Evolution, including speculative evolution, has been an important theme in fiction since the late 19th century. It began, however, before Charles Darwin's time, and reflects progressionist and Lamarckist views (as in Camille Flammarion's 1887 Lumen) as well as Darwin's. Darwinian evolution is pervasive in literature, whether taken optimistically in terms of how humanity may evolve towards perfection, or pessimistically in terms of the dire consequences of the interaction of human nature and the struggle for survival.[4][5][6] Other themes include the replacement of humanity, either by other species or by intelligent machines.[5]