It is often the case in scientific inquiry that complexity yields to grand simplicity, and ecology may have arrived at such a moment. A dazzling new theory of the environment has been worked out in a series of papers published in the last two years by a microbiologist and an atmospheric chemist. They suggest that the biosphere, as a whole, on a global basis, regulates such features of the environment as the composition of the atmosphere, aspects of the climate, the acidity of the soil, and the cycling of elements from the continents to the sea and back.
The devisers of this hypothesis are James Lovelock, F.R.S., an atmospheric chemist associated with the University of Reading in England, and Lynn Margulis, a microbiologist at Boston University. Both are scholars with substantial professional achievements. Lovelock and Margulis call their theory the Gaia hypothesis (from a suggestion by the novelist William Golding), after the Greek goddess in whose body all living things were organs.
They begin their argument by observing things about our planet that “oughtn’t to be.” Earth, although similar in many ways to Mars and Venus, has a very different atmosphere and surface. These three planets were made at the same time, of about the same constituents, are of roughly the same size, and occupy generally the same neighborhood in the solar system. If one uses as a base line what a planet orbiting between Mars and Venus “ought” to look like, Earth can be seen as having “too much” nitrogen and “too little” carbon dioxide and sulfuric acid. Such gases as ammonia, hydrogen, and methane are present in our atmosphere in amounts some thirty orders of magnitude (a quadrillion squared) higher than they “should be.” “Indeed,” the authors write, “so great is the disequilibrium among the gases of the Earth’s atmosphere that it tends towards a combustible mixture, whereas the gases of Mars and Venus are close to chemical equilibrium and are more like combustion products.”
And there is something else peculiar about Earth: many features of the biosphere, including those mentioned above, would appear to be inherently unstable, yet in fact they endure very well. For one thing, an oxygen atmosphere like Earth’s “ought” to produce acids that would in turn lower the pH of the soil, thus making it sour and eventually sterile. Yet this has not happened. A second example: As rainfall washes such biologically vital elements as iodine, sulfur, and phosphorus into the oceans, the continents (which are not replaced geologically) “ought” to become steadily less favorable to life. This has not happened.
Another anomaly: It has been argued for many years that a planet “ought” not to be able to hold its stock of fluids in liquid form permanently; eventually they should stabilize into either gases, like Venus’s, or ices, like Mars’s. The argument runs this way: Assume a fluctuation of solar energy that raises temperatures. The higher temperatures would evaporate more water; the atmosphere would become hazier and therefore more likely to absorb radiations which, reflected from Earth’s surface, would otherwise have bounced out into space. Absorbing these radiations would heat the water gas, thereby raising the temperatures of the planet still more, and setting off another round of evaporation, radiation absorption, and heat generation. Eventually the process would produce a Venus-like planet.
On the other hand, if the solar fluctuation is one that lowers temperatures, there would be an increase in the snow and ice cover, and because this cover is white, it would reflect more sunlight out into space than when the area was uncovered ocean or land. The result would be still lower temperatures, an increase in the size of the ice cover, and so on through a descending, accelerating spiral, until all the surface fluids had frozen and we arrived at an ice ball with a thin atmosphere, much like Mars today. Clearly neither of these climatic catastrophes has happened on Earth— yet there is a lot of evidence to suggest that the sun’s output has fluctuated often, both up and down, over the last three billion years.
Lovelock and Margulis point to a common thread running through these anomalies: in all cases the direction in which our expectations are violated is to the benefit of life. “There are, in the atmosphere, ‘too many’ of exactly those elements that are required by living things,” they write. “The temperature is ‘too moderate’ and is apparently hovering around an average value, just about room temperature, which is very comfortable for a majority of living organisms on the surface. Instead of being acidic, the way certainly Venus is, the Earth is slightly basic. Acid . . . is a powerful destroyer of proteins and nucleic acids. . . . The mild basicity (the oceans are about pH 8.2) is just fine. . . .”
They find it hard to believe that all the alterations favor the conditions for most living things by chance alone. It is possible that the theories on which these expectations are based are wrong, and that if we really understood physics, chemistry, and astronomy, we would see that biologically hospitable conditions are as inevitable for a planet in Earth’s orbit as are, say, the perturbations induced in that orbit by the influence of Jupiter. Or there might be some unknown “hidden hand,” which existed before life and under the protection of which life evolved, imposing stability on these phenomena. Finally one can argue, as Lovelock and Margulis do, that life itself, acting as a collectivity, has seized control of the relevant processes and is running them for its own benefit.
The bulk of the Lovelock and Margulis papers describe how biology might be able to manage these global life-support systems successfully. For instance, in 1972 Lovelock found flows of volatilized (gaseous) sulfur and iodine being blown out of the oceans back onto the land. Previous calculations had shown that continental river systems were washing more sulfur into the ocean than “ought” to have been available to those rivers through erosion. Apparently, once that sulfur reached the ocean it was absorbed by marine algae and excreted in gaseous form. Lovelock measured these sulfur emissions and found that they were large enough to replenish the continental sulfur washed out to sea by the rivers. On the pH-acid question, Lovelock and Margulis point out that many organisms excrete ammonia and ammonia neutralizes acid. Approximately two billion tons of ammonia are excreted into the atmosphere each year, enough to sweeten many fields.
Life depends on oxygen levels staying constant. If they rise too high, the plants will burn; if they fall too low, the animals will choke. Yet oxygen is a very active element, combining freely with a range of both organic and inorganic substances. How is it maintained at a constant level? Professor Michael McElroy of Harvard has worked out, as a speculative exercise, a Gaia-style mechanism that might be responsible, or partly responsible, for holding oxygen levels constant. His system works through the interplay of three classes of biological actors: marine bacteria, photosynthesizing algae, and zooplankton, tiny animals that graze on the algae.
The algae make oxygen, as all plants do, that can either be released into the atmosphere or be taken up in the respiration and decay cycles of the animals. The more animals, the more oxygen will be thus absorbed. The population levels of the animals are controlled, in turn, by a nutrient (fixed nitrogen) for which they must compete with the marine bacteria. The circle closes with this fact: the intensity with which the bacteria compete for the nutrient depends on the amount of oxygen in their environment. If they can get oxygen they do not absorb as much of the nutrient, but if oxygen levels are low, their appetite for fixed nitrogen grows rapidly. As the supplies of this nutrient dwindle the zooplankton begin to starve and their populations plummet. The result: a reduced consumption of the algae-produced oxygen, which floats up into the atmosphere to replace the deficit that so influenced bacterial behavior.
McElroy’s suggestion is important because it show’s that the Gaia idea can stimulate thoughtful proposals in minds other than those of its founders—which is not always the case when new theories are propounded. It is in addition a useful working model of a Gaian mechanism: the marine bacteria serve first as detectors of the oxygen deficit, then as amplifiers, by shunting the decrease into an impact on the fixed-nitrogen cycle.
It also points to one of the problems with the Gaia idea. The population crash of the zooplankton is an essential part of the machine; what would happen if they should evolve the ability to fix their own nitrogen? In that event, what might seem an evolutionary breakthrough for them would turn out to be a disaster for the whole globe, since at the least that particular mechanism for maintaining the planetary oxygen balance would be lost.
Gaia seems difficult to integrate into evolutionary theory as presently taught: “Natural selection will never produce in a being anything injurious to itself,” Darwin stressed, “for it acts solely by and for the good of each.” But an organization of any kind depends on its members remaining in their places and executing their roles faithfully, even at some personal sacrifice. Discipline is maintained at General Motors by firing those individuals who try to benefit themselves at the cost of the organization. Perhaps ant colonies also do this; if not, order is probably kept by the extinction of nests with too many self-seeking individuals in them. How does the Gaian society prevent its members from straying out of their allotted assignments? And how did it evolve in the first place?
Still, evolutionary theory has gone through many revolutions over the last hundred years, and no one who follows the debates currently crackling through the literature can doubt that it will go through many more. The evolutionary background of some aspects of the Gaia model is easy to imagine: one can see how a plant growing on a shoreline, and in need of some nutrient, might profit if it stumbled on a way of encouraging the growth of a local species of marine algae that excreted that nutrient. For example, the phosphorus needed by the algae that grow in certain Alaskan lakes is provided by the decaying bodies of salmon who have completed their spawning migration to those lakes and then died. The following year those same algae give up that phosphorus to the salmon young, who eat them, return to the ocean, absorb more phosphorus, and return to the same lakes. Any algal variant which prevented the salmon young from eating it would suffer in the long run, since soon the flow of new phosphorus would dry up and all the old stores of the nutrient would eventually be lost through becoming trapped in sediment on the lake bottom. Perhaps even so vast an organism as Gaia might have assembled itself from a host of smallscale links of this kind.
One has to wonder how humans might be related to this entity. Possibly we are already, unconsciously, immersed in and busy executing a whole range of Gaian duties. For more than a hundred years our industrial civilization has been pouring carbon dioxide into the atmosphere. For almost that length of time scientists have worried about the impact of the C02 on our climate. C02 is, of course, transparent on the frequencies of visible light, but on other wavelengths it will block and absorb radiation. This absorbed radiation will heat the atmosphere. Is it not probable, therefore, that increasing the amount of C02 will increase the heat generated by the atmosphere? The debate is a complicated one, and one of the unknowns is the degree to which other mechanisms are removing all this “extra” C02. Calculations seem to show that most of the C02 one would have expected to find in the atmosphere, given the rate at which we have been burning fossil fuels, is not there.
Fred MacKenzie, a geologist at Northwestern University, has recently pointed out that at the same time our industrial effort has been expanding, our agricultural technologies have been improved—the two necessarily go hand in hand. We use a lot of fertilizer, both the fixed-nitrogen kind and phosphates. These nutrients eventually become volatilized and wind up in the atmosphere, where they circulate and are then rained out over the landscape. MacKenzie’s figures suggest that the ratio of carbon (from the industrial CO2) to fixed nitrogen to phosphorus (800:9:1) is about what is needed to build plant tissues. The global plant biomass, he concludes with another set of calculations, may have increased by some 10 pecent over the last several decades. This would account for the missing CO2. “Man,” he says, “has inadvertently and clumsily balanced his own pollution problem.” Further, even the fraction of CO2 that has permanently entered the atmosphere has not led to the warming predicted; global temperatures seem to have declined slightly since World War II. Some atmospheric chemists have proposed that the reason for this lies in the increased amount of industrial soot in the atmosphere: the dirt might have a scattering, reflective effect on the sun’s rays, or might facilitate the formation of clouds which would also reflect sunlight back into space, or both.
An earlier century would have rejected the idea that there was anything “inadvertent” about these results and would have held them to be evidence that man’s purposes are in harmony with those of Providence; that the world was designed by One who anticipated the development of industry and created nature to support that activity. A Gaian reformulation of this theology might be that man is really too much a part of nature to drift very far out of harmony with it; that the rhythms of self-regulation, and of integration with larger forces, pervade us so deeply that we could not break away even if we would; and that the same motions that seem to set us at odds with the environment simultaneously bring us back.
There is considerable comfort in the idea that Gaia protects us from our misdeeds, that it is so robust, sophisticated, and competent that it can even tidy up after so dirty a customer as modern civilization. Nicholas Fisher of the Woods Hole Oceanographic Institute recently tested the idea that the oil residues floating in the ocean might so adversely affect the photosynthesizing plankton that oxygen production would fall. He found that while the currently dominant species of algae are adversely affected, resistant forms replace them so rapidly that production of oxygen remains unaffected even at high pollutant concentrations. The MacKenzie argument can also be looked at with this perspective: The difference between a factory pouring out smoke and a herd of buffalo thundering over the plain seems great to a human (one is a blight and an outrage; the other is a panorama of natural majesty), but perhaps nature is less passionate about it. They both put a lot of dust and CO2 in the air, and perhaps both can be coped with in the same way.
This argument is strengthened, at least intuitively, by the Gaian success in turning old, anthropocentric “higher” and “lower” classifications topsy-turvy. The Lovelock and Margulis papers make clear that the identity of the globe has been set and is maintained by organisms that are very distant indeed from man, or the primates, or the mammals, or even the vertebrates, in any taxonomic or evolutionary sense. It is the contributions and activities of the plants, bacteria, algae, and the protozoans that carry weight. We vertebrates are the silverfish and cockroaches of this great house, living marginally, in the interstices, profiting from a structure built for and maintained by a different order of being.
And yet I do not see how one can doubt that the impact of humans on the biosphere is perfectly capable of destroying any plausible organization in nature. Perhaps a better way of using the Gaian theory is to alert us to the existence of critical links in the environment, the destruction of which would have serious consequences. Given the McElroy suggestions for the regulation of oxygen, one must ask what impact all the fixed nitrogen we are flushing into the oceans in the form of fertilizer runoffs is going to have. Might it be increasing the populations of zooplankton to such proportions that the oxygen production of the oceans is falling? Is anyone even monitoring, on a systematic basis, the concentration of oxygen (and other gases) in the atmosphere?
The major contribution of the Gaian hypothesis may be that it makes those familiar with it apprehensive about the
answers to such questions. What will happen when the Amazonian rain forest is cut down? Lovelock and Margulis do not and cannot spell any of this out, but the reader cannot but suspect that all hell is going to break loose.