14 THE ORIGIN OF MAN 



soil, and are thus able to exist independently, 

 while animals are dependent for their nourish- 

 ment, and so for their very existence on plants. 

 Plants are therefore the primary magazines of 

 food. 



Now that we know to a certain extent what 

 life is: namely the formation, growth and repro- 

 duction of cells, let us trace the progress of evo- 

 lution of animal life from the very beginning to 

 the age where man first came into existence. 



By means of the science of Paleontology, 

 which deals with the life of past ages, as shown 

 by the remains or natural molds and imprints of 

 plants and animals, called fossils, which have been 

 preserved, enclosed in rocks, scientists have been 

 able to trace the evolution of life from the very 

 beginning. The evolution of animal life is di- 

 vided into three eras: the first being the Paleo- 

 zoic or Ancient Life; the second the Mesozoic 

 or Medieval Life ; the third the Cenozoic or Mod- 

 ern Life. And the Psychozoic or the Age of 

 Man. 



