Bernard Lewis has also cited historians and geographers of the Middle East and North Africa region, including Al-Muqaddasi, Al-Jahiz, Al-Masudi, Abu Rayhan Biruni, Nasir al-Din al-Tusi, and Ibn Qutaybah. Though the Qur'an expresses no racial prejudice, Lewis argues that ethnocentric prejudice later developed among Arabs, for a variety of reasons: their extensive conquests and slave trade; the influence of Aristotelian ideas regarding slavery, which some Muslim philosophers directed towards Zanj (Bantu) and Turkic peoples; and the influence of Judeo-Christian ideas regarding divisions among humankind. The Afro-Arab author Al-Jahiz, himself having a Zanj grandfather, wrote a book entitled "Superiority of the Blacks to the Whites", and explained why the Zanj were black in terms of environmental determinism in the "On the Zanj" chapter of "The Essays". By the 14th century, a significant number of slaves came from sub-Saharan Africa; Lewis argues that this led to the likes of Egyptian historian Al-Abshibi (1388–1446) writing that "is said that when the [black slave is sated, he fornicates, when he is hungry, he steals." According to Lewis, the 14th-century Tunisian scholar Ibn Khaldun also wrote: