This passage gave Mr. Darwin no less trouble than it must have given to many of his readers.  In the original edition of the “Origin of Species” it stood, “Further, we must suppose that there is a power always intently watching each slight accidental variation.”  I suppose it was felt that if this was allowed to stand, it might be fairly asked what natural selection was doing all this time?  If the power was able to do everything that was necessary now, why not always? and why any natural selection at all?  This clearly would not do, so in 1861 the power was allowed, by the help of brackets, actually to become natural selection, and remained so till 1869, when Mr. Darwin could stand it no longer, and, doubtless for the reason given above, altered the passage to “a power represented by natural selection,” at the same time cutting out the word “accidental.”

It may perhaps make the workings of Mr. Darwin’s mind clearer to the reader if I give the various readings of this passage as taken from the three most important editions of the “Origin of Species.”

In 1859 it stood, “Further, we must suppose that there is a power always intently watching each slight accidental alteration,” &c.

In 1861 it stood, “Further, we must suppose that there is a power (natural selection) always intently watching each slight accidental alteration,” &c.

And in 1869, “Further, we must suppose that there is a power represented by natural selection or the survival of the fittest always intently watching each slight alteration,” &c. {94a}

The hesitating feeble gait of one who fears a pitfall at every step, so easily recognisable in the “numerous, successive, slight alterations” in the foregoing passage, may be traced in many another page of the “Origin of Species” by those who will be at the trouble of comparing the several editions.  It is only when this is done, and the working of Mr. Darwin’s mind can be seen as though it were the twitchings of a dog’s nose, that any idea can be formed of the difficulty in which he found himself involved by his initial blunder of thinking he had got a distinctive feature which entitled him to claim the theory of evolution as an original idea of his own.  He found his natural selection hang round his neck like a millstone.  There is hardly a page in the “Origin of Species” in which traces of the struggle going on in Mr. Darwin’s mind are not discernible, with a result alike exasperating and pitiable.  I can only repeat what I said in “Evolution Old and New,” namely, that I find the task of extracting a well-defined meaning out of Mr. Darwin’s words comparable only to that of trying to act on the advice of a lawyer who has obscured the main issue as much as he can, and whose chief aim has been to leave as many loopholes as possible for himself to escape by, if things should go wrong hereafter.  Or, again, to that of one who has to construe an Act of Parliament which was originally drawn with a view to throwing as much dust as possible in the eyes of those who would oppose the measure, and which, having been found utterly unworkable in practice, has had clauses repealed up and down it till it is now in an inextricable tangle of confusion and contradiction.