In 1969, Lethbridge published "The Monkey's Tail", in which he discussed Darwinian evolution. Although agreeing that the evolution of species was an objective fact, he nevertheless argued that there was a blueprint for existence and that genetic memory was a reality. In a sequel published in 1969, "The Legend of the Sons of God – A Fantasy?", Lethbridge argued that extraterrestrials had been responsible for aiding Earth's evolutionary development. Echoing many of the claims made by Erich von Däniken in "Chariots of the Gods" (1968), Lethbridge argued that the late prehistoric stone circles of the British Isles had been beacons for extraterrestrial spacecraft. In this, his work has been cited as an anticipation of the Earth mysteries movement that expanded across Britain in the following decade.