What happened was that Aveling's mistress was Marx's daughter, and when both Darwin and Marx were dead, Marx's papers became muddled up with Aveling's papers, and a letter from Darwin saying, "My dear sir, thank you very much but I don't want you to dedicate your book to me," was mistakenly supposed to be addressed to Marx, and that gave rise to this whole myth, which you've probably heard.
真相はどうかと言えば 当時エイヴリングの愛人はマルクスの娘であり ダーウィンとマルクスの死後 マルクスの論文はエイヴリングの論文と ごちゃ混ぜにされてしまい 「拝啓 大変感謝いたしますが あなたの本を 私に捧げて欲しいとは思いません」 というダーウィンの手紙が マルクスに宛てられたものだと勘違いされてしまい これが皆さんがご存じであろう この俗説の引き金となったのです