“Since natural selection “selects” or preserves functionally advantageous mutations or variations, it can explain the origin of systems that could have arisen through a series of incremental steps, each of which maintains or confers a functional advantage on a living organism. Nevertheless, by this same logic, selection and mutation face difficulty in explaining structures or systems that could not have been built through a close series of functional intermediates. Moreover, since selection operates only on what mutation first produces, mutation and selection do not readily explain appearances of design that require discrete jumps of complexity that exceed the reach of chance; that is to say, the available probabilistic resources.”