THE STRUGGLE FOE EXISTENCE 25 



and beneficial qualities happen to arise as slight varia- 

 tions from the ancestral type, they will (other things 

 permitting), be seized upon by natural selection, and 

 being transmitted by heredity to subsequent generations, 

 will be added to the previously existing type. This then, 

 is natural selection or the survival of the fittest, the 

 one term referring mainly to the process, the other to 

 the result. 



The process is analogous to that by which the gardener 

 and the cattle-breeder bring about their wonderful re- 

 sults. Just as these men, by always "selecting" their 

 best individuals to breed from, slowly but continuously 

 improve their stock, so Nature by a process of "selec- 

 tion," slowly but continuously makes the various species 

 of plants and animals better suited to the conditions of 

 their life. What the skill of Luther Burbank has ac- 

 complished in the course of a few generations, Nature 

 takes years or even centuries of experimentation to pro- 

 duce. By artificial selection, man works on external 

 characters irregularly and imperfectly for a short time. 

 Nature works on the whole machinery of life by con- 

 sistent accumulation during whole geological epochs. 

 Silently and insensibly working, natural selection is daily 

 and hourly scrutinizing the slightest variation, rejecting 

 those that are bad, preserving and adding up all that 

 are good. 6 



Under natural conditions there is an endless range of 

 variation. We have seen in chapter I how like tends 

 to beget like, but that although the offspring is similar to 

 the parent there is never precise reduplication. There 

 is latitude allowed for individual variation. The indi- 

 vidual differences are due to age, sex, modification, and 



Thomson & Goddos, op. cit., p. 156. 



