NATURAL SELECTION SINCE DARWIN 93 



(too long for some critics, too short for some others) 

 which the development of the organic world would 

 require, if it were due to the selection of slight indi- 

 vidual differences. It has taken many million years 

 for the organic world to develop itself, while the earth, 

 according to physicists, has only existed a few million 

 years. In 1862, William Thompson (the late Lord 

 Kelvin), estimated the earth's age (basing his calcu- 

 lations on the cooling of the terrestrial crust and the 

 high temperature in the depths), as not exceeding 

 forty million years. According to Geike the solid 

 crust of the earth is almost a hundred million years 

 old; other calculations made by other physicists have 

 given about the same figures. We cannot help no- 

 ticing the arbitrariness of these calculations; physi- 

 cists may make them, for they have in their possession 

 exact data as to the cooling off of the earth within a 

 given time, but what basis of calculation has the bi- 

 ologist who has never seen any new species spring up 

 and cannot guess even approximately how long the 

 processus would require? 



The conclusion to be drawn from this controversy 

 is, that the meaning of the word "li fe struggle " has 

 been wrongfully narrowed down and limited to com- 

 petition between individuals. The life struggle as- 

 sumes much greater proportions between species and 

 also between the living things and their organic en- 

 vironment. Purely individual peculiarities are insuf- 



