﻿8 
  Descent 
  

  

  ations 
  as 
  the 
  exclusive 
  factor. 
  Of 
  late, 
  however, 
  

   this 
  point 
  of 
  view 
  has 
  been 
  abandoned 
  by 
  many 
  

   investigators, 
  especially 
  in 
  America. 
  

  

  The 
  actual 
  occurrence 
  of 
  mutations 
  is 
  now 
  

   recognized, 
  and 
  the 
  battle 
  rages 
  about 
  the 
  ques- 
  

   tion, 
  as 
  to 
  whether 
  they 
  are 
  be 
  regarded 
  as 
  the 
  

   principal 
  means 
  of 
  evolution, 
  or, 
  whether 
  slow 
  

   and 
  gradual 
  changes 
  have 
  not 
  also 
  played 
  a 
  

   large 
  and 
  important 
  part. 
  

  

  The 
  defenders 
  of 
  the 
  theory 
  of 
  evolution 
  by 
  

   slow 
  accumulation 
  of 
  slight 
  fluctuations 
  are 
  di- 
  

   vided 
  into 
  two 
  camps. 
  One 
  group 
  is 
  called 
  the 
  

   Neo-Lamarckians 
  ; 
  they 
  assume 
  a 
  direct 
  modi- 
  

   fying 
  agency 
  of 
  the 
  environment, 
  producing 
  a 
  

   corresponding 
  and 
  useful 
  change 
  in 
  the 
  organ- 
  

   ization. 
  The 
  other 
  group 
  call 
  themselves 
  Dar- 
  

   winians 
  or 
  selectionists, 
  but 
  to 
  my 
  mind 
  with 
  

   no 
  other 
  right 
  beyond 
  the 
  arbitrary 
  restriction 
  

   of 
  the 
  Darwinian 
  principles 
  by 
  Wallace. 
  They 
  

   assume 
  fluctuating 
  variations 
  in 
  all 
  directions 
  

   and 
  leave 
  the 
  choice 
  between 
  them 
  to 
  the 
  sieve 
  

   of 
  natural 
  selection. 
  

  

  Of 
  course 
  we 
  are 
  far 
  from 
  a 
  decision 
  between 
  

   these 
  views, 
  on 
  the 
  sole 
  ground 
  of 
  the 
  facts 
  as 
  

   known 
  at 
  present. 
  Mutations 
  under 
  observa- 
  

   tion 
  are 
  as 
  yet 
  very 
  rare; 
  enough 
  to 
  indicate 
  

   the 
  possible 
  and 
  most 
  probable 
  ways, 
  but 
  no 
  

   more. 
  On 
  the 
  other 
  hand 
  the 
  accumulation 
  of 
  

   fluctuations 
  does 
  not 
  transgress 
  relatively 
  nar- 
  

  

  