Plato was most definitely a eugenicist. And "modern" eugenics was practiced before Darwin. There were later popularizers, but they didn't invent the concept.
Greek warrior Spartan civilization. Weakling infants were left in the mountains to die.
The Republic, Book 5, Section 1. Plato recommended state-supervised selective breeding of children.
History of Australia. Before Darwin, England exiled criminals to purify the race.
That's fair. I hedged on Plato because he states that, while its pattern may exist in the stars, the Republic is not a place that can ever be realized on Earth. i don't think "The Laws", which, being for the real world, is much more restrained, includes similar ideas about eugenics.
The other examples you bring up-- and Aristotle could in some measure be added to it-- show what an exception and great man Hippocrates must have been to reject what was standard in his culture.
But it's no gratuitous dig at Darwin to say that Francis Galton (a brilliant man in his own right and the father of modern statistics) wa sthe father of modern eugenics and was inspired by Darwin, especially the Descent of Man, who had been inspired by Malthus.
My point is noty to hust hop up and down on Darwin. I think the relationship between the theory of natural selection and eugenics is one that should be investigated, just as the conservative consequences of the theory we all like that Freeper Arnhart writes about in his book, Darwinian Conservatism, should be investigated (speaking of which, there's a generally positive review of his book in the normally anti-Darwinism Weekly Standard by James Seaton, who I think is an awesome literary critic, here http://www.weeklystandard.com/Utilities/printer_preview.asp?idArticle=12157&R=EC5A29952 )
The reason why I say that is that some would say professor Arnhart is wrong in his interpretation of Darwin, and Galton was right, and I'm interested in which is correct.