THE INFLUENCES OF NURTURE 99 



of individually acquired modifications let us consider 

 indirect arguments. 



(1) How can there be progressive evolution at all, 

 it is asked, if acquired characters or structural modi- 

 fications due to peculiarities of nurture are not accu- 

 mulated by transmission ? The answer is that pro- 

 gressive evolution probably depends on a sifting and 

 singling of the continuous crop of germinal variations 

 or mutations. About 1818 the record speed of the 

 trotting horse was 3 minutes to the mile, in 1814 it was 

 2 min. 34 sees., in 1848 2 min. 30 sees., in 1868 2 min. 

 20 sees., in 1879 2 min. 16 sees., in 1888 2 min. 11 J sees., 

 and (when our information stops) 2 min. 10 sees. The 

 question is whether the progressive gain in speed was 

 in any way due to exercising, or wholly due to breeding 

 from the constitutionally swiftest variants. 



(2) It is easy to interpret a giraffe's long neck as the 

 cumulative hereditary result of hundreds of thousands 

 of years' stretching at branches, and a cave-animal's 

 blindness as due to thousands of years of darkness and 

 disuse. Herbert Spencer interpreted his small hands 

 as the result of the minutely manipulative work in which 

 his father and grandfather were engaged. But inter- 

 pretation is not proof. (3) A common fallacy is to start 

 with a peculiarity which is not proved to be a modifica- 

 tion. The argument runs as follows : — Short-sightedness 

 is due to straining young eyes over small print ; short- 

 sightedness is transmitted ; therefore modifications are 

 transmitted. But it has not been proved that short- 

 sightedness is a modification. It occurs in people who 



