EVOLUTION, HEREDITY, EUGENICS 531 



that the history of the individual is a recapitulation of the history 

 of the race, but we cannot escape the observation that there are 

 notable differences, each species introducing its own specializations. 



Evidence from Classification. — The very assumption underlying 

 classification is that the closest fundamental similarities between 

 animals are found in those forms most closely related, and that the 

 greatest differences are found in those forms that are distantly 

 related. That we can place the animal kingdom in an orderly 

 progressive series is an indication of such a thing as Evolution. 



Evidence from Geographic Distribution. — The evolutionary 

 theory furnishes an explanation of the phenomena of distribution 

 of animals and plants. A species arises at one place and spreads out 

 over large areas, becoming modified as it goes, and new species are 

 formed from old through modification after isolation from the parent 

 stock. We find cosmopolitan groups, those with the widest dis- 

 tribution being the ones to whom no barriers are sufficient to check 

 migration; such as parasitic worms carried by man and other ani- 

 mals; and birds able to span large bodies of water (Newman). 

 Restricted groups are those to which barriers are readily set up, and 

 are frequently the only remnants of a once successful fauna or flora. 

 Again the faunas and floras of continental islands are what we should 

 expect on the basis of former land connection with the nearest 

 continent, since they are like those of the nearest mainland and 

 include types most readily blown there by wind or carried on floating 

 debris. 



Chief Sources of the Foregoing Summary 



Darwin, C. Origin of Species. D. Appleton and Co. 



Newman, H. H. 1925. Evolution, Genetics and Eugenics. U. of Chi. 



Press. 

 NuTTALL, G. H. F. Blood Immunity and Blood Relationship. Camb. 



Univ. Press. 

 Scott, W. B. 191 i. The Theory of Evolution. Macmillan Co. 

 Thomson, J. A. 1909. Darwinism and Human Life. Henry Holt & 



Co. 



Sex Determination, — The theories of sex determination afford an 

 opportunity to test the relative importance of the chromosomes as 

 opposed to environmental influence. Since there are but two sexes, 

 it must be conceded at the start that any theory of sex determination 

 will appear to be right, one-half of the time. 



