 160 million, and so on, until the growth curve becomes near vertical. In part, it may have been this realization that caused so many less developed countries to adopt slow-growth policies that have been met with varying degrees of success. 

Calculation of the doubling time is complicated by the fact that though the growth rate may remain constant, the population is changing year by year. It is like the growth of money in a compound interest savings account in the bank. 

A good approximation to find the doubling time of a population in years or of anything which increases by a certain percent every year is to divide the number 70 by the annual (yearly) growth rate. So, if you have $100 in the bank at 2% interest it will double in about 70/2 = 35 years. In how many years will your money double if the interest rate is 4% or 10%? 

Doubling Time

D = 70 ÷ I

Where D = doubling time and I = % annual increase.


PG4.2. Investigation: Doubling Time

Use the formula to calculate the doubling time for each nation or region shown in the table.

Average annual growth rates for period 1990-1995
United States1.03%
South America1.67%

(Source: The World Resources Institute 1994-1995 Guide to the Global Environment)


PG4.3. Investigation: Too Many People?

“It was a mob scene.” 

“I had to wait in line.” 

“ I was caught in traffic.”

“I don’t have room enough to think!”

“I want to be alone!”

“I got there early but the job was already filled.” 

At one time or another we all feel that we are surrounded by too many people. Although the presence of others is important to us there are times when it is simply too much. Something is lost from the quality of our lives when our fellow human beings press in too closely. Many people occasionally feel the need to be by themselves. The movement to vacation in less populated areas has crowded previously deserted beaches and mountains. 

Using graph paper and two different colors of pencils, make a bar graph showing each of the top 5 nations in population for the year 2001 and the year 2025. Use the data in the chart in the main page. How crowded do you think you will feel by the year 2025?

VII. The Fertility Factor

In order to better understand their subject, demographers, those who study population changes, use a factor called the total fertility factor. This is defined as the average number of children a woman will have during her entire period of reproduction. That period is taken to be between the ages of 15 and 44. There are many economic and social factors that influence the fertility rate. The availability of abortion and contraceptives and their social acceptability are additional factors. 

Fertility Factor in the U.S. 1925-1995.

Graph of fertility factor 1925-1995
Information from: G. Tyler Miller, Jr. Living in the Environment, 4th Ed. World Resources Institute, World Resources, 1994-95.

The relationship between the total fertility factor and population growth rate is not simple, since the growth of population depends not only on how many babies women have, but on how long people live, as well as how many females in the population have reached childbearing age. 

Although a fertility factor of two children per couple would replace their parents, some female children die before reproducing. In addition, a slightly higher number of male than female babies are born. If women in the United States had an average of 2.1 children population would, in theory, be stable. 


PG4.4. Investigation:
Population Growth in the United States

Use the information in the tables on this page to make a graph of the United States population from 1800–2040. 

Calculate and graph the rate of growth for each decade beginning with 1810. The formula for rate of growth is: 

Rate of growth = The (present decade population) minus (previous decade population) divided by 10 Investigation Population Growth in the United States Begin with: (population in 1810 – population in 1800) 10 

Graph the United States rate of growth for each decade using your data. 

Question 4.13. 
Do you get any negative numbers? 

Question 4.14. 
Can the rate decrease even though population increases? Explain your answer. 

Compare the the rest of the world by completing the Table 5B. You may use the graph on the next page to estimate values of world population in the future. Note that the graph is of yearly increase, not actual population numbers.

Table 5A: U.S. Population

Table of U.S. population
(The projections for the United States population are from the United States Bureau of the Census, Current Population Reports, P25-1092)

Table 5B: U.S./World Population

Table of U.S./World Population

VIII. Recent History of Population in the U.S.

Let us take a look at our own nation and see how it compares to the rest of the world in terms of population growth. 

In the early days of our nation, at the very beginning of our demographic change, a large growth in population took place. In addition to those born in the New World, the ranks of settlers were swelled by waves of immigrants. 

In the U.S. today there are approximately 2.6 million more births each year than there are deaths. Additionally, approximately 1 million immigrants are attracted to our shores each year. That makes a total of 3.6 million people each year, or a new city of 70,000 people each week. The U.S. is the world’s fastest-growing industrialized nation. 

Analyzing America’s Population

Age structure graphs, also known as population pyramids, help explain how population changes in time. 

Age structure graphs
Adapted from: U.S. Bureau of Census and Population Reference Bureau

The age structure graphs above show the population structures of 1960, 1980 and 1990. The horizontal bands represent the age groups into which the population is divided. Each band represents five years of aging. The bands are separated by the center line into males (to the left) and females (to the right) in each age group. The width of the bands shows what percent of the total population are males and females in their age groups. 

In the 1960 pyramid, ages birth to 14, that part of the population which had not yet reached reproductive age in 1960, represent the large numbers of children born after World War II, the so-called baby-boom. The two narrow striped bands above the baby-boomers, ages 20 to 29, represent the low numbers of children born during the economic depression of the 1930s. In 1960, these children of the depression were in their reproductive years and are the parents of the baby-boom children. 

In the 1980 and 1990 graphs, the baby boom population bulge moves upward 20 and 30 years. The baby-boom children are now adults in their reproductive years and the width of the gray bands below them represent their children. 

Question 4.15. 
How would you explain the widths of the gray bands near the bottoms of the 1980 and 1990 pyramids? 

Question 4.16. 
In a year 2000 graph what do you expect the width of the bottom two bands would be? They represent the children born from 1991 to 1999. Will they be wider or narrower than the bands above them? 

To see a really cool animated pyramid of U.S. population from 1050 to 2050, go to the following site:

To see the present U.S. population to date, go to: 

Fast Facts About Population Growth

Over four million babies are born each year in the United States. 

The U.S. population is growing by about 2.5 million people each year. Of that, immigration contributes over one million people to the U.S. population annually. 

The U.S. fertility rate is currently 2.0 births per woman, an increase from 1.8 in 1988. 

The United States has one of the highest natural growth rates (0.7%) of any industrialized country in the world. For comparison, the United Kingdom’s natural increase is one quarter the rate of the U.S. at 0.2%, while Germany’s natural increase is 0. 

Using the Census Bureau’s projections, U.S. population will grow to 394 million by 2050. 

Eight states have population growth rates over 2.0%, which means their population will double in less than 35 years. 

Along our coasts, where nearly half the population lives, the U.S. is among the more densely populated countries in the world. The Northeast averages 767 people per square mile, while Haiti, for comparison, has 580. 

By 2010, when California’s population reaches 50 million, population densities in coastal California will reach 1,050 people per square mile. 

46% of the U.S. population lives in coastal regions where ecosystems are the most fragile. 

California, Florida and Texas account for one-quarter of the U.S. population and were responsible for 38% of all U.S. population growth between 1940 and 1990. 

Florida’s population has grown from 1.9 million in 1940 to 15 million today. That is over a 600% increase in just 50 years.

IX. What is Overpopulation?

How shall we define an overpopulated country? Is it one where a large number of its citizens live in poverty and there are vast numbers of unemployed? Or is it where everybody is working very hard, where every tiny parcel of land is devoted to agriculture and the food supply is still insufficient? Or is it a country where the population has exceeded the carrying capacity of its own territory? Or is it all of these?

In the U.S. there is no shortage of food. The supermarket shelves are full. There is a problem with the distribution of available food, however, there is no doubt that some people in our country go hungry. But is it fair to say that the United States is overpopulated? The concept of overpopulation is a fuzzy one. 

Top contributors to world population growth

We might say that a country is overpopulated when the number of people in an area exceed that area’s resource capacity to sustain human activities at a decent standard of living. When the population cannot be maintained without rapidly depleting nonrenewable resources or converting renewable resources into nonrenewable resources quickly enough, measures must be taken either to control the population or increase the area’s resources. 

Examine the graph on this page. You will notice that the two nations that contribute the most to the growth of the world’s population are India and China. 

Both nations have made concerted efforts for many years to slow their rates of population growth. The methods used by these governments, especially the methods used in China, have stirred up a great deal of controversy and have even led to the withholding of funds and services desperately needed in these countries. 

Fifty years ago finding a parking space for an automobile on most city streets was easy. Today “Where shall I park the car?” is a constant problem in urban centers and is taken for granted as part of daily living. 

Waiting in line to pay at the checkout counter was not the experience of many Americans fifty years ago when they went shopping. It may be hard to imagine today, but in most towns and cities the usual grocery store was a small shop around the corner where you stood behind a counter and asked the clerk for what you wanted. Frequently the proprietor would know your name and chat about the weather or some current news. As you called off the items the clerk would get them from different places in the store and put them on the counter before you. When you were done the individual prices were written on a paper bag and your bill was totaled up. Rarely did you have to wait. Today, we wheel carts through a huge stockroom of packaged food, select our items, and then wait in line until a clerk passes the premarked packages over an automatic price reading machine which adds up our total. The only personal exchange is likely only to be the question, “Paper or plastic?” 

Today when we drive through the countryside in the U.S. there are still vast tracts of open land. Forests and open plains seem to be plentiful. Even though we know our population is increasing it seems as if our country can handle the problem. The thought that America is already overpopulated is hard to believe.


PG4.5. Investigation:
What Will Our Future Growth Really Be?

Our species is unique on this planet; so what we have learned about the mathematics of population growth may or may not apply to the Earth’s human population. 

Question 4.17. 
How does the growth of the world’s human population differ from that of an animal population? 

Question 4.18. 
What are the space limitations for human population growth? 

Question 4.19. 
What other factors might limit human population growth? 

Question 4.20. 
Are there any indications that limiting factors are currently inhibiting human population growth?

Question 4.21. 
How does the concept of carrying capacity relate to human populations? 

Question 4.22. 
On Goat Island we saw two patterns for what can occur when a population nears its carrying capacity—gradual tapering off to a stable population, or a series of “crashes,” when carrying capacity is exceeded. In your opinion, which (if any) of these patterns might be a good model for Earth’s human population growth?

Graph of world human population

Environmentalists concerned about the long-range sustainability of the Earth’s systems see the explosion of the human population as a danger. As people all over the world push for a better quality of life for themselves and their children they are pressing against the ability of the Earth to supply water, food, space and manufactured goods. It is not the numbers of people that are the problem.

As you will see in our next chapter, it is what an increase in population does to the environment in order to meet its needs that are a cause for concern. 

See Staying current for this chapter.