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Lovelock originally thought that some purposeful design organized living things to stabilize the atmosphere and climate. Now he and Margulis believe this regulation is achieved through the simple mechanism of feedback. For instance, in a hypothetical scenario, Lovelock shows that a planet covered simply by light- and dark-colored daisies could control the sun's heat. In this self-regulating model, dark daisies would absorb sunlight and warm the planet, until it became too warm for the dark daisies and instead favored the proliferation of light-reflecting daisies. That would have the effect of cooling the planet until the cycle reversed itself again.
Scientists have yet to uncover the actual mechanisms by which life processes regulate earth's climate and atmosphere. Lovelock maintains that this makes it all the more imperative that man halt the mass extinctions threatened by the destruction of tropical forests, because he does not know what creatures are essential to his own survival. At the American Geophysical Union conference on Gaia, Lovelock argued that diversity makes earth both stable and habitable: "You cannot have a sparse planet any more than you can have half an animal."
Gaia's critics have by no means been silenced. Some dispute the degree to which life-forms stabilize the atmosphere and temper the climate. Others contend that the emergence of oxygen in earth's atmosphere contradicts Gaia because it made the air poisonous for anaerobic creatures of primordial times. Evolutionary scholar Richard Dawkins argues that earth cannot be considered an organism because it does not reproduce. Gaian proponents respond that the increase of oxygen in the atmosphere was slow enough to allow the mix of life- forms to adjust, and physician-author Lewis Thomas answers Dawkins by coyly suggesting that, through space exploration, mankind may be acting as an inadvertent disseminator of earth's spore.
Its critics notwithstanding, Gaia seems to be gaining in influence among both scientists and theologians. To some, Gaia's appeal is that it promises to end the long estrangement of Western science and religion. Even if the biosphere regulates the planet by feedback, Gaia still integrates living things and inanimate forces into a unified system, allowing both science and religion to look at life as something more than a mere accident. Says James Parks Morton, dean of New York City's St. John the Divine Episcopal Cathedral and a leading religious advocate of Gaia's: "The very nature of this hypothesis shows that we are now at a new moment when scientific and religious inquiry is directed to the same reality and discussed in a common language."