Continued expansion of the desert forced the early ancestors of the Egyptians to settle around the Nile and adopt a more sedentary lifestyle during the Neolithic. The period from 9000 to 6000 BC has left very little archaeological evidence, but around 6000 BC, Neolithic settlements began to appear all over Egypt. Studies based on morphological, genetic, and archaeological data have attributed these settlements to migrants from the Fertile Crescent returning during the Neolithic Revolution, bringing agriculture to the region. However, other regions in Africa independently developed agriculture at about the same time: the Ethiopian highlands, the Sahel, and West Africa.