In his paper "The Design Argument," Elliott Sober predicts that "human beings will eventually build organisms from nonliving materials." In that case, we could obtain clear evidence that certain organisms resulted from intelligent design whereas earlier we might have thought they were due to a Darwinian process. I consider a similar possibility in chapter 6 of No Free Lunch.
Such examples, however, raise a curious dilemma for the Darwinist. Suppose humans do become sufficiently advanced technologically that they can build life "from scratch." Consider now some organism in the wild. How could we tell whether it was designed from scratch and escaped from a laboratory, or whether it was the result of a Darwinian process operating without human intervention in nature (assuming, for the moment, that a Darwinian process is capable of generating the needed biological complexity)? Perhaps there will be tell-tale signs. Perhaps evolved biology will be more efficient and less labile that designed biology. Or perhaps the opposite will be true. Perhaps, the difference will be a matter of style or art -- like the difference between Egyptian and Greek art.
But consider a related thought experiment. Tomorrow space travelers show up loaded with unbelievably advanced technology. They tell us (in English) that they've had this technology for hundreds of millions of years and give us solid evidence of it (perhaps by pointing to some star cluster hundreds of millions of light years away whose arrangement signifies a message that confirms the aliens' claim). Moreover, they demonstrate to us that with this technology they can atom by atom and molecule by molecule assemble the most complex organisms.
Suppose we have good reason to think that these aliens were here at key moments in life's history (e.g., at the origin of life, the origin of eukaryotes, the origin of metazoans, and the origin of the animal phyla in the Cambrian). Suppose further that in forming life from scratch the aliens would not leave any evidence (their technology is so advanced that they clean up after themselves perfectly -- no garbage or any other signs of activity would be left behind). Suppose, finally, that none of the facts of biology are different from what they are now. Should we think that life at key moments in its history was designed?
How would this thought experiment differ in its logical and probabilistic structure from the following gambling example: A gambling casino has a (quantum) roulette wheel that outputs the numbers 0, 00, 1, ... , 36 with independent and identically distributed probabilities of exactly 1/38, but which can be overridden by the casino owner, who can make the numbers come out as he or she wills. Suppose the spins of the roulette wheel on a given day (April 1, 2003) produce great literary texts such that the numbers 1 to 26 correspond to the letters of the alphabet (1 --> A, 2 --> B, etc.) and the remaining numbers correspond to punctuation (e.g., 0 --> period, 00 --> comma, 27 --> space, etc.). Suppose that there is no and need be no direct evidence of the casino owner tampering with the roulette wheel (the casino owner can tamper away without anyone's direct knowledge, the only give-away being the sequences of rolls of the roulette wheel itself).
It seems that in both instances, a relevant consideration for precluding design is whether some unguided natural process could with reasonable probability have generated the output in question (living forms in one case; great literary texts in the other). What do I mean by "reasonable probability"? I mean events that one is quite likely to see at least once given the time and opportunity allotted (i.e., with probability considerably greater than 1/2).
But what if that's not the case? What if our best probabilistic analysis of the biological systems in question tells us that unguided natural processes could not have produced them with anything like reasonable probability? Could the design of life in that case become more probable than a Darwinian explanation (probabilities here being interpreted in a Bayesian or likelihood sense) simply in virtue of there being independent empirical evidence attesting to designers with the capacity to produce biological systems?
This, however, should raise a worry for Darwinists. The facts of biology, after all, have not changed. Yet design would be a better explanation if designers capable of, say, producing the animal phyla of the Cambrian could be attested through independent evidence. Note that there's no smoking gun here (no direct evidence of alien involvement in the fossil record, for instance). All we know is that beings with the power to generate life exist and could have acted. Would it help to know that the aliens really like building carbon-based life? But how could we know that? Do we simply take their word for it? The data of biology and natural history, we assume, stay as they are now.
But if design is a better explanation simply because of the independent attestation of technologically advanced space aliens, why should it not be a better explanation absent their independent attestation? If Darwinism is so poor an explanation that it would cave the instant space aliens capable of generating living forms in all their complexity could be independently attested, then why should it cease to be a poor explanation absent those space aliens? Again, the facts of biology themselves have not changed.
It's not clear, therefore, that independent evidence is doing any useful work here at all. If Sober is saying that independent evidence requires direct "eye-witness" evidence of a designer actually manipulating the designed object in question, then clearly he is ruling out design from biology on a priori grounds. But that would be inconsistent with what Sober claims in his text Philosophy of Biology, where he leaves open that design might be a viable explanation in biology. What's more, it raises the question of a double-standard inasmuch as natural selection and other naturalistic mechanisms that are reputed to be capable of accomplishing biology's design-work are just as unsupported by direct "eye-witness" evidence.
But once independent evidence for design needs merely to establish that there exists a designer with the causal power and opportunity to produce the effect in question (as in the alien thought experiment and in the gambling example), we have exactly the same set of data to explain that we did before we had this independent evidence. The requirement for independent evidence is therefore either vacuous (if independent evidence can be circumstantial) or prejudicial (if required to be direct). And in either case it obstructs inquiry into any actual design that might be embedded in the item under investigation.