TRANSLATOR'S PREFACE XIX 



dies. Within those limits the result of the development 

 varies to a very great degree with the variations of the 

 conditions. In the cultivation of domesticated animals and 

 plants, no degree of skill or patience in selection will pro- 

 duce improvement in a race, or even maintain its valuable 

 qualities, unless favourable conditions are provided. Every- 

 body knows that in a given district, even on a given farm, 

 certain varieties of animals and plants cannot be produced 

 in perfection. Individuals can be procured, the most perfect 

 in existence, but in a particular district or on a particular 

 farm they do not " thrive " ; that is to say, the (pialities for 

 which they are valued disappear in the individuals, or, as is 

 more often the case, in a few generations, in spite of all 

 care and selection. Thus English races of dogs have been 

 shown by Darwin {Domestication, vol. i. p. 3 7) to degenerate 

 in India in a few generations, losing entirely the peculiarities 

 of form and mental character which distinguish their race, 

 and this in spite of the greatest care in selection and the 

 prevention of crossing. According to Weismann's assump- 

 tions, these degenerated dogs if removed back to England 

 would in the next generation recover entirely their lost 

 qualities ; but I do not think any sportsman would purchase 

 one of them on Weismann's guarantee. What I wish to 

 emphasize here is, that it is a fact that characters are only 

 constant under approximately the same conditions ; and that, 

 when under new conditions new characters appear constantly 

 in successive generations, we have exactly the same grounds 

 for asserting that these new characters are inherited as for 

 saying that the old characters under the old conditions were 

 inherited. The very fact that characters are acquired proves 

 that heredity is not a fixed and constant tendency independ- 



