﻿GENETIC 
  PROGRESS 
  — 
  EAST. 
  291 
  

  

  seeds 
  from 
  various 
  parts 
  of 
  the 
  same 
  plant 
  apparently 
  transmit 
  

   different 
  characters, 
  would 
  be 
  less 
  likely 
  to 
  appear 
  so 
  puzzling 
  if 
  

   this 
  were 
  clearly 
  recognized. 
  And 
  even 
  if 
  we 
  admit 
  our 
  inability 
  

   at 
  present 
  to 
  contribute 
  much 
  toward 
  the 
  solution 
  of 
  the 
  question, 
  

   so 
  well 
  delimited 
  by 
  Weismann, 
  of 
  somatic 
  specialization 
  during 
  

   the 
  development 
  of 
  the 
  individual, 
  one 
  can 
  not 
  but 
  feel 
  that 
  further 
  

   progress 
  in 
  dealing 
  with 
  problems 
  of 
  straight 
  heredity 
  will 
  ulti- 
  

   mately 
  be 
  helpful. 
  

  

  As 
  to 
  the 
  grand 
  problem 
  of 
  evolution, 
  I 
  believe 
  there 
  has 
  been 
  a 
  

   concrete 
  offering. 
  True, 
  the 
  question 
  of 
  " 
  how 
  " 
  is 
  still 
  in 
  statu 
  quo; 
  

   but 
  one 
  must 
  be 
  rather 
  a 
  pessimist 
  if 
  he 
  does 
  not 
  consider 
  that 
  the 
  

   current 
  conception 
  of 
  the 
  gene 
  presents 
  something 
  tangible 
  on 
  the 
  

   subject. 
  It 
  certainly 
  allows 
  a 
  definite 
  distinction 
  between 
  variations 
  

   due 
  to 
  environmental 
  fluctuations, 
  variations 
  due 
  to 
  rearrangements 
  

   and 
  combinations 
  of 
  genes, 
  and 
  variations 
  due 
  to 
  change 
  in 
  the 
  con- 
  

   stitution 
  of 
  the 
  unit 
  of 
  heredity 
  itself. 
  Furthermore 
  the 
  data 
  now 
  

   being 
  gathered 
  on 
  the 
  type 
  of 
  gene 
  changes 
  occurring, 
  and 
  on 
  the 
  

   frequency 
  with 
  which 
  they 
  take 
  place, 
  are 
  not 
  to 
  be 
  cast 
  aside 
  as 
  of 
  

   no 
  value 
  to 
  the 
  evolutionist. 
  A 
  statement 
  as 
  to 
  just 
  what 
  they 
  mean 
  

   would 
  be 
  a 
  daring 
  assertion, 
  but 
  that 
  they 
  mean 
  something 
  now 
  and 
  

   will 
  mean 
  more 
  later 
  can 
  not 
  be 
  doubted. 
  

  

  Let 
  us 
  take, 
  for 
  example, 
  the 
  following 
  illustrations, 
  which, 
  I 
  

   think, 
  are 
  fair. 
  

  

  1. 
  Mutations 
  (gene 
  variations) 
  are 
  now 
  occurring 
  in 
  all 
  species 
  

   that 
  have 
  been 
  investigated 
  intensively. 
  

  

  2. 
  There 
  is 
  a 
  wide 
  range 
  to 
  mutation 
  frequency 
  in 
  different 
  species. 
  

  

  3. 
  The 
  number 
  of 
  useless 
  or 
  of 
  harmful 
  mutations 
  is 
  many 
  times 
  

   the 
  number 
  of 
  useful 
  or 
  of 
  beneficent 
  mutations. 
  

  

  4. 
  The 
  number 
  of 
  mutations 
  affecting 
  chiefly 
  certain 
  organs 
  or 
  

   particular 
  tissues 
  greatly 
  exceeds 
  those 
  affecting 
  other 
  parts 
  of 
  the 
  

   individual. 
  

  

  5. 
  The 
  " 
  conservative 
  " 
  parts 
  as 
  measured 
  by 
  mutation 
  frequency, 
  

   appear 
  to 
  have 
  slight 
  relation 
  to 
  the 
  " 
  conservative 
  " 
  parts 
  as 
  deter- 
  

   mined 
  by 
  the 
  circumstantial 
  evidence 
  of 
  the 
  phylogenist. 
  For 
  ex- 
  

   ample, 
  loss 
  of 
  the 
  ligule, 
  a 
  characteristic 
  of 
  the 
  grass 
  family, 
  has 
  been 
  

   found 
  in 
  a 
  goodly 
  number 
  of 
  the 
  cultivated 
  grasses 
  — 
  these 
  being 
  the 
  

   only 
  ones 
  that 
  have 
  been 
  studied 
  very 
  carefully. 
  

  

  6. 
  Mutations 
  are 
  often 
  reversible. 
  Reversibility 
  may 
  not 
  be 
  uni- 
  

   versal, 
  though 
  the 
  mere 
  fact 
  that 
  it 
  has 
  not 
  been 
  observed 
  in 
  every 
  

   case 
  proves 
  only 
  that 
  the 
  reaction 
  does 
  not 
  take 
  place 
  in 
  both 
  direc- 
  

   tions 
  with 
  the 
  same 
  ease. 
  

  

  7. 
  Mutations 
  which 
  from 
  their 
  major 
  effects 
  can 
  be 
  arranged 
  in 
  a 
  

   graded 
  series 
  — 
  for 
  example, 
  eye 
  color 
  of 
  Drosophila 
  melanogaster 
  — 
  

   are 
  found 
  not 
  to 
  have 
  originated 
  in 
  that 
  order. 
  That 
  is 
  to 
  say, 
  such 
  

  

  