100 NATURAL SELECTION v 
When once a particular mode of building has been adopted, 
and has become confirmed by habit and by hereditary custom, 
it will be long retained, even when its utility has been lost 
through changed conditions, or through migration into a very 
different region. As a general rule, throughout the whole 
continent of America, native houses, when permanent, are 
built directly upon the ground—strength and security being 
given by thickening the low walls and the roof. In almost 
the whole of the Malay Islands, on the contrary, the houses 
are raised on posts, often to a great height, with an open 
bamboo floor; and the whole structure is exceedingly slight 
and thin. Now, what can be the reason of this remarkable 
difference between countries, many parts of which are 
strikingly similar in physical conditions, natural productions, 
and the state of civilisation of their inhabitants? We appear 
to have some clue to it in the supposed origin and migrations 
of their respective populations. The indigenes of tropical 
America are believed to have immigrated from the north— 
from a country where the winters are severe, and raised 
houses with open floors would be hardly habitable. They 
moved southwards by land along the mountain ranges and 
uplands, and in an altered climate continued the mode of 
construction of their forefathers, modified only by the new 
materials they met with. By minute observations of the 
Indians of the Amazon Valley, Mr. Bates arrived at the 
conclusion that they were comparatively recent immigrants 
from a colder climate. He says: “No one could live long 
among the Indians of the Upper Amazon without being 
struck with their constitutional dislike to the heat. ... Their 
skin is hot to the touch, and they perspire little. . . . They 
are restless and discontented in hot, dry weather, but cheerful 
on cool days, when the rain is pouring down their naked 
backs.” And, after giving many other details, he concludes, 
“How different all this is with the Negro, the true child of 
tropical climes! The impression gradually forced itself on 
my mind that the Red Indian lives as an immigrant or 
stranger in these hot regions, and that his constitution was 
not originally adapted, and has not since become perfectly 
adapted, to the climate.” 
The Malay races, on the other hand, are no doubt very 
