AND PERSONALITY 



an alligator and a crocodile, each about n feet long, 

 weighing 450 and 295 pounds, respectively, were easily 

 held by hand. Separated from their water and mud environ- 

 ment, they were more or less helpless creatures. In contrast 

 was the fearful power of the lion and the tiger as it was 

 partially revealed while they were being chloroformed. 



In contrasting lions and tigers with alligators and croc- 

 odiles, we are considering animals equal in mass of muscle 

 but wholly unequal in muscular power and in length of 

 life. An alligator or a crocodile may live a hundred or more 

 years, whereas a lion or tiger in the wild seldom attains an 

 age of fifteen years. At first one wonders why evolution 

 could not have made an alligator or crocodile as powerful 

 as a lion- or tiger. The answer is that evolution exploited 

 all the possibilities of power for animals constructed on the 

 cold-blooded principle. 



Warm-blooded animals, cold-blooded animals, fish, rep- 

 tiles, birds, carnivores, grass eaters, and leaf eaters are 

 each as large and as powerful as they can be. Since growth, 

 function, and work relate solely to energy, it is clear that 

 the fundamental principle of evolution is the play of energy. 

 Evolution, therefore, centers on the organs controlling the 

 rate of oxidation, namely, the brain, the heart, the blood 

 volume, the thyroid gland, and the adrenal-sympathetic 

 nervous system. This energy system in animals has the 

 power to endow warm-blooded animals with all the energy 

 they can utilize to the level of heatstroke. A cold-blooded 

 alligator weighing 204 kilograms (450 pounds) has a brain 

 and a metabolism only approximately equal to that of a 

 hare weighing 2 kilograms (4.41 pounds). Thus the compar- 

 ative size of the brain, the thyroid gland, the adrenal- 

 sympathetic nervous system, the heart and the volume of 

 the blood, in relation to the weight of the animal, tells the 

 story of the evolution of energy in the various species. 



The difference in energy characteristics between such a 

 somnolent animal as an alligator, which does not have to 



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