Paul R. Ehrlich & Anne H. Ehrlich, The Population Explosion, 1990.
The One-Time Bonanza
More people would be demanding action now if they realized that global civilization is behaving in a manner they would not tolerate in themselves, their families, or a corporation they work for or invest in.
Think of it this way. Suppose there were two brothers who as young men each inherited a great fortune from their father. Suppose the elder brother invested his fortune in sound enterprises that yielded regular dividends and in an interest-bearing savings account in a bank. The dividends and interest from his invested capital would provide this young man with an income on which he could live comfortably, if not munificently, for the rest of his life. Mindful of the many decades of effort and work by his father and earlier forebears to build up the fortune, he was always careful to husband his capital and invest in ways that would further enlarge it if possible, in order to pass on the inheritance to his children and their descendants.
Suppose the younger brother, by contrast, was more interested in enjoying the present than in planning for the future. 
He invested his money, too, but with a less careful eye to protecting and enhancing his inheritance. He lived beyond the income from his investments, becoming increasingly dependent on inroads on his capital to support himself and his large family in luxury. In addition, some of his inheritance was lost through unwise investments. As the capital diminished, so did the income; so he was forced to depend more and more on capital to maintain his affluent lifestyle. The younger brother had run through his entire fortune well before his death and had nothing left to support himself in his old age or to hand on to his children, who instead were left with the burden of supporting their profligate parent.
SQUANDERING OUR INHERITANCE
Homo sapiens, like the two sons in our story, "inherited" a priceless fortune: the planet Earth and the riches it contained. Part of that one-time bonanza is, of course, the great deposits of fossil fuels that have powered industrial civilization. Even politicians and economists have gradually become aware of the finite nature of the fossil-fuel supply. But there are other riches, less obvious, perhaps, but even more valuable.
Arguably the greatest treasure consists of the millions of other kinds of organisms -- plants, animals, and microbes -- with which people share the planet. These other living beings have provided us with all our foods; with wood, fibers, and skins for clothing and shelter; and with medicines, oils, soaps, resins, rubber, and uncountable other useful items. Many organisms, of course, we domesticated and often improved by selective breeding to make them even more useful to us. Here we "invested" wisely; but we weren't investing income, we were investing part of our inheritance to increase income.
More important, that treasure of other species plays critical roles in providing us a hospitable environment. That environment includes such essentials as a favorable climate, breathable air, and deep, fertile soils. All these came into existence over eons, in part as outcomes of the evolution of the Earth's diversity of life forms. Similarly, the fossil fuels -- coal, oil, peat, and natural gas -- are the geologically processed and
 preserved remains of ancient plants and microorganisms. The human inheritance also includes inorganic treasures, such as vast underground supplies of pure fresh water as well as concentrated deposits of dozens of useful metals, from copper, iron, and mercury to zinc, all of which our clever species eventually learned to exploit.
For the first several million years of their existence, human beings, like other animals, were dependent for their resources (apart from air to breathe and water to drink) almost entirely on other living organisms -- the plants and animals they ate or used for fuel or to fashion simple tools, shelter, and clothing. All these are renewable resources, naturally reproducing themselves, or, in the case of water, continually being replenished by natural processes that involve plants, animals, and microorganisms. In a real sense, early people, like the prudent elder son of our analogy, were living on the income from their inheritance.
With the invention of agriculture, things began to change. Human beings not only learned to manipulate their biological environment to enhance their food supplies, they soon discovered the value of metals -- the first significant use of nonrenewable resources. Agricultural people later overexploited some renewable resources such as soil (by depleting it of nutrients, failing to control erosion, or allowing irrigated fields to accumulate salts) and forests (by cutting them faster than they could regenerate). These resources, once naturally replenished, were thus effectively made nonrenewable. By using metals and converting renewable resources to nonrenewable ones, human beings unwittingly began making inroads on their capital endowment. And those inroads, slightly at first and then more and more, provided the support for humanity's expanding populations.
Human beings greatly accelerated their shift from living on income (renewable resources) to depleting capital (nonrenewable resources) with the advent of the industrial age and the harnessing first of coal and then of petroleum and natural gas
 as fuels. These seemingly abundant and cheap sources of energy permitted large-scale replacement of human labor in both manufacturing and agricultural production. They also allowed more rapid exploitation of other nonrenewable resources, making extraction easier and remote deposits more accessible.
The availability of "cheap" energy also made possible the development of powerful farm machinery, and abundant oil and gas allowed development of synthetic fertilizers, pesticides, and other products to boost crop yields (production per acre) considerably above those achieved with traditional methods. Similarly, we can thank fossil energy for facilitating the production of many useful goods1 and for stimulating unprece-dentedly rapid expansion of economies and of food production. In effect, fossil energy facilitated the population explosion of the twentieth century.
Finally, cheap energy has accelerated humanity's conversion of resources from renewable to nonrenewable, both through overuse and through pollution. Overuse converts renewable resources to nonrenewable ones by using them faster than they can be "renewed." Pollution, on the other hand, can simply render them unusable.
Overexploitation of two essential "renewable" resources, topsoil and groundwater, has resulted from efforts to maximize agricultural production in the short term to support ever-increasing numbers of people. Because the necessary actions to conserve soil have been neglected, enormous amounts of priceless topsoil have been washed or blown away.2 Soil is irreplaceable on any time scale of interest to society today; centuries or millennia (depending on the situation) are normally required to produce a few inches. Losses of soil to erosion in natural ecosystems,3 such as grasslands and forests, are negligible and are usually compensated by natural processes of soil generation. In agricultural systems, by contrast, losses can be measured in inches per decade or tons per acre per year.
Contrary to popular impressions, manufactured fertilizers are not substitutes for natural fertility in soils, and certainly not for soils themselves. The use of fertilizers can  temporarily mask losses due to erosion, but they ordinarily provide only
two or three of the twenty or so nutrients required by crops. Nor do they supply needed soil structure or the complex living community of soil organisms that often are involved in the uptake of nutrients by the crops.4
While certain tilling and planting methods can dramatically reduce rates of erosion, short-term economics commonly works against soil protection. Global soil losses in excess of new soil formation have been estimated at 24 to 26 billion tons per year.5 As agricultural economist Lester Brown, president of Worldwatch Institute, has observed, civilization might survive the exhaustion of petroleum reserves, but not exhaustion of the world's agricultural topsoil.6
Similarly, water is being withdrawn from underground stores (aquifers) many times faster than it is being replaced by nature -- all to support the expanding human enterprise. Most people realize there are limits to how much oil can be pumped, but few realize that humanity is also mining a finite reservoir of groundwater. A good example is the rapid depletion of accessible portions of the Ogallala aquifer underlying the Great Plains of the United States. That water accumulated during the last ice age; in some places (especially in the southern high plains) where the Ogallala takes in about a half inch of water a year, the water level drops four to six feet annually as pumps empty the aquifer to irrigate cropland. Mining southern parts of the aquifer to economic exhaustion in less than half a century amounts to the greatest overdraft of groundwater in human history. The rate of net withdrawal today is roughly equal to the flow of the Colorado River.7
That overdraft is deliberate, a policy established on the assumption that an infinite number of tappable water resources exists. As the state engineer of New Mexico put it, "We can always decide to build some more water projects."8 But we can't if the water isn't there. The draining of accessible portions of the Ogallala aquifer in the next few decades will result in bankruptcy for many farmers in the Great Plains and a loss of production of much of the grain that the United States now exports. Overdrafts can destroy aquifers permanently. The water-filled cavities in rock formations sometimes collapse after the water is pumped out, or, in coastal areas, aquifers may be infiltrated by salt water. 
The Ogallala overdraft is just one case of turning a renewable water resource into one that is, in essence, nonrenewable. In California's San Joaquin Valley, aquifers are being pumped at a rate that exceeds recharge by more than 500 billion gallons annually -- and the rate is rising. That enormous overdraft to support irrigation in one California valley is difficult to visualize. It can perhaps best be pictured as roughly double the flow of oil into the American economy each year. Think of it. Double the number of arriving supertankers, double the flow of all those oil wells offshore and onshore, just to represent the drainage of the supply of groundwater under the southern half of California's Central Valley!
How long it can continue is not clear, although as the aquifer is depleted, the cost of pumping will rise substantially. As water analyst Marc Reisner put it, "It depends on a lot of things, such as the price of food and the cost of energy and the question of whether, as carbon dioxide changes the world's climate, California becomes drier."9 All those factors, of course, partly depend on the size of the human population.
Overdrafts on aquifers are a worldwide problem; in India, for example, tube wells are lowering water tables under? much of the nation. One Indian scientist recently noted about India's "water crisis":
Natural resources of the drought-affected and drought~prone lands become too limited to sustain and nourish the vastly multiplying human populations and the livestock . . . we shall have to put in a herculean endeavour to maintain any viable balance between the hungry people and the remnants of fertile land. . . . Our scientific know-how has no potential to increase the natural water supply. At the same time we are exerting too much pressure on the ground water for irrigating senji-arid lands without replenishing it.10
In China, per-capita water consumption is only one-fifth that of the United States, and demand is increasing rapidly. Industrial water use is expected almost to double from 1980 to 2000, and that by urban residents to quadruple. Water shortages are expected in 450 of China's 644 cities by the turn of
the century; by 1989, the
aquifers supplying Beijing and Tianjin had already been drained.11
Overdrafts on aquifers are one reason some of our geologist colleagues are convinced that water shortages will bring the human population explosion to a halt. There are substitutes for oil; there is no substitute for fresh water.12 Unfortunately, the mindless attitudes of some engineers (and economists and politicians) are found worldwide: "We can always decide to build some more water projects."
Overdrafts are not the only problem facing aquifers. They can also be poisoned by human activities and their contents thus rendered unusable. The expanding U.S. economy produces more and morej products whose manufacture creates toxic wastes. Poisons peeping into the ground from accidental spills and unsealed dumps can more or less permanently pollute aquifers. Sunlight and microorganisms are essential to natural purifying processes, but the former is absent underground and the latter in short supply. Some aquifers have even been poisoned by longJived radioactive materials seeping into them from sites of nuclear-weapons manufacturing and processing facilities scattered over a dozen states.13
Our growing population also "demands" more highways, streets, sidewalks, and parking lots. Paving over large areas often results in rainfall streaming into rivers or the sea directly or through sewers, rather than percolating into the ground to recharge aquifers. So at the same time that we are draining aquifers for agriculture, industry, and drinking water, we are interfering with the processes that replenish them.
THE ASSAULT ON BIOTIC DIVERSITY
Perhaps the most crucial part of humanity's inheritance being squandered to support rising overpopulation is Earth's biotic diversity ("biodiversity"). The planet's plants, animals, and microorganisms are now threatened with a colossal extinction epidemic.14 It may prove to be a crisis even more severe than the natural episode that ended the reign of dinosaurs some 65 million years ago. There are aesthetic and ethical reasons for deep concern about the decimation of humanity's only known
 living companions in the universe, but most people will probably feel the impacts of lost biodiversity through repercussions on the economic system.
Humanity has already borrowed the very basis of its civilization from nature's "genetic library" -- including all crops and domestic animals, important industrial materials, and the active ingredients of numerous prescription medicines. A handful of species of scruffy grasses from that library, through thousands of years of selective breeding, have been turned into wheat, rice, maize (corn), and other grains. The 1.7 billion or so tons of those grains produced annually are the feeding base of humanity.
Even so, the potential of the library to provide such useful items has barely been tapped. In exterminating genetically distinct populations and species, Homo sapiens is foreclosing myriad opportunities to improve the health and welfare of its exploding population through as-yet-undiscovered new foods, medicines, and industrial materials.15 Indeed, we are even removing the raw material on which genetic engineering depends, threatening to close down a technology that many are counting on to improve the human condition. Genetic engineers do not create brand-new genes, they transfer genes of known function from one organism to another. They are dependent on nature's library to provide the genes they transfer.
Even more worrisome, the reduction of genetic diversity threatens humanity's capacity to maintain high-yielding strains of its most important crops, which often can be improved only by transferring genes from wild relatives. In many parts of the world, close relatives of crop plants are being wiped out. As a result, the crops may become increasingly vulnerable to pest attacks and adverse weather.
But the most serious impacts of extinctions on society are not these direct economic losses, but the consequences of disrupting ecological systems, which support humanity by supplying us with indispensable "ecosystem services."16 All of these services depend on the participation of plants, animals, and microorganisms. Two vital services are control of the proportions of gases in the atmosphere (which influences the climate) and regulation of the hydrologic cycle -- the circulation of
 water through oceans, atmosphere, and land (including flood control and aquifer recharge). Additional services are generation and maintenance of soils, disposal of wastes, and recycling of nutrients; the pollination of crops and control of the vast majority of pests that potentially could attack them; and the provision of forest products and food from the sea.
One of the main reasons that many people are able to avoid facing the population problem is that they remain ignorant of the functioning of those most critical parts of the human inheritance -- the ecological systems that support civilization. (A brief review of some basics of "how earth works" can be found in the Appendix.)17
Without the necessary biological background, laypeople are not in a position to understand either the constraints within which humanity must operate or the origins of those constraints. They can't understand why the human population has exploded or why the exploding human population threatens the very existence of civilization. They have little awareness of interactions between themselves and populations of other living beings and their nonliving environment.
This lack of understanding represents a colossal failure of education, a failure that goes unrecognized by most "educated" people. Years ago, the great naturalist
observed that ecologists live in a "world of wounds" that thinks itself whole.18 Today that world is bleeding to death, yet the average person goes about his or her business quite oblivious to it.
EXTINCTIONS AND NATURE'S GENETIC LIBRARY
Let's look more closely at a major part of that hemorrhage, the loss of biotic diversity. Evolution and coevolution (the reciprocal evolutionary interactions of ecologically intimate organisms)19 have produced the vast variety of life forms that make up Earth's biotic resources and that comprise the extraordinary richness of tropical forest communities.20 Evolution and coevolution are also responsible for the enormous variety of chemical compounds that organisms, especially microorganisms and plants, produce to serve their own ends -- especially
 defense against their enemies. That diversity of life forms constitutes the genetic library that we have already found so valuable; the biochemicals produced by organisms are among its chief benefits.
The library also contains those wild relatives of crops that serve as sources of genes to help the crops keep winning their coevolutionary races with the pests that attack them. Genetic variability is an essential tool of the plant evolutionists who are responsible for maintaining agricultural productivity. For instance, new wheat strains resistant to rust fungi have a life expectancy of only about five years in the northwestern United States. Then a new variety of fungus evolves that can attack the strain, and a new crop strain that is resistant to the rust must be ready for planting. But creation of that new strain is possible only if the requisite genes are available.
Genetic variability is also necessary to permit crops (and domestic animals) to adjust to variations in climate. The importance of being able to do that is highlighted by the prospect of extremely rapid climate change in coming decades as a result of global warming.
As humanity destroys biodiversity in tropical forests and elsewhere, it reduces the pool of genetic variability needed to stay in the game of high-yield agriculture. The loss of biodiversity also deprives us of tools that might help in the struggle to feed ever-increasing numbers of people. For example, only a few of the more than a quarter-million kinds of plants that exist have been investigated for their potential as crops. Some, such as some Central American grain amaranths (cereals in the pigweed family), appear capable of greatly increasing food production in some tropical areas.21 Many other opportunities for creating new foods are doubtless "out there" in the library, awaiting discovery and development. But the destruction over the next few decades of the tropical forests promises to remove permanently virtually all possibilities of benefiting from that part of the genetic library.
Growing human populations are not only eroding the basis of agriculture, they are destroying the source of many of the most effective medicines (compounds such as aspirin and quinine were evolved as plant defenses). About a third of all  prescription medicines are either plant defensive chemicals or chemicals modeled on them. Moreover, the chemicals present vary both from one plant species to another and among populations of the same species, so preserving different populations is as important as preserving representatives of each species. Conceivably, every time a square mile of tropical rain forest is burned, a drug with potential to help treat cancer or AIDS or some other deadly or crippling disease is lost forever.
Human overpopulation contributes in many ways to the destruction of rain forests and the species they contain, ironically compromising the chances for those increasing numbers of people to live long and productive lives. But the extinction of populations of plants and animals often disrupts ecosystem services well before entire species are seen to be threatened. The extermination of plant populations, for instance, can change the climate locally and also have severe regional effects through disturbance of the hydrologic cycle.
Human population growth in the Himalayas of central Asia after World War II has led to the disappearance of many populations of trees on the mountain slopes. The ecosystem's control of the hydrologic cycle was impaired, as exposed soil, no longer held in place by roots and sheltered from the force of downpours, eroded away. Much of that soil was washed downstream and has ended up in the joint delta of the Ganges and Brahmaputra rivers -- the nation of Bangladesh.
Bangladesh is vastly overpopulated by any standard, its 115 million people jammed into a country the size of Wisconsin. Many Bangladeshis have been forced onto low-lying silt-bars ("chars"), built partly of Himalayan soil.22 There the people are especially vulnerable to the larger and more frequent floods originating in the now denuded parts of the Himalayas, and to storm surges caused by cyclones in the Bay of Bengal. In 1970, at least 150,000 people in Bangladesh perished when a storm surge swept over the coastal lowlands.23 In 1984, tens of thousands were killed in a similar disaster, and the toll from the 1988 flooding (caused first by rising rivers and then by another cyclone) probably was at least that high. That disaster, which inundated three quarters of the country, left at least 50 million people homeless and destitute. 
COMPETING WITH NATURE
Such events are among the consequences of the ever-increasing scale of human activities. Most people are unaware of the degree to which humanity has taken over Earth's land surface. Eleven percent of the world's land is used to grow crops; perhaps 2 percent is paved over or covered by cities and towns; a quarter serves as pasture for livestock; and most of the 30 percent that is still forested is exploited at some level by humanity or has been converted to tree farms.24 Nearly all the remaining third of Earth's land is in arctic or antarctic regions or desert, or it's too mountainous or otherwise too inhospitable to be of much use to civilization.
Expanding human populations everywhere are replacing natural plant communities with ones that serve human needs, competing with populations of other animals for Earth's bounty, and destroying natural communities outright. As a consequence, the natural ecosystems upon which the human economy is utterly dependent are being degraded as myriads of their living components are exterminated.
The extent of this replacement, competition, and destruction is vast. Humanity directly or indirectly is appropriating a large and growing fraction of the sun's energy that is harnessed through the process of photosynthesis, which is carried out by green plants, algae, and many kinds of bacteria. Virtually all animals and other nonphotosynthesizing organisms ultimately depend on that energy, which they acquire in their food.25 All the solar energy annually captured worldwide by photosynthesizers and not used by them to run their own lives is known as net primary production (NPP).
Human beings and domestic animals directly consume (as food, fodder, and timber) about 4 percent of the NPP produced on land and about 2 percent of that in the oceans.26 This is certainly a disproportionate share for only one of 30 million or so species of animals. Yet an even greater proportion of NPP on land is diverted into human-directed systems, such as vast stretches of land planted in genetically similar crops, with their attendant pests. This widespread replacement of natural communities with human-created ones thus multiplies the human
impact on terrestrial NPP to over 30 percent. Included in this calculation are the NPP produced in recently converted pastures, the NPP consumed when grazing lands are burned to improve forage, and the NPP in plant materials that are killed though not used in timber harvesting or when land is cleared for agriculture. Thus almost eight times as much of the NPP on land as is directly consumed is changed or diverted by human activities into human-controlled systems, featuring different kinds of organisms than live in natural ecosystems.
But that's not all. The conversion from natural to human-dominated ecosystems more often than not results in diminished productivity. Cropland (except when irrigated) usually yields less NPP than the grassland or forest it replaced; pasture is less productive than forest. In addition, people have reduced or eliminated productivity in many areas by paving them over or by creating deserts (a process called desertification), usually through overgrazing, overcultivation, or poorly managed irrigation. Just in the last forty years, global terrestrial NPP has been cut back in these various ways by roughly 13 percent,27 and the reduction is proceeding at an accelerating pace.
Humanity's direct consumption, indirect cooption, and suppression of photosynthetic production thus add up to nearly 40 percent of the planet's potential NPP on land. Including the lesser effects on oceanic systems, the total global impact is about 25 percent. This enormous diversion of the energy resource of all life on Earth goes a long way toward explaining why the vital services supplied by natural ecosystems are deteriorating, why the expansion of food production is becoming increasingly difficult, and why, as a consequence, all nations are less and less secure.
Laypeople might get the mistaken impression that there's no problem if 60 percent of Earth's basic food resources are not directly affected by humanity; but to ecologists these are frightening figures. Perhaps more frightening than the level of takeover, indeed, is the rising fraction of potential productivity that is being lost -- literally a reduction in total carrying capacity for all animal life, including ourselves.
Humanity is not only rearranging the biotic systems of Earth, its impact on the planet's physical makeup is far from
 negligible. For some time, civilization has been mobilizing many minerals at rates much faster than geologic processes such as erosion and weathering. Even in the mid-1960s, humanity was mining iron at a rate roughly twelve times faster than it was being eroded from Earth's crusts by rain and rivers; four times as much manganese was being mined, fifteen times as much lead, and thirty times as much phosphorus.28 Those rates have continued to rise in the last two decades.
This evidence from physical systems, as well as changes in cycles of nutrients such as carbon, nitrogen, and phosphorus and in concentrations of atmospheric gases, reinforces conclusions based on the scale of the diversions and losses of biotic production. Altogether, they show unequivocally that humanity has truly become a global force threatening the very habit-ability of Earth -- its ability to support civilization.
The fraction of terrestrial NPP already lost or diverted into human systems becomes all the more impressive when one realizes that our species seems to be "planning" to double its population again well before the end of the next century. Many people talk of a quintupling of economic activity, in order to allow for taking care of the additional people and raising standards of living.29 Such an expansion implies an assault on global NPP far beyond that already observed. Given current technologies and those that can be foreseen, the planet could not support a quintupled level of human activity for even a brief time.
As any banker or businessman knows, one cannot continue to spend capital at a rapid and increasing rate for very long without going bankrupt -- no matter how rich one is at the start. But society seems unaware that it is swiftly squandering its inheritance. Worse yet, in the process of expending its capital, humanity is steadily degrading the systems that supply it with income. We're eating the goose that lays our golden eggs. Not a very clever course for a species with the hubris to call itself Homo sapiens.30
Having considered some of the ways that humanity is destroying its inheritance, we can look more closely at the concept of
"overpopulation." All too often, overpopulation is thought of simply as crowding: too many people in a given area, too high a population density. For instance, the deputy editor in chief of Forbes magazine pointed out recently, in connection with a plea for more population growth in the United States: "If all the people from China and India lived in the continental U.S. (excluding Alaska), this country would still have a smaller population density than England, Holland, or Belgium."31
The appropriate response is "So what?" Density is generally irrelevant to questions of overpopulation. For instance, if brute density were the criterion, one would have to conclude that Africa is "underpopulated," because it has only 55 people per square mile, while Europe (excluding the USSR) has 261 and Japan 857.32 A more sophisticated measure would take into consideration the amount of Africa not covered by desert or "impenetrable" forest.33 This more habitable portion is just a little over half the continent's area, giving an effective population density of 117 per square mile. That's still only about a fifth of that in the United Kingdom. Even by 2020, Africa's effective density is projected to grow to only about that of France today (266), and few people would consider France excessively crowded or overpopulated.
When people think of crowded countries, they usually contemplate places like the Netherlands (1,031 per square mile), Taiwan (1,604), or Hong Kong (14,218). Even those don't necessarily signal overpopulation -- after all, the Dutch seem to be thriving, and doesn't Hong Kong have a booming economy and fancy hotels? In short, if density were the standard of overpopulation, few nations (and certainly not Earth itself) would be likely to be considered overpopulated in the near future. The error, we repeat, lies in trying to define overpopulation in terms of density; it has long been recognized that density per se ineansvery little.34
The key to understanding overpopulation is not population density but the numbers of people in an area relative to its resources and the capacity of the environment to sustain human activities; that is, to the area's carrying capacity. When is an area overpopulated? When its population can't be maintained without rapidly depleting nonrenewable resources
 (or converting renewable resources into nonrenewable ones) and without degrading the capacity of the environment to support the population. In short, if the long-term carrying capacity of an area is clearly being degraded by its current human occupants, that area is overpopulated.35
By this standard, the entire planet and virtually every nation is already vastly overpopulated. Africa is overpopulated now because, among other indications, its soils and forests are rapidly being depleted -- and that implies that its carrying capacity for human beings will be lower in the future than it is now. The United States is overpopulated because it is depleting its soil and water resources and contributing mightily to the destruction of global environmental systems. Europe, Japan, the Soviet Union, and other rich nations are overpopulated because of their massive contributions to the carbon-dioxide buildup in the atmosphere, among many other reasons.
Almost all the rich nations are overpopulated because they are rapidly drawing down stocks of resources around the world. They don't live solely on the land in their own nations. Like the profligate son of our earlier analogy, they are spending their capital with no thought for the future.
It is especially ironic that Forbes considered the Netherlands not to be overpopulated. This is such a common error that it has been known for two decades as the "Netherlands
Fallacy."36 The Netherlands can support 1,031 people per square mile only because the rest of the world does not. In 1984-86, the Netherlands imported almost 4 million tons of cereals, 130.000 tons of oils, and 480,000 tons of pulses (peas, beans, lentils). It took some of these relatively inexpensive imports and used them to boost their production of expensive exports -- 330,000 tons of milk and 1.2 million tons of meat. The Netherlands also extracted about a half-million tons of fishes from the sea during this period, and imported more in the form of fish meal.37
The Netherlands is also a major importer of minerals, bringing in virtually all the iron, antimony, bauxite, copper, tin, etc., that it requires. Most of its fresh water is "imported" from upstream nations via the Rhine River. The Dutch built their wealth using imported energy. Then, in the 1970s, the
 discovery of a large gas field in the northern part of the nation allowed the Netherlands temporarily to export as gas roughly the equivalent in energy of the petroleum it continued to import. But when the gas fields (which represent about twenty years' worth of Dutch energy consumption at current rates) are exhausted, Holland will once again depend heavily on the rest of the world for fossil fuels or uranium.38
In short, the people of the Netherlands didn't build their prosperity on the bounty of the Netherlands, and are not living on it now. Before World War II, they drew raw materials from their colonies; today they still depend on the resources of much of the world. Saying that the Netherlands is thriving with a density of 1,031 people per square mile simply ignores that those 1,031 Dutch people far exceed the carrying capacity of that square mile.
This "carrying-capacitv'' definition of overgorpopulation is the one used in this book.39 It is important to understand that under this definition a condition of overpopulation might be corrected with no change in the number of people. For instance, the impact of today's 665 million Africans on their resources and environment theoretically might be reduced to the point where the continent would no longer be overpopulated. To see whether this would be possible, population growth would have to be stopped, appropriate assistance given to peasant farmers, and certain other important reforms instituted. Similarly, dramatic changes in American lifestyle might suffice to end overpopulation in the United States without a large population reduction.
But, for now and the foreseeable future, Africa and the United States will remain overpopulated -- and will probably become even more so. To say they are not because, if people changed their ways, overpopulation might be eliminated is simply wrong -- overpopulation is defined by the animals that occupy the turf, behaving as they naturally behave, not by a hypothetical group that might be substituted for them. 
UNEQUAL ACCESS TO THE HUMAN INHERITANCE
Thus far, for simplicity's sake, we've mostly treated humanity as a single family squandering its inheritance. In many ways, that unitary view is accurate, but it leaves out one of the major features of global society: the division of the human species into haves and have-nots, rich nations and poor nations. Even that, of course, is still a simplification; countries like Argentina and Portugal do not fit readily into either category, and almost all countries have both rich and poor segments in their populations.
The economic division of the world has changed somewhat in the four decades or so that we have been intellectually involved with population issues. In 1960, the rich-poor division of nations was sharper. In the 1990s, more countries are "semideveloped," and fewer of them still have the kind of total poverty typical of developing nations in the 1950s and 1960s. Still, the absolute numbers of people living in such poverty are much greater today, and the poorest of the poor have lost ground. Dividing humanity into rich and poor nonetheless remains a convenient simplification for considering how our onetime bonanza is being squandered. And recognizing the basic elements of the gross economic inequities that afflict the world is absolutely critical both to understanding the bind we are in and to finding ways out of it.
The numbers can be summarized briefly. Slightly over one billion people, less than a quarter of the world's population, live in nations whose standard of living -- health, education, diet, housing, and quantity of material possessions -- has improved dramatically over what the vast majority of the world's population enjoyed a century ago. But some four billion people don't. They live in nations where average per-capita wealth is only about a fifteenth of that of the rich nations and where their babies are some five to twenty times as likely to die by the age of one. Of those, nearly a billion live in "absolute poverty" -- defined as being too poor to buy enough food to maintain health or perform a job.40
Rich and poor nations also differ drastically in their rates
of population increase. The poor nations, except China, are growing at an average rate of 2.4 percent a year, which, if continued, would double their populations in about twenty-nine years.41 The poorest populations are among the fastest-growing ones. In contrast, the populations of rich nations are growing at only approximately 0.6 percent annually, which gives a doubling time of some 120 years. These numbers are, remember, averages -- they conceal considerable differences between nations within these groups, just as national statistics do not show the very different states of individuals within countries.
We must always also keep in mind that buried in dry statistics about differences between rich and poor is an enormous amount of human misery, an endless series of almost incomprehensible tragedies. But, even if you don't care about starving children and overburdened parents who live without hope for a future, selfishness alone demands attention to the problems of the poverty-stricken. That is because the plight of the underprivileged of Earth is probably the single most important barrier to keeping our planet habitable.
Without the cooperation of the poor, the most important global environmental problems cannot be solved; and at the moment the poor have precious little reason to listen to appeals for cooperation. Many of them are well aware that the affluent are mindlessly using up humanity's common inheritance -- even as they yearn to help us do it. And all poor people are aware that the rich have the ability to bear the suffering of the poverty-stricken with a stiff upper lip. To remove such attitudes and start helping the less fortunate (and themselves), the rich must understand the plight of the poor not just intellectually but emotionally.
Our own emotional involvement with the sorrows of poor nations began with a visit to India in 1966. The desperate situation of that nation, exacerbated that year by the Bihar famine, left a lasting impression. There was no sign of profligate use of Earth's capital in the form of superabundant consumer goods, but there was abundant evidence of the loss of soils and biodiversity.
In 1989, Paul returned briefly to India and found some 
things improved, some much worse, and the situation of the world's largest democracy even more precarious. The population of 500 million in 1966 had expanded by 325 million, and the results in urban sprawl and poverty were horrifying. But other aspects of the nation remained impressive: the admirable qualities of the Indians, both peasants and sophisticates, with whom he had contact, the rise of a substantial middle class (widely evident in Delhi), and success in increasing agricultural production (people looked comparatively well fed).
But an Indian government report estimated that 2.5 million Indians live their entire lives in the streets and that, of the urban poor, 65 percent have no tap water, 37 percent have no electricity, and 50 percent must defecate in fields and vacant lots.42 India has managed to "keep it together" better than many (including us) expected. Whether it will continue to do so even more overpopulated, with much less topsoil, ground-water, and biodiversity, and in the face of the greenhouse warming and other global ecological problems, is questionable. We cannot be optimistic about the future of that nation -- or ours -- if current trends are allowed to continue.
For one thing, some superficial differences between the two nations have faded. Among the shocking things we saw in our original trip to India were huge numbers of people living in the streets and an army of beggars. Now, in any large American city, one can see many homeless people sleeping in bus stops and on park benches and street gratings. Beggars in New York's Pennsylvania Station are as persistent as those in Old Delhi. In the wake of the Reagan years, several hundred thousand Americans are homeless, and the income gap between the rich and the poor in the United States has grown.43
Many of the consequences of overpopulation in the United States, especially the plight of America's own poor and the nation's huge contributions to global environmental deterioration and resource depletion, are too easily overlooked. But, as we've noted, signs of too many overconsuming people, such as gridlock on freeways and city streets, severe air pollution, growing mountains of garbage, ubiquitous toxic wastes, and escalating crime rates,44 are increasingly apparent.
The United States and India, the rich and the poor, face
 the same basic choice: either to shift in an orderly, planned way to a sustainable human life-support system or to be brutally forced into that shift by nature -- through the untimely deaths of large numbers of human beings. Population control in both rich and poor nations is absolutely essential. If that were achieved, and the rich chose to restrain themselves and to help the poor, the remaining nonrenewable resources could be used to build a bridge to that sustainable future. At the same time, the damage currently being done to nominally replenishable resources would have to be curbed and their replenishment encouraged. Otherwise, those resources will be capable of supporting even fewer people in the future. Sustainable development is needed not just in poor nations, but in rich nations as well (that certainly is not what they have now).45
In short, human numbers and human behavior must be brought into line with the constraints placed upon Homo sapiens by the limits of Earth and the laws of nature. People who think those can be ignored or evaded are living in a dream world. They haven't reflected on the four million years it took for humanity to build a population of two billion people, in contrast to the forty-six years in which the second two billion appeared and the twenty-two years it will take for the arrival of the third two billion. They have overlooked the most important trend of their time.
THE END OF THE GAME
Rich nations have developed an economic system that increasingly depends on consuming humanity's stored inheritance, but which provides very unequal access to it, a system that has encouraged humanity to reach an astonishing level of overpopulation. It is a temporary game.
It should be obvious that an economic system based on consuming our limited capital is inherently self-destructive, but our short-term vision blinds us to the results of our actions. Society has already received warnings that the party may soon be over. Among the most obvious signs in addition to increasing environmental deterioration are the rapidly rising costs of discovering and exploiting new reserves of petroleum and
 other resources, and growing difficulty in expanding supplies of groundwater. The petroleum situation was spotlighted by the Exxon Valdez disaster, which underlined the price to be paid for exploiting oil fields in ecologically sensitive areas. Still, humanity seems incapable of reading the signs properly or of reaching a consensus on appropriate actions to avoid a disastrous final reckoning.46
Instead, each nation seems bent on competing for and quarreling over the pieces of the shrinking resource pie -- even diverting large portions of it into dangerous and wasteful arms races. One need only contrast the great efforts expended to find and defend access to petroleum reserves in the 1980s with the negligible efforts to increase energy efficiency and control population growth. The world might yet be plunged into nuclear war over the Persian Gulf, and the petroleum situation is often discussed in the media. But few people protested the Reagan administration's pro-natalist population po|jcjes. its relaxation of fuel-efficiency requirements for new automobiles, or its dismantling of research and development programs for energy efficiency and alternative energy sources -- all of which were senseless policies when viewed in a long-term perspective.
Serious consequences arising from such irresponsible behavior will sooner or later overtake us. The depletion of the one-time bonanza of resources will eventually force humanity to return to dependence on renewable resources -- to live on income rather than burn capital.
Could a population as large as today's -- let alone one much larger -- ever be supported only on income? At the moment, we don't know how to do it, and it may not be possible. Among the things that may make it impossible will be the social and political responses to increasing scarcity and environmental deterioration.
But before looking at these questions, let's get some background by tracing how we got into our current predicament. How did we ever get ourselves into a situation of squandering our capital and calling it "growth"?
1. Including synthetic substances such as plastics derived directly from the fossil fuels themselves.
2. L. Brown et al., State of the World 1989 (Norton, New York, 1989). See also Council on Environmental Quality and the Department of State, The Global 2000 Report to the President (Government Printing Office, Washington, D.C., 1980).
3. All the organisms -- plants, animals, and microbes -- that live in an area are the community (more technically, "biological community") of that area. The community and the physical environment with which it interacts are an ecosystem. It is usually important to specify the ecosystem one is discussing. The plants, fishes, snails, and microorganisms in an aquarium along with the water and the gravel are an ecosystem; so is the entire "shell" near the surface of Earth that contains all living organisms. For more on ecosystems (and communities), see P. Ehrlich, The Machinery of Nature (Simon and Schuster, New York, 1986). For a more technical treatment, see P. Ehrlich and J. Roughgarden, The Science of Ecology (Macmillan, New York, 1987).
4. For a brief overview of soil ecosystems, see P. Ehrlich, The Machinery of Nature. More detail is provided in P. Ehrlich, A. Ehrlich, and J. Holdren, Ecoscience: Population, Resources, Environment (Freeman, San Francisco, 1977).
5. Brown et al., State of the World 1989.
6. L. R. Brown, Building a Sustainable Society (Norton, New York, 1981), p. 13.
7. An excellent discussion of America's profligate use of the limited water of its semidesert West can be found in Marc Reisner, Cadillac Desert: The American West and Its Disappearing Water (Viking, New York, 1986). This book reads like a novel -- a true horror story of how part of humanity's one-time bonanza is being consumed. Numbers on overdrafts come from this source. See also M. Glantz and J. Ausubel, "The Ogallala Aquifer and Carbon Dioxide: Comparison and Convergence," Environmental Conservation, vol. 11, pp. 123-31 (1984). Curiously, the latter doesn't mention population control as part of the solution to either the overdraft of the aquifer or the rise in greenhouse gases.
8. Quoted in Reisner, Cadillac Desert, p. 11.
9. Reisner, op. cit., p. 10.
10. G. M. Oza, "Water Crisis for the Indian Subcontinent," Environmental Awareness (Baroda), vol. 12, pp. 1-2 (1989).
11. Data from China Environmental Review, reported in K. Forestier, "The Degreening of China," New Scientist, July 1, 1989, p. 52.
12. Unlike oil burned as a source of energy, water can be reused if it is
cleaned up. In practice, however, in some uses such as agriculture, much of the water cannot be recovered. In general, we are converting a basically renewable resource into a nonrenewable one by draining aquifers too rapidly and by polluting surface waters beyond our capability of economically purifying them.
13. A. Ehrlich and J. Birks, eds., Hidden Dangers, in press (Sierra Club Books, San Francisco, 1990). See also A. Makhijani, "The Hidden Nuclear Legacy," Technology Review, August/September 1988; and Radioactive Waste Campaign, Deadly Defense (625 Broadway, New York, NY 10012, 1988).
14. For overviews of the biodiversity crisis, see N. Myers, The Sinking Ark (Pergamon Press, New York, 1979); P. Ehrlich and A. Ehrlich, Extinction: The Causes and Consequences of the Disappearance of Species (Random House, New York, 1981); and E. O. Wilson, ed., Biodiversity (National Academy Press, Washington, D.C., 1988).
15. For more details, see Ehrlich and Ehrlich, Extinction.
16. If you are unfamiliar with the concept of an ecosystem, see pages 256-57.
17. See appendix. More can be found in P. Ehrlich, The Machinery of Nature. A more technical treatment can be found in Ehrlich and Roughgarden, The Science of Ecology.
18. Aldo Leopold, Round River (Oxford Univ. Press, New York, 1953). Available in paperback in A Sand County Almanac, with Essays from Round River (Ballantine Books, New York, 1966), p. 197.
19. For more on coevolution, see the Appendix.
20. Here we refer to all the organisms found in tropical forests. Sometimes ecologists will discuss a community restricted to a particular taxonomic group such as the "bird community of the Amazon basin" or the "fish community of the Great Barrier Reefs."
21. For more on the potential of developing new crops, and on the problems caused by the decay of biodiversity in general, see Ehrlich and Ehrlich, Extinction; and N. Myers, A Wealth of Wild Species: Storehouse for Human Welfare (Westview, Boulder, Colo., 1983).
22. Overpopulation often forces people to live in areas where they are more vulnerable to disasters, and the situation isn't limited to poor nations. Lack of space in the San Francisco Bay Area has resulted in tens of thousands of people residing on unstable bay fill and along slide-prone cliff faces. This guarantees longer casualty lists after the next giant earthquake. The phenomenon of differential impacts on large populations resulting from climatic and other factors seemingly not related to population size was first pointed out by H. Andrewartha and L. C. Birch, in their classic text The Distribution and Abundance of Animals (Univ. of Chicago Press, Chicago, 1953).
23. A. Wijkman and L. Timberlake, Natural Disasters: Acts of God or Acts of Man? (Earthscan, Washington, D.C., 1984), p. 69. Since this section was written, a new work has appeared analyzing the Himalayan situation and showing it to be extremely complex. See J. D. Ives and B. Messeric, The Himalayan Dilemma: Reconciling Development and Conservation (Routledge, London, 1989).
24. See any recent edition of United Nations Food and Agriculture Organization (FAO), Production Yearbook (FAO, Rome, Italy).
25. For details, see the Appendix, pages 259-60.
26. P. M. Vitousek, P. R. Ehrlich, A. H. Ehrlich, and P. A. Matson, "Human Appropriation of the Products of Photosynthesis," BioScience, vol. 36 (1986), pp. 368-73.
28. Study of Critical Environmental Problems, Man's Impact on the Global Environment (MIT Press, Cambridge, Mass., 1970).
29. See, for example, J. G. Speth, "A Luddite Recants," The Amicus Journal, Spring 1989. People realize, of course, that if the population doubles with just a doubling of economic activity, gigantic levels of poverty will be perpetuated. They therefore hope that development can greatly increase the size of the economic pie and pull many more people out of poverty. It is basically a humane idea, made insane by the constraints nature places on human activities (constraints that, by the way, Speth partially recognizes in his article, which is a plea for a "greening" of technology).
30. It means the wise or knowing man. Carl von Linne did the actual naming more than two centuries ago, but people have adopted the epithet with abandon.
31. M. Forbes, "Fact and Comment II," Forbes, March 20, 1989. This short article is an unwitting plea for more education on population/resource/ environment issues in America's boardrooms.
32. Population Reference Bureau, 1989 World Population Data Sheet.
33. Paul Harrison, The Greening of Africa (Penguin, New York, 1987).
34. Part of the notion that overpopulation is a matter of density traces to experiments with rats (J. B. Calhoun, "Population Density and Social Pathology," Scientific American, February 1962). If rats are crowded far beyond the densities that are usually found in nature, they start turning homosexual and become irresponsible parents -- even eventually eating their young! That condition of overpopulation is self-correcting. But even in cities like New York and Tokyo, which have enormous human population densities, the number of people is not controlled either by a decline of heterosexuality or by cannibalism. Large cities usually have more social problems than small cities, but so many other factors are at work, and cities differ in so many characteristics besides size, that it's not possible to say much about what constitutes overpopulation in terms of density. The results of experimental research on human crowding are interesting, but shed little light on the issues discussed here. (For the little that is known, see P. R. Ehrlich and J. L. Freedman, "Population, Crowding, and Human Behavior," New Scientist, April 1, 1971.)
35. Defining the area occupied by a human population can be a very complex matter. Parts of New Mexico and Arizona are clearly part of the Los Angeles "area," since electricity for the city is generated there. Much of the city's water comes from the Rockies in Wyoming and Colorado; some comes from northern California. And food for Los Angeles comes from all over the world. The entire U.S. in this sense "occupies" much more area than is found within its borders and contributes to the degradation of the long-term carrying capacity of a great deal of that outside territory. The same, of course, applies to the discussion of the "Netherlands Fallacy" below.
36. See P. Ehrlich and A. Ehrlich, Population, Resources, Environment: Issues in Human Ecology (Freeman, San Francisco, 1972), p. 257; Ehrlich, Ehrlich, and Holdren, Ecoscience.
37. 1984-86 data from World Resources Institute (WRI) and International Institute for Environment and Development (IIED), World Resources 1988-89 (Basic Books, New York, 1989).
38. In 1986, the Netherlands consumed some 3 x 1018 joules of commercial energy, and its 1984 proven recoverable reserves of natural gas were 1.5 X 1012 cubic meters. Each cubic meter contains 3.9 X 107 joules, so that amounts to roughly 6 X 1019 joules, or a 20-year supply (data from World Resources 1988-89; conversions are in John Harte's Consider a Spherical Cow [Wm. Kaufmann, Los Altos, Calif., 1985]). Of course, this calculation assumes no substantial changes either in consumption or in the extent of the reserves.
39. It is, in essence, the definition used in technical ecological work. When a population starts depleting its resources, it is said to be above the carrying capacity of the environment, and a subsequent decline is assumed. Natural populations ordinarily are constrained by the availability of renewable resources and rarely "pollute" their environments. Note that, while a rough definition of human carrying capacity is easily given, calculating that carrying capacity for a given area is usually extremely difficult.
40. World Bank figures cited in WRI and IIED, World Resources 1988-89. The World Health Organization in its annual Report on World Health in 1989 noted that one billion people are suffering from malnourishment or disease (reported in New York Times, Sept. 26, 1989).
41. If China were included, that rate in 1989 would have been 2.1 percent, with a doubling time of 32 years. China, with 1.1 billion people, had a rate of natural increase of 1.4 percent in 1989, but the birthrate was going up ("China Population Hits 1.1 Billion -- Births Called 'Out of Control,' " San Francisco Chronicle, April 15, 1989).
42. Times of India, Feb. 20, 1989.
43. Numerous reports and articles have appeared recently documenting the economic redistribution of wealth in the U.S. since 1980; for example: P. Passell, "Forces in Society, and Reaganism, Helped Dig Deeper Hole for Poor," New York Times, July 16, 1989; E. F. Hollings, "Decaying America: The Underside of Reagan Legacy," Washington Post Weekly Edition, May 8-14, 1989; P. Peterson, "The Morning After," Atlantic Monthly, October 1987; S. H. Preston, "Children and the Elderly in the U.S.," Scientific American, December 1984.
44. The exact relationship of urban problems such as crime to population size and growth is not well understood, and many other factors are clearly involved. The issue is discussed further in Chapter 7.
45. The present status of the rich nations is best described as "overdevelopment" (see Ehrlich, Ehrlich, and Holdren, Ecoscience, pp. 926-30).
46. R. Ornstein and P. Ehrlich, New World/New Mind: Moving Toward Conscious Evolution (Doubleday, New York, 1989).