One other item of immense importance in the genesis of the full Darwinian doctrine deserves mention here--I mean, the exact moment of time occupied by Charles Darwin in the continuous history of scientific thought. A generation or two earlier, in Erasmus Darwin's days, biology had not yet arrived at the true classification of animals and plants upon an essentially hereditary basis. The Linnæan arrangement, then universally accepted, was wholly artificial in its main features; it distributed species without regard to their fundamental likenesses of structure and organisation. But the natural system of Jussieu and De Candolle, by arranging plants into truly related groups, made possible the proofs of an order of affiliation in the vegetable kingdom; while Cuvier's similar reconstruction of the animal world gave a like foothold to the evolutionary philosopher in the other great department of organic nature. The recognition of kinship between the various members of the same family necessarily preceded the establishment of a regular genealogical theory of life in its entirety. Though we are here concerned mainly with Charles Darwin the thinker and writer--not with Charles Darwin the husband and father--a few words of explanation as to his private life must necessarily be added at the present point, before we pass on to consider the long, slow, and cautious brewing of that wonderful work, the 'Origin of Species,' Darwin returned home from the voyage of the 'Beagle' at the end of the year 1836. Soon after, he was elected a Fellow of the Royal Society, no doubt through the influence of his friend Lyell, who was quite enthusiastic over his splendid geological investigations on the rate of elevation in the Pampas and the Cordillera. Acting on Lyell's advice, too, he determined to seek no official appointment, but to devote himself entirely for the rest of his life to the pursuit of science. In 1838, at the age of twenty-nine, he read before the Geological Society his paper on the 'Connection of Volcanic Phenomena with the Elevation of Mountain Chains,' when, says Lyell admiringly in a private letter, 'he opened upon De la Beche, Phillips, and others'--the veterans of the science--'his whole battery of the earthquakes and volcanoes of the Andes.' Shortly after, the audacious young man was appointed secretary to the Geological Society, a post which he filled when the voyage of the 'Beagle' was first published in 1839.