40 ILLUSTRATIONS OF THE ACTION 



of these remarks cannot, I think, be disputed. If, foi 

 instance, a bird of some kind could procure its food more 

 easily by having its beak curved, and if one were born with 

 its beak strongly curved, and which consequently flourished, 

 nevertheless there would be a very poor chance of this one 

 individual perpetuating its kind to the exclusion of the com- 

 mon form ; but there can hardly be a doubt, judging by 

 what we see taking place under domestication, that this 

 result would follow from the preservation during many gen- 

 arations 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 individual 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 individuals of the same 

 species have been similarly modified without 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 guillemots 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 laery- 

 mans. In cases of this kind, if the variation were of a 

 beneficial nature, the original form would soon 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 may be 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 

 *pot. Consequently each newly-formed variety would gen- 

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

 varieties in a state or 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 successful in 



