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.
El que va passar és que l'amant d'Aveling era la filla de Marx. I quan els dos, Darwin i Marx, van morir, els documents de Darwin i els d'Aveling es van barrejar i una carta de Darwin que deia: «Estimat senyor: Moltes gràcies, però no vull que em dediqui el seu llibre», va ser erròniament interpretada com a dirigida a Marx originant tot aquest mite del que probablement hagin sentit a parlar abans.