bsorb light and heat their environment, and white daisies that reflect light and cool their environment. At higher temperatures, black daisies suffer from the heat and are impaired until they eventually die. Similarly, white daisies cannot cope with low temperatures. With a heat and light input which starts weak then steadily becomes stronger, this planet tends towards an equilibrium temperature and the varying proportion of black to white daisies will maintaintain the planet at that equilibrium temperature. This is in contrast to a bare gray planet, whose temperature would steadily rise with the increased input of heat and light. The model remains valid even with many modifications (daisy-consuming rabbits; meteor strikes killing most of the daisies, "cheat" grey daisies which produce no pigment and have a higher rate of growth and reproduction) However, Lovelock intended Daisyworld as a starting point. It provides a model of how a Gaian system might work. It does not prove that the Earth functions as a Gaian system, and does not fully address the assertion that the emergence of a Gaian system is incompatible with current views on evolution. Gaia's advocates are engaged in asking "How do results from Daisyworld transfer to the real world?".
 Initial scientific criticism
Dr. W. Ford Doolittle is one of the most well-known critics of the Gaia hypothesis. In 1981, he wrote an article for CoEvolution Quarterly titled "Is Nature Motherly?" in which he conjectured that there is nothing in the genome of organic life which could provide the feedback mechanisms the Gaia hypothesis proposes, and that, therefore, the Gaia hypothesis was an unscientific theory without any explanatory mechanism, in violation of the scientific method. Richard Dawkins, in his book The Extended Phenotype, wrote in affirmation of Doolittle's critique of the hypothesis, arguing that organisms cannot act in a concerted effort, as it would require foresight and planning from them on a global scale.
Dr. James Kirchner criticized the hypothesis for its imprecision, asserting that Lovelock had not presented one particular theory, but rather four separate, but closely linked, hypotheses:
- Co-evolutionary Gaia — that life and the environment evolve in a coupled way, which Kirchner claims was not new and already accepted scientifically.
- Homeostatic Gaia — that life maintained the stability of the natural environment, and that such stability allowed life to continue to exist.
- Geophysical Gaia — that the Gaia hypothesis generated interest in geophysical cycles, therefore leading to new research in terrestrial geophysical dynamics.
- Optimising Gaia — that Gaia shaped the planet in a way which made it an optimal environment for life, which Kirchner claims was not testable and therefore was pseudoscientific.
Furthermore, of homeostatic Gaia, Kirchner recognized only two alternatives: "weak Gaia", which asserts that life tends to make the environment stable for the flourishing of all life, and/or "strong Gaia" which asserts that life tends to make the environment stable in order to enable the flourishing of all life. Strong Gaia, Kirchner claims, is untestable and therefore pseudoscientific.
In Joseph Lawrence's book, Gaia: The Birth of an Idea, Lawrence argued that Kirchner's attacks were principally against Lovelock's integrity, and not against the hypothesis itself. Lovelock did not attack Kirchner's views until his autobiography Homage to Gaia, in which he dismissed Kirchner's position as sophistry. Lovelock, however, did attempt to disprove the claim that the theory is not scientific because it is impossible to test it by researching and developing a controlled experiment.
Lovelock was also careful to present a version of the Gaia hypothesis which had no claim that the Earth's biological systems intentionally or consciously maintained the complex balance in the environment that life needed to survive. Instead, it appears that the claim that Earth acts intentionally was a metaphoric statement and was not meant to be taken literally. This restatement of the G