In one sense, indeed, it may be said that, given Malthus on the one hand and the Lamarckian evolutionism on the other, some great man somewhere must sooner or later, almost of necessity, have combined the two, and hit out the doctrine of natural selection as we actually know it. Quite so; but then the point is just this: Darwin _was_ the great man in question; he _did_ the work which in the very essence of things some such great man was naturally and inevitably predestined to do. You can always easily manage to get on without any particular great man, provided, of course, you have ready to hand another equally able great man by whom to replace him in the scheme of existence. But how many ordinary naturalists possess the width of mind and universality of interest which would prompt them to read, mark, learn, and inwardly digest a politico-economical treatise of the calibre of Malthus? How many, having done so, have the keenness of vision to perceive the ensuing biological implications? How many, having seen them, have the skill and the patience to work up the infinite chaos of botanical and zoological detail into the far-reaching generalisations of the 'Origin of Species'? Merely to have caught at the grand idea is in itself no small achievement; others did so and deserve all honour for their insight; but to flesh it out with all the minute care and conclusive force of Darwin's masterpiece is a thousand times a greater and nobler monument of human endeavour. During the fifteen years from 1844 to 1859, however, Darwin's pen was by no means idle. In the first-named year he published his 'Geological Observations on Volcanic Islands'--part of the 'Beagle' exploration series; in 1846 he followed this up by his 'Geological Observations on South America;' in 1851 he gave to the world his monograph on 'Recent Barnacles;' and in 1853, his treatise on the fossil species of the same family. But all these works of restricted interest remained always subsidiary to the one great central task of his entire lifetime, the preparation of his projected volume on the Origin of Species.