see what influence zoology had on Darwin and his contemporaries. I shall not try your patience by attempting to review the history of the subject, but it would not belittle the greatness of Darwin's achievement one whit to find that brilliant discoveries had been made before his time, the theory of evolution plainly enunciated, the doctrine of spontaneous generation disproved; comparative anatomy widely studied; the important functions of the body elucidated, the foundations of the science of embryology laid, and the principles of pedigree breeding followed.
In the eighteenth century, when the study of different kinds of animals inhabiting sea and land attracted the attention of zoologists, great classifications were invented. Two main facts emerged. On the assumption of fixity of type, a classification of the different forms of animals and plants became possible. But on the other hand the more extensive the material to be classified, the more difficult it became to make such systems, for the fixity of type was often lost in apparent transitions to other types. Counter claims arose as to the superiority of one system over another, and the question of an artificial system versus a natural one was widely debated. Now, an artificial system, like the arrangement of the words in a dictionary, is obviously only a matter of convenience, but it became a question of deep philosophical importance to decide what was meant by a natural classification. To us at the present time a natural classification implies a relation due to descent; it is neither more nor less than the natural relation of a man to his ancestors. But it were a fatal mistake to read our meaning backwards to the time before Darwin.
To the great Cuvier a natural system meant an assemblage of groups having a common plan of structure, and he was enraged by Geoffroy St. Hilaire's attempt to put all animals from the bottom to the top in a straight line. A common plan of structure might only mean that idea which best expressed the outcome of a wide study of structure; but to those who tried to peer behind the scenes it meant not seldom to fathom the creation of the world; and it required no vivid imagination to add that it gives an insight into the plan by which the world was created.
A historian of the times wrote:
Contrast, in passing, this pious conviction with Geoffroy's modest lines: