84 WORLD-POWER AND EVOLUTION 



white and colored races. So far as physical activity is concerned, 

 the tests with the dynamometer indicate an optimum like that 

 of the white race. That is, the greatest scores were made when 

 the mean temperature was 60°, which is practically identical with 

 the figure that I obtained from the daily piece work of hundreds 

 of men and girls in Connecticut factories. The optimum for the 

 mental tests of the negroes was almost the same as for the physi- 

 cal. If this is due to the fact that physical activity formed part 

 of the test, it has no significance except to emphasize the unity 

 of the human race. If it means that the mental optimum of the 

 black race is really higher than that of the white race, it is of 

 great importance. It then indicates that while the human race 

 as a whole apparently made its chief physical evolution before 

 the separation of the various races, the most rapid evolution of 

 the white race took place after the negroes had branched off. 

 Thus we may suppose that man's chief physical evolution occurred 

 in a fairly warm region, not tropical, but like Mesopotamia or 

 northern Africa as they are today. Then the negro race split 

 off from the others and moved southward. Before the epoch when 

 the severe glacial climate caused Mesopotamia and the Mediter- 

 ranean region to be as cold and stormy as northwestern Europe 

 now is, we may suppose that the negro was in the sheltered climate 

 of southern Arabia or of Africa south of the Sahara. Meanwhile 

 the ancestors of the world's more progressive races underwent 

 further evolution. That evolution was largely mental. Its result 

 was to enlarge man's mental powers enormously. At the same time 

 he acquired a peculiar adaptation whereby his mind is stimulated 

 by much colder weather than that which is most healthful for his 

 body. Thus his problem today is to avoid harm to his body and 

 yet live where the climate is cool enough to stimulate his mind. 



The difference between the mental and physical optima by no 

 means explains all of man's adaptations to climate. Humidity 

 is of great importance. Glance over Figures 8 to 19. Notice 

 that in every case the curved lines or isopracts separating the 



