THE NEW EVOLUTION 



the present day and those of the past, the accuracy of 

 which comparisons forms our sole criterion for the 

 interpretation of the latter. 



All of the major groups of animals may be supported 

 either by the algae or related groups of plants, or by 

 the flowering plants, or by a mixture of plant types. 

 Thus in the sea we find the walrus and the seals and 

 whales feeding upon animals dependent for their 

 existence upon the diatoms, while on the land we see 

 the elephant and the dogs and wolves supported 

 wholly by flowering plants or by creatures feeding 

 on them. 



So with an abundance of plant food quite regardless 

 of the kind the possibility exists for the appearance of 

 some representative or representatives in every major 

 group of animals. 



In regard to plants the situation is quite different, 

 for in the case of plants there is a direct relation to the 

 amount and quality of sunlight. The amount and 

 quality of sunlight plays but a minor part in the 

 animal world taken as a whole. It is largely a neg- 

 ligible factor. For instance some fishes and some 

 crustaceans are found along the shores and on the 

 beaches in the sunniest portion of the tropics, while 

 others live in the deepest and darkest portions of the 

 sea and also far under ground in lightless — or prac- 

 tically lightless — caves. Sunlight is essential only 

 for relatively small groups of animals, as for instance 

 birds and many of the reptiles, especially the turtles 

 and the crocodilians. Animals as a whole are depend- 

 ent only on an adequate supply of plant food, air and 



[ii6] 



