The recognition and the accumulation of difficulties naturally involved modification of views. Indeed any really vital theory is bound to develop and modify itself with the vitality of the man who holds it. And Darwin was as vital as any man, and his theories as vital as any ever were. No man ever recognized more fully than he the desirability, the necessity of modification: ‘I look at it as absolutely certain that very much in the _Origin_ will be proved rubbish; but I expect and hope that the framework will stand.’[373] He groans over the burden and difficulty of perpetual correcting: ‘I am grieved to hear that you think I must work in the notes in the text; but you are so much better a judge that I will obey.’[374] Again: ‘It is only about two years since last edition of _Origin_, and I am disgusted to find how much I have to modify, and how much I ought to add.’[375] Nevertheless, as the successive editions of the ‘Origin’ and the other books show, he continued to add and to alter and to correct, to the very end. The minute, thoughtful, and far-reaching character of these alterations shows well in the concluding sentence of the eleventh chapter of the ‘Origin,’ which in the first edition read, ‘old forms having been supplanted by new and improved forms of life produced by the laws of variation still acting round us and preserved by natural selection,’ and later, ‘old forms having been supplanted by new and improved forms of life, the products of Variation and the Survival of the Fittest.’