High Quality Content by WIKIPEDIA articles! Evolutionary thought, the conception that species change over time, has roots in antiquity, in the ideas of the ancient Greeks, Romans, and Chinese as well as in medieval Islamic science. However, with the beginnings of biological taxonomy in the late 17th century, Western biological thinking was influenced by essentialism, the belief that every species has essential characteristics that are unalterable, a concept from medieval Aristotelian metaphysics that fit well with natural theology. On the other hand as the Enlightenment progressed evolutionary cosmology and the mechanical philosophy spread from the physical sciences to natural history. Naturalists began to focus on the variability of species; the emergence of paleontology with the concept of extinction further undermined the static view of nature. In the early 19th century, Jean-Baptiste Lamarck proposed his theory of the transmutation of species, the first fully formed theory of evolution.