Good point; I checked the wrong book. I could use some help finding comments in it on eugenics, as the word doesn’t appear in the book. I found the section which he’s referring to with “negro” and “australian”, though:
The great break in the organic chain between man and his nearest allies, which cannot be bridged over by any extinct or living species, has often been advanced as a grave objection to the belief that man is descended from some lower form; but this objection will not appear of much weight to those who, from general reasons, believe in the general principle of evolution. Breaks often occur in all parts of the series, some being wide, sharp and defined, others less so in various degrees; as between the orang and its nearest allies–between the Tarsius and the other Lemuridae–between the elephant, and in a more striking manner between the Ornithorhynchus or Echidna, and all other mammals. But these breaks depend merely on the number of related forms which have become extinct. At some future period, not very distant as measured by centuries, the civilised races of man will almost certainly exterminate, and replace, the savage races throughout the world. At the same time the anthropomorphous apes, as Professor Schaaffhausen has remarked (18. ‘Anthropological Review,’ April 1867, p. 236.), will no doubt be exterminated. The break between man and his nearest allies will then be wider, for it will intervene between man in a more civilised state, as we may hope, even than the Caucasian, and some ape as low as a baboon, instead of as now between the negro or Australian and the gorilla.
However, it looks to me like he’s quoting someone else — so I went and looked that up, and found Shaafhausen’s comments. It does look like Darwin is simply citing him:
In the present state of things, the distance between man and the animal increases under our own eye. Not merely the human races standing lowest, in the scale, and presenting in their organisation many resemblances to animal forms, are gradually becoming extinct, but the superior apes approaching nearest to man become more rare from century to century; and will, perhaps, in a few centuries have entirely disappeared. What is there illogical in the idea that thousands of years back the distance between the lowest man and the highest ape was less than at present, and that it would still lessen the more we ascend the
past?
Schaafhausen also explains what he feels the differences between different human races are and between different species:
The assertion of Mr. Huxley that men, even as regards the volume of the brain, differ among themselves more than apes, is equally erroneous ; an opinion which is founded upon the arbitrary employment of measurements of crania both rare and doubtful. The brain of the Australian exceeds two or three times the volume of the brain of the gorilla, whilst the brain of a European exceeds that of the Australian only by one-fifth. Another allegation of Mr. Huxley to the effect that, as regards the volume of the brain, the inferior apes differ from the superior as much as the latter differ from man is also without scientific value, inasmuch as this author has not taken into account the incomparable difference of size of the above-mentioned simia, whilst in this respect man and the gorilla are nearly equal. This distance between man and ape must not be ignored; in fact, one glance at the cranial cavity reveals it. I think, however, that it was less in times past, or perhaps did not exist at all. The differences of volume in organised beings of the present world are only gaps produced in the chain by time. Transitional forms will, no doubt, be found still reposing in the bosom of the earth which covers palaiontological creation.
It’s rather interesting to jump into these people’s heads and see what makes them tick.
You looked at the wrong Darwin book. Check out his "The Descent of Man" That was the book I referred to. It is a refutation of the idea that we could become stronger by killing our weakest. Oh sure, you'll probably post the following quote some source has given you:
It is surprising how soon a want of care, or care wrongly directed, leads to the degeneration of a domestic race; but excepting in the case of man himself, hardly any one is so ignorant as to allow his worst animals to breed.
That does look like he promotes eugenics. But that is, of course, completely out of context. Using a common argument device, he sets up the logical-sounding proposition of eugenics above, then proceeds to shoot it down in the next paragraph:
Nor could we check our sympathy, even at the urging of hard reason, without deterioration in the noblest part of our nature. The surgeon may harden himself whilst performing an operation, for he knows that he is acting for the good of his patient; but if we were intentionally to neglect the weak and helpless, it could only be for a contingent benefit, with an overwhelming present evil.
It helps to have read the whole book, rather than relying on out-of-context quotes by people who have a problem with the author.