Down
Feb 22/63.
Dear Sir
I am gratified by your approval of my book on species.1 No doubt in many cases it is impossible to conjecture by what steps certain structures have been acquired. When we reflect on such cases as the stomach of the Pigeon secreting a nutritive fluid—the back of certain Batrachians secreting mucus on which the young feed, we can see that there may have been gradation in the formation of Mammary glands.—2
I have often thought over the case of the degeneration of civilized man; what you suggest, & especially for more care in marriage with more skill in detecting weak constitutions, and the germs of disease, seems to to be our only hope3
I have the &c &c | Yours faithfully | C. Darwin
Please cite as “DCP-LETT-4005,” in Ɛpsilon: The Charles Darwin Collection accessed on