232 THE ORIGIN AND EVOLUTION OF LIFE 



we may not attribute this relatively arrested development of 

 the reptiles either to an arrested physicochemical environment, 

 to an arrested life environment, or to the relative bodily iner- 

 tia of reptiles which affects the body-protoplasm and body- 

 chromatin. These four reasons appear to be as follows: 



First: We have noted that among the reptiles the velocity 

 of purely mechanical adaptation is quite independent both of 

 brain power and of nervous activity, a fact which seems to 

 strike a blow at the psychic-direction hypothesis (p. 143), on 

 which the explanations of evolution by Lamarck, Spencer, and 

 Cope so largely depend. The law that perfection of mechan- 

 ical adaptation is quite independent of brain power also holds 

 true among the mammals, because the small-brained mammals 

 of early Tertiary time, the first mammals to appear, evolve as 

 mechanisms quite as rapidly or more rapidly than the large- 

 brained mammals. 



Second: The law of rapidity of character evolution is inde- 

 pendent also of body temperature, for, while the mechanical 

 evolution of the warm-blooded birds and mammals is very 

 rapid and very remarkable it can hardly be said to have ex- 

 ceeded that of the cold-blooded reptiles. Thus the causes of 

 the velocity of character evolution in mechanism need not be 

 sought in the psychic influence of the brain, in the nervous 

 system, in the "Lamarckian" influence of the constant exer- 

 cise of the body, nor in a higher or lower temperature of the 

 circulatory system. 



Third: Nor has the relatively arrested evolution of the 

 Reptilia during the period of the Age of Mammals been due 

 to arrested environmental conditions, for during this time the 

 environment underwent a change as great as or greater than 

 that during the preceding Age of Reptiles. 



Fourth, and finally, there is no evidence that natural selec- 



