The Descent of Man

But as with our domesticated animals, a crossbreed
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 exposure to different
climates; but Pallas first shewed that this is not
tenable, and he has since been followed by almost
all anthropologists. (52. Pallas, 'Act. Acad.
St. Petersburg,' 1780, part ii. p. 69. He was fo-