The mediocrity principle is the philosophical notion that "if an item is drawn at random from one of several sets or categories, it's more likely to come from the most numerous category than from any one of the less numerous categories". The principle has been taken to suggest that there is nothing very unusual about the evolution of the Solar System, Earth's history, the evolution of biological complexity, human evolution, or any one nation. It is a heuristic in the vein of the Copernican principle, and is sometimes used as a philosophical statement about the place of humanity. The idea is to assume mediocrity, rather than starting with the assumption that a phenomenon is special, privileged, exceptional, or even superior. David Bates ascribed the mediocrity principle to Sebastian von Hoerner, who as early as 1961 wrote the following: Extraterrestrial life The mediocrity principle suggests, given the existence of life on Earth, that should life exist elsewhere in the universe, it will typically exist on Earth-like planets. Measurement of distance to stars The mediocrity principle was implicitly applied during the 17th century, when astronomers attempted to measure the distance between distant stars and the Earth. By assuming that the Sun was just an average star, and that some stars seemed brighter simply because they were closer to us, they were able to estimate how far these stars were from the Earth. Although this method was flawed in view of the differences among stars, it gave astronomers at that time a rough idea of how far the stars were from the Earth. For example, James Gregory, Isaac Newton and Christiaan Huygens were able to estimate the distance between Sirius and the Earth through this method. Comparison with other approaches The mediocrity principle is in contrast with the anthropic principle, which asserts that the presence of an intelligent observer (humans) limits the circumstances to bounds under which intelligent life can be observed to exist, no matter how improbable. Both stand in contrast to the fine-tuning hypothesis, which asserts that the natural conditions for intelligent life are implausibly rare. The mediocrity principle implies that Earth-like environments are necessarily common, based in part on the evidence of any happening at all, whereas the anthropic principle suggests that no assertion can be made about the probability of intelligent life based on a sample set of one (self-described) example, who are necessarily capable of making such an