that the increase of each species and each race is constantly checked
in various ways; so that if any new check, even a slight one, be
superadded, the race will surely decrease in number; and decreasing
numbers will sooner or later lead to extinction; the end, in most
cases, being promptly determined by the inroads of conquering tribes.
ON THE FORMATION OF THE RACES OF MAN.
In some cases the crossing of distinct races has led to the formation
of a new race. The singular fact that the Europeans and Hindoos, who
belong to the same Aryan stock, and speak a language fundamentally the
same, differ widely in appearance, whilst Europeans differ but little
from Jews, who belong to the Semitic stock, and speak quite another
language, has been accounted for by Broca (49. On Anthropology,
translation, Anthropological Review, Jan. 1868, p. 38.), through
certain Aryan branches having been largely crossed by indigenous tribes
during their wide diffusion. When two races in close contact cross, the
first result is a heterogeneous mixture: thus Mr. Hunter, in describing
the Santali or hill-tribes of India, says that hundreds of
imperceptible gradations may be traced from the black, squat tribes of
the mountains to the tall olive-coloured Brahman, with his intellectual
brow, calm eyes, and high but narrow head ; so that it is necessary in
courts of justice to ask the witnesses whether they are Santalis or
Hindoos. (50. The Annals of Rural Bengal, 1868, p. 134.) Whether a
heterogeneous people, such as the inhabitants of some of the Polynesian
islands, formed by the crossing of two distinct races, with few or no
pure members left, would ever become homogeneous, is not known from
direct evidence. But as with our domesticated animals, a cross-breed
can certainly be fixed and made uniform by careful selection (51. The
Variation of Animals and Plants under Domestication, vol. ii. p. 95.)
in the course of a few generations, we may infer that the free
intercrossing of a heterogeneous mixture during a long descent would
supply the place of selection, and overcome any tendency to reversion;
so that the crossed race would ultimately become homogeneous, though it
might not partake in an equal degree of the characters of the two
parent-races.
Of all the differences between the races of man, the colour of the skin
is the most conspicuous and one of the best marked. It was formerly
thought that differences of this kind could be accounted for by long
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