I want to begin by saying that I am an ardent evolutionist, and I think that creationism and intelligent design are a load of rubbish. But I do want to raise a certain point regarding one of the criticisms of intelligent design, mainly because I am at a bit of a loss as to how I can resolve this question by myself.
I have read before that one reason why intelligent design is unscientific is that you cannot effectively design any test to determine whether something, i.e. a protein, has been intelligently designed or has spontaneously occurred in nature. Put in stronger terms, to look at a biological phenomenon and conclude "intelligent design!" is said to be a highly unscientific way of thinking. And so I want to bring up the comparison between intelligent design theory and crop circles.
Whether they are created by pranksters or extraterrestrials (almost definitely the former, I think), crop circles as a phenomenon DO occur. Furthermore, it seems generally agreed that they are intelligently designed, even though we cannot claim to know definitively who or what designed each and every crop circle, and how they were made. So here, we have a phenomenon that takes place in the real world, the cause of which we have not always fully observed and therefore do not fully understand, and yet we can seem to agree that an unknown intelligence has guided this process. And this conclusion does not seem to be criticized as being unscientific.
So my question is, what is the inherent difference between our interpretation of crop circles as being intelligently designed, and a creationists interpretation of biological structures as being intelligently designed? Because I find the former to be completely reasonable, and the latter to be unreasonable, and I am wondering if this difference in my opinion is due to an objective difference between the two situations or whether I am just exhibiting a personal bias.
I'd just like to clarify something. PaulK, when you said:
"However so far as I am aware science has NOT concluded that any unknown intelligence is involved."
do you mean ANY unknown intelligence (human or extraterrestrial), as I had meant in my OP, or do you mean an intelligent species that we have not yet met (i.e. extraterrestrial)?
I ask, because if we are both talking about any intelligence, then your post reveals the same dilemma that I tried to underscore in my OP. You stated that:
"it is true that most [crop circles] are considered the result of intelligent work."
So as your statements imply, it seems to be reasonable and in fact intuitively obvious (by looking at crop circles) to conclude intelligent design, but science has not definitively concluded intelligent design. We can take this a bit further, and say that a perfectly reasonable conclusion such as intelligent design cannot be verified scientifically.
This leads me to think that a reasonable conclusion may not necessarily be possible to investigate by scientific means, and yet this impossibility doesn't detract from how reasonable the conclusion is. It also leads me to wonder how reasonable the intelligent design theory really is, if you momentarily ignore the fact that it is obviously non-science.
It also makes me wonder whether, given future advances in technology, the so-called theory of intelligent design may someday become a valid scientific theory. If SETI scientists are able to someday invent powerful telescopes and other devices that can detect and observe aliens actually drawing crop circles in our fields, then the study of crop circles may fall within the realm of true science (exobiology?). Likewise, if we can invent what may now seem to be impossibly powerful detection techniques that allow us to peer into the past, we may be able to verify whether or not an intelligence has guided evolution.
But of course, if we did develop such techniques, then we would probably end up falsifying intelligent design at last.