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 defined 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. R., “ Distribution of Animals,” II., p. 9, 
f Stichel, H., and H. Riffarth, “Heliconiidae.” 
