Note 8 — Chapter XVIII · ON THE ADVANTAGES AND DISADVANTAGES OF CHANGED CONDITIONS OF LIFE: STERILITY FROM VARIOUS CAUSES.
Reading edition
Mr. Spencer has fully and ably discussed this whole subject in his ‘Principles of Biology,’ 1864, vol. ii. ch. x. In the first edition of my ‘Origin of Species,’ 1859, p. 267, I spoke of the good effects from slight changes in the conditions of life and from cross-breeding, and of the evil effects from great changes in the conditions and from crossing widely distinct forms, as a series of facts “connected together by some common but unknown bond, which is essentially related to the principle of life.”