Man in the Light of Evolution 



were much like fishes, and did not bring out 

 clearly and sharply the amphibian characteristics. 

 The oldest bird, Archaeopteryx, had the teeth 

 and long tail of a lizard. The lowest, and 

 probably the oldest, mammals laid eggs, like 

 reptiles. Such a generalized or comprehensive 

 form was placed by common consent at the bot- 

 tom of its line or branch. Specialized forms, 

 which brought out more distinctly the charac- 

 teristics of the group, were placed at the ends 

 of branches. Finer branchlets and twigs repre- 

 sented the genera and species. 



According to Mr. Darwin's theory this tree 

 of classification was a genealogical tree, similar 

 to that which might be made of the members 

 of any family, with the oldest known ancestor 

 at the bottom and the living members at the 

 end of the branches. The relation between suc- 

 cessive groups along each branch was that of 

 descent with modification. 



Deep-seated characters had become fixed in 

 some remote ancestor and been handed down to 

 all his descendants. Superficial traits naturally 

 characterized the more changeable species. Gen- 

 eralized forms stood at the base of each branch, 

 because their descendants were continually be- 



14 



