Wednesday, April 09, 2003

On Interpreting Evidence From the good folks at the pro-Intelligent-Design website Access Research Network comes the following advice on properly interpreting evidence:

"A parallel can be made to Darwinian evolution, as it often embraces multiple competing outcomes and then interprets any evidence as support for the theory. One example would be the two-horse race of explaining biological order. If what we see is exquisite, then we are reminded of the degree of fine-tuning that the selection/mutation mechanism can reach when given enough time, but if there appears to be a flaw or if the form seems crude, then we are reminded that we are working with a blind and purposeless mechanism - after all what can we expect? Armed with both explanations, every possible outcome has been successfully accounted for and so nothing appears surprising. Is there any doubt, then, why you never hear a Darwinian say; “Now if I saw that, I’d know it was designed”? Design conclusions are ruled out ahead of time by putting a Darwinian bet on every horse." -Paul Nesselroade, "Betting on All the Horses".

This is a curious criticism coming from an ID theorist. After all, they are the ones who point to the beauty and perfection of nature as evidence of a designer, but interpret flawed or crude designs as evidence only of the inscrutibility of the designer's motives.

Leaving this aside, the criticism is not valid even taken on its own terms. It is a simple logical consequence of the nature of natural selection that under certain conditions it can explain organs of great perfection, and in other situations can produce vastly imperfect structures. That is not the fault of biologists. But the fact remains that there are severe limits to the kinds of structures and behaviors that can be attributed to natural selection. For example, any trait that existed solely for the benfit of members of another species could not be explained by selection. Similarly, any complex structure whose parts can not be indentified as arising from simpler structures that were common in the organism's lineage, possible for other purposes, would also be hard to explain.

Furthermore, scientists do not use natural selection as a mystical incantation they can use to dispell any biological mystery. Instead, it is used as a way of generating testable hypotheses about the history of the structure. Examples of this are ubiquitous in the professional literature of evolutionary biology.

Biologists routinely points to biological structures and say, "That structure was not crafted by natural selection." The recent discovery that lateral gene transfer is an important mode of evolutionary change in prokaryotes is just one example of this. But Nesselroade, like all of the prominent ID theorists, does not care about the actual state of modern biological research. His job is to produce plausible sounding rhetoric. Truth be damned.


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