At least on the surface, there seems to be something incongruous in regarding some artifact (like a watch) as clearly implying some kind of intelligent, crafty mind, but then regarding that intelligent, crafty mind as not implying any sort of further creator, but coming about through natural causes. A watchmaker is if anything more impressive and more in need of some explanation than the watch. So by what principle do we say that the watch requires design and artifice, but the watchmaker does not?

It’s a tricky question, because it is difficult to sort out “order that requires design” from “order that does not require design”. If we point out that all of an entity’s parts work together, that its behavior is regular or uniform, and that it is clearly not a simple heap or aggregate of parts, it is not clear whether we are talking about a watch or a giraffe. Natural objects and artificial objects all exhibit order; but which kind of order implies design, and which does not?

To sharpen the question a bit further, imagine the following case. Suppose we land on Mars and we find remarkable entities composed of stone. These entities can move themselves over the landscape, and they have parts. We observe that they are able to seek out specific kinds of rocks and assemble them into copies of themselves. Sometimes they break or wear down, but enough of them are able to make copies of themselves before this happens that there seems to be a steady population of them on the planet.

Imagine further that, in response to this discovery, the scientists on earth form two camps. One camp proclaims, “We have found life on another planet! The surprise is that living beings can be made of rock.” The second camp proclaims, “These robotic artifacts are evidence for intelligent robot engineers, who either once lived on Mars, or at least were able to send some clever rock robots to Mars.” One might initially say these are just two equivalent descriptions of the entities, but that isn’t so, because the two theories are very different in what they imply about the past: one theory says the robots arose naturally, without any designers, and the other theory says there must have been designers. So they are saying different things.

How can we tell which theory is right? Suppose we examine the entities more closely, and learn that they are powered by some chemical process involving the rocks and the Martian atmosphere, and that each one has the parts it has because their “parent” made them that way. They don’t “grow” or change on their own, except through erosion and minor collisions. They don’t heal, and, being rocks, they don’t have DNA. They don’t communicate in any way we can see, and each one of them, when put into a similar situation, “robotically” will do a similar thing. So far, no clear reason to regard them decisively as living beings or decisively as artificial robots.

In this imagined case, there is nothing inherent in the rock entities that tells us whether they are natural or designed. But there should be some fact of the matter, because these rock things must have come from somewhere, after all. 

This leads us to another possible way of answering the question. Could these rock entities have evolved through natural selection? Answering this question requires that we try to construct an explanation for them that appeals to some sort of random generating process, some sort of environment that selects for some entities over others, and enough time for these factors to result in the rock entities in question. The explanation we construct will have to be consistent with Mars’ history, so far as we know it, and should not rely upon too many improbable, lucky accidents (each one counts against the explanation). 

If it turns out that we can construct such an explanation, then it is possible that these rock entities have come about naturally, and if we have no real evidence for Martian or other-worldly engineers, then that’s the more likely explanation. If it turns out there is no way to construct such an explanation, then we will judge the design hypothesis as more probable (leaving some room for the possibility that future theorists will know more than we do, and come up with an evolutionary explanation). So there is a way to answer the question, and it comes down to what kinds of explanations we are able or not able to construct.

This offers a surprising lesson about the role of Darwinian evolution by natural selection in the distinctions we make between what is natural and what is designed. Indeed, the story suggests that “natural” just means “can be explained through evolution”–and old Charlie Darwin may not have realized that, in his work, he was in fact providing a criterion for nature itself! It also helps us to understand why “the design argument” held such powerful sway over intellectuals before Darwin: there was no clear criterion for when we should regard an ordered thing as natural, and so there was really nothing to keep anyone from seeing any ordered thing as designed.