operation than was once supposed. A. de Quatrefages brings forward
(_Unite de l'espece humaine_) his strongest arguments for the
variability of races under change of climate, &c. (_action du milieu_),
instancing the asserted alteration in complexion, constitution and
character of Negroes in America, and Englishmen in America and
Australia. But although the reality of some such modification is not
disputed, especially as to stature and constitution, its amount is not
enough to upset the counter-proposition of the remarkable permanence of
type displayed by races, ages after they have been transported to
climates extremely different from that of their former home. Moreover,
physically different peoples, such as the Bushmen and Negroes in Africa,
show no signs of approximation under the influence of the same climate;
while, on the other hand, the coast tribes of Tierra del Fuego and
forest tribes of tropical Brazil continue to resemble one another, in
spite of extreme differences of climate and food. Darwin is moderate in
his estimation of the changes produced on races of man by climate and
mode of life within the range of history (_Descent of Man_, part i. ch.
4 and 7). The slightness and slowness of variation in human races having
become known, a great difficulty of the monogenist theory was seen to
lie in the apparent shortness of the Biblical chronology. Inasmuch as
several well-marked races of mankind, such as the Egyptian, Phoenician,
Ethiopian, &c., were much the same three or four thousand years ago as
now, their variation from a single stock in the course of any like
period could hardly be accounted for without a miracle. This difficulty
the polygenist theory escaped, and in consequence it gained ground.
Modern views have however tended to restore, though under a new aspect,
the doctrine of a single human stock. The fact that man has existed
during a vast period of time makes it more easy to assume the
continuance of very slow natural variation as having differentiated even
the white man and the Negro among the descendants of a common
progenitor. On the other hand it does not follow necessarily from a
theory of evolution of species that mankind must have descended from a
single stock, for the hypothesis of development admits of the argument,
that several simian species may have culminated in several races of man.
The general tendency of the development theory, however, is against
constituting separate species where t