If A is adapted to B, then B was (as a rule) not designed for A, and (it’s possible that) A was not designed for B. If I use a nail to mark where to put a window, this is not because nails were designed for this nor because windows need to be marked out by anything. I just used something in the tool belt to mark where I should start cutting. Nature does this sort of thing all the time, like when teeth adapt to eating something. This undercutting of design by adaptation might continue ad infinitum: we adapted DVD players to run off of cigarette lighters, but perhaps the engineers might tell us that car cigarette lighters were just adaptations of another other, more original mechanism, like a pit for lighting signal flares.
But just because one can extend a series ad infinitum does not mean that one can get away with saying that it is possible for everything to be adapted as opposed to designed. When we say that the series DVD power source, cigarette lighter, signal flare igniter, etc. can be infinite, what we mean is that there is no reason why we couldn’t have one more regression after any given one. It’s not as if we hit a limit of possible adaptations after 3, 7, or 4,362.* But this does not allow us to deny the need for some original designed activity or to something that just is, by its nature, ordered to some goal or end. The pit in the dashboard was put there for some purpose, even if adaptations might arise from it ad infinitum.
Analogized to nature, we get the idea that nature is teleological, but that it is very hard to know where precisely this teleology is found. Nature might be adaptive in all or most of its interesting respects. Such a view is at least common.
*IOW, after any given number you can have one more, but some given number is the first. This occurs because it is causally first, not because it is some given number.