The planet Earth is a mixed living and nonliving system. It is the suprasystem of an supranational systems as well as the total ecological system, with all its living and nonliving components. The Earth is studied in this article in terms of a general theory of all concrete systems, with special attention to the important subset of living systems. The Earth is an open system, interacting with its atmosphere and with matter and energy in space. Its systemwide processes and the processes of its various components, as well as their variables and indicators, are discussed. In the light of known facts about the Earth as a system, consideration is given to future worldwide problems which must be dealt with by human planners and statesmen.
KEY WORDS: Earth, suprasystem of supranational systems and total ecological systems, all living systems, nonliving systems, all subsystems, worldwide policy.
THE PLANET EARTH, from its center to the outer limits of its atmosphere, including everything in and on it, is a mixed living and nonliving system within the solar system, the Milky Way galaxy, and, ultimately, the universe. -
When we say that something is a system, we are saying that it has a set of characteristics that are common to all systems and lacking in things that are not systems. A system necessarily has parts (or units, or components); these parts have some common properties, are interdependent, and interact within the system.
The parts of this system are aggregations of matter and energy that differ greatly in size, in other aspects of physical structure, in behavior, and in duration of existence. These parts are observed to interact in exceedingly complex ways. The pervasiveness of the interdependence among all parts of the Earth system is becoming increasingly apparent as the widespread effects of changes in variables are traced.
The world is a concrete system, which we define as a nonrandom accumulation of matter and energy in a region in physical Space-time organized into interacting, interrelated subsystems and components. The word "system" also refers to systems of actions abstracted from the behavior of organisms (abstracted svstems) and to systems of ideas expressed in symbolic form (conceptual systems); but the first meaning will be intended here unless we specify one of the others.
Concrete systems are phenomena of the physical world. They include atoms, molecules, planets, solar systems, star systems, galaxies, and; ultimately, the entire universe. Living systems of all sorts are also concrete systems, as are ecological systems with biotic and abiotic components. The various machines people make and use as well as man-machine and animal-machine systems are concrete systems also.
An orderly progression in complexity is evident from subatomic particles to the total universe. Atoms make up molecules, molecules combine into all the substances of the physical world, planets make up the planetary systems that revolve around suns, and so onto the as yet unfathomed totality of the universe.
The components of concrete systems are systems at the level of complexity immediately below them in this hierarchy of concrete systems except that the smallest systems, which may be atoms, have components which are not themselves systems. Below atoms are electrons, protons, neutrons, and other subatomic particles.
The concept of level is of major importance. Systems at any given level are more like each other in many ways than like systems at other levels. They are the same sorts of things and have similar components. Although systems at a given level may vary greatly in size, their median is usually larger than that of systems at the level below and smaller than the median of the level above. One sort of molecule, for example, is like all the others in being composed of atoms. The median molecule is larger than the median atom.
Structure and process.
At any time, the parts of a concrete system, living or nonliving, are arranged in space in a specific pattern. This spatial arrangement is the system's structure. As the parts of the system move in relation to one another, structure changes. System change can be continuous or episodic, or may remain relatively fixed over long time spans.
All change in a system over time is process. Some processes are essentially reversible, as when a car moves forward and then slips back into the same rut. Others are difficult or impossible to reverse. A cat can withdraw the paw it has stretched out toward its toy, but a diver cannot rise feet first from the water and ascend to the diving board, as he appears to do when a film is run backwards.
Process includes both the system's function, the often reversible actions that succeed each other from moment to moment, and its history, the less reversible or irreversible changes that alter both the structure and the function of the system. The succession of reversible structural changes in a typist as she works at her machine are functional processes. Aging of organisms, decay of mountain ranges, and cooling of suns are historical processes. The regular beating of a heart is functional. The scars that result from a coronary occlusion make a permanent historical change in the heart, muscle.
The structure, function, and history of a system interact. Structure changes as the system functions from moment to moment. When a change is great enough to be essentially irreversible, a historical process has occurred.
Living systems are multimolecular aggregates like the nonliving objects in the environment. Life, however, requires a degree of molecular complexity beyond that of nonliving substances. All living systems are composed of organic molecules. Most importantly, they all contain nucleic acids and a score of amino acids organized into proteins. These nucleic acids and proteins are produced in nature only in living systems. AU living systems have a remarkable molecular similarity that makes it reasonable to assume that they arose from the same primordial genes, diversified by evolutionary change. The overall evolutionary progression has been toward increasingly complex systems.
The increase in complexity came about by an evolutionary process which we call -,shred-out. It is as if each strand of a manystranded rope had unraveled progressively into more and more pieces, as more and increasingly complicated units were needed to perform each life process.
Living systems exist at seven levels, each with characteristic structure and processes. The seven levels are:
(a) Cells. These systems occur as freeliving or colonial forms and as specialized components of the tissues of organisms. Although cells are exceedingly complicated systems, they are the least complex organization of matter and energy that can carry out essential life processes. Their components are nonliving molecules and multimolecular complexes. Viruses are not living systems, but they occupy the borderland between living and nonliving systems. They are very large protein molecules which have genes and can reproduce inside cells by gaining control of the cell's protein-synthesizing process but are otherwise inert.
(b) Organs. These are the specialized structures which carry out organism processes. Their components are cells aggregated into tissues.
(c) Organisms. This level includes multicellular plant and animal life forms. The components of organisms are organs.
(d) Groups. Two or more organisms interacting as systems form groups. No social system at a higher level than this is found among animals. Although the complex "societies" of social insects have many similarities to human societies, their structures and processes are more similar to those of human groups than to those of either organizations or societies.
(e) Organizations. These systems are distinguished from groups not by their size but by the presence of two or more echelons in their decider structures (Miller, 1978, p. 595). Their components are groups and smaller organizations. This level includes a diversity of types of systems, some of which are: governmental units like cities, states, provinces, and legislatures; manufacturing and business concerns; religious organizations; charitable organizations; and universities.
(f) Societies. Society has been defined as . the type of social system which contains within itself all the essential prerequisites for its maintenance as a self-subsistent system (Parsons, Shils, AUport, Kluckhohn, Murray, Sears, Sheldon, Stouffer, & Tolman, 1951, p. 26). In our terminology, such a system is totipotential. The modern form of society is the nation. Nations claim and defend specific geographical territories, have some form of central government, and ordinarily have distinct cultural characteristics. The components of societies are organizations of diverse types and functions.
(g) Supranational systems. These systems are composed of two or more societies which undertake cooperative decision making and, to a greater or lesser extent, submit to the control of a decider superordinate to themselves. The level includes alliances, coalitions, and blocs as well as single-purpose and multipurpose intergovernmental organizations. Societies are represented in the meetings of these organizations by delegates. Examples of multipurpose intergovernmental organizations are the United Nations, the Warsaw Pact, and the European Economic Community. The European Organization for Nuclear Research (CERN) and the Food and Agriculture Organization (FAO) are single-purpose intergovernmental organizations.
Emergents. Each higher level of living system, as it evolved, developed capacities for behavior qualitatively different from that of lower-level systems. As a result, the more complex, higher-level systems have characteristics that cannot be described only in terms used for systems below them in the hierarchy without neglecting significant aspects of the higher-level systems. Such characteristics are emergents. Life emerged with the first primitive cells. The ability to adjust to more and severer stresses by pooling resources among the cells of a multicellular structure emerged with organs. Many aspects of adaptive behavior emerged at the organism level as increasingly complex nervous systems provided for learning and other higher mental processes. Groups have the emergent ability to perform motor activities and to make artifacts beyond the capacity of a single organism. The use of Symbolic language in communication also emerged at the group level, in human groups. There is no evidence that apes in the wild use symbols in interspecific communication, although certain research suggests that they may have the ability to learn to use them (Gardner & Gardner, 1969). New forms of social organization emerged with the appearance of larger social systems.
Most people readily agree that cells, organs, and organisms are alive. Some may question whether systems at levels above the organism can be considered alive in a comparable sense. Their system characteristics are evident enough, but there is no physical connection among the components as there is among the cells and organs of lower level systems. Components can move from one system to another. In addition, such systems, particularly those at levels above the group, include a great many nonliving components. A city is made up not only of people but of buildings, power lines, buses, and innumerable other things that are clearly not alive.
These systems, however, carry out the same basic life processes as do lower-level systems with more cohesive components. What is more, the structure of at least some systems at lower levels is less fixed than it appears to be, although components do not freely leave one system to join another, but remain within the system boundaries. Many of the cells in an organism's body are n the process of continual replacement. The white blood cells are much like freeliving amoebas as they move from one part of the body to another to dispose of invading proteins.
Further, systems at levels below the group are not always devoid of nonliving components, although such components are usually less massive as compared with the living components than they are at higher levels. At the organ level, pacemakers keep hearts beating regularly. Prostheses like artificial legs and plastic aortas substitute for missing parts or augment the function of defective components of organisms.
Artifacts in higher-level systems, particularly in systems above the group, are essential parts of systems, but it is the living components that form the living system. An abandoned city is not a living system.
In addition to the greater complexity of certain essential molecules, living systems differ from nonliving in several significant ways.
(a) Living systems are more complex in structure and process. cells, minute as they are, have an awesome array of structural parts and carry out innumerable chemical reactions. Free-living cells exhibit adaptive behavior of various sorts. Computers are generally agreed to be the most complex machines so far invented. They do not yet approach the complexity of organism nervous systems. The levels above the organism, which are composed of more than one organism, each complete with cells and organs, are necessarily more complex than any system at a lower level.
(b) This greater complexity permits living systems to combat, for varying lengths of time, the inevitable increase in entropy that leads to dissolution of matter-energy of all sorts. Nonliving systems do not do this.
Living systems achieve this temporary victory by taking in matter and energy (matter-energy), using it in their processes, and returning a part of it to the environment. The input substances are lower in entropy than the output. Because they have inputs and outputs, living systems are open systems.
(c) Living systems ordinarily process more information than nonliving, and, furthermore, animals do more such processing than plants. Information is patterning or order, as distinguished from randomness or disorder. It is the opposite of entropy, that is, negative entropy or negentropy. information may be conveyed in the shape of a molecule that fits receptors on a cell's surface, making it possible for the molecule to enter the cell. It may be in the patterning of the symbols and words of a letter that allow the receiver to decode its message. The recognizable shape of an object is also information.
Information is not the same as meant . meaning, which is the significance of information to a receiving system as shown by immediate or delayed change in the receiver's overt behavior or internal processes.
Steady state. By the input, processing, and output of matter-energy and information, livings systems maintain themselves for varying periods of time in steady states. The concept of steady state is similar to the concepts of equilibrium and homeostasis. Homeostasis is a physiological term that applies to a state of balance of the variables of an organism. An equilibrium exists when opposing variables of a system are in balance. If a child on one end of a teeterboard balances the weight of a child on the other, the board can remain level until someone applies a force to it. An equilibrium that is preserved in the face of dynamic flux is a steady state.
The flows of matter-energy and information into and out of a living system change in nature and in rate as both the environment and the system itself vary. Living systems have adjustment processes that allow them to keep many critical variables in steady state ranges in the face of such change.
One example of a steady state that must be maintained by cells and organisms is water balance. These systems must excrete water at about the same rate that they take it in or they suffer damage. Adjustment processes in both cells and organisms increase or decrease water input and output to maintain water balance.
Although no delicate balance is preserved between input and output of information in living systems, both overloads and underloads of information input can stress them.
System change, associated with normal growth and development, pathology, or some environmental event, moves living systems w new, and sometimes very different, overall steady states. A small town that doubles its population as a result of a new factory being located there, a city that is damaged by a tornado, or an insect that undergoes metamorphosis-all must find new steady states.
Living systems at all levels, in order to remain alive and continue beyond a single generation, must be capable of performing certain critical processes or have some other means of achieving the same result. Our general living systems theory identifies 19 of these critical processes, each of which is performed by a set of structural units, or components (Miller, 1978, pp. 30-31). All the components that together perform a particular process in the system form a subsystem, whether or not they are spatially contiguous.
If a system lacks structure for a given subsystem process, it may depend upon a parasitic or symbiotic relationship with another living system or require a favorable environment to provide for it. Examples are plants, which cannot move from place to place and must depend upon bees, wind, or water for fertilization, and human infants who depend upon adults to provide food for them and put it into their mouths.
All subsystems process both matter-energy and information by virtue of being system,-, in their own right. In the system of which they are components, however, some process primarily matter-energy, others process primarily information, and some process significant amounts of both matter-energy and information. Table I lists and defines the 19 subsystems of living systems.
Of the 19 subsystem processes, one, reproduction, is not necessary for the survival of individual systems. Reproduction is, however, necessary for the continuance of the species from generation to generation.
The decider in any living system is the essential information-processing subsystem that coordinates and controls systems and determines how their processes operate. This does not imply that living systems always have a single executive component. Coordination and control are decentralized in many systems. Subjective consciousness is not necessarily involved in the determination of system outcomes.
Deciders are usually structured into hierarchically arranged echelons, each of which is responsible for certain sorts of decisions. The highest echelon ordinarily has some degree of control over all the others. Lower echelons control more specific and more localized processes. Leaderless groups are living systems with no top echelon in their decider structures. If a group develops two or more echelons, it becomes, by our definition, an organization.
If a living system loses all its decider components, it is no longer a separate system. Parts of'the decider process may be taken over by another system, but if a society, for example, is conquered by another society which dissolves its government and dictates its policies and activities, it becomes temporarily or permanently a component of the ruling society.
Each subsystem of a living system maintains the steady states of a number of variables by the use of adjustment processes that alter flows of whatever forms of matter-energy or information are used in that subsystem's processes. Many adjustment processes are negative feedbacks.
At every level of a living system changing values of certain objectively determinable measures or indicators can be used to evaluate the current condition of subsystems, to measure the amount of departure of variables from established norms, or, by extrapolation, to forecast changes in system states in the immediate or more distant future.
Some variables occur in all subsystems at all levels since a number of characteristics of both matter-energy and information flows are similar no matter where they occur. Others are present at some levels or in certain subsystems but not at others. Rate of processing, for example, is a variable of all subsystems whether they process matter-energy, information, or both. Costs can be assessed for all subsystem processes. Meaning variables, lags, and distortions are characteristic of all information flows. The processes to which a variable relates may be quite different from one level or type of system to another.
SUB8YSTEMS WHICH PROCESS BOTH MATTER-ENERGY AND INFORMATION
Feedback loops among subsystems, and to and from the environment, are found in all living systems. In general, lower-level systems have a more limited range of adjustments than higher level systems and, within each level, the more highly evolved systems have a greater range than those below them in the evolutionary scale. Total system variables are measurable in the same way subsystem variables are. Matter-energy and information input-output relationships, for example, are measurable in at least some systems at each level. Within levels, systems can be compared with norms established for their particular types to determine adequacy of adjustment processes. Pathology resulting from lacks or excesses of matter-energy or information inputs, maladaptive information in genes or charter, and abnormalities in internal processing can be discovered in this way at all levels.
Much of the work of biological and social science is concerned with measuring the variables of living systems and establishing normal ranges of variation for them in particular types of systems. It is critical that quantification of as many variables as possible be achieved and it is important that, to the extent possible, measures be in standard units, such as centimeters, grams, and seconds, so that cross-level comparisons are possible and interdisciplinary studies are facilitated.
Development of measures and indicators has proceeded much farther for some levels and types of living systems than for others. At the organism level, for example, values of thousands of matter-energy and information processing variables have been determined, particularly for laboratory animals and human organisms. Measurement of variables of supranational systems has been instituted more recently and is less advanced.
Nonliving systems include the natural physical systems of Earth, considered separately from Earth's living inhabitants, as well as mechanical and electronic artifactual systems without their human producers and operators.
Aside from the attributes that all concrete systems must have, there are few characteristics necessarily common to all nonliving systems. Although no system, except possibly the total universe, is completely closed, nonliving systems can be more closed than living systems since they do not require continual inputs of nutrients in order to "feed on negative entropy" as living systems do. There is more variation in structure and process among nonliving than among living systems. While they may have any of the subsystems necessary to living -,.systems, they need not provide for the limited range of these subsystem processes that plants have or the entire range that animals have.
Nonliving systems, of course, have provisions for control and coordination, but decider and, other information processing components are not obligatory aspects of their structure. Computers have components that carry out decision and other information-processing activities, but some other machines do not, and certain man-machine systems have the human component as decider.
The natural nonliving systems of the Earth, such as those that determine climate, act strictly in response to the mechanical and thermodynamic laws that govern our universe. These laws "decide" when volcanoes erupt, the course of winds, and the sudden shifts in forces that cause earthquakes.
The Earth system. Earth is an open system. Its primary input is energy from the sun and from space. Input of matter, in the form of meteors and cosmic dust, is ordinarily not great, although major impacts from planetoids occur every 100 million years or so. Earth outputs heat and light to space, maintaining an approximate overall steady state with respect to energy.
Earth is an intensely energetic system, unlike similar bodies in our -solar system (Drake & Maxwell, 1981, p. 20). From the moment of its formation, it has been evolving, with the result that its present state is unlike its state in earlier geologic periods. Its future is a matter for speculation. This is in contrast to the moon, Mars, and Mercury, which lack the dynamic processes responsible for the changes that have taken place in the Earth in the estimated 4.6 billion years since its formation.
Scientist, have identified several concentric layers of the modem Earth, each with distinct geological and thermal characteristics. The solid crust surrounds a more plastic mantle. Alternative models of the core describe it as entirely or predominantly iron, either in liquid form or with a liquid center surrounded by a solidified layer (Stevenson, 1981, p. 614). Earth scientists agree that the center is hot. Gravitational energy and radioactive decay are considered probable sources of this heat. Earth's strong magnetic field is believed to result from action of the liquid metal in the core as a hydromagnetic dynamo (Stevenson, 1981, p. 617).
Earth has been described as a "heat engine" in which matter is continually cycled by convection from the hot mantle to the crust and atmosphere and back to the mantle. Volcanic eruptions that carry magma from the deep interior to the surface and spew volcanic ash and gases into the atmosphere are part of this cycling process. So too are movements of the great tectonic plates into which the crust is divided. Their movement in relation to each other changes the geography of Earth. Continents change their boundaries and relative positions. Plates collide to build mountains, separate to form new seas, and slide beneath the sea bottom to be melted in the mantle as new crust is formed from upwelling magma. Tectonic strains build up and are reduced in earthquakes. Sea water moves in repetitive cycles between the ocean bottom and hot basaltic rocks below the sea floor, transferring dissolved minerals from lower layers to the sea. Matter circulates at rates and in temporal patterns characteristic of each of these cycles.
Geologic evidence indicates that the heat that drives these cycles and causes development of the crust and atmosphere has declined during the lifetime of the earth (Stevenson, 1981, p. 617). Consequently, cycling of material through the system has slowed. Since, like all physical systems, this one is subject to entropy, Earth will continue to cool.
Powered by radiant energy from the sun, water moves in cycles from sea and land surfaces to the atmosphere, forms clouds, and falls back to the surface as rain or snow. The atmosphere itself is in continual motion as temperature and pressure gradients and the earth's rotation produce winds and air currents.
Subsystems of the Earth system consist of sets of interacting components, each such set concerned with particular processes. Because of interactions, including feedbacks among subsystems, changes in one part of the system may have effects throughout the whole system.
Measures and indicators are available for many variables of the Earth system. New instruments and techniques are being developed to penetrate deep into the crust, explore the sea bottom, and study the processes of sea water and the atmosphere. Except for the first 800 million years of Earth's history, for which the record has been obliterated, the record of the Earth's evolution is stored in its present geological structure, to be read as appropriate methods are developed. Scientists are collecting the data that win increase their understanding of the past and present states of Earth as a system.
In ecological systems, living systems at levels from cells to supranational systems interact with each other and with the nonliving environments upon which they depend. Typically, bacteria, other free-living cells, and both plant and animal organisms occupy a region with physical characteristics to which they have adapted, although some parts of Earth are so inhospitable to life that only bacteria survive in them. Local ecosystems are parts of larger systems up to the total ecological system of Earth with all its living and nonliving components. Whether or not this is a hierarchy is unclear.
Life emerged more than 3.8 billion years ago, after a period of chemical evolution, during which the primitive Earth atmosphere that was chemically reducing rather than oxidizing, while availability of appropriate chemical molecules and abundance of energy potent enough to break chemical bonds favored synthesis of the complex molecules necessary for life. Life was "an almost utterly improbable event with almost infinite opportunities of happening" (Lovelock, 1979, p. 14). The oldest known bacterial microfossils are found in 3.5 billion-year-old rocks. Nucleated cells were present less than a billion years later.
The first living cells left no fossil record. Although little is known of them, they must have been simpler in structure and process than even the least complex present-day cells (Woese, 1981, p. 120). They had, nevertheless, sufficient complexity to provide for the subsystem processes essential for life. Like all cells, they must have had a limiting membrane that enclosed a colloidal ground substance in which molecular reactions occurred and a means whereby matter-energy exchanges could occur across this boundary. If commonly accepted theories of the nature of the primitive atmosphere are correct, the first cells were anaerobic. They necessarily had a means ot converting the radiant energy of the sun into chemical energy. That is, they were photosynthetic. In all their modem descendants, energy conversion involves the formation and hydrolysis of phosphate bonds, commonly adenosine triphosphate (Morowitz, 1968, p. 55). Some provision for coding genetic information into molecular form, duplicating it, and translating it into proteins is essential for all self-replicating cells, including the earliest ones. Th DNA RNA-protein process that characterizes all living cells probably was used by these ancestors as well, although the genome was probably smaller and the translation less precise than in modern cells (Woese, 1981, p. 120). This imprecision would lead to a high mutation rate, such as appears to have been the case. During the eons when bacteria were the only form of life on Earth, they evolved into a wide variety of types and radiated over almost the entire Earth, adapting to a great range of different environments.
From the moment of its formation, life interacted with the nonliving physical and chemical systems of Earth, shaping and being shaped by them. Morowitz describes the global ecological system, or biosphere, as:
That part of the terrestrial surface which is ordered by the flow of energy mediated by photosynthetic processes.... Energy enters the system as photons and is transformed into energetic covalent bonds. AR subsequent biochemical changes involve a series of rearrangements which are accompanied by the production of heat.... The energy outflow is usually accompanied by the loss Of C02, water and nitrogenous compounds. This material then moves through the well-known cycles and eventually back into the biosphere. (Morowitz, 1968, p. 81).
Earth is apparently the only body in our solar system with conditions appropriate for the emergence and continuance of life (Drake & Maxwell, 1981, p. 20). Its size and mass prevent its volatile materials from escaping into space and its distance from the sun allows water to exist upon it in solid, liquid, and gaseous forms. Its surface temperature has never been too hot or too cold for life, once it had started to continue.
As Earth evolved, life also evolved, always adapted physically and behaviorally to the climate, atmospheric composition, and chemical make-up of its environment. The view of life as adapting to changes in an environment over which it has little influence has been challenged in recent years, particularly with regard to the highly probable shift from a reducing to an oxidizing atmosphere. Several lines of evidence support such a shift, including the fact that organic syntheses of the sort necessary for life could not have occurred in an oxidizing atmosphere. The change had been considered the result of the breakdown of water vapor in the atmosphere, with the lighter hydrogen atoms escaping to space and the heavier oxygen atoms remaining in the atmosphere. This process would not, however, have produced the quantity of oxygen that, in fact, is present. The alternative, and now commonly accepted view, is that the photosynthetic process, in which carbon is fixed in the substance of living systems and oxygen is released to the environment, was the major influence in the change.
Lovelock regards this atmospheric change, and other aspects of the living system-nonliving environment match, as evidence for a complex interrelationship between living systems and the nonliving physical and chemical systems of Earth (1979, p. 11). He suggests that the entire range of living matter can be regarded as constituting a single living entity capable of manipulating the atmosphere to suit its needs and "endowed with faculties and powers far beyond those of its constituent parts (1979, p. 11)." This entity, the Earth's biosphere, together with the atmosphere, oceans, and soil, forms a complex cybernetic system which seeks an optimal physical and chemical environment for life. The relatively constant conditions that make life possible are maintained by active control of this system, which he calls Gaia, named for the Greek Earth goddess.
Gaia controls the composition of the atmosphere, which can be considered an extension of the biosphere. The amounts of oxygen and nitrogen in the atmosphere do not conform to the expectations of a steadystate chemical equilibrium "by at least 100 orders of magnitude (Lovelock, 1979, p. 7)." The amount of ammonia in the atmosphere is just sufficient to maintain the pH of normal rainfall optimal for life. Variables of soil and sea water composition are similarly controlled. Gaia also has an important role in maintaining suitable surface temperatures over most of Earth. Feedbacks in this system correct deviations from acceptable steady-state ranges.
Ecology is fundamentally concerned with the manner in which light is related to ecological systems and with the manner in which energy is transformed in those systems. The steady states of biological systems are highly improbable states. They have a high degree of order. Cells and organisms can sustain such a state only by doing continual work, and for this they require both an energy source and a sink. The stream of radiant energy from the sun and the flow of heat into the environment and, ultimately, into space in the form of infrared radiation provide these. Energy input into these systems is used for system maintenance, synthesis of macromolecules, and the mechanical energy that is expended in motion. Morowitz describes these relationships as follows:
(a) The surface of the earth belongs to that class--, of physical systems which receives energy from a source and gives up energy to a sink. There is a constant and (on the appropriate time scale) almost steady flow of energy through the system.
(b) This flow of energy is a necessary and, we believe, sufficient condition to lead to molecular organization of the system experiencing the energy flow.
(c) This flow of energy led to the formation of living systems, and ecological process is the continued maintenance of order by the energy flow. Thus, the problem of the origin of life and the development of the global ecosystem merge into one and the same problem.
(d) The flow of energy causes cyclic flow of matter. This cyclic flow is part of the organized behavior of systems undergoing energy flux. The converse is also true; the cyclic flow of matter such as is encountered in biology requires an energy flow in order to take place. The existence of cycles implies that feedback must be operative in the system. Therefore, the general notions of control theory and the general properties of servo networks must be characteristic of biological systems at the most fundamental level of operation. (1968, p. 120)
The ultimate ecological system of the whole Earth is composed of smaller ecological systems in which representatives of a number of species interact with each other and with their physical surroundings. In the terminology of ecology, the community is the unit of system organization (Allee, Emerson, Park, Park, & Schmidt, 1949, p. 437). Community is also a standard term in social science, referring to local settlements in which people live and interact, including such human systems as preliterate tribes and primitive villages as well as modern towns, cities, and metropolitan areas. Instead of including such systems at the organization level as has been the practice of many general living systems theorists, some hold that human communities constitute a separate level between the organization and the society (Anderson & Carter, 1974, pp. 45-57).
The concept of community as it is used in ecology is more inclusive than it is in social science, referring to all the living systems that interact within a given area of the Earth. Free-living cells, plant and animal organisms, human and animal groups, human organizations, communities, societies, and supranational systems are all components of ecological communities, although the latter may be geographically discontinuous and be located in more than one.
A major community, which includes a number of smaller communities, has been defined as:
A natural assemblage of organisms (We would say "living systems
at any level.,,] which, together with its habitat, has reached a survival
level such that it is relatively independent of adjacent assemblages of
equal rank; to this extent, given radiant energy, it is selfsustaining....
The formation of the community may be considered as a resultant of ecological
selection, in which the building blocks, or organisms [living systems at
any level] unable to exist alone, fall into place to produce a self-sustaining
whole of remarkable complexity. Organization of such an accumulation is
obligatory and the universality of the community is the proof of this general
proposition (Allee, Emerson, Park, Park, & Schmidt, 1949, p. 436).
Communities include populations of several species which occupy continuous or discontinuous portions of the physicochemical environment known as habitat niches. The natural groupings satisfy the requirements for food, shelter, and reproduction of each of the various sorts of living systems in them.
How do communities of this sort relate to the hierarchy of living systems from cells to supranational systems outlined above? A community is a living system with components at more than one level and of several species or types, whereas the seven level' of living systems have their typical components at the next lower level and of the same species or type. That is, animal groups are all wolves or all deer or all some other species, and human groups include only people.
Ecological communities are organized and coordinated largely by matter-energy, rather than information, flows. The bacteria, green plants and algae, protozoa, animal organisms, and higher-level systems that form a community are linked in a complex metabolism of matter-energy. They all participate in food chains, which are connected into a food web that is analogous in some ways to the distributor for matterenergy in the subsystems. Bacteria in the soil and in aquatic communities are fundamental to the metabolic process since each species is specialized for some critical role in the flow of energy and recycling of matter that makes possible the relative independence of communities. Soil bacteria live by oxidizing inorganic materials like ammonia, carbon monoxide, hydrogen, iron, and sulphur, making them all available for use in ,organic syntheses by photosynthesizers. Also, they decompose the protoplasm of the dead bodies of plants and animals into simpler organic and inorganic molecules suitable for photosynthesis. In the nitrogen cycle., for example, protein from plant and animal tissues is broken down into its constituent amino acids, which are used in chemical reactions that produce ammonia. This is combined into ammonium salts and nitrites and oxidized to nitrates. These successive steps result in fixing nitrogen in the soil and making it usable in synthesis of plant proteins. Other soil bacteria reduce nitrites and nitrates to gaseous oxygen, and still others combine oxygen with other molecules to form amino acids. Some of these nitrogen-fixing bacteria are free-living. Others live symbiotically with the roots of legumes. Their bodies store the amino acids which, at their death, are digested by the bacteria that produce ammonia. In addition to these critical functions, bacteria are food for soil protozoans and zooplankton.
Each successive living system in the food chain breaks energetic bonds of molecules in its matter-energy input and synthesizes other forms of matter-energy that are useful for its own metabolism. There is a cost for the process at each step since some energy is degraded into heat.
To avoid a continual loss of energy to the total system, energy must be input directly or indirectly from the sun. Green plants, photosynthetic bacteria, algae, and phytoplankton can convert radiant energy to chemical energy and store it within their boundaries. Systems that cannot photosynthesize must consume plants or other animal organisms that consume them, since they are unable to carry out the fundamental chemical reactions that make both matter and energy available to the food chain.
Ecological community subsystem processes. Community metabolism involves many of the subsystem processes found in the seven levels of living systems discussed in this article previously. Ecological systems that include communities and their habitat,-, do not ordinarily have sharply defined boundaries, but grade into each other. The communities they contain, however, have certain boundary subsystem processes, like exclusion of species closely equivalent to those already established in niches suitable for both. Bacteria and green plants carry out the ingesting process as they bring chemicals from the earth and energy from the sun into the system. The food chain is the distributor for matterenergy. Converting and producing take place at each step in the food chain as cells and organisms break down the matter-energy in their input to repair tissues, grow, and reproduce. Matter-energy is stored in various forms in cells and organisms and by multiorganism systems. Finally, matter-energy is returned to the soil and energy is dissipated in the form of heat in the extruder process.
The structure of the supporter subsystems of communities is determined by the habitats they provide and the species and types of living systems that occupy them. Ordinarily, no niches are unused. Niches in terrestrial communities are found below the surface of the Earth, on the surface where natural shelter is available, in artifacts of various kinds, and on or in living members of the community, like trees or other organisms. Aquatic communities similarly divide their habitats. The Earth, the living systems that are themselves habitats for other systems, and artifacts like nests or hives are supporter components, since they "maintain the spatial relationships among components so that they can interact without weighting each other down or crowding each other" (see Table 1). Communities usually lack motor subsystems.
Information flows are less important in these systems than in cells, organisms, and single-species multiorganism systems. Many of the information-processing subsystems are lacking. The channel and net for interspecific information transmissions is much less developed, but some communication does take place among organisms of different species. A bird that drags its wing as if it had been broken in order to lead a predator away from her nest is transmitting information and so are animals that warn others away by growls or aggressive displays. Most information, however, is coded for intraspecific transmission. The pheromones, which are chemical messengers, of one species have no effect on the behavior of individuals of even closely related species.
Ecological communities, however, do not lack the essential decider subsystem. Decider components are dispersed throughout the system. The decider functions through adjustment processes and feedbacks among components that control system variables and coordinate the system. These are largely matter-energy feedbacks and adjustment processes.
Both the biotic and the abiotic components of ecological systems are part of the evolutionary process. The structure and processes of living systems have become modified, over time, in ways that suit them to particular environments. Physical differences among closely related species that live in different temperature zones are evidence of such modifications. Migration of birds, hibernation, and circadian and other biological rhythms adjust the activity of living systems to environmental variables. The biotic components of ecological systems also modify their abiotic environments in various ways and adjust their structures and processes to one another.
Species that have evolved together become mutually adapted so that predator and prey, parasite and host, and participants in symbiotic relationships seem made for each other.
Each community has a typical life cycle. It becomes established, develops to maturity, ages, and finally terminates (Allee, Emerson, Park, Park, & Schmidt, 1949, p. 563). Some communities end catastrophically, but termination is ordinarily gradual, as natural forces and the activities of living systems alter the environment so that it is no longer suitable for one or more of its species populations. As they die out or move away, competing populations of other species move in. Eventually, historical changes produce a new community. Usually this process is repeated several times, until a relatively stable climax community develops.
Each community in this ecological succession maintains a large number of variables in steady states by adjustment processes among the living systems that compose it. The relationships among living systems of differing species and types are consequences of the need of each to provide for its essential matter-energy and information processes. Some are mutually beneficial. A herd grazes and its droppings are a source of matter-energy needed by the grass. Bacteria in the intestinal tracts of animal organisms meet all their own needs and are essential to processes of the converter subsystem of the host system. Other relationships involve exploitation of one species by another with no immediate benefit to the exploited system. Such relationships obviously threaten both species. When a parasite destroys its host or a predator kills off a prey species, it may also destroy itself. This sort of thing does happen in nature, but usually when the species involved have had no previous opportunity to become adapted (Allee, Emerson, Park, Park, & Schmidt, 1949, p. 699). European mammals introduced into Australia, for example, threaten the existence of native marsupials. More usually, feedback adjustment processes control numbers of each species so that a balance is maintained that avoids Malthusian extremes. Populations rarely approach the limits of their food supplies (Allee, Emerson, Park, Park, & Schmidt, 1949, p. 375).
Relationships between predator and prey often take the form of oscillations or cycles (Allee, Emerson, Park, Park, & Schmidt, 1949, p. 374). Predators increase until the prey becomes scarce; then the number of predators declines, allowing prey populations to recover. This, in turn, results in increase of the predators, until, again, they have limited their food supply and the cycle is repeated. Some moose that crossed the ice from Canada to Isle Royale early in this century illustrate two different intraspecies relationships, the first with the plants on which they fed, the second with both plants and animals (Wilson, 1975, p. 86). Since no predators threatened them on the island, their population expanded to the limit of the food supply. Finally, starvation reduced their numbers. When the vegetation had recovered, the moose again prospered and increased. This "boom and bust" cycle was repeated until 1949, when some wolves discovered the same route to the island. Their predation reduced the moose herd to a comfortable 600 to 1000 animals, a number that the vegetation could support. The moose that fell to the wolves were usually young, weak, or sick. The wolf population remained steady at 20 to 25 because moose are hard to catch, and the wolves made a kill only every three days. Vegetation, moose, and wolves remained more or less healthy and the steady state "balance of nature" was preserved.
Variables of ecological systems. Many variables of ecological systems can be observed and measured. Variables of nonliving components are such things as physical and chemical compositions of soil, air, or water; the amount of radiant energy that enters the system; air or water and pressure and movement; ambient temperature range; and seasonal changes in weather.
Living system variables include: kinds of living systems in the community, e.g., pine trees, lichens, crustaceans, deer herds, or human settlements; the number, density, or other quantitative measures of species populations or types of systems; the number of individual systems in human or animal groups; the characteristics of species populations, e.g., age or sex distribution; the health of populations; and interspecific community relationships and interactions.
Variables of the mixed living and nonliving ecological system include distribution of living systems within the environment, habitats in use, species that occupy particular habitats, flows of matter-energy and information through the total system or parts of it, effects of living components upon the nonliving environment, and effects of environmental changes on living systems. Table 2 includes representative variables and indicators which measure those variables of ecological systems.
Modern Homo Sapiens is a recent arrival on Earth, having evolved from earlier hominid ancestors in the late Pleistocene era. Human beings have intelligence, manipulative skills, and the ability to adapt to a wide variety of environments, and so they have been able to exert a profound effect upon the total Earth system in a relatively brief period of several thousand years.
Little is known about the first men, but they must have lived, like other animals, in balance with the ecological communities of which they were a part, subject to similar population-limiting pressures. The discovery of agriculture, which brought the Pleistocene to an end 10,000 years ago, and the development of industry were step-function changes in human culture that established new and different steady states and made possible an exponential rise in human population as well as the evolution of living systems larger than groups. The effect or this human expansion has been deleterious in many ways to the living and nonliving components of the world system, including human systems. Fyfe says that a man of the modern industrial developed world uses 2 x 107 grams (20 tons) of new mineral material annually. He continues:
For a billion people, about 15 percent of the global population by 2000, this annual usage (2 x 10" grams) about equals in mass the most impressive geological processes of our planet, that is, ocean crust formation, erosion, and mountainbuilding rates. If we add to such a figure the amount of earth moved in agriculture, then there is no doubt that man has become the most important agent modifying the surface of our planet. (Fyte, 1981, p. 105)
Human systems are already exceeding the carrying capacity of some parts of the Earth, including sub-Saharan Africa and Parts 'If Asia, reducing their capacity to support life (Council on Environmental Quality and the Department of State, p. 3). They are depleting natural resources faster than they can be replaced. Extruded wastes of human systems pollute land, air, and water. Pollution and loss of wild habitats are destroying nonhuman living systems at a rate that could extinguish 15-20% of all species on Earth by the year 2000 (Council on Environmental Quality and the Department of State, p. 37). Many of these are tropical forest species that are potential suppliers of foods, pharmaceutical chemicals, specialty woods, fuel, and building materials.
Depletion of resources. White has described culture as "an elaborate thermodynamic -mechanical system" designed to carry on the life processes of man by harnessing and controlling energy (White, 1949, p, 369). Culture has been said to evolve as the amount of energy harnessed per capita per year increases (Cook, 1971, p. 135). Before the domestication of fire, primitive man used only his own physical energy, derived from his food, probably about 2000 calories per person per day. The use of fire may have doubled his energy use. Agricultural societies with domesticated work animals increased their daily per capita energy use to about 12,000 kilocalories. Between 1850 and 1870 developing technology increased per capita daily energy consumption in England, Germany, and the United States to 70,000 kilocalories. Following installation of central electrical power stations in the late 1890s, energy use rose at an increasing rate until, in 1970, the United States, the world's biggest energy user, required about 230,000 kilocalories per capita per day.
The supply of petroleum, upon which the still-increasing world demand for energy at present primarily depends, is exhaustible. By 1968 American oil production was reaching the limits of its capacity. By 1970, it had begun to decline (Stobaugh & Yergin, 1979, p. vii). More recently discovered supplies in the Middle East remain abundant, but the world supply is expected to peak before the end of this century. Already production capacity is increasing more slowly than demand and by 2000 the world's petroleum resources will have declined by at least 50% (Council on Environmental Quality and the Department of State, p. 39).
Petroleum is necessary not only to fuel the motors of societies, but to make fertilizers and other materials required for producing food, mining, home heating, and other processes. A conservative estimate of world population in the year 2000 is about six billion, a number that would require doubling of the present energy consumption rate to avoid famine and other disastrous consequences. Similar problems exist with nonfuel minerals, metals, and other resources, including fertile land and water.
The depletion of resources and the need for an ever-increasing supply of energy to sustain human life has been interpreted by some as evidence of the entropic degradation of Earth. In this view, history is a reflection of the second law of thermodynamics. Progress in civilization has been made possible not only by the leisure to experiment provided by increasing surpluses in societies but by hardships that have resulted from dissipation of resources. Repeatedly, accumulated increases in entropy change the environment so that a shift to a new source of energy must occur. Each of these shifts is made at the cost of extracting the low-entropy substances with which the Earth is endowed. GeorgescuRoegen's (1971, p. 304) gloomy conclusion is:
Up to this day, the price of technological progress has meant a shift from the more abundant source of low entropy-the solar radiation-to the less abundant onethe earth's mineral resources. True, without this progress some of these resources would not have come to have any economic value. But this point does not make the balance outlined here less pertinent. Population pressure and technological progress bring ceteris paribus the career of the human species nearer to its end only because both factors cause a speedier decumulation of its dowry.
Pollution. In ecological communities that live in steady states, the number and distribution of organisms is appropriate to the amount of matter-energy available for all essential inputs and to the capacity of the environment to recycle wastes. A balanced-life aquarium, in which fish live without clouding the crystal clarity of the water, is a small-scale model of such a system.
Large human societies, unfortunately, do not maintain a balanced steady state with their living and nonliving environments. In these, organic wastes which, in small primitive systems, can be recycled without damage to the environment, become a problem because the large output cannot be absorbed by soil and water. In addition, chemicals and the products of burning fossil fuels emitted into air, soil, and water further strain global buffer systems. When poisons enter the food chain, they threaten the health and life of living systems at all levels. Nuclear wastes are particularly important because of the difficulty of disposing of them and the extremely long periods of time over which they are dangerous.
Acid rain and snow, effects of atmospheric pollution, are already threatening living systems. They occur when the sulfur dioxide and nitrogen oxides that enter the atmosphere from burning fossil fuels undergo a series of chemical reactions and combine with water to form sulfuric and nitric acid. The average acidity of rain in the United States and Europe has increased 40-fold in the last 50 years (Graves, 1980, p. 1).
As a lake's acidity increases, acids leach nutrients and increase the solubility of such toxic metals as mercury. The eggs of salamanders, and then frogs, fail to hatch and those species are lost to the ecosystem. Then bacteria, plankton, and many aquatic plants disappear. Finally the eggs of fish cannot survive. Brook trout and Atlantic salmon are among the vulnerable species. The result is a beautifully clear, blue-and dead-lake. In high concentrations these acids also destroy plant tissue, interfere with photosynthesis, and affect the nitrogen-fixing process in legumes and soybeans (Graves, 1980, pp. 76-77).
A second threat to the Earth system is apparent in the increasing amount of carbon dioxide in the atmosphere, also largely a product of the burning of fossil fuels. In the hundred years from 1880 to 1980, atmospheric C02 increased from about 300 to 335-340 parts per minion. The effect of carbon dioxide is to close the "window" through which thermal radiation from the Earth's surface and lower atmosphere escapes into space so that outgoing radiation must flow from higher, colder atmospheric levels, warming the lower atmosphere and surface by what is known as the "greenhouse effect." Atmospheric C02 is expected to reach 600 parts per million in the next century.
If warming from this cause has already begun, it should rise above the noise level of natural climate variability by the end of this century. Atmospheric physicists consider global warming sufficiently likely, however, that a number of global models have been developed to study its probable consequences. These simulate present and past climatic conditions and examine the effects of increased C02 on the simulated systems.
A series of models developed by Hansen and his associates predicts global warming of from l' to 4' C by the end of the next century, depending upon the rate of growth of energy use and the amount of fossil fuel that has been replaced by fuels that do not increase atmospheric C02 (Hansen, Johnson, Lacis, Lebedeff, Lee, Rind, & Russell, 1981, p. 964). Among the possible effects of even a relatively moderate warming would be large regional climatic changes that would alter the location of deserts, fertile areas, and marginal lands and cause largescale dislocation of human settlements and land use.
In addition, since warming at high latitudes would be much greater than the global mean, the world's ice sheets would either shrink or increase in area, depending upon what temperature difference was produced between the ice sheets and the air above them. An increase of five meters would flood many lowlands throughout the world, including heavily settled coastal areas. Hansen and co-authors conclude that (1981, p. 966): "The climate change induced by anthropogenic release Of C02 is likely to be the most fascinating global geophysical experiment that man will ever conduct."
A "scenario" by Flohn (1980, p. 71) brings together results of a large body of models and researches on possible man-made climatic changes. This also predicts regional changes "more profound than mankind has experienced during the last 10,000 years." Flohn does not consider a rise in sea level as a likely outcome, but considers the risk of a 400 to 800 km. displacement of climatic zones unacceptable because of its effect on mankind as a whole. He warns that the change could occur quite abruptly, in a few decades or less, and would be essentially irreversible since the new steady state would continue for at least 1000 years before the deep ocean could absorb the additional input Of C02.
Man has certainly not been an unmixed blessing to the Earth system since, in his relatively brief tenure, he has shown an alarming capability to destroy not only himself but @ other critical components of the system as a whole. Fyfe (1981, p. 105) says:
It is only now that we are beginning to study the major chemical flux rates between the major geospheres (atmosphere, hydrosphere, biosphere, crust, and mantle). It is these rate processes that ultimately provide the global buffer systems. We now know that man is perturbing some of these rates on a scale that is easily observed.
Almost all the problems associated with understanding the rate processes @l, at control environmental stability concern interfaces. There are the great interfaces between the atmosphere and the oceans, rainwater and the continental crust, ocean water and sediments, the living cell and the hydrosphere, and the crust and the deep interior. We are also concerned with the interface between the atmosphere and the radiation field of space.
Human systems are characterized by an enormous capacity to process and disseminate information. If the ecological system of Earth in all its variety is to be preserved, it is important to collect the information necessary to quantify the variables that control the evolution of our planet and are critical to the environment and to apply it in making rational environmental decisions. Although Earth scientists have greatly expanded knowledge of the system, the amount yet to be learned is awesome. The Earth sciences are now in a period of advance in theory, experiment, observation, and instrumentation that is producing the necessary data.
The sun will continue to shine on the Earth, perhaps, almost as bright as today even after the extinction of mankind. and will feed with low entropy other species those with no ambition whatsoever. For we must not doubt that, man's nature being what it is, the destiny of the human species is to choose a great but brief, not a long and dull career. (George Roegen, 1971, p. 304)
This is a gloomy view, but it is not unique. In fact, it is hard to find any student of the world system who is really optimistic about the future. One of the most important results of the world models of Forrester, published in the early 1940s, was to make clear how exceedingly difficult it would be to change our complex world system even if a determination to do so was shared by policy makers in all of the separate nations into which the modern world is divided (Forrester, 1971, pp. 94-95). Because of the complicated feedbacks connecting population, natural resources, capital investment, food supplies, and pollution, change in one may produce unexpected and undesirable consequences in others. In addition, shortand long-term outcomes of attempts to make adjustments were shown to be opposite in effect, with the result that success in the short run in controlling a given variable may, in the long run, lead to its increase beyond its state prior to the intervention.
The simulated world of Forrester, as well as the similar system of Meadows and his colleagues agues, tends toward equilibrium since growth cannot continue without reaching limits imposed by resource shortage, pollution, crowding, food failure, or some other powerful force (Meadows, Meadows, Randers, & Behrens, 1972, p. 23).
The conclusion drawn from both simulations is that unless world policy makers choose to suppress growth in the world system, the internal dynamics of the system itself will produce an undesirable equilibrium. Characteristics of a desirable equilibrium, according to Meadows and his colleagues, would be a constant population number, and a constant capital stock. Population, capital, and the ratio between them would be determined in accordance with the society's values. A society could, for example, decide to keep its population lower in order to provide a better standard of living for all. In addition, all input and Output rates, such as birth, death, investment, and depreciation would be kept to a minimum (Meadows, Meadows, Randers, & Behrens, 1972, p. 170-175). An equilibrium society of this sort would not, they believe, necessarily be stagnant and, in fact, a society based on justice is more likely to develop in such a system.
In its concern for similar problems, the United Nations has sponsored a global input-output analysis and a set of alternative projections of the demographic, economic, and environmental states of the world in 1980, 1990, and 2000, under the direction of Leoiitief (Leontief, W., et al., 1977).
This economic model divides the world into 15 regional blocs, each described in terms of 45 sectors of economic activity. Sectors are linked by export,-, and imports of some 40 classes of goods and services, capital flows and transfers, and foreign interest payments. The model allows detailed analysis of prospective changes in technology, costs of production, and relative prices. It contains 2625 equations in 15 interconnected sets, one for each of the 15 regional blocs. The solution for the base year, 1970, was made to be consistent with actual data for that year. Estimates for the years 1980, 1990, and 2000 were based on information from national and international statistical and research organizations.
The model was used to project several alternative developmental "scenarios," each derived from a different set of factual assumptions. Some of these scenarios reflect alternative estimates of future values of variables like population growth, gross product per capita, and the total of unexplored reserves of various mineral resources. Others examine the implications of various sets of income targets and the alternative means by which they could be attained. The several solutions describe possible futures of the world and make it possible to determine some of the changes that would be necessary in order to achieve desirable goals for the total world system.
A goal of the United Nations is growth in gross product per capita in the developing countries. If this is to be achieved, increased transfer of technology and/or technical assistance would be necessary. The model showed that implementation of minimum targets of the United Nations until the year 2000 did not diminish the gap in gross product per capita between established and developing countries. It appears that the economies of developing countries will be a problem for the rest of this century.
World population is projected to increase steeply for the remainder of the 20th century, which will put enormous pressure upon societies to produce food. If, however, the land could be fully used and if the technological revolution in agriculture were completely exploited, the task of feeding the multitudes could be accomplished (Leontief, W., et al., 1977, p. 5).
A further conclusion of the analysis is that the endowment of mineral resources and fossil fuels is generally adequate to last until the year 2000 and probably into the early part of the next century. Costs of extraction are, however, expected to increase (Leontief, W., et al., 1977, p. 6)
The critical questions about pollution abatement are whether increased pollution is avoidable and whether costs are too high, with the result that they would constrain resources for consumption and investment Leontief finds that, although this is a grave problem, available abatement standards do not present unmanageable problems, nor is pollution an insurmountable barrier to economic development of developing regions (Leontief, W., et al., 1977, p. 7).
The principle limits to sustained economic growth and accelerated development revealed by this very detailed economic analysis are political, social, and institutional rather than physical (Leontief, W., et al., 1977, p. 10). For favorable outcomes in food production, resource availability, and pollution abatement, policies leading to profound political and social changes would necessarily be adopted and implemented.
There is today no worldwide political system with the power to set policy and secure the cooperation of the world's nations in a unified analysis, development of a remedial plan, and implementation of such a plan. Systems at the level of the society are the dominant human political systems. A great deal of supranational decision making goes on in the world in supranational and international organizations, conferences, and meetings among national deciders, but nations comply with decisions of these bodies only when they perceive that the recommended courses of action are in their own best interests. It may well be that securing such cooperation is the most important task now facing human beings.
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