72 THE ORIGIN OF SPECIES 



strongly against its survival. Supposing it to survive and to breed, 

 and that half its young inherited the favorable variation; still, as 

 the reviewer goes on to show, the young would have only a slightly 

 better chance of surviving and breeding; and this chance would 

 go on decreasing in the succeeding generations. The justice of 

 these remarks cannot, I think, be disputed. If, for 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 ex- 

 clusion of the common 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 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 in- 

 dividual differences, frequently recur owing to a similar organiza- 

 tion 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 

 lacrymans. In cases of this kind, if the variation were of a bene- 

 ficial 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 spot. Consequently each 

 newly-formed variety would generally be at first local, as seems to 

 be the common rule with varieties in a state of nature; so that 



