This page is for myths involving politics or the application of politics by third parties involving Darwin.
Marx sent a personally inscribed copy of the second edition of Das Kapital to Darwin and wanted to dedicate it to him, but Darwin wrote a letter back declining.
Darwin wrote a letter declining the dedication of an unnamed book on atheism, but the letter was not to Marx, but rather to Edward Aveling. Aveling's common-law wife was Elanor Marx, daughter of Karl Marx. Darwin did, however, own a copy of Das Kapital, but the pages were unseparated showing he had never read it.
Charles Darwin inspired the Holocaust and is thus directly responsible.
There's no evidence to suggest that Darwin promoted anti-Semitism or genocide, in fact he didn't. Even if it was proven that Charles Darwin advocated it and it inspired Adolf Hitler or Adolf Eichmann, there's no reason why he'd bear the personal responsibility. I've only seen this myth promoted by young-Earth creationists who wish to make Darwin look bad - sort of like how they blame Islam and Mohammad for September 11th, and not the people that carried out the acts.
The book The Next Million Years was written by Darwin's grandson Charles Galton Darwin, and he was inspired to write this book by Thomas Malthus' work who advocated killing the poor.
Thomas Malthus did inspire him to write the book, which advocated selective breeding, and other controls. Charles Galton believed overpopulation would displace agricultural production and there would be a collapse in society. Malthus did advocate killing the poor, but there's no real evidence that Charles Galton's solutions to overpopulation were inspired by Malthus' own solutions. Even if it did, who cares? They were both eugenicists and they're both dead; good riddance. There's no evidence to say any of Charles Galton Darwin's children are (in some cases were) eugenicists, it was a philosophy that he developed in his later years, after retirement.