The Descent of Man

I afterwards found that this same idea had long
ago occurred to Dr. Wells. (56. See a paper read
before the Royal Soc. in 1813, and published in
his Essays in 1818. I have given an account of
Dr. Wells' views in the Historical Sketch (p.
xvi.) to my 'Origin of Species.' Various cases of
colour correlated with constitutional peculiarities
are given in my 'Variation of Animals and
Plants under Domestication,' vol. ii. pp. 227,
335.) It has long been known that negroes, and
even mulattoes, are almost completely exempt
from the yellow-fever, so destructive in tropical
America. (57. See, for instance, Nott and Gliddon,
'Types of Mankind,' p. 68.) They likewise
escape to a large extent the fatal intermittent
fevers, that prevail along at least 2600 miles of
the shores of Africa, and which annually cause
one-fifth of the white settlers to die, and another
fifth to return home invalided. (58. Major
Tulloch, in a paper read before the Statistical
Society, April 20, 1840, and given in the 'Athenaeum,'
1840, p. 353.) This immunity in the