The theory of natural selection may be so formulated that it is far from tautological. In this case it is not only testable, but it turns out to be not strictly universally true.
The usefulness of the models in constructing a testable theory of the process is severely limited by the quickly increasing number of parameters which must be estimated in order to compare the predictions of the models with empirical results.Anatol Rapoport
A well-understood and testable hypothesis like sexual selection surely trumps an untestable appeal to the inscrutable caprices of a creator.jerry coyne
Though he was proud of his scientific method, most of Marx' predictions are like Jewish prophecies and Christian revelations, inspiring, sometimes self-fulfilling, certainly true for the faithful, but not testable by scientific means.karl marx
One truth we have been able to count on concerning scientific persuit over the centuries has been that only testable theories survive the intense scrutiny of experimental science.john moffat
Darwinism is not a testable scientific theory, but a metaphysical research program.karl popper
Today secularists do pretty much the same thing. Modern secular thought has its own dualism: It treats only the physical world as knowable and testable, while locking everything else - mind, spirit, morality, meaning - into the realm of private, subjective feelings. The so-called fact/value split.