The concept of an ecological footprint (Wackernagel and Rees, 1996) provides a persuasive and reasonably simple way for measuring and visualizing the resources required to sustain households, communities, regions, and nations. The complex issues of the planet's carrying capacity for humans (e.g., Abernethy, 2001), sustainability (e.g., Hawken et al., 1999), and resource use are interrelated. The ecological footprint in hectares per person is 4.3 in Canada, 5.1 in the United States, 0.4 in India, and 1.8 for the world as a whole. The average immigrant to the United States would increase his/her individual ecological footprint size by 3.3 hectares (from 1.8 world average to 5.1 United States average).

Wackernagel and Rees (1996) note that small ecological footprints do not necessarily imply a low quality of life. Kerala, a southern state in India, has a per capita income of about $1/day (less than 1/60 of North American incomes). However, life expectancy, infant mortality, and literacy rates in Kerala are similar to those of industrialized countries, and the inhabitants have good health care and educational systems and a fairly stable population size. Wackernagel and Rees (1996) conclude that Kerala's exceptional standard of living, coupled with a small ecological footprint, is based more on accumulated social capital than on manufactured capital.

Some of the attributes that most societies profess to value, such as literacy, good health, and social capital, are not closely correlated with the size of the ecological footprint, either per capita or as a society. It is ironic, as Cairns (2000) notes, that people in the United States and many other cultures prize longevity while they continue to despoil the environment. One would think that they would be interested in sustainable use of the planet so that a longer life would not be subjected to a quality of life that has deteriorated dramatically during this period. Increasing the size of the per capita or societal footprint virtually guarantees that the quality of life will deteriorate from more polluted air, water, noise, and all the other factors associated with rapid growth on a finite planet.

If Americans were willing to decrease their per capita ecological footprint to that of Kerala's per capita footprint size, the immigration process in the United States could continue for longer than half a century. Ultimately, immigration would have to stop to avoid diminishing those attributes the United States professes to prize. Immigration is only viable on a long-term basis if the inhabitants of a country are not reproducing at replacement rates or are willing to reduce their per capita ecological footprint so as to share resources with the newcomers. Immigration is a threat if it increases the size of the per capita ecological footprint and pushes a population beyond the carrying capacity for the desired quality of life.
 

As Kuhn (1970) noted, a paradigm is a belief so strongly held that, even when contrary evidence appears, the evidence is rejected. Paradigms bring a sense of reality to a chaotic world. However, they are not reality, merely models of it. Paradigms are extraordinarily durable and humans cling to them tenaciously. So, paradigms are not only models, but tenaciously held beliefs.

A quotation from George Washington (Ellis, 2001, p. 7) depicts the United States as a fount of unlimited resources that is available to enterprising individuals of whatever background.

The Citizens of America placed in the most enviable condition, as the sole Lords and Proprietors of a vast Tract of Continent, comprehending all the various soils and climates of the World, and abounding with all the necessaries and conveniences of life, are now by the late satisfactory pacification (Peace Treaty of Paris], acknowledged to be possessed of absolute freedom and Independence, They are, from this period, to be considered as Actors on a most conspicuous Theatre, which seems to be peculiarly designed by Providence for the display of human greatness and felicity.

Unremarked here but understood and made explicit elsewhere in colonial writings (e.g., Ellis, 2001) is the idea that, even though the citizens had had access to these resources for a length of time, they had "done" nothing to them: the rivers remained unharnessed, the timber uncut, etc., so that the commercial value was not realized. A modern example is the idea that oil in Alaska is no good in the ground when Americans are paying "high" prices at the gas pump. In short, the paradigm of limited or finite resources is un-American. And if resources are viewed as infinite, why not invite the less fortunate to immigrate and share them?

A poem by Emma Lazarus entitled "The New Colossus" is engraved on a tablet within the pedestal on which the Statue of Liberty stands and is an eloquent statement of a paradigm that clearly has outlived its usefulness, but that United States citizens are extremely reluctant to abandon. The poem reads in part: "Give me your tired, your poor, /Your huddled masses yearning to breathe free, /The wretched refuse of your teeming shore. /Send these, the homeless, tempest-tost to me, /I lift my lamp beside the golden door!"

This nation must consider if these words are still valid today.

In addressing this statement, everyone should remember that all Americans are former immigrants or descendants of immigrants. Persuasive archeological evidence indicates that humans only recently arrived in the Americas, in geologic time. Since all humans are similar genetically, no particular group of immigrants, as a category, is superior to any other group. Altering immigration policy should be neither characterized as racist nor prejudiced in other ways. However, it is legitimate to inquire whether present immigration practices are ecologically sound —that is, are they sustainable for an indefinite period?

Leo (2001) notes for the United States immigration policies that "under the Immigration and Naturalization Act foreigners are eligible for asylum if they face the risk of persecution on the basis of `race, religion, nationality, membership in a particular social group, or political opinion."' Leo also notes that the term social group "has been stretched to include disabled people, women who fear genital mutilation, and homosexuals who fear persecution. The compassion is admirable but identity politics and ideology are creeping in."

While the criteria for entrance into the United States are continually being weakened, or made more inclusive, many citizens of the United States, including large numbers of children, lack adequate medical care and medical insurance. The educational system badly needs strengthening at all levels, and the infrastructure of the country, including such things as the water delivery systems for many large cities, sewage treatment plants, and the like, are badly in need of modernization. Clearly, if the nation is unwilling to provide medical care for the huge numbers of people who are already citizens and a better education for the young, the United States is not likely to be willing to share resources with immigrants. In short, the immigration policy seems to be a political statement with no substance or intention to treat immigrants any better or as well as some of the presently needy and homeless already present in the United States as lawful citizens.

If human society is truly interested in sustainable use of the planet and leaving a habitable planet for its descendants, there is an ultimate test of these aspirations and that is to ask, "is the present practice sustainable for an indefinite period of time?" Present immigration practices and policies are probably not sustainable for even another century or less (e.g., Lutton and Tanton, 1994). If the United States were to continue increasing its population at the present rate and maintain per capita resource consumption at its present levels, the American society would be using an even more disproportionate share of the planet's resources than it now does.

With one billion people already receiving substandard nutrition globally and billions more only modestly better fed, it seems unlikely that these people will cheerfully relinquish already inadequate resources so that those in the United States can have still more to increase the per capita ecological footprint size of immigrants to that of the average present American citizen.

Politics aside, the United States tends to encourage immigration by those with particular technological, scientific, or engineering skills, who are ambitious for upward mobility economically, who are entrepreneurs, and, above all, who are apparently willing to risk their lives to achieve their goals. In return, the immigrants expect to enjoy the same material blessings as present American citizens.

As an aside, Charles Kennedy (personal communication) has commented on the era when the state of India was organizing itself after independence. The large estates of the nabobs and maharajahs were to be broken up into holdings for individual citizen-farmers. The question then arose, what size should these parcels be? A sociological study was carried out by sending interviewers into the villages and asking the farmers how much land they could handle. The response average was four hectares and the number explained this way: "I can live on one hectare with my family and lease out the other three as a landlord." Clearly, allocating resources will not be easy.
 

Bhutan became the last country in the world to have its own television station (Guha et al., 2001) when the Bhutanese government's long-standing ban on television came to an end on 2 June 1999. At present, the new station broadcasts only to the capital city of Thimphu, using English and Dzongkha, the national language. Although television can be a great educational tool, its dominant message, particularly in the United States and many other parts of the world, is materialistic. Without doubt, the degree of materialism is highly correlated with human impact on natural systems.
 

The precautionary principle (Raffensperger and Tickner, 1999) states that, when an activity raises threats of harm to human health or the environment, precautionary measures should be taken even if some cause-and-effect relationships are not fully established scientifically.

Essentially, the precautionary principle challenges individuals and society collectively to use common sense and to act wisely and well. This rephrasing of an old rule ("an ounce of prevention is worth a pound of cure") shifts the burden of proof for the consequences of a particular course of action to those espousing it rather than those trying to prevent it. The quest for sustainable use of the planet involves assessing all of the multiple dimensions likely to affect the outcome in an aggregate or holistic fashion rather than individually, however important the individual issue might be. Further, sustainability requires studying highly complex, poorly understood systems for which the breakpoints and/or thresholds are not amenable to laboratory studies and may not be apparent until they have been crossed.

Immigration policy seems a superb, though extremely challenging, test of the difficulties of implementing the precautionary principle! Certainly the precautionary principle is a sine qua non for sustainable use of the planet because sustainable use should be based on preventing mistakes rather than correcting them after they occur.

Too many countries have unsustainable practices, and, without public participation in decision making, taking preventative action in the face of uncertainty would be extremely difficult, arguably impossible. This situation is especially true when economic growth is needed while simultaneously protecting the integrity of natural systems. Some publications have explored these difficult issues (e.g., National Research Council, 1996; Nattrass and Altomare, 1999; Hawken et al., 1999).

The immigration problem would be diminished if all countries had more sustainable practices, including the United States, which is a magnet for immigrants because of its disproportionate use of the world's resources. The average Mexican making thirty-five pesos (U.S. $3.60) per day is well aware of the disparity in affluence as are anti-globalization demonstrators world-wide (e.g., Carl, 2001). The central issue is, how compatible are present rates of immigration and concomitant demographic changes with political stability and sustainable use of the natural resources of the United States?

Unquestionably, the precautionary principle is one of the crucial keys to facilitating sustainable use of the planet and, concomitantly, the key to the badly needed feedback relationships between scientists and policymakers. The American Association for the Advancement of Science has taken a major step by establishing the Program in Scientific Freedom, Responsibility and Law/Court Appointed Scientific Experts, < http://www.aaas.org/spp/case/advisory.htm > or < http://www.aaas. org/spp/case/panel.htm >. It is important for scientists to maintain their objectivity and integrity while carrying out their research, but they must be increasingly aware of the policy implications of what they do and their concomitant social responsibility to contribute to the protection of human health and the interdependent web of life.

My own preliminary assessment follows on some of the issues important in implementing the precautionary principle with regard to immigration policy:

1. Barring some tremendous increase in mortality in the present population of the United States, immigration cannot continue at its present level for an indefinite period without serious damage to the integrity of the ecological life support system and the quality of life of individual citizens.

2. Immigration to the United States does not appear to have helped donor countries in markedly progressing towards sustainability nor in reducing the problems that prompted individuals to leave the country. Clearly the United States could not reasonably accept even one-fourth of the one billion or more people presently on the planet whose living conditions are dramatically substandard (i.e., living on less than U.S. $1 per day per capita). The precautionary principle might be best implemented by helping other countries to make conditions more attractive for their inhabitants and to live more sustainably than to create problems in the United States by accepting only a tiny fraction of the world's migrating inhabitants.

3. Given the pulsating paradigm eloquently stated by the Odums (1995), one of the non-ecological pulses under human control is the rate of immigration. The fewer pulses policymakers must contend with, the more likely they are to achieve sustainable use of the planet. When other cultures have exceeded the carrying capacity of their territory substantially, it has not only resulted in famine, disease, and a lowering of the population, but also a lowering of the carrying capacity. The precautionary principle suggests that when environmental thresholds are uncertain and/or pulsating, it is prudent not to approach them too closely and definitely not to exceed thresholds such as carrying capacity.

4. Immigration is far less reversible than many other factors affecting sustainability. For example, the size of the country's ecological footprint can be reduced by using less polluting, more fuel efficient automobiles or by consuming fewer resources, but it cannot, barring extreme acts of cruelty, reduce the size of the population substantially by means other than natural death, etc.

5. Immigration to the United States (or any other country) permits donor countries to prolong unsustainable practices by reducing their population size and, thus, their aggregate environmental impact.

6. Immigration frequently alters the demographics of a country and makes sustainable planning more difficult since demographics are extremely important when developing policies for sustainable use of a country or of the planet. For the planet as a whole, of course, the demographics are shifting, but reducing immigration may achieve a local balance without affecting the global balance. Both sustainable practices and policies must be developed locally and changing the demographics seriously affects both.

7. Over the long term, if present rates of immigration into the United States are continued, resource availability per capita will almost certainly diminish, thus making the country less attractive to immigrants. The transition to sustainable practices requires more efficient resource use and concomitantly reducing the size of the ecological footprint of the average citizen as well as that of the nation as a whole. It is difficult to envision the circumstances under which the present immigration rate would facilitate this process. The quest for sustainability appears to mean putting other species ahead of humans and that there is a lack of compassion for less fortunate people elsewhere on the planet —a serious ethical problem.

8. The Durants (1968, pp. 19-21) list some biological lessons of history. The first of these is that life is competition. Competition is not only the life of trade, it is the trade of life —peaceful when food abounds, violent when the mouths outrun the food.

The second biological lesson of history is that life is selection. In the competition for food or mates or power, some organisms succeed and some fail. In the struggle for existence, some individuals are better equipped than others to meet the test of survival. Nature loves difference as the necessary material of selection and evolution. Inequality is not only natural and inborn, it grows with the complexity of civilization.

The third biological lesson of history is that life must breed. Nature has no use for organisms, variations, or groups that cannot reproduce abundantly. She has a passion for quantity as prerequisite to the selection of quality. She is more interested in the species than in the individual, and does not care that a high birth rate has usually accompanied a culturally low civilization and a low birth rate a civilization culturally high.

Thus, to the extent that encouraging immigration is a form of egalitarianism and a drive toward equality, the lessons of history are that nature will frustrate this attempt. To the degree that the quest for sustainable use of the planet is a concomitant drive toward egalitarianism and equality within the human species, it will be frustrated by nature. If, however, the quest for sustainable use of the planet is an attempt to preserve and accumulate natural capital (as espoused by Hawken et al., 1999) and protect the planet's ecological life support system and the services it provides to humanity, it is not egalitarian but rather enlightened self-interest.