WEAKNESS OF USE-INHERITANCE. 95 



slow and slight. 1 Darwin tells us that " there is 

 no good evidence that this ever follows in the 

 course of a single generation." " Several generations 



1 Wallace shows that the changes in our domestic animals, if 

 spread over the thousands of years since the animals were first 

 tamed, must be extremely insignificant in each generation, and he 

 concludes that such infinitesimal effects of use and disuse would be 

 swallowed up by the far greater effects of variation and selection 

 (Darwinism, p. 436). Professor Romanes has replied to him in the 

 Contemporary Review (August 1889), showing that this is no disproof 

 of the existence of the minor factor, inasmuch as slight changes in 

 each generation need not necessarily be matters of life and death to 

 the individual, although their cumulative development by use- 

 inheritance might eventually become of much service. But selection 

 would favour spontaneous variations of a similarly serviceable 

 character. The slightest tendency to eliminate the extreme 

 variations in either direction would proportionally modify the 

 average in a breed. Use-inheritance appears to be so relatively 

 weak a factor that probably neither proof nor disproof of its 

 existence can ever be given, owing to the practical impossibility of 

 disentangling its effects (if any) from the effects of admittedly far 

 more powerful factors which often act in unsuspected ways. Thus 

 wild ducklings, which can easily be reared by themselves, invariably 

 " die off" if reared with tame ones (Variation, &c., i. 292, ii. 219). 

 They cannot get their fair share in the competition for food, and are 

 completely eliminated. Professor Romanes fully acknowledges 

 that there is the "gravest possible doubt " as to the transmission of 

 the effects of disuse (Letter on Panmixia, Nature, March 13, 1890). 



