The development of the Gaia Hypothesis is described with some emphasis on how the concept has evolved in response to other scientist's skepticism. The Gaia concept itself is described and discussed. A possible means for reconciliation of the holistic Gaia hypothesis with reductionist thinking is discussed. I conclude by summarizing what the paper has accomplished.
The Gaia Hypothesis was first published by James E. Lovelock in 1972 (Lovelock, par. 23). It was, at the time, the end product of a series of observations Lovelock had made about Earth, Mars and Venus (Margulis and Lovelock, p. 11(2)).
The premise underlying the Gaia hypothesis is that the entire planet evolves over time because of the interaction of living things with their surrounding environment. Because of the interdependence of the evolution of environment and biome, Lovelock likened the entire planet Earth to a living thing with complex interlocking planet-wide systems that maintain a condition of homeostasis conducive to Earth's long-term habitability.
While the existence of symbiotic relationships between some species has been long observed and accepted, the ultimately symbiotic relationship of every living thing on Earth proved too broad a claim for many scientists to accept. Consequently, the Gaia hypothesis has been generally lambasted by most mainstream scientists.
In the next section, I describe the hypothesis in some detail and provide background information. This will be followed by a discussion contrasting Lovelock's claims with those of his critics and proffers an approach toward reconciliation and my concluding comments.
In 1957 James E. Lovelock invented a device called the electron capture detector that can accurately measure minute traces of specific elements and chemical compounds. He used this in Antarctica to detect the presence of CFCs in the atmosphere as well as the presence of DDT in many samples from around the world, including human breast milk (Holden, p. 1977). In other words, James Lovelock is the person more responsible than any other for getting DDT and CFCs removed from the market, for it was his invention that first allowed accurate measurements of these pollutants.
In 1961 he was invited to join NASA and contribute toward America's exploration of Earth's moon (Lovelock, par. 16). Later, he found himself advising NASA on its Viking Project planned to land stationary probes on the Martian surface. Part of the mission goal was to establish whether life was present on the Red Planet.
Before the mission was launched, Lovelock advised NASA to cancel the biological research portion of the mission because, he surmised, there was not currently any significant life on Mars. His reasons had to do with his examination of the Martian atmosphere.
Mars' atmosphere consists primarily of carbon dioxide at very low atmospheric pressure. It is essentially chemically inert and thus in a state of chemical equilibrium. Lovelock reasoned that were there living things on Mars capable of photosynthesis, we would expect to find free oxygen in the Martian atmosphere. He drew a similar conclusion based on the absence of methane from Mars' atmosphere. Methane is a common byproduct of the decomposition of dead plants and animals. With neither methane nor oxygen in detectable quantities in Mars' atmosphere, there seemed ample reason to conclude that nothing lives there that could be detected by the Viking landers' (there were two of them) instruments.
He drew the same conclusion about the likelihood of finding life on Venus, based on similar evidence.
Earth's atmosphere is not in a state of chemical equilibrium. It is full of gases that have an affinity for each other. Oxygen, nitrogen, and methane exist in sizable quantities, and left to their own devices, would quickly interact to form a new atmosphere of inert gases, very much like Mars' atmosphere (Margulis and Lovelock, p. 13(2)). So the persistent presence of uncombined methane, nitrogen, and oxygen in the atmosphere is strong evidence that something is replenishing these gases as fast as they naturally interact.
The answer is life (Margulis and Lovelock, p. 88 (1)). Organisms that can perform photosynthesis continuously pump oxygen into the atmosphere faster than it can react with methane or nitrogen. Microbes break down nitrates in the soil and pump out nitrogen faster than it can react with atmospheric oxygen. Decaying flora and fauna release methane into the environment in the same way. Essentially, the current state of Earth's atmosphere is the inevitable result of the kind of things that live here.
This realization was the seed for Lovelock's Gaia hypothesis. Among other things, the Gaia hypothesis proposes that the complexity of Earth's ecosystem is analogical to the complexity of an organism. Thus, Earth, while not being actually alive, is like a living thing in many respects.
One of the key features of the hypothesis is that the Gaia principle operates to maintain a condition of environmental homeostasis, just as an organism maintains a condition of biological homeostasis. If a person gets overheated, his or her body automatically responds to restore the previous state by perspiring. Moisture moved to the surface of the skin is subject to the cooling process of evaporation.
Lovelock surmised that Earth has planet-wide systems operating in similar fashion to preserve environmental homeostasis. Consider the following scenario in which carbon dioxide is allowed to accumulate to high levels in Earth's atmosphere.
A surplus of carbon dioxide actually promotes the growth of vegetation two ways. First, vegetation requires carbon dioxide to perform photosynthesis, so more carbon dioxide leads to more vegetation because it facilitates this process (Laurence, p. 96). Second, carbon dioxide is a greenhouse gas, and if enough accumulates in the atmosphere there is a proportional increase in average global temperature. One implication of this is that the annual freeze lines in both hemispheres gradually move closer to the poles, freeing up more territory for plants to exploit.
With a larger percentage of Earth's surface covered by faster-growing vegetation, more carbon dioxide becomes impounded in the new biomass. The ratio of carbon dioxide to oxygen falls. The annual freeze lines move away from the poles as Earth cools, thus reducing the territory vegetation can exploit. The net effect is that long-term ratios of atmospheric gases (and consequently, global temperatures) vary within otherwise very stable parameters.
This feedback loop is fundamental to the Gaia hypothesis; life influences its environment, which in turn influences the proliferation of life.
In spite of what may seem innate plausibility, the Gaia hypothesis was not received by the scientific community with open arms. In fact, Lovelock himself states that for a long time none of the peer-reviewed journals would publish his papers (as quoted in Potts, p. 33).
Perhaps the most vocal of Lovelock's critics is Oxford University's Richard Dawkins. Dawkins has said the Gaia hypothesis is teleological, untestable and, further, that it is based upon assumptions about the nature of natural selection that are "profoundly erroneous" (Fairbairn, 1994, p. 1210). More specifically, Dawkins criticizes the Gaia concept in its conclusion that natural systems evolve symbiotically over time because this implies an element of altruism in the behavior of the organisms concerned.
The introduction of a selfish individual into a population formerly consisting only of altruistic individuals will give the selfish individual a tremendous advantage to exploit the others, who will not respond negatively since they are, by definition, altruistic. Since this selfish individual's biological "success" is assured, his offspring will inherit his selfish tendencies. The conclusion is inevitable; the descendents of the original selfish individual completely replace the altruists, who become extinct.
Starting from such a premise it is not difficult to understand the problem Dawkins has with Lovelock's hypothesis. How can mutually beneficial relationships evolve when natural selection favors selfishness?
Part of the problem may be semantics; what is meant when we say "beneficial" or "symbiotic?" There may be some connotation to these words that is inappropriate given the actual relationships that Lovelock is trying to describe. The symbiotic interdependence of living things is not necessarily planned nor arrived at consensually. It may be simply inadvertent.
Plants and microbes are not consuming carbon dioxide and producing oxygen to benefit animal life, and likewise, the animals aren't consuming oxygen and producing carbon dioxide to benefit the plants. Each benefits the other as a consequence of what each does in self-interest.
Partly in response to criticism by Dawkins and others, Lovelock developed the Daisy World computer model (Lenton, p. 441). In Daisy World, a planet is populated by an arbitrary population of two species of daisy, white and black. The amount of solar radiation the world receives increases with time, just as scientists claim has happened on the real Earth (Newman and Rood, p. 1035). Since the white daisies tend to reflect light, they have a cooling effect on Daisy World's environment; conversely for the black daisies.
When the simulation is run, the intensity of solar radiation received by Daisy World stimulates the growth of one or the other type of daisy until an equilibrium is reached. From that point, the daisies either proliferate or decline depending on the…