Part 2: The Dark History of Contraception
. . . There is reason to believe that vaccination has preserved thousands, who from a weak constitution would formerly have succumbed to small-pox. Thus the weak members of civilised societies propagate their kind. No one who has attended to the breeding of domestic animals will doubt that this must be highly injurious to the race of man.”
(Source: Descent of Man, Chap 5 - Pg. 168)