60 WATER REPTILES OF THE PAST AND PRESENT 



is not the preservation of self, but the prosperity of the race. What- 

 ever the causes may be whereby the offspring are better adapted to 

 conquer in the struggle for existence, whatever may be the laws 

 governing changes and specialization, whether heredity, Mendelism, 

 mutation, natural selection, or Lamarckism, we call the process 

 evolution. 



To escape from the severe competition of the overcrowding 

 animals of the sea, some of those creatures we call fishes long ago 

 became air-breathers and took possession of the unoccupied land. 

 From among the myriads which were driven into unbreathable 

 water, by accident or by their enemies, or led there in the search 

 for more easily acquired or- better food, some survived and found 

 that the oxygen of the air was quite as breathable as that of the 

 water. Steadily their progeny became better and better adapted 

 to the unusual life until they ceased to be fishes and became amphib- 

 ians, from which have arisen in like manner all the reptiles and 

 birds and mammals that live or have lived upon the earth. 



With more and better powers, developed under better oppor- 

 tunities, not a few of these descendants have repeatedly sought 

 safety from their newly acquired enemies of the overcrowded land, 

 or a better supply of food in the sea; gradually, perhaps incidentally 

 at first, as we shall see is the case with some lizards today, but 

 later with increased adaptation to their new surroundings, they 

 become truly sea or water animals, no longer able to live upon 

 the land. In these changed conditions and with concomitantly 

 changed habits they never reverted to the primitive condition of 

 fishes, never became water-breathing animals again, for that would 

 be actual retrogression, a seeming impossibility in evolution. Nor 

 indeed does it seem possible that a land creature after its reversion 

 to water life ever can return to the land again. 



A fish through long ages of evolution has become well adapted 

 to its environments; its shape is the best for speed or varied 

 evolutions in the water; its teeth and mouth-organs are best suited 

 for the food it requires. Now it is evident that if animals of very 

 different habits and form should go back to the water and seek 

 to compete with creatures already well adapted to their surround- 

 ings, they must, so far as possible, acquire like forms and like 



