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The Four Laws of Ecology: The Clearest Explanation of What Ecology Really Means

Ecology is the study of relationships and processes linking living things to the physical and chemical environment. Exciting, right?

In the 1971 book The Closing Circle, Barry Commoner gives us a clear and understandable example of what ecology really means, while being one of the first to sound the alarm on the impending environmental crisis. (Although Rachel Caron’s Silent Spring certainly holds the mantle for implanting ecological thought into the popular consciousness.)

Commoner’s life was devoted to helping people see the benefits of ecological thinking:

Ecology has not yet explicitly developed the kind of cohesive, simplifying generalizations exemplified by, say, the laws of physics. Nevertheless there are a number of generalizations that are already evident in what we now know about the ecosphere and that can be organized into a kind of informal set of laws of ecology.

He goes on to lay out four basic and inescapable laws of ecology (which nicely complement Garett Hardin’s Three Filters). The principles describe a beautiful web of life on earth.

The Four Laws of Ecology

The First Law of Ecology: Everything Is Connected to Everything Else

It reflects the existence of the elaborate network of interconnections in the ecosphere: among different living organisms, and between populations, species, and individual organisms and their physicochemical surroundings.

The single fact that an ecosystem consists of multiple interconnected parts, which act on one another, has some surprising consequences. Our ability to picture the behavior of such systems has been helped considerably by the development, even more recent than ecology, of the science of cybernetics. We owe the basic concept, and the word itself, to the inventive mind of the late Norbert Wiener.

The word “cybernetics” derives from the Greek word for helmsman; it is concerned with cycles of events that steer, or govern, the behavior of a system. The helmsman is part of a system that also includes the compass, the rudder, and the ship, If the ship veers off the chosen compass course, the change shows up in the movement of the compass needle. Observed and interpreted by the helmsman this event determines a subsequent one: the helmsman turns the rudder, which swings the ship back to its original course. When this happens, the compass needle returns to its original, on-course position and the cycle is complete. If the helmsman turns the rudder too far in response to a small deflection of the compass needle, the excess swing of the ship shows up in the compass—which signals the helmsman to correct his overreaction by an opposite movement. Thus the operation of this cycle stabilizes the course of the ship.

In quite a similar way, stabilizing cybernetic relations are built into an ecological cycle. Consider, for example, the fresh water ecological cycle: fish-organic waste-bacteria of decay inorganic products—algae—fish. Suppose that due to unusually warm summer weather there is a rapid growth of algae. This depletes the supply of inorganic nutrients so that two sectors of the cycle, algae and nutrients, are out of balance, but in opposite directions. The operation of the ecological cycle, like that of the ship, soon brings the situation back into balance. For the excess in algae increases the ease with which fish can feed on them; this reduces the algae population, increases fish waste production, and eventually leads to an increased level of nutrients when the waste decays. Thus, the levels of algae and nutrients tend to return to their original balanced position.

In such cybernetic systems the course is not maintained by rigid control, but flexibility. Thus the ship does not move unwaveringly on its path, but actually follows it in a wavelike motion that swings equally to both sides of the true course. The frequency of these swings depends on the relative speeds of the various steps in the cycle, such as the rate at which ships responds to the rudder.

Ecological systems exhibit similar cycles, although these are often obscured by the effects of daily or seasonal variations in weather and environmental agents.


The dynamic behavior of a cybernetic system—for example, the frequency of its natural oscillations, the speed with which it responds to external changes, and its overall rate of operation, depends on the relative rates of its constituent steps. In the ship system, the compass needle swings in fractions of a second; the helmsman’s reaction takes some seconds; the ship responds over a time of minutes. These different reaction times interact to produce, for example, the ship’s characteristic oscillation frequency around its true course.


Ecosystems differ considerably in their rate characteristics and therefore vary a great deal in the speed with which they react to changed situations or approach the point of collapse.


The amount of stress which an ecosystem can absorb before it is driven to collapse is also a result of its various interconnections and their relative speeds of response. The more complex the ecosystem, the more successfully it can resist a stress. … Most ecosystems are so complex that the cycles are not simple circular paths, but are crisscrossed with branches to form a network or a fabric of interconnections. Like a net, in which each knot is connected to others by several strands, such a fabric can resist collapse better than a simple, unbranched circle of threads—which if cut anywhere breaks down as a whole. Environmental pollution is often a sign that ecological links have been cut and that the ecosystem has been artificially simplified and made more vulnerable to stress and to final collapse.

The feedback characteristics of ecosystems result in amplification and intensification processes of considerable magnitude. For example, the fact that in food chains small organisms are eaten by bigger ones and the latter by still bigger ones inevitably results in the concentration of certain environmental constituents in the bodies of the largest organisms at the top of the food chain. Smaller organisms always exhibit much higher metabolic rates than larger ones, so that the amount of their food which is oxidized relative to the amount incorporated into the body of the organism is thereby greater. Consequently, an animal at the top of the food chain depends on the consumption of an enormously greater mass of the bodies of organisms lower down in the food chain. Therefore, any non-metabolized material present in the lower organisms of this chain will become concentrated in the body of the top one. …

All this results from a simple fact about ecosystems—everything is connected to everything else: the system is stabilized by its dynamic self-compensating properties; those same properties, if overstressed, can lead to a dramatic collapse; the complexity of the ecological network and its intrinsic rate of turnover determine how much it can be stressed, and for how long, without collapsing; the ecological network is an amplifier, so that a small perturbation in one network may have large, distant, long-delayed effects.

The Second Law of Ecology: Everything Must go Somewhere

This is, of course, simply a somewhat informal restatement of a basic law of physics—that matter is indestructible. Applied to ecology, the law emphasizes that in nature there is no such thing as “waste.” In every natural system, what is excreted by one organism as waste is taken up by another as food. Animals release carbon dioxide as a respiratory waste; this is an essential nutrient for green plants. Plants excrete oxygen, which is used by animals. Animal organic wastes nourish the bacteria of decay. Their wastes, inorganic materials such as nitrate, phosphate, and carbon dioxide, become algal nutrients.

A persistent effort to answer the question “Where does it go?” can yield a surprising amount of valuable information about an ecosystem. Consider, for example, the fate of a household item which contains mercury—a substance with serious environmental effects that have just recently surfaced. A dry-cell battery containing mercury is purchased, used to the point of exhaustion, and then “thrown out.” But where does it really go? First it is placed in a container of rubbish; this is collected and taken to an incinerator. Here the mercury is heated; this produces mercury vapor which is emitted by the incinerator stack, and mercury vapor is toxic. Mercury vapor is carried by the wind, eventually brought to earth in rain or snow. Entering a mountain lake, let us say, the mercury condenses and sinks to the bottom. Here it is acted on by bacteria which convert it to methyl mercury. This is soluble and taken up by fish; since it is not metabolized, the mercury accumulates in the organs and flesh of the fish. The fish is caught and eaten by a man and the mercury becomes deposited in his organs, where it might be harmful. And so on.

This is an effective way to trace out an ecological path. It is also an excellent way to counteract the prevalent notion that something which is regarded as useless simply “goes away” when it is discarded. Nothing “goes away”; it is simply transferred from place to place, converted from one molecular form to another, acting on the life processes of any organism in which it becomes, for a time, lodged. One of the chief reasons for the present environmental crisis is that great amounts of materials have been extracted from the earth, converted into new forms, and discharged into the environment without taking into account that “everything has to go somewhere.” The result, too often, is the accumulation of harmful amounts of material in places where, in nature, they do not belong.

The Third Law of Ecology: Nature Knows Best

In my experience this principle is likely to encounter considerable resistance, for it appears to contradict a deeply held idea about the unique competence of human beings. One of the most pervasive features of modern technology is the notion that it is intended to “improve on nature”—to provide food, clothing, shelter, and means of communication and expression which are superior to those available to man in nature. Stated baldly, the third law of ecology holds that any major man-made change in a natural system is likely to be detrimental to that system. This is a rather extreme claim; nevertheless I believe it has a good deal of merit if understood in a properly defined context.

I have found it useful to explain this principle by means of an analogy. Suppose you were to open the back of your watch, close your eyes, and poke a pencil into the exposed works. The almost certain result would be damage to the watch. Nevertheless, this result is not absolutely certain. There is some finite possibility that the watch was out of adjustment and that the random thrust of the pencil happened to make the precise change needed to improve it. However, this outcome is exceedingly improbable. The question at issue is: why? The answer is self-evident: there is a very considerable amount of what technologists now call “research and development” (or, more familiarly, “R & D”) behind the watch. This means that over the years numerous watchmakers, each taught by a predecessor, have tried out a huge variety of detailed arrangements of watch works, have discarded those that are not compatible with the over-all operation of the system and retained the better features. In effect, the watch mechanism, as it now exists, represents a very restricted selection, from among an enormous variety of possible arrangements of component parts, of a singular organization of the watch works. Any random change made in the watch is likely to fall into the very large class of inconsistent, or harmful, arrangements which have been tried out in past watch-making experience and discarded. One might say, as a law of watches, that “the watchmaker knows best,”

There is a close, and very meaningful, analogy in biological systems. It is possible to induce a certain range of random, inherited changes in a living thing by treating it with an agent, such as x-irradiation, that increases the frequency of mutations. Generally, exposure to x-rays increases the frequency of all mutations which have been observed, albeit very infrequently, in nature and can therefore be regarded as possible changes. What is significant, for our purpose, is the universal observation that when mutation frequency is enhanced by x-rays or other means, nearly all the mutations are harmful to the organisms and the great majority so damaging as to kill the organism before it is fully formed.

The Fourth Law of Ecology: There Is No Such Thing as a Free Lunch

In my experience, this idea has proven so illuminating for environmental problems that I have borrowed it from its original source, economics. The “law” derives from a story that economists like to tell about an oil-rich potentate who decided that his new wealth needed the guidance of economic science. Accordingly he ordered his advisers, on pain of death, to produce a set of volumes containing all the wisdom of economics. When the tomes arrived, the potentate was impatient and again issued an order—to reduce all the knowledge of economics to a single volume. The story goes on in this vein, as such stories will, until the advisers are required, if they are to survive, to reduce the totality of economic science to a single sentence. This is the origin of the “free lunch” law.

In ecology, as in economics, the law is intended to warn that every gain is won at some cost. In a way, this ecological law embodies the previous three laws. Because the global ecosystem is a connected whole, in which nothing can be gained or lost and which is not subject to over-all improvement, anything extracted from it by human effort must be replaced. Payment of this price cannot be avoided; it can only be delayed. The present environmental crisis is a warning that we have delayed nearly too long.

Lest you feel these are all scientific, Commoner ends by referring you to classic literature:

A great deal about the interplay of the physical features of the environment and the creatures that inhabit it can be learned from Moby Dick.”


Still Interested? Check these related posts out:

Garrett Hardin on the Three Filters Needed to Think About Problems — “The goal of these mental filters, then, is to understand reality by improving our ability to judge the statements of experts, promoters, and persuaders of all kinds.”

The Effect of Scale in Social Science, or Why Utopia Doesn’t Work — Why can’t a mouse be the size of an elephant? Weclome to the effect of scale on values.