Long before Charles Darwin, other people made important contributions to the historical development of the theory of evolution. It all began in the 5th century BC, when early Greek philosophers defined the origin of the natural world as the power of nature rather than supernatural force. They proposed the theory of evolution to explain the basis of the natural world. Therefore, evolutionary theory began with the Ionian philosopher Anaximander (611-546 BC) who proposed that living things gradually developed from water and that humans came from animals. He proposed that the world arose from an undifferentiated and indeterminate substance. In the 6th century BC, Xenophanes (570475 BC) developed Anaximander's theories using fossils as evidence for the theory that the Earth originated from water. In the 5th century Empedocles postulated that the universe was composed of the elements: earth, air, fire and water. Darwin pays homage to Empedocles for his theory of natural selection; Empedocles advocated reproductive fitness and survival of the fittest. In Roman times, the poet and philosopher Lucretius (99-55 BC) followed in the footsteps of Empedocles, proposing a similar evolutionary theory in which species arose from the Earth formed by the combination of the elements with natural selection and the survival of the fittest. Plato (428-348 BC) and Aristotle (384-322 BC) were the two most influential philosophers of Western thought. Plato introduced the concept of eidos, the immutable ideal forms of all phenomena in the world, stating that variations were imperfect manifestations of the ideal, divinely inspired form. Therefore, Plato excluded evolutionary thinking. Aristotle questioned Plato's philosophy - stating that the gradation in the natural... at the center of the paper... is evidence of divine design. Although naturalistic models of origins have existed for many centuries, only since the work of Charles Darwin (1809-1882) has biological evolution propagated in society due to the Christian worldview of his time. The critical break with the concept of fixed species began with Darwin's theory of evolution by natural selection. Influenced by Thomas Malthus, Darwin hypothesized that population growth would lead to a “struggle for existence” in which favorable variations would prevail while others would die. In each generation, many descendants fail to survive to the age of reproduction due to limited resources, which explains the diversity of organisms from a common ancestry through the workings of natural laws. In late 1859, Darwin's publication of On the Origin of Species led to widespread acceptance of Darwinian evolution.