At my scholarship preparation day yesterday I was asked if students could expect an exam question about evolution and intelligent design. My answer? No, because "intelligent design" is not a scientific explanation for the diversity of life on earth. My reasons for saying this? Read on…
What is "intelligent design"? It was first proposed as an explanation for biological diversity by William Paley, in 1802. The modern version is extensively promoted, particularly (but by no means exclusively) in the US. Its proponents argue that life is too complex to have evolved through the operation of natural selection alone, and that there must have been some element of 'design' (i.e. that there is a designer). Intelligent design (ID) theorists also argue that intelligent design is a valid alternative to evolutionary theory, and that if some aspect of evolutionary theory can be disproved, then ID is correct.
What's wrong with this?
Well, the second part of that argument exploits people's misunderstanding about how science operates. Science isn't 'fair', and providing evidence that one explanation is wrong doesn't automatically make the opposing explanation correct. You need to provide strong supporting evidence for your point of view. Equally, just because a large number of people believe something to be true, doesn't make it a scientific explanation. So, in order to attempt to replace evolution as a scientific explanation for the diversity of life, ID needs to be evidence-based, explanatory, testable, and predictive.
What evidence is there to support ID (i.e. positive evidence for this explanatory model, not negative evidence against evolution)? A key concept of ID is irreducible complexity: the idea that some structures are far too complex to have evolved by chance, and that individual features of those structures have no function on their own. The structure of the bacterial flagellum is still promoted as an example of such complexity. But scientists have known since 2003 that many of the individual proteins involved in a flagellum are present in non-flagellate bacteria – where they have other functions, including adhesion to other cells. The flagellum is not irreducibly complex. And to argue that, while this is true, some part of its substructure is irreducibly complex is an example of the "God of the gaps" way of thinking. (The camera-type eye is another claimed example of irreducible complexity, but I'll talk more about that in another post.)
Does ID have predictive power? Again, the answer must be 'no', because ID is ultimately incapable of disproof. The statement, "a Designer did it", cannot generate useful predictions. In contrast, historical sciences (such as evolution and astronomy) use hypothetico-deductive reasoning: form an hypothesis on the basis of existing data; deduce predictions from that hypothesis; and test those predictons against further data.
Or, in the words of biologist E.O. Wilson (2005): Any researcher who can prove the existence of intelligent design within the accepted framework of science will make history and achieve eternal fame… But no one has even come close, because unfortunately there is no evidence, no theory and no criteria for proof that even marginally might pass for science."