"Naturalistic science will usually retort that examination of present materials and processes enables us to extrapolate backwards so as to determine what must have occurred. But here again, forsaking his own basic methods, the scientist is speculating (not observing) on the course of historical development; he assumes (but cannot show experimentally) that not only is nature uniform now but always has been, that processes seen today have always worked as they do now. (The 'theistic evolutionist' likewise assumes that today's processes must be basically similar to God's creative activities. This, in effect, is to say that creation was 'immature,' that God did not finish his creative work at a point in the past.) To pretend to answer questions about origins by extrapolating the observable present into the unobservable past is to reason in a circle; it is to forsake the proper descriptive role of science and to make it an arbitrary determiner of the past instead."
Greg Bahnsen, "Revelation, Speculation, and Science"