Hand drawn diagram of Gaia: the Earth system and feedback loop by James Lovelock. Drawn in coloured ink on photographic paper. Undated.

Scientist and inventor James Lovelock used these diagrams to explain the Gaia hypothesis during his lectures. The Gaia hypothesis describes the Earth as a self regulating system that maintains conditions suitable for life. The diagram on the bottom is an electrical circuit – an example of a simple feedback loop where electrical components maintain a constant output from a light bulb even when the power supply changes. The top diagram lists the constraints on life that affect complex feedback loops on the Earth.