In scientific work, even as in everyday life, one proceeds on the basis, not only of established facts, but also of unproven assumptions. This is inevitable, and by no means blameworthy. What is blameworthy is to refuse occasionally to examine the assumptions, or worse still to try to prevent those who would examine them from getting a hearing. The evolutionary dogma, in particular, depends on many unproven assumptions; and thee has been too often been a reluctance on the part of those who propound the view to examine the underlying assumptions critically.