0^ NATURAL SELECTION. g5 



there can hardly be a doubt, judging by wluit we see taking 

 place under domestication, that this result would follow 

 from the preservation during many generations of a large 

 number of individuals with more or less strongly curved 

 beaks, and from the destruction of a still larger number 

 with the straightest beaks. 



It should not, however, be overlooked that certain 

 rather strongly marked variations, which no one would 

 rank as mere individual differences, frequently recur 

 owing to a similar organization being similarly acted on — 

 of which fact numerous instances could be given with our 

 domestic productions. In such cases, if the varying indi- 

 vidual did not actually transmit to its offspring its newly- 

 acquired character, it would undoubtedly transmit to them, 

 as long as the existing conditions remained the same, a 

 still stronger tendency to vary in the same manner. There 

 can also be little doubt that the tendency to vary in the 

 same manner has often been so strong that all the individ- 

 uals of the same species have been similarly modified with- 

 out the aid of any form of selection. Or only a third, 

 fifth, or tenth part of the individuals may have been thus 

 affected, of which fact several instances could be given. 

 Thus Graba estimates that about one-fifth of the guille- 

 mots in the Faroe Islands consist of a variety so well 

 marked, that it was formerly ranked as a distinct species 

 under the name of Uria lacrymans. In cases of this kind, 

 if the variation were of a beneficial nature, the original 

 form would scon be supplanted by the modified form, 

 through the survival of the fittest. 



To the effects of intercrossing in eliminating variations of 

 all kinds, I shall have to recur; but it maybe here remarked 

 that most animals and plants keep to their proper homes, 

 and do not needlessly wander about; we see this even with 

 migratory birds, which almost always return to the same 

 spot. Consequently each newly-formed variety would gen- 

 erally be at first local, as seems to be the common rule with 

 varieties in a state of nature; so that similarly modified indi- 

 viduals would soon exist in a small body together, and 

 would often breed together. If the new variety were suc- 

 cessful in its battle for life, it would slowly spread from a 

 central district, competing with and conquering the ini- 

 changed individuals ou the margins of an ever-increasing 

 circle. 



