50 Merriam Geographic Dixlrihvtion of Life. 



bution of life. He lays great stress upon the dissimilarity of the 

 faunas and floras of parts of Africa, South America, and Aus- 

 tralia lying in the same latitude and calls particular attention to 

 the circumstance that although the climate may be identical 

 over these widely separated areas, the species and higher groups 

 are totally distinct, because the regions have been disconnected 

 since early geologic times as if these facts were not self-evident. 

 On the other hand, in single continental areas where there is no 

 break or barrier of any kind between widely different faunal 

 zones, he tries to invent some unnatural reason for the differences 

 observed and is reluctant to admit that even in these cases 

 climate or climatic conditions can constitute the barriers to dis- 

 persion that undoubtedly exist. He says of climate : "Probably 

 its action is indirect, and is determined by its influence on vege- 

 tation, and by bringing diverse groups into competition." 



In another place he states : u Hot countries usually differ 

 widely from cold Ones in all their organic forms ; but the differ- 

 ence is by no means constant, nor does it bear any proportion to 

 difference of temperature. Between frigid Canada and sub- 

 tropical Florida there are less marked differences in the animal 

 productions than between Florida and Cuba or Yucatan, so 

 much more alike in climate and so much nearer together." He 

 states further : " The eastern United States possess very peculiar 

 and interesting plants and animals, the vegetation becoming 

 more luxuriant as we go south but not altering in essential 

 character; so that when we reach the southern extremity of 

 Florida we still find ourselves in the midst of oaks, sumacs, 

 magnolias, vines, and other characteristic forms of the temperate 

 flora ; while the birds, insects, and land-shells are almost iden- 

 tical with those found further north. But if we now cross over 

 the narrow strait, about fifty miles wide, which separates Florida 

 from the Bahama Islands, we find ourselves in a totally different 

 country, surrounded by a vegetation which is essentially tropical 

 and generally identical with that of Cuba. The change is most 

 striking, because there is no difference of climate, of soil, or 

 apparently of position, to account for it." (Island Life, 1880, 

 p. 5.) 



Let us examine this statement with some care to see if the facts 

 warrant the assertions and conclusions of the author. But first 

 let me protest against Wallace's habit of contrasting insular 

 faunas with those of continuous land areas, in his efforts to mini- 

 mize the effects of climate. In most cases the great majority of 



