In studying the history of Evolutionary ideas, it is necessary to keep in mind that there are two perfectly distinct lines of thought, the origin and development of which have to be considered.

First. The conviction that species are not immutable, but that, by some means or other, new forms of life are derived from pre-existing ones.

Secondly. The conception of some process or processes, by which this change of old forms into new ones may be explained.

Buffon, Kant, Goethe, and many other philosophic thinkers, have been more or less firmly persuaded of the truth of the first of these propositions ; and even Linnaeus himself was ready to make admissions in this direction. It was impossible for anyone who was convinced of the truth of the doctrine of continuity or evolution in the inorganic world, to avoid the speculation that the same arguments by which the truth of that doctrine was maintained must apply also to the organic world.

Hence we find that directly the Principles of Geology was published, thinkers, like Sedgwick and Whewell, at once taxed Lyell with holding that ‘the creation of new species is going on at the present day,’ and Lyell replied to the latter:—