In the present chapter I propose to discuss the more obvious and often repeated objections to Darwin's theory, and to show how far they affect its character as a true and sufficient explanation of the origin of species. The more recondite difficulties, affecting such fundamental questions as the causes and laws of variability, will be left for a future chapter, after we have become better acquainted with the applications of the theory to the more important adaptations and correlations of animal and plant life.

One of the earliest and most often repeated objections was, that it was difficult “to imagine a reason why variations tending in an infinitesimal degree in any special direction should be preserved,” or to believe that the complex adaptation of living organisms could have been produced “by infinitesimal beginnings.” Now this term “infinitesimal,” used by a well-known early critic of the Origin of Species, was never made use of by Darwin himself, who spoke only of variations being “slight,” and of the “small amount” of the variations that might be selected. Even in using these terms he undoubtedly afforded grounds for the objection above made, that such small and slight variations could be of no real use, and would not determine the survival of the individuals possessing them. We have seen, however, in our third chapter, that even Darwin's terms were hardly justified; and that the variability of many important species is of considerable amount, and may very often be properly described as large.