The Ecology Book

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the interactions of living organisms

and their physical surroundings—

including the cycles of oxygen,

carbon, nitrogen, and sulfur—

form a dynamic system that

stabilizes the environment.

According to Lovelock, Gaia

is controlled by the action of

“feedback loops,” which are

the checks and balances that

compensate for disturbances in

the system, bringing it back into

equilibrium. To function well, life

on Earth depends on a particular

balance of variables such as water,

temperature, oxygen, acidity, and

THE GAIA HYPOTHESIS

salinity in its environment. When

these are constant, Earth is in

a stable state of homeostasis, but

if the balance is disturbed, the

planet encourages the organisms

that will restore the equilibrium,

while being hostile to those that

reinforce the disturbance. The

organic components of the Earth

system do not simply react to

changes in their environment, but

control and regulate them.

These feedback mechanisms

operate in a complex global network

of interconnected natural cycles, to

maintain the optimum conditions

for the organisms within them.

They can resist change, but only

to a certain extent. A big enough

disturbance can push the system

to a “tipping point,” where, with the

balance of its components altered,

it is likely to settle into a very

In the Gaia hypothesis, Earth, the

only known planet to support life, is

itself a “superorganism,” where the sea,

land, and atmosphere work together to

maintain the right living conditions.

Daisyworld

At first, scientists criticized

the Gaia hypothesis for its

supposed implication that the

ecosystems in the biosphere

could collectively influence

Earth’s environment. So to

enhance the plausibility of the

Gaia theory, in 1983 James

Lovelock and fellow British

scientist Andrew Watson

produced “Daisyworld,” a

simple explanatory model.

Daisyworld is a barren

planet, orbiting a sun. As the

intensity of the sun’s rays

increases, black daisies start

to grow. They absorb heat and

warm the planet’s surface to

the point where white daisies

can thrive. They, in turn,

reflect the sun’s energy, so

cooling the ground. The two

kinds of daisy reach a point

of equilibrium, whereby they

regulate the temperature of

the planet. When the sun’s

heat increases further, the

white daisies, able to reflect

the sunlight and stay cool,

replace the black daisies.

Finally, the sun heats up so

much that even the white

daisies can no longer survive.

different state of equilibrium. Such

a tipping point, argued Lovelock,

occurred about 2.5 billion years

ago, at the end of the Archean Eon,

when oxygen first appeared on

Earth. At this time, Earth was a

hot, acidic place in which methane-

producing bacteria were the only

life that thrived. Bacteria capable of

photosynthesis then evolved, which

created an atmosphere that was

If there were

a nuclear war,

and humanity were

wiped out, Earth

would breathe

a sigh of relief.

James Lovelock

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