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.
O que aconteceu foi que  a amante de Aveling era filha de Marx e depois de Darwin e Marx terem morrido, os artigos do Marx misturaram-se  com os de Aveling e uma carta de Darwin que dizia, "Caro senhor, muito obrigado,  mas não quero que me dedique o seu livro", foi incorrectamente suposto  que seria endereçada a Marx. Isso fez surgir este mito, de que devem ter ouvido falar.