﻿Experimental 
  Pedigree-Cultures 
  571 
  

  

  tempt 
  to 
  surmount 
  it. 
  Darwin 
  tried 
  to 
  re- 
  

   place 
  the 
  unknown 
  cause 
  by 
  natural 
  agencies, 
  

   which 
  lie 
  under 
  our 
  immediate 
  observation. 
  

   On 
  this 
  point 
  Darwin 
  was 
  superior 
  to 
  his 
  . 
  

   predecessors, 
  and 
  it 
  is 
  chiefly 
  due 
  to 
  the 
  clear 
  

   conception 
  of 
  this 
  point 
  that 
  his 
  theory 
  has 
  

   gained 
  its 
  deserved 
  general 
  acceptance. 
  Accord- 
  

   ing 
  to 
  Darwin, 
  changes 
  occur 
  in 
  all 
  directions, 
  

   quite 
  independently 
  of 
  the 
  prevailing 
  circum- 
  

   stances. 
  Some 
  may 
  be 
  favorable, 
  others 
  detri- 
  

   mental, 
  many 
  of 
  them 
  without 
  significance, 
  

   neither 
  useful 
  nor 
  injurious. 
  Some 
  of 
  them 
  

   will 
  sooner 
  or 
  later 
  be 
  destroyed, 
  while 
  others 
  

   will 
  survive, 
  but 
  which 
  of 
  them 
  will 
  survive, 
  

   is 
  obviously 
  dependent 
  upon 
  whether 
  their 
  

   particular 
  changes 
  agree 
  with 
  the 
  existing 
  

   environic 
  conditions 
  or 
  not. 
  This 
  is 
  what 
  

   Darwin 
  has 
  called 
  the 
  struggle 
  for 
  life. 
  

   It 
  is 
  a 
  large 
  sieve, 
  and 
  it 
  only 
  acts 
  as 
  

   such. 
  Some 
  fall 
  through 
  and 
  are 
  annihilated, 
  

   others 
  remain 
  above 
  and 
  are 
  selected, 
  as 
  the 
  

   phrase 
  goes. 
  Many 
  are 
  selected, 
  but 
  more 
  are 
  

   destroyed 
  ; 
  daily 
  observation 
  does 
  not 
  leave 
  any 
  

   doubt 
  upon 
  this 
  point. 
  

  

  How 
  the 
  differences 
  originate 
  is 
  quite 
  another 
  

   question. 
  It 
  has 
  nothing 
  to 
  do 
  with 
  the 
  theory 
  

   of 
  natural 
  selection 
  nor 
  with 
  the 
  struggle 
  for 
  

   life. 
  These 
  have 
  an 
  active 
  part 
  only 
  in 
  the 
  ac- 
  

   cumulation 
  of 
  useful 
  qualities, 
  and 
  only 
  in 
  so 
  

  

  