Our willingness to accept scientific claims that are against common sense is the key to an understanding of the real struggle between science and the supernatural. We take the side of science in spite of the patent absurdity of some of its constructs, in spite of its failure to fulfill many of its extravagant promises of health and life, in spite of the tolerance of the scientific community for unsubstantiated just-so stories, because we have a prior commitment, a commitment to materialism. It is not that the methods and institutions of science somehow compel us to accept a material explanation of the phenomenal world, but, on the contrary, that we are forced by our a priori adherence to material causes to create an apparatus of investigation and a set of concepts that produce material explanations, no matter how counter-intuitive, no matter how mystifying to the uninitiated. Moreover, that materialism is absolute, for we cannot allow a Divine Foot in the door. The eminent Kant scholar Lewis Beck used to say that anyone who could believe in God could believe in anything. To appeal to an omnipotent deity is to allow that at any moment the regularities of nature may be ruptured, that miracles may happen. -Richard Lewontin, "Billions and billions of Demons," New York Times Review of Books, January 9, 1997.Pretty much gives the game away, doesn't it? To summarize, what Lewontin (who is a leading scientist by the way, not a fringe crackpot) is saying is this: We believe in evolution based on philosophy, not based on science. Science is supposed to be a search for truth about the way the world really works, but certain explanations are rejected out of hand a priori. That's not science, that's a philosophical commitment masquerading as objectivity.
Not that I am surprised. I too have my pre-existing worldview that I bring to the data. And my commitment to that worldview is not fully rational (in the sense of being fully explained by some sort of "view from nowhere" logic), just as theirs is not. I just wish more scientists were willing to admit that their philosophy/worldview colors their observations and interpretations of what they see no less than the most "rabid creationist."