One of the first serious modern scientific explanations of the Moon's origin was put forward by the aformentioned George Darwin, son of the celebrated Charles Darwin. George followed in the footsteps of his father by developing an evolutionary theory of the Moon, more commonly called the 'fission theory'.

Beginning in 1878, Darwin argued that the Moon could have split off from proto-Earth when it was still a liquid body, flung off by Earth's rapid rotation and the action of the Sun's tides, after which it gradually moved outward over the aeons to its present position. Darwin's theory, which he arrived at by applying accepted physical principles about the action of the tides, was the first scientific speculation about the origin of the Moon that treated it as a unique event, rather than a commonplace part of the ongoing process of the formation of celestial bodies within the Solar System.