Daisyworld demonstrates that self-regulation of the global environment can
emerge from organisms altering their local environment in different ways. I
n Daisyworld, natural selection is directly linked to environmental effects
such that what is selected for at the individual level is beneficial to th
e global environment. The model has been modified and extended in many stud
ies that have highlighted the effect of biological processes on system self
-regulation. Here we better quantify their effects and present new variants
of the model in an attempt to resolve outstanding debates. The results con
firm that Daisyworld is a remarkably robust self-regulating system and they
offer some general lessons about systems where life has a strong effect on
the environment, which we think are relevant to the Earth. As forcing beco
mes extreme, such systems can exhibit co-existing stable states with and wi
thout life (bi-stability), and rapid transitions From one to the other that
are difficult to reverse. The growth response of organisms to the environm
ent has a role in determining the range of forcing over which a system can
regulate. Density-dependent ecological interactions improve Daisyworld's re
gulatory properties, although increased inter-species competition destabili
ses the environment in one interval. Self-regulation is little affected by
introducing organisms that "cheat" by not altering their local environment
and in so doing gain a growth advantage. Increased variation in an environm
ent-altering trait (albedo) can weaken the negative feedback it provides on
the environment. However, random mutation of this trait and subsequent nat
ural selection can generate and extend the range of temperature regulation
and improve the system's response to perturbation with time. Internal adapt
ation of organisms toward prevailing environmental conditions, or to tolera
te extremes, can also extend the range of forcing over which life persists.