Paul R. Ehrlich & Anne H. Ehrlich, The Population Explosion, 1990.

Why Isn't Everyone as Scared as We Are?

In the early 1930s, when we were born, the world population was just 2 billion; now it is more than two and a half times as large and still growing rapidly.1 The population of the United States is increasing much more slowly than the world average, but it has more than doubled in only six decades -- from 120 million in 1928 to 250 million in 1990.2 Such a huge population expansion within two or three generations can by itself account for a great many changes in the social and economic institutions of a society. It also is very frightening to those of us who spend our lives trying to keep track of the implications of the population explosion.


One of the toughest things for a population biologist to reconcile is the contrast between his or her recognition that civilization is in imminent serious jeopardy and the modest level of concern that population issues generate among the public and even among elected officials. [14]

Much of the reason for this discrepancy lies in the slow development of the problem. People aren't scared because they evolved biologically and culturally to respond to short-term "fires" and to tune out long-term "trends" over which they had no control.3 Only if we do what doesn't come naturally -- if we determinedly focus on what seem to be gradual or nearly imperceptible changes -- can the outlines of our predicament be perceived clearly enough to be frightening.

Consider the very slow-motion origins of our predicament. It seems reasonable to define humanity as having first appeared some four million years ago in the form of australo-pithecines, small-brained upright creatures like "Lucy."4 Of course, we don't know the size of this first human population, but it's likely that there were never more than 125,000 australopithecines at any given time.

Our own species, Homo sapiens,5 evolved a few hundred thousand years ago. Some ten thousand years ago, when agriculture was invented, probably no more than five million people inhabited Earth -- fewer than now live in the San Francisco Bay Area. Even at the time of Christ, two thousand years ago, the entire human population was roughly the size of the population of the United States today; by 1650 there were only 500 million people, and in 1850 only a little over a billion. Since there are now well past 5 billion people, the vast majority of the population explosion has taken place in less than a tenth of one percent of the history of Homo sapiens.

This is a remarkable change in the abundance of a single species. After an unhurried pace of growth over most of our history, expansion of the population accelerated during the Industrial Revolution and really shot up after 1950. Since mid-century, the human population has been growing at annual rates ranging from about 1.7 to 2.1 percent per year, doubling in forty years or less. Some groups have grown significantly faster; the population of the African nation of Kenya^was estimated to be increasing by over 4 percent annually during the 1980s -- a rate that if continued would double the nation's population in only seventeen years.6 That rate did continue for over a decade, and only recently has shown slight signs of slowing. Meanwhile, other nations, such as those of northern Europe, have grown much more slowly in recent decades. [15]

But even the highest growth rates are still slow-motion changes compared to events we easily notice and react to. A car swerving at us on the highway is avoided by actions taking a few seconds. The Alaskan oil spill caused great public indignation, but faded from the media and the consciousness of most people in a few months. America's participation in World War II spanned less than four years. During the last four years, even Kenya's population grew by only about 16 percent -- a change hardly perceptible locally, let alone from a distance. In four years, the world population expands only a little more than 7 percent. Who could notice that? Precipitous as the population explosion has been in historical terms, it is occurring at a snail's pace in an individual's perception. It is not an event, it is a trend that must be analyzed in order for its significance to be appreciated.


The time it takes a population to double in size is a dramatic way to picture rates of population growth, one that most of us can understand more readily than percentage growth rates. Human populations have often grown in a pattern described as "exponential."7 Exponential growth occurs in bank accounts when interest is left to accumulate and itself earns interest. Exponential growth occurs in populations because children, the analogue of interest, remain in the population and themselves have children.8

A key feature of exponential growth is that it often seems to start slowly and finish fast. A classic example used to illustrate this is the pond weed that doubles each day the amount of pond surface covered and is projected to cover the entire pond in thirty days. The question is, how much of the pond will be covered in twenty-nine days? The answer, of course, is that just half of the pond will be covered in twenty-nine days. The weed will then double once more and cover the entire pond the next day. As this example indicates, exponential growth contains the potential for big surprises.9

The limits to human population growth are more difficult to perceive than those restricting the pond weed's growth. Nonetheless, like the pond weed, human populations grow in [16] a pattern that is essentially exponential, so we must be alert to the treacherous properties of that sort of growth. The key point to remember is that a long history of exponential growth in no way implies a long future of exponential growth. What begins in slow motion may eventually overwhelm us in a flash.

The last decade or two has seen a slight slackening in the human population growth rate -- a slackening that has been prematurely heralded as an "end to the population explosion." The slowdown has been only from a peak annual growth rate of perhaps 2.1 percent in the early 1960s to about 1.8 percent in 1990. To put this change in perspective, the population's doubling time has been extended from thirty-three years to thirty-nine. Indeed, the world population did double in the thirty-seven years from 1950 to 1987. But even if birthrates continue to fall, the world population will continue to expand (assuming that death rates don't rise), although at a slowly slackening rate, for about another century. Demographers think that growth will not end before the population has reached 10 billion or more.10

So, even though birthrates have declined somewhat, Homo sapiens is a long way from ending its population explosion or avoiding its consequences. In fact, the biggest jump, from 5 to 10 billion in well under a century, is still ahead. But this does not mean that growth couldn't be ended sooner, with a much smaller population size, if we -- all of the world's nations -- made up our minds to do it. The trouble is, many of the world's leaders and perhaps most of the world's people still don't believe that there are compelling reasons to do so. They are even less aware that if humanity fails to act, nature may end the population explosion for us -- in very unpleasant ways -- well before 10 billion is reached.

Those unpleasant ways are beginning to be perceptible. Humanity in the 1990s will be confronted by more and more intransigent environmental problems, global problems dwarfing those that worried us in the late 1960s. Perhaps the most serious is that of global warming, a problem caused in large part by population growth and overpopulation. It is not clear whether the severe drought in North America, the Soviet Union, and China in 1988 was the result of the slowly rising [17] surface temperature of Earth, but it is precisely the kind of event that climatological models predict as more and more likely with continued global warming.11 In addition to more frequent and more severe crop failures, projected consequences of the warming include coastal flooding, desertification, the creation of as many as 300 million environmental refugees,12 alteration of patterns of disease, water shortages, general stress on natural ecosystems, and synergistic interactions among all these factors.13

Continued population growth and the drive for development in already badly overpopulated poor nations will make it exceedingly difficult to slow the greenhouse warming -- and impossible to stop or reverse it -- in this generation at least. And, even if the warming should miraculously not occur, contrary to accepted projections,14 human numbers are on a collision course with massive famines anyway.


Global warming, acid rain, depletion of the ozone layer, vul-nerability to epidemics, and exhaustion of soils and ground-water are all, as we shall see, related topopulation size. They are also clear and present dangers to the persistence of civilization. Crop failures due to global warming alone might result in the premature deaths of a billion or more people in the next few decades, and the AIDS epidemic could slaughter hundreds of millions. Together these would constitute a harsh "population control" program provided by nature in the face of humanity's refusal to put into place a gentler program of its own.

We shouldn't delude ourselves: the population explosion will come to an end before very long. The only remaining question is whether it will be halted through the humane method of birth contol, or by nature wiping out the surplus. We realize that religious and cultural opposition to birth control exists throughout the world; but we believe that people simply don't understand the choice that such opposition implies. Today, anyone opposing birth control is unknowingly voting to have the human population size controlled by a massive increase in early deaths. [18]

Of course, the environmental crisis isn't caused just by expanding human numbers. Burgeoning consumption among the rich and increasing dependence on ecologically unsound technologies to supply that consumption also play major parts. This allows some environmentalists to dodge the population issue by emphasizing the problem of malign technologies. And social commentators can avoid commenting on the problem of too many people by focusing on the serious maldistribution of affluence.

But scientists studying humanity's deepening predicament recognize that a major factor contributing to it is rapidly worsening overpopulation. The Club of Earth, a group whose members all belong to both the U.S. National Academy of Sciences and the American Academy of Arts and Sciences, released a statement in September 1988 that said in part:

Arresting global population growth should be second in importance only to avoiding nuclear war on humanity's agenda. Overpopulation and rapid population growth are intimately connected with most aspects of the current human predicament, including rapid depletion of nonrenewable resources, deterioration of the environment (including rapid climate change), and increasing international tensions.15

When three prestigious scientific organizations cospon-sored an international scientific forum, "Global Change," in Washington in 1989, there was general agreement among the speakers that population growth was a substantial contributor toward prospective catastrophe. Newspaper coverage was limited, and while the population component was mentioned in The New York Times's article,16 the point that population limitation will be essential to resolving the predicament was lost. The coverage of environmental issues in the media has been generally excellent in the last few years, but there is still a long way to go to get adequate coverage of the intimately connected population problem.

Even though the media occasionally give coverage to population issues, some people never get the word. In November 1988, Pope John Paul II reaffirmed the Catholic Church's ban [19] on contraception. The occasion was the twentieth anniversary of Pope Paul's anti-birth-control encyclical, Humanae Vitae.

Fortunately, the majority of Catholics in the industrial world pay little attention to the encyclical or the Church's official ban on all practical means of birth control. One need only note that Catholic Italy at present has the smallest average completed family size (1.3 children per couple) of any nation. Until contraception and then abortion were legalized there in the 1970s, the Italian birth rate was kept low by an appalling rate of illegal abortion.

The bishops who assembled to celebrate the anniversary defended the encyclical by announcing that "the world's food resources theoretically could feed 40 billion people."17 In one sense they were right. It's "theoretically possible" to feed 40 billion people -- in the same sense that it's theoretically possible for your favorite major-league baseball team to win every single game for fifty straight seasons, or for you to play Russian roulette ten thousand times in a row with five out of six chambers loaded without blowing your brains out.

One might also ask whether feeding 40 billion people is a worthwhile goal for humanity, even if it could be reached. Is any purpose served in turning Earth, in essence, into a gigantic human feedlot? Putting aside the near-certainty that such a miracle couldn't be sustained, what would happen to the quality of life?

We wish to emphasize that the population problem is in no sense a "Catholic problem," as some would claim. Around the world, Catholic reproductive performance is much the same as that of non-Catholics in similar cultures and with similar economic status. Nevertheless, the political position of the Vatican, traceable in no small part to the extreme conservatism of Pope John Paul II, is an important barrier to solving the population problem.18 Non-Catholics should be very careful not to confuse Catholics or Catholicism with the Vatican -- most American Catholics don't. Furthermore, the Church's position on contraception is distressing to many millions of Catholics, who feel it morally imperative to follow their own consciences in their personal lives and disregard the Vatican's teachings on this subject. [20]

Nor is unwillingness to face the severity of the population problem limited to the Vatican. It's built into our genes and our culture. That's one reason many otherwise bright and humane people behave like fools when confronted with demographic issues. Thus, an economist specializing in mail-order marketing can sell the thesis that the human population could increase essentially forever because people are the "ultimate resource,"19 and a journalist can urge more population growth in the United States so that we can have a bigger army!20 Even some environmentalists are taken in by the frequent assertion that "there is no population problem, only a problem of distribution." The statement is usually made in a context of a plan for conquering hunger, as if food shortage were the only consequence of overpopulation.

But even in that narrow context, the assertion is wrong. Suppose food were distributed equally. If everyone in the world ate as Americans do, less than half the present world population could be fed on the record harvests of 1985 and 1986.21 Of course, everyone doesn't have to eat like Americans. About a third of the world grain harvest -- the staples of the human feeding base -- is fed to animals to produce eggs, milk, and meat for American-style diets. Wouldn't feeding that grain di-rectly to people solve the problem? If everyone were willing to eat an essentially vegetarian diet, that additional grain would allow perhaps a billion more people to be fed with 1986 production.

Would such radical changes solve the world food problem? Only in the very short term. The additional billion people are slated to be with us by the end of the century. Moreover, by the late 1980s, humanity already seemed to be encountering trouble maintaining the production levels of the mid-1980s, let alone keeping up with population growth. The world grain harvest in 1988 was some 10 percent below that of 1986. And there is little sign that the rich are about to give up eating animal products.

So there is no reasonable way that the hunger problem can be called "only" one of distribution, even though redistribution of food resources would greatly alleviate hunger today. Unfortunately, an important truth, that maldistribution is a cause of [21] hunger now, has been used as a way to avoid a more important truth -- that overpopulation is critical today and may well make the distribution question moot tomorrow.

The food problem, however, attracts little immediate concern among well-fed Americans, who have no reason to be aware of its severity or extent. But other evidence that could make everyone face up to the seriousness of the population dilemma is now all around us, since problems to which overpopulation and population growth make major contributions are worsening at a rapid rate. They often appear on the evening news, although the population connection is almost never made.

Consider the television pictures of barges loaded with garbage wandering like The Flying Dutchman across the seas, and news stories about "no room at the dump."22 They are showing the results of the interaction between too many affluent people and the environmentally destructive technologies that support that affluence. Growing opportunities to swim in a mixture of sewage and medical debris off American beaches can be traced to the same source. Starving people in sub-Saharan Africa are victims of drought, defective agricultural policies, and an overpopulation of both people and domestic animals -- with warfare often dealing the final blow. All of the above are symptoms of humanity's massive and growing negative impact on Earth's life-support systems.


The average person, even the average scientist, seldom makes the connection between such seemingly disparate events and the population problem, and thus remains unworried. To a degree, this failure to put the pieces together is due to a taboo against frank discussion of the population crisis in many quarters, a taboo generated partly by pressures from the Catholic hierarchy and partly by other groups who are afraid that dealing with population issues will produce socially damaging results.

Many people on the political left are concerned that focusing on overpopulation will divert attention from crucial [22] problems of social justice (which certainly need to be addressed in addition to the population problem). Often those on the political right fear that dealing with overpopulation will encourage abortion (it need not) or that halting growth will severely damage the economy (it could, if not handled properly). And people of varied political persuasions who are unfamiliar with the magnitude of the population problem believe in a variety of farfetched technological fixes -- such as colonizing outer space -- that they think will allow the need for regulating the size of the human population to be avoided forever.23

Even the National Academy of Sciences avoided mentioning controlling human numbers in its advice to President Bush on how to deal with global environmental change. Although Academy members who are familiar with the issue are well aware of the critical population component of that change, it was feared that all of the Academy's advice would be ignored if recommendations were included about a subject taboo in the Bush administration. That strategy might have been correct, considering Bush's expressed views on abortion and considering the administration's weak appointments in many environmentally sensitive positions. After all, the Office of Management and Budget even tried to suppress an expert evaluation of the potential seriousness of global warming by altering the congressional testimony of a top NASA scientist, James Hansen, to conform with the administration's less urgent view of the problem.24

All of us naturally lean toward the taboo against dealing with population growth. The roots of our aversion to limiting the size of the human population are as deep and pervasive as the roots of human sexual behavior. Through billions of years of evolution, outreproducing other members of your population was the name of the game. It is the very basis of natural selection, the driving force of the evolutionary process.25 Nonetheless, the taboo must be uprooted and discarded.


There is no more time to waste; in fact, there wasn't in 1968 when The Population Bomb was published. Human inaction [23] has already condemned hundreds of millions more people to premature deaths from hunger and disease. The population connection must be made in the public mind. Action to end the population explosion humanely and start a gradual population decline must become a top item on the human agenda: the human birthrate must be lowered to slightly below the human death rate as soon as possible. There still may be time to limit the scope of the impending catastrophe, but not much time. Ending the population explosion by controlling births is necessarily a slow process. Only nature's cruel way of solving the problem is likely to be swift.

Of course, if we do wake up and succeed in controlling our population size, that will still leave us with all the other thorny problems to solve. Limiting human numbers will not aloneend warfare, environmental deterioration, poverty, racism, religious prejudice, or sexism; it will just buy us the opportunity to do so. As the old saying goes, whatever your cause, it's a lost cause without population control.26

America and other rich nations have a clear choice today. They can continue to ignore the population problem and their own massive contributions to it. Then they will be trapped in a downward spiral that may well lead to the end of civilization in a few decades. More frequent droughts, more damaged crops and famines, more dying forests, more smog, more international conflicts, more epidemics, more gridlock, more drugs, more crime, more sewage swimming, and other extreme unpleasantness will mark our course. It is a route already traveled by too many of our less fortunate fellow human beings.

Or we can change our collective minds and take the measures necessary to lower global birthrates dramatically. People can learn to treat growth as the cancerlike disease it is and move toward a sustainable society. The rich can make helping the poor an urgent goal, instead of seeking more wealth and useless military advantage over one another. Then humanity might have a chance to manage all those other seemingly intractable problems. It is a challenging prospect, but at least it will give our species a shot at creating a decent future for itself. More immediately and concretely, taking action now will give our children and their children the possibility of decent lives.


1. The world population in 1990 is about 5.3 billion. Most demographic information in this book, unless otherwise noted, is from 1989 World Population Data Sheet, issued by the Population Reference Bureau (PRB), 777 Fourteenth St. NW, Suite 800, Washington, D.C. 20005. In some cases, as above, we have made simple extrapolations for the 1990 figures. Besides the fine annual data sheet, PRB produces several very useful publications on population issues.

2. Note that the U.S. population was growing much faster before then, spurred by substantial numbers of immigrants. It quadrupled in the 6 decades before 1928, turning a post-Civil War society largely restricted to the eastern half of the nation into a cosmopolitan world power spanning the continent.

3. This evolutionary blind spot is discussed at length in R. Ornstein and P. Ehrlich, New World/New Mind (Doubleday, New York, 1988).

4. D. Johanson and M. Edey, Lucy: The Beginnings of Mankind (Simon and Schuster, New York, 1981). While there is still controversy over details of human history, there is no dispute that an erect, small-brained hominid something like Lucy was one of our ancestors. This exciting book beautifully presents the view of human origins of one outstanding group of scientists. For more on the controversies and on other discoveries, see R. Lewin's excellent Bones of Contention (Simon and Schuster, New York, 1987).

5. Note that we are considering Homo sapiens as the latest human species and are applying the term "human" to all hominids since the australo-pithecines (just as the term "ape" is applied to several species). Some people would restrict the term "human" to Homo sapiens.

6. When annual growth rates are under 5 percent, a working estimate of the number of years required to double the population at that rate can be obtained by simply dividing the percentage rate into 70. Thus, with Kenya's growth rate of 4.1 percent, the estimate of doubling time is 70/4.1 = 17.1 years. A recent decline in Kenya's birthrate was reported in J. Perlez, "Birth Control Making Inroads in Populous Kenya," New York Times, Sept. 10, 1989, but the population still has a doubling rate of less than 20 years.

7. Exponential growth occurs when the increase in population size in a given period is a constant percentage of the size at the beginning of the period. Thus a population growing at 2 percent annually or a bank account growing at 6 percent annually will be growing exponentially. Exponential growth does not have to be fast; it can go on at very low rates or, if the rate is negative, can be exponential shrinkage.

Saying a population is "growing exponentially" has almost come to mean "growing very fast," but that interpretation is erroneous. True exponential growth is rarely seen in human populations today, since the percentage rate of growth has been changing. In most cases, the growth rate has been gradually declining since the late 1960s. Nevertheless, it is useful to be aware of the exponential model, since it is implied every time we project a population size into the future with qualifying statements such as "if that rate continues."

8. For mathematical details on exponential growth, see P. R. Ehrlich, A. H. Ehrlich, and J. P. Holdren, Ecoscience: Population, Resources, Environment (Freeman, San Francisco, 1977), pp. 100-104. The term "exponential" comes from the presence in the equation for growth of a constant, e, the base of natural logarithms, raised to a power (exponent) that is a variable (the growth rate multiplied by the time that rate will be in effect).

9. The potential for surprise in repeated doublings can be underlined with another example. Suppose you set up an aquarium with appropriate life-support systems to maintain 1.000 guppies, but no more. If that number is exceeded, crowding will make the fishes susceptible to "ich," a parasitic disease that will kill most of the guppies. You then begin the population with a pair of sex-crazed guppies. Suppose that the fishes reproduce fast enough to double their population size every month. For eight months everything is fine, as the population grows 2→4→8→16→32→64→128→256→>512. Then within the ninth month the guppy population surges through the fatal 1,000 barrier, the aquarium becomes overcrowded, and most of the fishes perish. In fact, the last 100 guppies appear in less than five days -- about 2 percent of the population's history.

10. Note that "doubling times" represent what would happen if the growth rates of the moment continued unchanged into the future. Demographic projections include changes in growth rates, usually caused by reductions in birthrates and/or declines in death rates (demographers classically don't consider rises in death rates in their global projections). Projections therefore often show the population taking more, and occasionally less, time to double than was indicated by the "doubling time" of a recent year.

11. For a fine discussion of climate models, see S. H. Schneider, Global Warming (Sierra Club Books, San Francisco, 1989).

12. "Eco-Refugees Warning," New Scientist, June 10, 1989.

13. Synergisms occur when the joint impact of two (or more) factors is greater than the sum of their separate impacts.

14. See S. H. Schneider, Global Warming, and the extensive references therein.

15. Statement released Sept. 3, 1988, at the Pugwash Conference on Global Problems and Common Security, at Dagomys, near Sochi, USSR. The signatories were Jared Diamond, UCLA; Paul Ehrlich, Stanford; Thomas Eisner, Cornell; G. Evelyn Hutchinson, Yale; Gene E. Likens, Institute of Ecosystem Studies; Ernst Mayr, Harvard; Charles D. Michener, University of Kansas; Harold A. Mooney, Stanford; Ruth Patrick, Academy of Natural Sciences, Philadelphia; Peter H. Raven, Missouri Botanical Garden; and Edward 0. Wilson, Harvard.

The National Academy of Sciences and the American Academy of Arts and Sciences are the top honorary organizations for American scientists and scholars, respectively. Hutchinson, Patrick, and Wilson also are laureates of the Tyler Prize, the most distinguished international award in ecology.

16. May 4, 1989, by Philip Shabecoff, a fine environmental reporter. In general, the Times coverage of the environment is excellent. But even this best of American newspapers reflects the public's lack of understanding of the urgency of the population situation.

17. Washington Post, Nov. 19, 1988, p. C-15.

18. Italy is a not freak case. Catholic France has an average completed family size of 1.8 children, the same as Britain and Norway; Catholic Spain, with less than half the per-capita GNP of Protestant Denmark, has the same completed family size of 1.8 children. We are equating "completed family size" here with the total fertility rate, the average number of children a woman would bear in her lifetime, assuming that current age-specific birth and death rates remained unchanged during her childbearing years -- roughly 15-49. In the United States, a Catholic woman is more likely to seek abortion than a non-Catholic woman (probably because she is likelier to use less-effective contraception). By 1980, Catholic and non-Catholic women in the U.S. (except Hispanic women, for whom cultural factors are strong) had virtually identical family sizes. (W.D. Mosher, "Fertility and Family Planning in the United States: Insights from the National Survey of Family Growth," Family Planning Perspectives, vol. 20, no. 5, pp. 202-17, Sept,/Oct. 1988.) On the role of the Vatican, see, for instance, Stephen D. Mumford, "The Vatican and Population Growth Control: Why an American Confrontation?," The Humanist, September/October 1983, and Penny Lernoux, "The Papal Spiderweb," The Nation, April 10 and 17, 1989.

19. J. Simon, The Ultimate Resource (Princeton Univ. Press, Princeton, N.J., 1981).

20. B. Wattenberg, The Birth Dearth (Pharos Books, New York, 1987).

21. R. W. Kates, R. S. Chen, T. E. Downing, J. X. Kasperson, E. Messer, S. R. Millman, The Hunger Report: 1988 (The Alan Shawn Feinstein World Hunger Program, Brown University. Providence, R.I., 1988). The data on distribution in this paragraph are from this source.

22. The name of a series of reports on KRON-TV's news programs, San Francisco, the week of May 8, 1989.

23. For an amusing analysis of the "outer-space" fairy tale, see Garrett Hardin's classic essay "Interstellar Migration and the Population Problem," Journal of Heredity, vol. 50, pp. 68-70 (1959), reprinted in G. Hardin, ed., Stalking the Wild Taboo, 2nd ed. (William Kaufmann, Los Altos, Calif., 1978). Note that some things have changed; to keep the population of Earth from growing today, we would have to export to space 95 million people annually!

24. This story received broad coverage in both electronic and print media; for instance, New York Times, May 8, 1989.

25. For a discussion of natural selection and evolution written for nonspecialists, see P. R. Ehrlich, The Machinery of Nature (Simon and Schuster, New York, 1986).

26. As discussed in Chapter 10, "population control" does not require coercion, only attention to the needs of society.