The Long Answer:
|The Short Answer: Intelligent design does not merely claim that the origin of complex (i.e. irreducibly complex) biological structures are unexplained, but rather that they are in principle unexplainable. They are not unexplainable because they are unexplained, but rather the converse is true, for they are unexplained because it is in principle impossible for Darwinian evolution to explain the origin of irreducibly complex biological structures. Thus, this is not an argument from ignorance or "god-of-the-gaps" type reasoning, for irreducible complexity is a theoretical falsifier of Darwinian evolution.|
The claim being made here is that intelligent design theory looks at the state of evolutionary theory and finds that it has not come up with explanations for the evolution of certain biological systems, and thus infers that they therefore must be unexplainable and the product intelligent design.
Intelligent design theory does indeed note evolutionary theorists are lacking explanations for the origin of many biological systems. However, intelligent design theory is not inferring that they are "unexplainable" simply because they are unexplained. In fact, it is saying the converse--that they are unexplained because they are simply unexplainable through the Darwinian mechanism!
This question sometimes equates "Unexplained" with "Unexplainable." However, this is not the relationship that intelligent design theorists claim "unexplainable" and "unexplained" have. Intelligent design proponents do not claim that "if unexplained = then unexplainable", but rather are asserting the converse: "if unexplainable, then unexplained."
1. If A is unexplained then A is unexplainable.
And the converse:
2. If A is unexplainable then A is unexplained.
Intelligent design theorists are NOT making statement 1, which is obviously a fallacy. All things that are unexplained are not necessarily unexplainable.
On the contrary, however, intelligent design theorists are asserting the converse, statement 2, which is valid. All things that are unexplainable are indeed unexplained, insofar as we are seeking meaningful, consistent explanations that positively correlate to reality.
So what is intelligent design saying then? Intelligent design theory is saying that "irreducibly complex" structures cannot in principle be built by the Darwinian mechanism. As noted earlier, the Darwinian mechanism requires that biological systems remain functional along every step of their evolution, else they get selected out. Irreducibly complex systems cannot be built up in a step-by-step manner, because any change in their organization destroys the function. Indeed, even Charles Darwin, in The Origin of Species, recognized this as a fundamental obstacle to his theory:
"If it could be demonstrated that any complex organ existed which could not possibly have been formed by numerous, successive, slight modifications, my theory would absolutely break down."
In evolution, natural selection only preserves those structures which confer some advantage for the organism. If a structure isn't functional, then it confers no advantage, is a waste of the organism's resources, and will be selected out. Darwin says that there may exist structures for which functional intermediate stages would be impossible, i.e. the intermediates would not function. This is essentially the same challenge of irreducibly complex structures, where intermediate structures wouldn't be functional. Biochemist Michael Behe elaborates on this fact saying:
"A system which meets Darwin's criterion [listed in the above quote] is one which exhibits irreducible complexity. By irreducible complexity I mean a single system which is composed of several interacting parts that contribute to the basic function, and where the removal of any one of the parts causes the system to effectively cease functioning. An irreducibly complex system cannot be produced gradually by slight, successive modifications of a precursor system, since any precursor to an irreducibly complex system is by definition nonfunctional. Since natural selection requires a function to select, an irreducibly complex biological system, if there is such a thing, would have to arise as an integrated unit for natural selection to have anything to act on. It is almost universally conceded that such a sudden event would be irreconcilable with the gradualism Darwin envisioned."
Thus, intelligent design says that these irreducibly complex systems are in principle impossible to account for through the Darwinian mechanism. They are unexplained by evolutionary biologists simply because they are unexplainable. Behe's gives numerous examples in his book, Darwin's Black Box for what he sees as unexplained AND unexplainable irreducibly complex systems, including the bacterial flagellum and the mechanisms of blood clotting.
As explained by William Dembski in The Design Inference, irreducible complexity is a form of complex-specified information. William Dembski, in his book No Free Lunch, argues to prove that complex specified information cannot be produced by naturalistic processes, such as the Darwinian mutation-selection mechanism. The only, and, in fact, the commonly observable explanation for complex specified information, Dembski argues, is intelligent agency.
This question seems to present intelligent design as if it infers design by the following:
Observation X (a complex biological system) can be explained by Theory A (evolution) or Theory B (design). A hasn't yet figured out how X could arise, therefore the answer is B.
On the contrary, intelligent design theorists make a much more potent argument for inferring design:
Observation X (complex specified information) is found in the natural world to be only produced through Theory B (intelligent design). Theory A (evolution) cannot, in principle due to the very workings of its mechanism, account for the existence of X. X is observed. B predicts the existence of X. A predicts X will not be found. A scientist is justified in inferring B over A to account for X.