The vast majority of the Muslims in India belong to South Asian ethnic groups. However, some Indian Muslims were found with detectable, traceable, minor to some levels of gene flow from outside, primarily from the Middle East and Central Asia.[30][2][32] However, they are found in very low levels.[32] Sources indicate that the castes among Muslims developed as the result of the concept of Kafa'a.[33][34][35] Those who are referred to as Ashrafs (see also Sharif) are presumed to have a superior status derived from their foreign Arab ancestry,[36][37] while the Ajlafs are assumed to be converts from Hinduism, and have a lower status.