Imagine you are a single cell among millions that comprise a growing caterpillar. The structure around you has been operating like a well-oiled machine and the larva world has been creeping along predictably. Then one day, the machine begins to shudder and shake. The system begins to fail. Cells begin to commit suicide. There is a sense of darkness and impending doom.
From within the dying population, a new breed of cells begins to emerge, called imaginal cells. Clustering in community, they devise a plan to create something entirely new from the wreckage. Out if the decay arises a great flying machine - a butterfly - that enables the survivor cells to escape from the ashes and experience a beautiful world, far beyond imagination. Here is the amazing thing: the caterpillar and the butterfly have the exact same DNA. They are the same organism but are receiving and responding to a different organising signal.
Bruce Lipton and Steve Bhaerman, Spontaneous Evolution