Dobon et al. (2015) found that modern Nubians are genetically closer to their Cushitic and Ethio-Semitic (Afro-Asiatic) neighbors (such as the Beja, Sudanese Arabs, Ethiopians and Somalis) than to other Nilo-Saharan speakers. The study showed that populations from their "North-East cluster", which include Nubians, may be explained as a mixture of an ancestral North African population (similar to Copts) and an ancestral South-West population. Also, according to the authors, "Nubians were influenced by Arabs as a direct result of the penetration of large numbers of Arabs into the Nile Valley over long periods of time following the arrival of Islam around 651 A.D."