﻿Stability 
  and 
  Real 
  Atavism 
  171 
  

  

  very 
  narrowly 
  restricted 
  one, 
  and 
  includes 
  only 
  

   those 
  ancestors 
  from 
  which 
  a 
  form 
  is 
  known 
  to 
  

   have 
  been 
  derived. 
  But 
  such 
  evidence 
  is 
  of 
  

   course 
  historic. 
  If 
  a 
  variety 
  has 
  been 
  observed 
  

   to 
  spring 
  from 
  a 
  definite 
  species, 
  and 
  if 
  the 
  cir- 
  

   cumstances 
  have 
  been 
  sufficiently 
  ascertained 
  

   not 
  to 
  leave 
  the 
  slightest 
  doubt 
  as 
  to 
  its 
  pure 
  

   origin, 
  and 
  if 
  moreover 
  all 
  the 
  evidence 
  has 
  

   been 
  duly 
  recorded, 
  we 
  may 
  say 
  that 
  the 
  origin 
  

   of 
  the 
  variety 
  is 
  historically 
  known. 
  In 
  most 
  

   cases 
  we 
  must 
  be 
  content 
  with 
  the 
  testimony, 
  

   given 
  somewhat 
  later, 
  and 
  recorded 
  after 
  the 
  

   new 
  variety 
  had 
  the 
  opportunity 
  of 
  showing 
  

   its 
  greater 
  merits. 
  

  

  If 
  it 
  now 
  happens 
  that 
  such 
  a 
  variety 
  of 
  re- 
  

   corded 
  origin 
  should 
  occasionally 
  revert 
  to 
  its 
  

   parent-species, 
  we 
  have 
  all 
  we 
  can 
  wish 
  for, 
  in 
  

   the 
  way 
  of 
  a 
  thoroughly 
  proved 
  case 
  of 
  atavism. 
  

   But 
  such 
  instances 
  are 
  very 
  rare, 
  as 
  the 
  birth 
  

   of 
  most 
  varieties 
  has 
  only 
  been 
  very 
  imper- 
  

   fectly 
  controlled. 
  

  

  Next 
  to 
  this 
  comes 
  the 
  systematic 
  relation 
  of 
  

   a 
  variety 
  to 
  its 
  species. 
  The 
  historic 
  origin 
  of 
  

   the 
  variety 
  may 
  be 
  obscure, 
  or 
  may 
  simply 
  be 
  

   forgotten. 
  But 
  the 
  distinguishing 
  marks 
  are 
  

   of 
  the 
  order 
  described 
  in 
  our 
  last 
  lecture, 
  either 
  

   in 
  the 
  positive 
  or 
  in 
  the 
  negative 
  direction, 
  and 
  

   on 
  this 
  ground 
  the 
  rarer 
  form 
  is 
  considered 
  to 
  

   be 
  a 
  variety 
  of 
  the 
  more 
  wide-spread 
  one. 
  If 
  

  

  