Aesthetic modes and categories of perception and judgement were crucial to the development of Charles Darwin’s “theory of descent with modification through natural selection.” Indeed, Darwin understood the aesthetic as fundamentally constitutive of the natural historian’s method. In the closing retrospect of the journal of his circumnavigation as ship’s naturalist on HMS Beagle (1836), Darwin assesses his experience in aesthetic terms—of pleasure and pain, wonder and horror, the picturesque and sublime—rather than in terms of acquired scientific knowledge. Darwin’s account of the voyage makes aesthetic discrimination the main technique of natural-historical observation: it affords cognition of the natural world as a complex interplay of formal differences constituting a dynamic totality, a living system. A key aesthetic category, the sublime, articulates the awful discrepancy between human and natural scales of history, event, and meaning. Darwin makes a strategic appeal to the aesthetic to justify his new vision of nature to the Victorian public, overriding its scandalous ethical and political implications, in On the Origin of Species (1859): “There is grandeur in this view of life . . . from so simple a beginning endless forms most beautiful and most wonderful have been, and are being, evolved.” As well as the exposition of an argument, the Origin is a treatise on method. Darwin trains his readers to appreciate the evaluative scrutiny of formal difference that characterizes the operation of natural selection itself. The opening chapter, on artificial selection, proposes the domestic animal breeder as a “connoisseur,” expert in assessing minute morphological variations without concern for an ultimate end—that is, the improvement of the race. The figure is an analogue for natural selection, the motive principle of which is the fine but decisive discrimination (for life or death) of individual differences. The “powers of discrimination and taste” determine human evolution—constituting its medium, the semi-autonomous domain of culture—according to Darwin’s next synthetic statement of his theory. The Descent of Man (1871) proposes the supplementary agency of sexual selection as the main motor of human cultural development. Its productive principle is, once again, the evaluation of fine formal differences (“there is in the mind of man a strong love for slight changes in all things”), trained, however, upon pleasurable appearance rather than function or use. Sexual selection generates “the differences in external appearance between the races of man,” as well as between the sexes, explicitly on grounds of aesthetic preference: Darwin conflates skin color, body hair, and other physiological features with artificial ornaments in a rhapsodic vision of the infinite variety of human standards of beauty. Sexual selection claims a field of formal superfluity or redundancy, neutral with respect to the pressures of natural selection, in which the aesthetic comes into play, originated by the erotic drive but not functionally bound by it. Darwin decisively relocates aesthetic judgement—and the play of form—upon a principle of etiologically generated, infinite formal differentiation: emancipating it from the strongly normative teleological account that Victorian culture took over from German Idealism.