THE ORIGIN OF SPECIES AND GENERA 303 



variation, for they correspond to the countless diversities 

 of conditions to which animals have been exposed either 

 during their own development or that of their ancestors. 



This objection has really its only possible justification 

 in the ignorant belief that variations of any tangible 

 amount are rare events occurring at long intervals ; and 

 therefore that when any combination of special variations 

 was needed to bring an animal into harmony with changed 

 conditions, the number of individuals varying would not 

 be sufficiently great to prevent their being completely 

 swamped by the typical unvarying forms. Had such been 

 the case, some agency capable of producing a considerable 

 amount of variation when required would undoubtedly 

 have been needed, and this unknown agency might fairly 

 have been claimed to be one of the most important factors 

 in the " origin of species." But now that it is proved by 

 many independent observations, that a large percentage of 

 the individuals of most species vary, in each successive 

 generation, to an amount far greater than is required for 

 natural selection to act upon, the whole difficulty ceases 

 to exist. Variation is seen to be one of the most constant 

 and universal facts of nature, always producing what may 

 be termed the raw materials of species in overflowing- 

 abundance, so that, whenever and wherever alteration of 

 the conditions of existence is going on, there is always 

 ready to hand an ample stock of varying organisms, by 

 means of which an almost exact adjustment to those 

 conditions may be kept up. 



The facts and arguments now adduced will, it is hoped, 

 enable intelligent readers who are not naturalists to form 

 a clear conception of what is really meant by " the origin 

 of species by means of natural selection," and will satisfy 

 them that the most common and what seem at first sight 

 to be the most weighty objections to it, owe all their force 

 to the ignoring of some of the best established facts in 

 natural history. 



I have also attempted to show that the causes which 

 have produced the separate species of one genus, of one 

 family, or perhaps of one order from a common ancestor, 



