The traditional view is that design can only arise thanks to a sentient designer. Thus in the teleological argument, also known as the argument from design, the obvious presense of design in the world is thought to prove the existence of a designer, namely God.
In the past few decades, some at the intersection of philosophy and Neo-Darwinian evolutionary theory have proposed an alternative, in which it is meaningful to speak of design without always speaking of a sentient designer. It is seen as insightful to see see humans, gods, and certain impersonal forces, especially natural selection, as equally capable of giving rise to one unified phenomenon: design. Daniel C. Dennett (1995) offers perhaps the most comprehensive framework along these lines.
Note that others at the intersection of philosophy and evolutionary theory argue that the term design should still be reserved for cases involving a sentient designer. This implies that followers of the standard, biological, materialistic account of the origin of the species should not use design or designed in discussions of organisms or parts thereof; since these have no designer, they were not designed in the propper sense of the word. Proponents of this view include Richard Dawkins.