What Animals Attained 147 



insects frequent moist places close to the soil and are often noc- 

 turnal; specialized insects fly in the open sunlight when time of day 

 and season of year make most energy available. 



One quality of terrestrial environment is variability. This has 

 been a factor in the development of that most effective adaptation 

 to land life — homoiothermism. Birds and mammals, which keep 

 their body temperatures and their body fluids close to optimum con- 

 ditions for cell activity, are so independent of environment that they 

 can, if stored energy is available in the form of food, live in polar 

 regions and tropical deserts where life is impossible for poikilother- 

 mic land animals. Homoiothermism makes continuity of activity 

 and thoughtful endeavor possible. 



The variability of land habitats stimulates animals to greater 

 versatility in response to environmental changes. It is on land that 

 animals have developed greatest ability to solve complex problems. 

 The most astute thinkers are land animals. Even on land monotony 

 is conducive to lack of progressive accomplishment. Man has not 

 done his greatest works in the tropics, where much radiant energy 

 is available and temperatures are always high. Conditions of life 

 are too monotonous. The most progressive modern races and na- 

 tions are found in temperate regions where humidities and tempera- 

 tures vary. In such localities men are most healthy, competent, and 

 productive (Huntington, 1927) . 



Perhaps the fairest flower of progressive evolutionary growth on 

 land is human civilization. This is the product of homoiothermism, 

 which permits continuity of activity, social life, which multiplies and 

 strengthens individual accomplishment and, by the overlapping of 

 generations and the accumulation of works in the way of social 

 procedures, homes, inventions, libraries, etc., also contributes to 

 continuity of cumulative activity. Man through knowledge has 

 means for controlling environment or compensating for changes in 

 it. Such extra-corporal assets are far above those at the command 

 of any other animal. He is able more or less to keep conditions 



