"On one point all biologists are agreed: the basic concept of organic evolution has, for a century, stood unrivaled. … The status of natural selection is not quite so high. True, it is the only theory we have; but when judged as a working hypothesis it is disappointing to find so little advance in a hundred years. … No amount of argument, or clever epigram, can disguise the inherent improbability of orthodox theory; but most biologists feel it is better to think in terms of improbable events than not to think at all."