The perennial question – what is life? The simple answer is that life, either considered in the totality of all its incredible diversity or even in the context of an individual organism, is a highly complex chemical system with a capacity for self-reproduction. But what fuels this system, and what drives the evolution of such extreme apparent complexity? The principle underlying the answer to the first question was initially propounded by Ludwig Boltzmann, the nineteenth-century physicist and natural philosopher. Boltzmann had a tremendous admiration for Darwin and suggested, ‘Available energy is the main object at stake in the struggle for existence and the evolution of the world’.