The fundamental rationale for implementing sustainable development remains associated with the notion of 'Spaceship Earth'(Boulding 1966). The environment is in effect our life support system in the vacuum of Space. Our planet can be viewed within this analogy as a spaceship flying through space with its own life-support system. You take away this life support system - the environment and its associated biodiversity - then the future of all species on the planet will be under threat. In this sense the environment and its biodiversity are of an infinite value to humans as a species. Yet bizarrely the environment is often considered to be part of the 'global commons' (IUCN 1980) and a free good of no definable value. It therefore gets consumed for free (e.g. the resources of the oceans or rainforests) on a massive scale.

The Gaia hypothesis (Lovelock and Margulis 1976) has also been a prevailing area of debate and in some circles controversy. It is based on the notion that the biodiversity of the planet is inextricably linked with the life support system which gives us the air we breathe. In short, the Gaia Hypothesis states that life on earth controls the physical and chemical conditions of the environment (the biotic controls the abiotic) and so by impacting on the biodiversity of the planet man is fundamentally impacting on the planetary environmental control systems.