﻿DISTRIBUTION 
  OF 
  FISHES 
  JORDAN" 
  357 
  

  

  added 
  to 
  the 
  fauna. 
  The 
  rest 
  disappear 
  and 
  leave 
  no 
  trace. 
  A 
  

   knowledge 
  of 
  these 
  currents 
  and 
  their 
  influence 
  is 
  essential 
  to 
  any 
  

   detailed 
  study 
  of 
  the 
  dispersion 
  of 
  fishes. 
  

  

  The 
  occurrence 
  of 
  the 
  young 
  of 
  manj^ 
  shore 
  fishes 
  of 
  the 
  Hawaiian 
  

   Islands 
  as 
  drifting 
  plankton 
  at 
  a 
  considerable 
  distance 
  from 
  the 
  

   shores 
  was 
  first 
  noted 
  by 
  Dr. 
  Charles 
  H. 
  Gilbert. 
  Each 
  island 
  is, 
  in 
  

   a 
  sense, 
  a 
  " 
  sphere 
  of 
  influence," 
  affecting 
  the 
  fauna 
  of 
  neighboring 
  

   regions. 
  

  

  In 
  the 
  third 
  class, 
  that 
  of 
  species 
  changed 
  in 
  the 
  process 
  of 
  adapta- 
  

   tion, 
  most 
  insular 
  forms 
  belong. 
  As 
  a 
  matter 
  of 
  fact, 
  at 
  some 
  time 
  or 
  

   another 
  almost 
  every 
  species 
  must 
  be 
  in 
  this 
  category, 
  for 
  isola- 
  

   tion 
  is 
  a 
  source 
  of 
  the 
  most 
  potent 
  elements 
  in 
  the 
  initiation 
  and 
  

   intensification 
  of 
  the 
  minor 
  differences 
  which 
  separate 
  related 
  species. 
  

   This 
  is 
  a 
  factor 
  never 
  to 
  be 
  overlooked 
  in 
  the 
  study 
  of 
  the 
  origin 
  of 
  

   species. 
  It 
  is 
  not 
  the 
  preservation 
  of 
  the 
  most 
  useful 
  features, 
  but 
  

   of 
  those 
  which 
  actually 
  existed 
  in 
  the 
  ancestral 
  individuals, 
  which 
  

   distinguish 
  such 
  species. 
  Natural 
  selection 
  must 
  include 
  not 
  only 
  

   the 
  process 
  of 
  the 
  survival 
  of 
  the 
  fittest, 
  but 
  also 
  the 
  results 
  of 
  the 
  

   survival 
  of 
  the 
  existing. 
  This 
  means 
  the 
  preservation 
  through 
  

   heredity 
  of 
  the 
  traits 
  not 
  of 
  the 
  species 
  aione, 
  but 
  those 
  of 
  the 
  

   actual 
  individuals 
  who 
  have 
  been 
  the 
  first 
  in 
  the 
  line 
  of 
  descent 
  in 
  

   a 
  new 
  environment. 
  In 
  hosts 
  of 
  cases 
  the 
  persistence 
  of 
  characters 
  

   rests 
  not 
  on 
  any 
  particular 
  usefulness 
  or 
  fitness, 
  but 
  on 
  the 
  fact 
  

   that 
  individuals 
  possessing 
  these 
  characters 
  have, 
  at 
  one 
  time 
  or 
  

   another, 
  invaded 
  a 
  certain 
  area 
  and 
  populated 
  it, 
  being 
  subjected 
  

   thereby 
  to 
  new 
  selections 
  and 
  new 
  adaptations. 
  The 
  principle 
  of 
  

   utility 
  explains 
  survivals 
  among 
  competing 
  structures. 
  It 
  rarely 
  

   accounts 
  for 
  qualities 
  associated 
  with 
  geographical 
  distribution. 
  

  

  The 
  extinction 
  of 
  species 
  may 
  be 
  noted 
  here 
  in 
  connection 
  with 
  

   their 
  extension 
  of 
  range. 
  Several 
  writers, 
  following 
  Dr. 
  Herbert 
  

   Osborn, 
  have 
  recognized 
  five 
  different 
  types 
  of 
  elimination, 
  each 
  

   more 
  or 
  less 
  hypothetical. 
  1. 
  That 
  extinction 
  which 
  comes 
  from 
  

   modification 
  or 
  progressive 
  evolution, 
  a 
  relegation 
  to 
  the 
  past 
  as 
  

   the 
  result 
  of 
  a 
  transmutation 
  into 
  more 
  advanced 
  forms. 
  2. 
  Ex- 
  

   tinction 
  from 
  changes 
  of 
  physical 
  environment 
  which 
  outrun 
  the 
  

   powers 
  of 
  adaptation. 
  3. 
  The 
  extinction 
  which 
  results 
  from 
  com- 
  

   petition. 
  4. 
  The 
  extinction 
  from 
  extreme 
  specialization 
  and 
  limita- 
  

   tion 
  to 
  special 
  conditions. 
  5. 
  Extinction 
  as 
  a 
  result 
  of 
  exhaustion. 
  

  

  As 
  an 
  illustration 
  of 
  No, 
  1, 
  we 
  may 
  take 
  almost 
  any 
  species 
  which 
  

  

  has 
  a 
  cognate 
  species 
  on 
  the 
  further 
  side 
  of 
  some 
  barrier 
  or 
  in 
  the 
  

  

  Tertiary 
  seas. 
  Thus 
  the 
  trout 
  of 
  the 
  Twin 
  Lakes 
  in 
  Colorado 
  has 
  

  

  acquired 
  its 
  present 
  characters 
  in 
  the 
  place 
  of 
  those 
  brought 
  into 
  

  

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