Must We Directly Observe the Intelligent Agent to Detect Design?

Yesterday I discussed an email exchange with an atheist student who argued that we cannot detect design in nature unless we directly observe an intelligent designer. I explained the flaw in his objection through an analogy.

Let's say you find the remains of a campfire -- e.g., charred wood, a circle of stones, and smoldering ashes. You may reasonably infer that a campfire was present, even if you didn't see the fire as it burned. In the same way, we understand the kinds of effects that are...