﻿Geology 
  and 
  Natural 
  History. 
  385 
  

  

  For 
  those 
  unfamiliar 
  with 
  the 
  earlier 
  editions 
  it 
  should 
  be 
  

   stated 
  that 
  in 
  addition 
  to 
  the 
  general 
  explanation 
  of 
  the 
  Men- 
  

   delian 
  principles 
  of 
  heredity, 
  with 
  typical 
  illustrations 
  from 
  

   plants, 
  animals, 
  and 
  man, 
  there 
  are 
  chapters 
  on 
  variation 
  and 
  

   evolution 
  in 
  the 
  light 
  of 
  the 
  Mendelian 
  discoveries 
  ; 
  the 
  econom- 
  

   ical 
  aspects 
  of 
  increased 
  crops 
  and 
  improvement 
  of 
  breeds 
  of 
  

   domesticated 
  animals 
  by 
  application 
  of 
  the 
  Mendelian 
  laws; 
  

   and, 
  finally, 
  the 
  possibilities 
  of 
  applying 
  these 
  discoveries 
  to 
  the 
  

   human 
  race, 
  with 
  a 
  view 
  to 
  the 
  ultimate 
  elimination 
  of 
  the 
  unfit 
  

   and 
  defective 
  stocks 
  and 
  the 
  realization 
  of 
  superior 
  races 
  of 
  

   mankind 
  through 
  the 
  selective 
  marriages 
  of 
  those 
  with 
  the 
  best 
  

   germ-plasm. 
  w. 
  r. 
  c. 
  

  

  7. 
  Inbreeding 
  and 
  Outbreeding 
  ; 
  their 
  Genetic 
  and 
  Sociolog- 
  

   ical 
  Significance; 
  by 
  Edward 
  M. 
  East 
  and 
  Donald 
  F. 
  Jones. 
  

   Pp. 
  285, 
  with 
  46 
  illustrations. 
  Philadelphia 
  and 
  London, 
  1919 
  

   (J. 
  B. 
  Lippincott 
  Co.). 
  — 
  In 
  this 
  new 
  volume 
  of 
  the 
  series 
  of 
  

   Monographs 
  on 
  Experimental 
  Biology 
  the 
  authors 
  devote 
  the 
  

   four 
  introductory 
  chapters 
  to 
  a 
  general 
  account 
  of 
  the 
  methods 
  

   of 
  reproduction 
  and 
  the 
  mechanism 
  of 
  heredity 
  in 
  various 
  

   groups 
  of 
  organisms. 
  The 
  succeeding 
  chapters 
  give 
  the 
  results 
  

   of 
  recent 
  experiments 
  in 
  inbreeding 
  and 
  cross-breeding 
  in 
  many 
  

   groups 
  of 
  plants 
  and 
  animals, 
  with 
  evidence 
  and 
  theoretical 
  

   explanations 
  of 
  hybrid 
  vigor, 
  followed 
  by 
  a 
  discussion 
  of 
  ster- 
  

   ility 
  in 
  close 
  and 
  wide 
  crosses 
  and 
  the 
  role 
  of 
  inbreeding 
  and 
  

   outbreeding 
  in 
  evolution. 
  

  

  The 
  authors 
  demonstrate 
  that 
  the 
  popular 
  notion 
  that 
  even 
  

   the 
  closest 
  inbreeding 
  tends 
  to 
  degeneracy 
  or 
  sterility 
  or 
  other 
  

   undesirable 
  result 
  is 
  not 
  in 
  accord 
  with 
  the 
  evidence 
  either 
  of 
  

   experiment 
  or 
  of 
  natural 
  reproduction. 
  Such 
  inbreeding 
  merely 
  

   produces 
  uniform 
  strains 
  of 
  such 
  characteristics 
  as 
  are 
  present 
  

   in 
  the 
  parental 
  stocks. 
  Therefore 
  it 
  is 
  only 
  in 
  stocks 
  which 
  

   carry 
  heritable 
  defects 
  that 
  such 
  defects 
  appear 
  according 
  to 
  the 
  

   Mendelian 
  law 
  in 
  the 
  offspring. 
  The 
  superior 
  characteristics 
  

   which 
  may 
  be 
  present 
  in 
  these 
  stocks 
  will 
  likewise 
  make 
  their 
  

   appearance, 
  and 
  by 
  the 
  selection 
  and 
  breeding 
  of 
  such 
  offspring 
  

   as 
  show 
  these 
  desirable 
  qualities 
  a 
  greatly 
  improved 
  breed 
  may 
  

   be 
  established. 
  

  

  The 
  benefits 
  of 
  moderately 
  wide 
  crosses, 
  resulting 
  in 
  excep- 
  

   tional 
  vigor 
  in 
  the 
  first 
  generation, 
  are 
  explained, 
  with 
  practical 
  

   directions 
  for 
  securing 
  the 
  maximum 
  production 
  in 
  crops 
  and 
  'in 
  

   domesticated 
  animals 
  and 
  with 
  many 
  suggestions 
  for 
  the 
  im- 
  

   provement 
  of 
  breeds. 
  The 
  last 
  two 
  chapters 
  deal 
  with 
  human 
  

   heredity, 
  showing 
  the 
  results 
  of 
  various 
  racial 
  crosses 
  and 
  dis- 
  

   cussing 
  the 
  sociological 
  problems 
  involved. 
  A 
  sound 
  and 
  logical 
  

   plan 
  is 
  outlined 
  which 
  would, 
  if 
  followed 
  for 
  a 
  few 
  generations, 
  

   lead 
  to 
  a 
  great 
  improvement 
  in 
  both 
  the 
  physical 
  and 
  mental 
  

   constitution 
  of 
  mankind 
  and 
  the 
  elimination 
  of 
  a 
  large 
  propor- 
  

   tion 
  of 
  human 
  misery. 
  w. 
  R. 
  c. 
  

  

  