188 MISCELLANEOUS OBJECTIONS TO THE [CHAP. VII. 



has given rise to many well-adapted domestic races, and which 

 through the aid of natural selection would equally well give rise 

 by graduated steps to natural races or species. The final result 

 will generally have been, as already explained, an advance, but in 

 some few cases a retrogression, in organisation. 



Mr. Mivart is further inclined to believe, and some naturalists 

 agree with him, that new species manifest themselves "with 

 suddenness and by modifications appearing at once." For instance, 

 lie supposes that the differences between the extinct three-toed 

 Hipparion and the horse arose suddenly. He thinks it difficult to 

 believe that the wing of a bird " was developed in any other way 

 than by a comparatively sudden modification of a marked and 

 important kind ;" and apparently he would extend the same view 

 to the wings of bats and pterodactyles. This conclusion, which 

 implies great breaks or discontinuity in the series, appears to me 

 improbable in the highest degree. 



Every one who believes in slow and gradual evolution, will of 

 course admit that specific changes may have been as abrupt and 

 as great as any single variation which we meet with under nature, 

 or even under domestication. But as species are more variable 

 when domesticated or cultivated than under their natural 

 conditions, it is not probable that such great and abrupt variations 

 have often occurred under nature, as are known occasionally to 

 arise under domestication. Of these latter variations several 

 may be attributed to reversion; and the characters which thus 

 reappear were, it is probable, in many cases at first gained 

 in a gradual manner. A still greater number must be called 

 monstrosities, such as six-fingered men, porcupine men, Ancon 

 sheep, Niata cattle, &c. ; and as they are widely different in 

 character from natural species, they throw very little light on 

 our subject. Excluding such cases of abrupt variations, the few 

 which remain would at best constitute, if found in a state of 

 nature, doubtful species, closely related to their parental types. 



My reasons for doubting whether natural species have changed 

 as abruptly as have occasionally domestic races, and for entirely 

 disbelieving that they have changed in the wonderful manner 

 indicated by Mr. Mivart, are as follows. According to our 

 experience, abrupt and strongly marked variations occur in our 

 domesticated productions, singly and at rather long intervals of 

 time. If such occurred under nature, they would be liable, as 

 formerly explained, to be lost by accidental causes of destruction 

 and by subsequent inter-crossing ; and so it is known to be under 

 domestication, unless abrupt variations of this kind are specially 

 preserved and separated by the care of man. Hence in order that 

 a new species should suddenly appear in the manner supposed by 

 Mr. Mivart, it is almost necessary to believe, in opposition to all 



