years ago with the immigration of modern humans (Cro-Magnons). Neanderthals were characterised as a unique species of underdeveloped human, in particular by Marcellin Boule. By the mid-twentieth century, it was believed that human evolution progressed from an ape-like ancestor through a "Neanderthal phase" to modern humans. This gave way to the "Out of Africa" theory in the 1970s. With the sequencing of Neanderthal genetics first in 2010, it was discovered that Neanderthals interbred with modern humans.