Analysis of the reasoning founded on the foregoing evidence

The questions to which the preceding observations refer have been the subject of much vague speculation and vehement controversy. But in the present discussion, equally desirous of avoiding the one, and deprecating the other, I wish to take a perfectly unbiassed and dispassionate view of the real tenour of the evidence; and more especially to analyse certain arguments often brought forward, and regarded as based on indisputable principles, which nevertheless appear to me involved in considerable doubt and fallacy. And though, in some instances, they boast the sanction of names eminent in physiology and geology, yet the question is rather one of general principles of reasoning than of precise scientific details; and thus, without pretending to impugn their science, I venture to call in question their logic.

Argument for immutability of species from permanence of natural laws

In the first place, then, the belief in the essential and inherent immutability of species, not only in the present state of things, but as an eternal law of Nature, extending backward through all the countless ages of the ancient earth, has been upheld confessedly on the limited experience of modern observation, but thence extended by analogy in the same way (it is alleged) as in the case of other great natural laws.