﻿18 
  Descent 
  

  

  manifestly 
  with 
  specific 
  and 
  varietal 
  characters. 
  

   By 
  this 
  method 
  they 
  may 
  be 
  proved 
  to 
  be 
  in- 
  

   adequate 
  ever 
  to 
  make 
  a 
  single 
  step 
  along 
  the 
  

   great 
  lines 
  of 
  evolution, 
  in 
  regard 
  to 
  progressive 
  

   as 
  well 
  as 
  to 
  retrograde 
  development. 
  

  

  First 
  of 
  all 
  fluctuations 
  are 
  linear, 
  amplify- 
  

   ing 
  or 
  lessening 
  the 
  existing 
  qualities, 
  but 
  not 
  

   really 
  changing 
  their 
  nature. 
  They 
  are 
  not 
  

   observed 
  to 
  produce 
  anything 
  quite 
  new, 
  and 
  

   evolution 
  of 
  course, 
  is 
  not 
  restricted 
  to 
  the 
  in- 
  

   crease 
  of 
  the 
  already 
  existing 
  peculiarities, 
  but 
  

   depends 
  chiefly 
  on 
  the 
  continuous 
  addition 
  of 
  

   new 
  characters 
  to 
  the 
  stock. 
  Fluctuations 
  al- 
  

   ways 
  oscillate 
  around 
  an 
  average, 
  and 
  if 
  re- 
  

   moved 
  from 
  this 
  for 
  some 
  time, 
  they 
  show 
  a 
  

   tendency 
  to 
  return 
  to 
  it. 
  This 
  tendency, 
  called 
  

   retrogression, 
  has 
  never 
  been 
  observed 
  to 
  fail, 
  

   as 
  it 
  should, 
  in 
  order 
  to 
  free 
  the 
  new 
  strain 
  from 
  

   the 
  links 
  with 
  the 
  average, 
  while 
  new 
  species 
  

   and 
  new 
  varieties 
  are 
  seen 
  to 
  be 
  quite 
  free 
  from 
  

   their 
  ancestors 
  and 
  not 
  linked 
  to 
  them 
  by 
  

   intermediates. 
  

  

  The 
  last 
  few 
  lectures 
  will 
  be 
  devoted 
  to 
  ques- 
  

   tions 
  concerning 
  the 
  great 
  problem 
  of 
  the 
  anal- 
  

   ogy 
  between 
  natural 
  and 
  artificial 
  selection. 
  

   As 
  already 
  stated, 
  Darwin 
  made 
  this 
  analogy 
  

   the 
  foundation 
  stone 
  of 
  his 
  theory 
  of 
  descent, 
  

   and 
  he 
  met 
  with 
  the 
  severest 
  objections 
  and 
  crit- 
  

   icisms 
  precisely 
  on 
  this 
  point. 
  But 
  I 
  hope 
  to 
  

  

  