The diverse forms of nature, in particular and biological forms, have long been a preoccupation of the architect. As a special category of natural form, biological organisms exhibit extraordinary levels of design adaptability across multiple generations based upon the inherent "intelligence' of the evolutionary mechanism. Evolutionary design theory in architecture seeks to harness this generative intelligence as the foundation for a new architectural design process. This paper investigates the lineage of evolutionary thought in architectural design, paying particular attention to the current trend towards experimentation with generative algorithmic procedures and the theorization of an evolutionary architecture.