A talk by Stuart Kauffman in which he explains some of his thinking on the adjacent possible. His book 'Investigations' covers a great deal more of this territory at a mind-bending depth that leaves me floundering from time to time but the basic idea is wonderfully simple: that progress, self-organisation and evolution occur through a rachet process in which each new development opens up new possibilities for the next. It's a brilliantly straightforward explanation of the emergence of complexity that makes sense of Darwin's notion of pre-adaptation and Gould's ideas about exaptions in a more general and universal sense. Interestingly, this applies as much to the evolution of technologies and other complex systems as it does to the evolution of life.