THE NEW EVOLUTION 



sibilities for major diversifications offered in each of 

 these two regions. 



But while three times as many major groups of ani- 

 mals are found in the sea as are found upon the land, 

 the relatively few major groups of animals inhabiting 

 the land include more than three times as many differ- 

 ent kinds of animals as are found in the sea. 



This curious discordance results mainly from the 

 enormous diversity which occurs among the insects, 

 these creatures in number of different sorts exceeding 

 all other forms of life together by about three to one. 



How can this condition be explained? It is in 

 simple correlation with the fact that conditions on the 

 land are almost infinitely more diversified than the 

 conditions in the sea. 



In the first place the range of temperature from the 

 hottest desert region in the tropics under the noon-day 

 sun to the coldest spot under the Arctic winter night 

 in northern Siberia or in northern Canada is vastly 

 greater than the range in temperature from the warm- 

 est to the coldest seas. In the second place diurnal 

 variations in the temperature, which are always pres- 

 ent and sometimes extreme on land, in the sea are 

 absent, or at least quite negligible. In the third 

 place seasonal variations, which are more or less 

 marked everywhere on land and are very important 

 in the northern regions, affect the sea only in limited 

 areas and there only in relatively slight degree and 

 only in shallow or superficial waters. In the fourth 

 place the available supply of water on the land is 

 extremely variable, from place to place, from season 



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