In 2015 Poznik and Underhill have claimed haplogroup E, arose outside Africa, arguing that, "This model of geographical segregation within the CT clade requires just one continental haplogroup exchange (E to Africa), rather than three (D, C, and F out of Africa). The timing of this putative return to Africa, between the emergence of haplogroup E and its differentiation within Africa by 58 kya, is consistent with proposals, based on non–Y chromosome data, of abundant gene flow between Africa and Arabia 50–80 kya."