368 ORIGIN OF LIFE IN AMERICA 



invaded by the humming birds in earlier times from the west, 

 since several very distinct genera with well marked characters 

 have originated there. The humming birds constitute a 

 sharply denned family, whose nearest relatives are the tree- 

 swifts (Macropteryx) of southern Asia and western Polynesia. 

 The common ancestors of these two groups may possibly 

 have inhabited part of the supposed ancient Pacific continent, 

 and may have diverged from it east and westward when it sub- 

 sided. As Dr. Wallace* aptly remarks, no naturalist can 

 study in detail this single family of birds without being pro- 

 foundly impressed by the vast antiquity of the South 

 American continent, its long isolation from the rest of the 

 land surface of the globe, and the persistence through count- 

 less ages of all the conditions requisite for the development 

 and increase of varied forms of animal life. 



The chatterers (Cotingidae) which have already been alluded 

 to as comprising some of the most beautiful and noteworthy 

 of American birds, are almost confined to South and Central 

 America and the West Indies. Only a few species enter North 

 America in Mexico. The curious toucans (Rhamphastidae) 

 with their huge bills and strange texture and coloration of 

 their plumage, as well as several other families, are restricted 

 to South and Central America and have no near relations in 

 the Old World. 



If South America had been connected by land with Africa 

 in later Tertiary times, we should expect, at any rate, such 

 mobile creatures as birds and also butterflies to indicate by 

 their distribution the former existence of such a land bridge. 

 Among the most conspicuous butterflies in the Brazilian 

 forests, Mr. Bates mentions the Heliconiidae, which are 

 readily recognisable by their long narrow black wings, 

 variously ornamented with white, crimson and yellow dots 

 or stripes. Yet the family is almost purely South American. 

 A single species only (Heliconius charitonia) passes into 

 Mexico.f 



The Morphidae likewise range from Argentina to Mexico, 

 some of the larger species, with their dazzling metallic 



* Wallace, A. E., " Distribution of Animals," II., p. 9, 

 t Stichel, H., and H. Biffarth, "Heliconiidae," 



