It seems to me that if Darwin considered himself the intellectual father of Marxism, he would not have refused when Marx asked him to write the intro to Das Kapital.
This is just to let you know, it didn't happen.
Assertion 6.13: Karl Marx dedicated Das Kapital to Darwin.
(i) This is false. No edition of Das Kapital contains a dedication to Darwin.
(ii) It has been widely believed on the basis of a letter from Darwin found among Marx's papers that Marx had offered to dedicate Das Kapital to Darwin (and Darwin refused), but thanks to some amazing detective work by Margaret Fay, this is now known also to be false: the letter in question, declining to an unnamed person the honor of a dedication in an unnamed book, turns out not to have been to Marx at all, but to another author who later became Marx's son-in-law and apparently filed the letter with Marx's papers after Marx died. The whole story is reported very clearly and concisely by Richard Carter.
(iii) It is true that Marx sent Darwin a copy of Das Kapital with a personal inscription, but it is unclear what it is supposed to prove, even if we assume the very worst about Marx. Consider terrorists who have murdered in the name of God, and the inquisitors and witch-hunters who burned people at the stake for the glory of Christ. Do their "dedications" make God responsible for terrorism, or Jesus responsible for the Holy Inquisition or the witch hunts? Does the fact that the murderers in question took Islam or Christianity to be the justification for their acts somehow demonstrate that the religions or their founders are themselves the foundation of evil? No more does Marx's dedication to Darwin, or his abuse of evolutionary theory, constitute an indictment of evolution or of Darwin himself, even if we choose to hold Marx responsible for the Communists who abused his theories.
(iv) Finally, it is worth noting that Darwin himself never so much as cut the pages of the copy of Das Kapital sent to him by Marx, which means he could never have read it.