a great extent, the power of choice of their abode.  So that we again are asking ourselves, To what extent does competition really exist within each animal species?  Upon what is the assumption based?  The same remark must be made concerning the indirect argument in favour of a severe competition and struggle for life within each species, which may be derived from the “extermination of transitional varieties,” so often mentioned by Darwin.  It is known that for a long time Darwin was worried by the difficulty which he saw in the absence of a long chain of intermediate forms between closely-allied species, and that he found the solution of this difficulty in the supposed extermination of the intermediate forms.(33) However, an attentive reading of the different chapters in which Darwin and Wallace speak of this subject soon brings one to the conclusion that the word “extermination” does not mean real extermination; the same remark which Darwin made concerning his expression:  “struggle for existence,” evidently applies to the word “extermination” as well.  It can by no means be understood in its direct sense, but must be taken “in its metaphoric sense.”  If we start from the supposition that a given area is stocked with animals to its fullest capacity, and that a keen competition for the sheer means of existence is consequently going on between all the inhabitants—­each animal being compelled to fight against all its congeners in order to get its daily food—­then the appearance of a new and successful variety would certainly mean in many cases (though not always) the appearance of individuals which are enabled to seize more than their fair share of the means of existence; and the result would be that those individuals would starve both the parental form which does not possess the new variation and the intermediate forms which do not possess it in the same degree.  It may be that at the outset, Darwin understood the appearance of new varieties under this aspect; at least, the frequent use of the word “extermination” conveys such an impression.  But both he and Wallace knew Nature too well not to perceive that this is by no means the only possible and necessary course of affairs.

If the physical and the biological conditions of a given area, the extension of the area occupied by a given species, and the habits of all the members of the latter remained unchanged—­ then the sudden appearance of a new variety might mean the starving out and the extermination of all the individuals which were not endowed in a sufficient degree with the new feature by which the new variety is characterized.  But such a combination of conditions is precisely what we do not see in Nature.  Each species is continually tending to enlarge its abode; migration to new abodes is the rule with the slow snail, as with the swift bird; physical changes are continually going on in every given area; and new varieties among animals consist in an immense number of cases-perhaps