This proposition, which, in my opinion, is destined to do for history what Darwin’s theory has done for biology, we, both of us, had been gradually approaching for some years before 1845. How far I had independently progressed toward it, is best shown by my Condition of the Working Class in England . 2 But when I again met Marx at Brussels in the spring of 1845, he had it ready worked out, and put it before me, in terms almost as clear as those in which I have stated it here.

From our joint preface to the German edition of 1872, I quote the following: