The lives of creationists are dominated by the need for absolute certainty. Religious beliefs provide just that sort of certainty. In the case of fundamentalist Christianity the only way to achieve such certainty is to view the bible as inerrant and to be read literally. The theory of evolution, in that it challenges the creation story in Genesis, is thereby regarded as the thin edge of the wedge. Much of orthodox Christian theology is based upon the theory of original sin. This theory, of course, is an interpretation of the Genesis creation story. If Genesis falls so much else falls with it. That is the source of the creationists' fear and why they oppose evolution so vehemently, even to the point of using fraud and outright lies in their defensive tactics.