t 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. As this is
found to be the case both in animals and plants, and in all their chief
groups and subdivisions, and also to apply to all the separate parts and
organs that have been compared, we must take it as proved that the
average _amount_ of variability presents no difficulty whatever in the
way of the action of natural selection. It may be here mentioned that,
up to the time of the preparation of the last edition of _The Origin of
Species_, Darwin had not seen the work of Mr. J.A. Allen of Harvard
University (then only just published), which gave us the first body of
accurate comparisons and measurements demonstrating this large amount of
variability. Since then evidence of this nature has been accumulating,
and we are, therefore, now in a far better position to appreciate the
facilities for natural selection, in this respect, than was Mr. Darwin
himself.

Another objection of a similar nature is, that the chances are immensely
ag