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Sustainable Society:  A society that balances the environment, other life forms, and human interactions over an indefinite time period.







Population And The American Future

The Report Of The Commission On Population Growth And The American Future

John D. Rockefeller 3rd, Chairman
March 27, 1972


Chapter 2: Population Growth

The United States
    Table 2.1  Demographic Perspective of 20th Century United States
The “Birth Dearth”

    Figure 2.1 Total Fertility Rate
The Boom Generation
    Figure 2.2 The Momentum of Population Growth
Implications of Growth
    Figure 2.3: U.S. Population: 2 vs. 3-Child Family
    United States Population, 1970 and 2000

The tremendous growth in the world’s population is a recent development in the history of mankind. In pre-industrial times, birthrates were high; but hunger, ignorance, and disease combined to stack the odds against an infant surviving to the age of parenthood. Societies required high birthrates simply to keep themselves going.

In modern times, the reductions in mortality have given the average person a longer, healthier life and have inaugurated a phase of rapid population growth. The world’s population grew from one-half billion around 1650, to about 1½ billion by 1900, to 2½ billion in 1950, and had already surpassed 3½ billion by 1970. The world’s total has doubled during the last 50 years.

From the beginning of the Christian era to 1650, mankind increased by an average of 150,000 persons a year. Today, the world total is increasing by about 78 million persons annually. If current rates of growth continue for another 50 years, the world’s population will number some 10 billion.

The same civilization that achieved a lengthening of life in Europe and America also evolved an urban way of life in which the institutional supports to high fertility were gradually eroded, and developed a technology that reduced the role of ignorance and error in reproduction. The technology of mortality control was exported to the rest of the world. There was far less exporting of the underlying social and economic changes which gave rise to this technology, and only recently have efforts been made to export reproduction control.

Because of declining birthrates, the advanced nations have been narrowing the gap between birthrates and death rates in the 20th century. These nations have been approaching a stabilized population —one in which births and deaths have come into balance. The historical transition has been from a stabilized population maintained by high birthrates, high and erratic death rates, and short lifetimes, toward a stabilized population characterized by low birthrates, low death rates, and long lifetimes. When birthrates once again equal death rates, these nations will have completed the demographic transition.

Ultimately, this transition must be completed. Population growth at our current rate of about one percent per year would double the population every 70 years. Such growth leads to “standing room only” if continued indefinitely. By one means or another, such an impossible result will be avoided. An average of zero growth over the long term —a stabilized population— must and inevitably will be reestablished.1 The question is when it will happen, and how. In this, we in the United States may exercise choice.

The United States

No country has completed the demographic transition, and the United States will probably not be the first to do so. A discussion of our prospects for completing it requires some appreciation of the dynamics of our population during the first 70 years of the 20th century.

Even a cursory examination of the data reveals that, since 1900, the United States has undergone something of a demographic revolution. In terms of total numbers, our population has increased from about 76 million in 1900 to almost 205 million in 1970. This represents an additional 129 million people that our society has been called upon to accommodate over the past 70 years. By mid-1972, our country will have about 209 million people.

The growth of population is sustained only as long as the yearly number of new entrants (births and immigrants) exceeds the number required to replace those who die or emigrate. Although the United States has always been a growing population, the rapid growth rates characterizing our early years began to taper off in the 19th century.

In the 20th century, we have seen substantial changes in all three components of population growth —fertility, mortality, and migration. First, consider the birthrate. It is important to understand that this measure simply indicates the average level of yearly births in the population. Although it obscures a considerable amount of variation associated with such factors as age and socioeconomic status, it is nevertheless a useful measure of the contribution of births to population growth. The birthrate was about 32 births per 1,000 population in 1900, and declined fairly steadily to about 18 per 1,000 in the depths of the Depression. Just when the experts had become convinced —some even concerned— that our level of fertility would soon dip below the level required for replacement of the population, couples began increasing their rates of childbearing.

This aberration in the history of American fertility, of which we will have more to say shortly, came to be called the “baby boom.” By 1947, the birthrate stood at 27 per 1,000, and it remained at around 25 per 1,000 for a decade before resuming its long-term decline. By the early 1960’s, the boom had run its course, and our birthrate today is below pre-World War II levels.2

Table 2.1  Demographic Perspective of 20th Century United States


Around 1900

Around 1970


76 million

205 million

Life expectancy

47 years

70 years

Median age

23 years

28 years

Births per 1000 population



Deaths per 1000 population



Immigrants per 1000 population



Annual growth

Growth rate

2.3 percent

1.1 percent

Sources: US. Bureau of the Census, Historical Statistics of the United States, Colonial Times to 1957, 1961. U.S. National Center for Health Statistics, Vital Statistics of the United States, Volume II, Section 5, Life Tables, 1968. Irene B. Taeuber, “Growth of the Population of the United States in the Twentieth Century” (prepared for the Commission, 1972).

 A second basic determinant of how fast a nation grows is the degree to which it succeeds in preserving and extending the lives of its people. We have seen dramatic progress toward reducing the threat of early death. The death rate has fallen from about 17 per 1,000 population at the turn of the century, to its present level of about nine per 1,000. The average life expectancy today is about 70 years,3 or 23 years longer than in 1900. Most of these declines in mortality were achieved prior to 1960, and all segments of our population have gained some, though not equal, benefits in terms of increased longevity.

In the
United States, mortality during the early years of life is already so low that any substantial further improvements in life expectancy will have to come primarily among persons over the age of 50. Since this segment of the population is generally beyond childbearing, the extension of their life span would not result in any significant increase in births. Consequently, further additions to the duration of life in this country would simply result in somewhat larger numbers of people at the older ages, where they still can be quite productive members of society.

The third factor associated with growth is, of course, immigration. Only the Indians, who numbered less than one million4 when the first English colonists settled in
Massachusetts and Virginia, can rightfully claim original status. Our population is comprised primarily of immigrants and their descendants. Since 1900 alone, 20 million more people have moved into this country than out of it. Approximately 40 percent of the population growth in the first decade of this century was attributable to immigration. During the 1930’s, the number of immigrants was slightly lower than the number of people leaving the country. Immigration once again increased following World War II, and during the 1960’s, it accounted for about 16 percent of our national growth.5

When all of these demographic credits and debits are tallied, we are left with either net population growth or net decline. The United States has had a long history of diminishing growth rates. Our annual rate of growth dropped from about 3.3 percent in the second decade of the 19th century to 2.1 percent by the first decade of this century, to an average of around 0.7 percent during the 19 30’s. It then rose to about 1.9 percent during the fifties, before falling to its present level of 1.1 percent. However, the size of our population is now so large that even our low current rate of growth translates into about 2¼ million people added to our society each year —more than enough to fill a city the size of Philadelphia.

We cannot predict how fast our population will grow in the years ahead, but we can be sure that, barring some unforeseen catastrophe, substantial additions to our numbers lie ahead. Our population has a potential for further growth greater than that of almost any other advanced country. The reasons for this are a pattern of early and nearly universal marriage and childbearing, fertility levels above those required to replace the parental generation, and a preponderance of youth in the population. The youngsters born during the baby boom are reaching adulthood today and beginning to do many of the things their parents and grandparents did before them —finishing school, seeking jobs, developing careers, getting married, and having children of their own.

The “Birth Dearth”

In the summer of 1971, the news media spread a report that, because women were having fewer babies than had been expected, we were in the midst of a “baby bust.” That story was based on data for the first six months of 1971, which showed a drop in birthrates at a time when most of the experts had expected them to rise again as the baby-boom generation reached adulthood. These expectations seemed to be realized when the birthrate, after reaching a new low of 17.5 in 1968, moved up to about 18.2 in 1970.6 But, instead of continuing upward in 1971, the rate dropped back to about 17.3, and so was born the idea of the "birth dearth."

Figure 2.1  Total Fertility Rate


*Prior to 1917, data available only for white population; after 1917, for total population.
Sources: Prior to 1917-Ansley Coale and Melvin Zelnik, New Estimates of Fertility and Population in the United States (Princeton: Princeton University Press, 1963). 1917 to 1968-U.S. National Center for Health Statistics, Natality Statistics Analysis, Series 21, Number 19, 1970. 1969 to 1971-U.S. Bureau of the Census, Current Population Reports, Series P-23, No. 36, "Fertility Indicators: 1970," 1971. The figure for 1971 is based on an unpublished Census staff estimate.

This phenomenon is notable because birthrates are showing declines at a time when everyone was expecting them to increase. It had long been assumed that birthrates would rise during the 1970's as potential parents who were born during the baby-boom years came of age. If general fertility (the rate of childbearing among women aged 15 to 44) remained constant, there would be an unavoidable "echo boom" in the birthrate of the total population, as larger and larger numbers of potential parents reached childbearing age. The increase in the number of people entering the childbearing ages is, however, presently being offset by a decline in the level of general fertility.

Two factors seem to account for this recent decline. One is temporary; the other may or may not be permanent. The first element arises from the fact that we are now in a period of gradually rising age at childbearing. This means that, in any given year, some fraction of the births is, in effect, postponed to a later year. The effect is temporary because the age at childbearing will not rise indefinitely; when it stabilizes, the postponement will stop and the birthrate will rise again.

The other and more important element is that today's young people expect to have far fewer children than people a few years their senior. On the average, women now in their late thirties already have more than three children. According to a 1971 Census Bureau survey, married women 18 to 24 say that they expect to have an average of 2.4 children before they complete their families.7 Not everyone will marry, so the total for this generation could ultimately be lower. On the other hand, experience with similar surveys in the past indicates that women usually end up having more children than they estimated when they were young. The baby-bust phenomenon is significant and somewhat surprising, but it would be premature to say that we are on the verge of a fertility level that would ultimately stabilize the population.

The baby-bust psychology may give rise to unwarranted complacency born of the notion that all of the problems associated with population growth are somehow behind us. Our population growth has developed its own momentum which makes it very difficult to stop, no matter how hard the brakes are applied. Even if immigration from abroad ceased and couples had only two children on the average
just enough to replace themselves our population would continue to grow for about 70 years. Our past rapid growth has given us so many young couples that, to bring population growth to an immediate halt, the birthrate would have to drop by almost 50 percent, and today's young generation of parents would have to limit themselves to an average of about one child.8 That is just not going to happen.

The Boom Generation

The postwar baby boom is over, but those born during the boom period are still very much with us. Our society has not had an easy time thus far in its attempts to accommodate the baby-boom generation, and their impact is not likely to diminish in the near future. Over the past couple of decades, most of the problems have been associated with providing for their schooling. Shortages of classrooms and teachers began to plague our elementary schools in the mid-1950's.

Similar difficulties have become commonplace in our secondary schools and colleges as the bulk of the boom generation advances to higher levels of education. At the same time, primary schools are now having to cope with smaller enrollments. The number of children entering first grade has stopped escalating, and is now declining. Furthermore, in contrast to the serious teacher shortage of the 1950's, we are now faced with more teachers than the system can readily absorb. The National Education Association recently observed that, during the remainder of this decade, there will be at least two qualified graduates seeking a teaching position for every available job.9

Thus, the baby boom has left us with a legacy of problems attendant on both rapid increases and decreases in the flow of people passing through our educational system.

This new wave of humanity has made itself felt in areas outside the educational arena as well. Many current problems that we do not normally associate with population growth can be understood, in part, as an effect of the growing-up of the baby-boom generation. For instance, it is generally recognized that young drivers have higher accident rates than the rest of the population. Hence, recent increases in traffic accidents are partially attributable to the fact that many of those born in the baby boom became drivers during the 1960's.

An awareness of the same sort of population dynamics can also help us to understand the increasing volume of crime during the past decade. Since the crime rate is higher among persons under 25 than among older people, much of the increase in crime during recent years is traceable to an expansion in the relative number of persons in the youthful age groups. About 28 percent of the reported increase between 1960 and 1970 in the number of arrests for serious crimes can be attributed to an increase in the percentage of the population under 25. Another 22 percent of the increase can be explained by the growing size of the population and other demographic factors. Thus, population change alone accounted for about half of the reported increase in the number of arrests for serious crimes over the past decade.10

Now, as the youth culture of the sixties evolves into the young adult society of the seventies, the impact is being felt in the housing and job markets. In the two decades before 1965, about 48 million Americans reached the age of 20. Between 1965 and 1985, over 78 million will cross this important threshold.

As those born during the baby boom move off the campus or leave their parents’ homes, we can expect a 33-percent jump in annual household formation by the end of this decade. Between 1950 and 1966, the number of households grew at a relatively steady rate of around 900,000 per year. After that, the rate began to climb, and last year we added well over one million households. Our research shows that the rate will increase to almost 1.5 million households added each year by the end of the seventies, and will remain at that level until about 1985. These figures understate future demand for the construction of new housing, since additional new housing units will be required to replace part of the older housing stock.

Along with increased housing demands will come greater demand for employment opportunities. The highest rates of joblessness are found among the young. Consequently, one factor to be considered, irrespective of the state of the economy itself, is the sheer increase in the numbers of young people seeking work. The Bureau of Labor Statistics tells us that we can expect about 3½ million persons to make their initial entry into the labor force each year during the 1970’s. This level of prospective job seekers exceeds the annual average for the 1960’s by about 700,000 persons a year. Here again, we can attribute the large numbers to a heavy influx of new job-seekers who were born during the baby boom.11

The boom generation will continue to exert a heavy impact on our society as they move up the age ladder. Eventually, they will reach retirement age; at that point, we can expect added pressure on retirement systems as the proportion of beneficiaries in the population increases. Today, we have an estimated 20 million senior citizens. About 50 years from now we will have an estimated 40 million, twice the present number.

In sum, it should be evident that, even if the recent unexpected drop in the birthrate should develop into a sustained trend, there is little cause for complacency. Whether we see it or not —whether we like it or not— we are in for a long period of growth, and we had best prepare for it.

Figure 2.2  The Momentum of Population Growth

Source: U.S. Bureau of the Census, Current Population Reports, Series P-25. Projections assume small future reductions in mortality, and assume future immigration at present levels.

Implications of Growth

It is clear that we are confronted with a continuing legacy of population growth in this country. Much of it is unavoidable, but its full extent will depend upon choices made by American couples in the years immediately ahead.

If families in the United States have only two children on the average and immigration continues at current levels, our population would grow to 271 million by the end of the century. If, however, families should have an average of three children, the population would reach 322 million by the year 2000. One hundred years from now, the 2-child family would result in a population of about 350 million persons, whereas, the 3-child family would produce a total of nearly a billion. Thus, a difference of only one extra child per family would result in an additional 51 million people over the next three decades, and if extended over a century, an additional two-thirds of a billion people.

When we speak of 2- or 3-child families, we are talking about averages which can be made up by many possible combinations of family sizes, ranging from childless couples to those with many children.

The total size of our future population is not our sole concern. Perhaps just as important are the changes which lie ahead in the size of various age categories that play an important role in the demands placed on our society.

If families average three children, we can expect to find about 46 percent more young people of elementary and secondary school age (5 to 17 years), and 36 percent more persons of college age (18 to 21 years) in the year 2000, than would be the case if families average only two children. Thus, a difference of only one child per family will have important consequences for the magnitude of the load on our educational system.

Figure 2.3  U.S. Population: 2 vs. 3-Child Family


The population of the United States passed the 100-million mark in 1915 and reached 200 million in 1968. If families average two children in the future, growth rates will slow, and the population will reach 300 million in the year 2015. At the 3-child rate, the population would reach 300 million in this century and 400 million in the year 2013. (Projections assume small future reductions in mortality, and assume future immigration at present levels.)

Prior to 1900-U.S. Bureau of the Census, Historical Statistics of the United States, Colonial Times to 1957, 1961. 1900 to 2020-U.S. Bureau of the Census Current Population Reports, Series P-25. 2021 to 2050-unpubiished Census Bureau projections. Beyond 2050-extrapolation.

United States Population, 1970 and 2000

(Numbers in Millions)






2 -child average


3-child average

All Ages





Under 5





5 to 17





8 to 21





under l8





18 to 64





65 and over





Dependency Ratioa










a Number of persons 65 and over plus persons under 18, per 100 persons aged 18 to 64

These data are based on the Census Bureau’s Current Population Reports, Series P-25, No. 470, “Projections of the Population of the United States by Age and Sex: 1970 to 2000.” These projections served as the basis for much of the research reported in this volume. We examined how the population would grow between now and the year 2000 under the 2-child family projection (Census Series E) and under the 3-child projection (Census Series B).
Series B assumes that in the future, women will be giving birth at an “ultimate” rate averaging out to 3.1 children per woman over her lifetime. The transition from the 1969 rate of 2.4 to the “ultimate” future rate is not instantaneous in the projections, but most of the change is assumed to occur by 1980. The 3.1 figure is an average for all women, regardless of marital status. In the United States today, almost all women (95 percent) marry at some time in their lives, so the Series B rate of childbearing represents a reasonable approximation to an average family size of 3 children.
Series E assumes an ultimate rate of childbearing that works out to an average of 2.1 children per woman over a lifetime. This is the rate at which the parental generation would exactly replace itself. The extra 0.1 allows for mortality between birth and the average age of mothers at childbearing, and for the fact that boy babies slightly outnumber girl babies.
Different generations born in the 20th century have reproduced at widely varying average levels, some exceeding three children (as did the women born from 1930 to 1935) and some approaching two (as did women who were born from 1905 to 1910). The fact that major groups in our modern history have reproduced at each of these levels lends credibility to projections based on either of these averages.
It is assumed in both projections that future reductions in mortality will be slight. The net flow of immigrants into the United States is assumed, in the projections, to continue at the present level of about 400,000 persons annually.

The burden placed on those in the economically active segment of the population, traditionally considered to be those aged 18 to 64, will also be influenced by future family size. The dependency burden is determined chiefly by the proportion of the population in the childhood and adolescent years. Projections indicate that the number of persons in the dependent ages under 18 in the year 2000 would be 52 percent greater if families average three children than if the 2-child average prevails.

The size of the population 65 and over in the year 2000 would be unaffected by changes in the average number of children, since everyone who will be over the age of 30 at the end of this century is already born. Consequently, the numbers in the dependent ages, relative to persons of working age, would be about one-third larger under the 3-child than under the 2-child projection.

To understand the importance of these prospects, we need first to see how the social and economic transformation of the United States has altered the geographic distribution of population and to assess the likely effect of alternative population futures on our economy, resources, environment, government, and social conditions. We turn to these in the following chapters.

[Return to Rockefeller Table of Contents. Go to Chapter 3.]

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