Aristotle Rediscovered: What Exactly Is the "Mechanism" for Intelligent Design?

In a post yesterday, I responded to a question from Discovery Institute's Chairman of the Board, Bruce Chapman ("A Maze with One Exit: Why Evolution Had No Choice"). He goes on to query me about how the direction in nature's evolution was imparted:

Darwinists often ask what they seem to regard as a killer question: If there is intelligent design, what is the mechanism for it? Of course it's possible to reply that the question is intended as a trap -- which it often is -- or the result of fa...