Naturally the most common matter of observation, the one which is more or less forced upon the attention of all of us, is humanity. We may be indifferent to trees and stones, but our pleasure, our labor, our existence depend upon a more or less constant study of the human beings whose existence interlocks at every point with ours. Therefore, from the earliest times of record there have been profound observers of humanity, persons who have examined the human aspect and the human heart, as read through that aspect, with the most persistent zeal and the most unwearying delight. In the vivid phrase of one of the most acute of these, ‘I glutted myself with observation.’ And even those of less gormandizing tendency find the analysis of the human subject one of the most inexhaustible pleasures that this world affords. All through the study of Darwin I shall have occasion to refer to one of Darwin’s contemporaries who in a different line of research was an equally brilliant and significant exemplification of the scientific spirit, Sainte-Beuve. As Darwin devoted years upon years to patient investigation of the secrets of the natural world, so Sainte-Beuve with the same patience, the same labor, the same infinite and ever-varied curiosity, probed human hearts, all sorts of human hearts, and portrayed them with unfailing accuracy and sympathy. He said of himself, using the strictly scientific expression: ‘I analyze, I herborize, I am a naturalist of souls.’[4] But in dealing with Darwin we are in the main concerned with the field of so-called natural science, with the varying aspects of the material world, which we are apt to sum up under the term, nature. General observation of this world is, of course, also as old as man. Greek, Hebrew, Egyptian, all ancient records, contain scientific facts of importance and interest to-day. Sophocles and Vergil had an exquisite sense of the exact beauty of birds and flowers. The vision of Chaucer and Shakespeare was as acute as that of Gautier, so far as they chose to employ it. At the same time we must recognize that with the middle of the eighteenth century a new interest in nature arose. The literature of Rousseau and Cowper, of Keats and George Sand, reflected the external world in a far different fashion from anything before imagined, and Linnæus, Cuvier, and many others laid the foundations of modern scientific study, which the nineteenth century developed until it overshadowed every branch of learning both for theoretical abundance and for practical utility.