From American Scientist:
The basic argument of intelligent design was famously set forth in the watchmaker analogy of William Paley in 1802: The complexity and functionality of a watch imply a watchmaker; analogously, the complexity and functionality of living things also imply a designer, albeit one vastly more potent than a mere watchmaker. This argument rests on a simple analogy between the design of human artifacts and the design of natural forms. For the analogy to work, we must first accept that we design our inventions with purpose and foresight. On this point, most evolutionists and creationists agree. What distinguishes these two camps is that, when accounting for the origin of living things, proponents of intelligent design summon a divine creator, whereas evolutionists credit natural selection. Thus, evolutionists share with creationists the same understanding of design; they differ only in how they invoke it.
Discussions of design are prominent in the writings of evolutionists from Darwin to Dawkins. Pondering the implications of his theory of natural selection for Paley’s “old argument of design in nature,” Charles Darwin wrote in his autobiography that we can no longer argue that “the beautiful hinge of a bivalve shell must have been made by an intelligent being, like the hinge of a door by man. There seems to be no more design in the variability of organic beings and in the action of natural selection, than in the course which the wind blows. Everything in nature is the result of fixed laws.” A century later, Richard Dawkins pursued the issue of design and divided the world “into things that look designed (such as birds and airliners) and things that don’t (rocks and mountains).” He further divided those things that look designed into “those that really are designed (submarines and tin openers) and those that aren’t (sharks and hedgehogs).”
More here.