 In many respects, the general idea of the possibility of species change is an old concept. The reflections of Empedocles (ca. 495–35 BCE) and the views of the Greek Atomists among the Presocratic nature philosophers formed a Classical heritage on which later speculations could be developed. These Presocratic speculations combined naturalistic myths of origins with reflections on the workings of chance-like processes to create a naturalistic account of the origins of existing forms of life (see the entry  ancient atomism).  Particularly as the Presocratic Atomist speculations were restated by the Roman poet Titus Lucretius (ca. 99–50 BCE) in book five of his On the Nature of Things (Lucretius [RN]), a source was available in Antiquity that set out a speculative account of the gradual origin of living beings from an initial atomic chaos through an undirected process that sorts out the best adapted forms and eliminates those not suited to their conditions.