This statement, by George Perkins Marsh – a nineteenth-century American diplomat, conservationist, and writer – expresses a concept that can be traced in western thought as far back as ancient Greece: the idea that nature in the absence of human intervention is in a state of balance which changes little over long periods of time. In the nineteenth century, this view became a credo for the young science of ecology.

The concept of balance figures so prominently in discussions about natural resource management that it is worth looking at in more detail. In scientific formulations, balance – or equilibrium – is defined as a state in which there is no net change in a system.