I Can Show It Isn't, But You Can't Show It Is

Continuing with discussion of intelligent design and the falsifiability thereof, I found a couple articles on talk.origins interesting.  Proponents of macro-evolutionism claim that intelligent design is not science because it cannot be refuted.  However, naturalist commonly use the presence of vestigial organs to support the evolutionary paradigm.  According to this line of thinking, nature has evolved a number vestigial organs which are not consistent with an intelligent designer.  An example of this can be found in this paper originally published in the Reports of the National Center for Science Education. One line of “independent evidence” is the evidence from vestigiality (#4) (Thanks to Paul’s comment for the link).  I quote:

4. Vestigial evidence
The vestigial features of whales tell us two things. They tell us that whales, like so many other organisms, have features that make no sense from a design perspective - they have no current function, they require energy to produce and maintain, and they may be deleterious to the organism. They also tell us that whales carry a piece of their evolutionary past with them, highlighting a history of a terrestrial ancestry.(emphasis mine)

There are a large number of examples of this argument.  Another one can be seen here, by Reed Cartright, frequent contributor to the Panda’s Thumb and Douglas Theobald:

Significance of Evidence:

Vestigial structures do offer evidence for evolution beyond the fact they are homologous. In the absence of evolutionary theory, there is no reason for wings to exist on flightless species or eyes to exist on blind species. The "proper" purpose (in Darwin's terms) of wings is for flight. The proper purpose of eyes is for sight. Rudimentary, flightless wings used for functions other than flight are vestigial, as are blind eyes used for something other than sight. Vestiges are truly functionless only with respect to their proper purposes. The coccyx may have many good functions, but as Naylor says, "certainly it is not functioning as an external tail for balance or grasping" (Naylor 1982, p 92). The human vermiform appendix may have a minor role in the development of the immune system, but it is not functioning as a cellulose-fermenting caecum.  (emphasis mine)

There are a number of problems with the vestigial organ arguments, but I wish to focus on the implications of these arguments on the falsifiability of ID and its place in science.  The argument for no design can be illustrated this way (using Cartright and Theobald’s example):

1. The “proper” purpose of wings is for flight
2. Rudimentary flightless wings do not have the “proper” function of wings (they are not for flight)
3. Therefore, flightless wings are vestigial organs
4. An intelligent designer would not have included vestigial organs in his design (they make “no sense” from a design perspective)
5. Therefore, vestigial organs are the product of naturalistic evolution

Evidence from vestigiality is considered scientific evidence, as noted here.  Note that the definition of vestiality is not that an organ is non-functional; but that it does it perform the “proper” function.  The ability to define what is proper within a theory that denies design is a whole post in itself.  Here is more from Theobald:

2. Positive evidence is used to demonstrate lack of function

Even though the conclusion may be negative ("structure x has no function"), the detection of biological functionality or lack thereof is based upon positive evidence, not negative evidence.

3. Negative data can be used as scientific evidence

Negative evidence is certainly valid when used properly, and negative evidence is used and reported routinely in the scientific literature. The general claim that negative evidence cannot be used to test a hypothesis is a nihilistic philosophy that has no place in experimental science.

Clearly the authors believe that it is scientifically possible to show empirical evidence that indicates a lack of design for vestigial structures.  They also believe they have evidence that refutes the theory that these organs were the product of an intelligent designer.

Yet this brings up a dilemma.  In order to show the absence of something, in this case characteristics of design, we have to be able to show the presence of something.   However, they claim that it is not possible to show scientifically that design characteristics are present.  In other words, the authors claim that they can show evidence of no design through science, but one cannot posit evidence for design (because it is then non-scientific).  It is science to show that something does not exist, but pseudoscience to show that the same entity may exist.  How can you provide evidence against something that is not scientifically even possible?

Also, isn’t this an example of an attempt to falsify a theory supporting ID?  If not, then why bother?  Why provide evidence against something that cannot be refuted?

Once again, how can we have scientific evidence against the presence of something when we are not allowed to have scientific evidence supporting the presence of something?