THE FACTORS OF EVOLUTION 159 



of life, it supplies no answer. Indeed, it naively takes the life- 

 process as granted. But must not even the most primitive 

 animal, the simplest plant, be already organized, and able to 

 react suitably to external stimuli in order to be capable of 

 existence and reproduction ? Of this fundamental fitness of 

 all life this doctrine supplies no explanation. 



Those who have ever tried when shooting without a dog to 

 stir a hare know how difficult it is unless lucky chance guides 

 our steps. We may time after time pass within a few steps of 

 a hare, cowering down in his nest and trusting for safety to the 

 colour of his fur, which with its brown, black, yellow and white 

 hairs harmonizes so completely with the colour of the soil or 

 dried leaves as to be almost indistinguishable. Thanks to this 

 protective coloration the hare has been able to preserve his 

 species in spite of the most merciless persecution both by man 

 and animals. But it is only in the summer that he enjoys this 

 protection. When in the winter the land is thickly covered with 

 snow there begins for the hare a hard time, for only too fre- 

 quently is he seen by his enemies even at great distances. 

 But suppose that the temperature in Europe should sink from 

 year to year and that the snow which now covers the earth 

 not longer than two months should remain three, five, or six 

 months. It is obvious that in that event the conditions of life 

 for hares would be completely changed and rendered unfavour- 

 able. According to the laws of probability, under this doctrine 

 only those animals would in that event have the best chances 

 of escape from their enemies which had the largest mixture 

 of white in their fur and were therefore less easily distin- 

 guished from the snow-landscape than other hares. Of course 

 even these animals would sometimes fall victims to their 

 enemies, but their average prospects of life would be more 

 favourable. Thus the light-coloured hares would survive, reach 

 maturity, and transmit their distinctive feature to their offspring. 

 Continuing this natural selection through many generations, all 

 dark-coloured hares would eventually become extinct, and there 

 would remain only the light-coloured variety. But natural 

 selection would again make a choice among these white- 

 coloured hares, for the best chances of escape would be to those 

 most nearly like the colour of the snow. Thus we should 



