A scientific theory is not a hunch or mere speculation. Rather the term refers to a comprehensive explanation of some aspect of nature that is supported by many congruent lines of data. A further explanation from the NAS web site is helpful. Many scientific theories are so well-established that no new evidence is likely to alter them substantially. For example, no new evidence will demonstrate that the Earth does not orbit around the sun (heliocentric theory), or that living things... Read more