Chap. XX VIII. CONCLUDING REMARKS. 411 



cannot thus connect the turbit or the pouter. The degree 

 of distinctness between the various domestic breeds depends 

 on the amount of modification which they have undergone, 

 and more especially on the neglect and final extinction of 

 intermediate and less- valued forms. 



It has often been argued that no light is thrown on the 

 changes which natural species are believed to undergo from 

 the admitted changes of domestic races, as the latter are 

 said to be mere temporary productions, always reverting, 

 as soon as they become feral, to their pristine form. This 

 argument has been well combated by Mr. Wallace; 2 and 

 full details were given in the thirteenth chapter, showing 

 that the tendency to reversion in feral animals and plants 

 has been greatly exaggerated, though no doubt it exists to 

 a certain extent. It would be opposed to all the principles 

 inculcated in this work, if domestic animals, when exposed 

 to new conditions and compelled to struggle for their 

 own wants against a host of foreign competitors, were not 

 modified in the course of time. It should also be remem- 

 bered that many characters lie latent in all organic beings, 

 ready to be evolved under fitting conditions ; and in breeds 

 modified within recent times, the tendency to reversion is 

 particularly strong. But the antiquity of some of our breeds 

 clearly proves that they remain nearly constant as long as 

 their conditions of life remain the same. 



It has been boldly maintained by some authors that the 

 amount of variation to which our domestic productions are 

 liable is strictly limited ; but this is an assertion resting on 

 little evidence. Whether or not the amount of change in 

 any particular direction is limited, the tendency to general 

 variability is, as far as we can judge, unlimited. Catt'e, 

 sheep, and pigs have varied under domestication from the 

 remotest period, as shown by the researches of Butimeyer 

 and others ; yet these animals have been improved to an 

 unparalleled degree, within quite recent times, and this 

 implies continued variability of structure. Wheat, as we 

 know from the remains found in the Swiss lake- dwellings, 



2 ' Journal Proc. Linn. Soc.,' 1858, vol. iii. p. 60. 



