Historians have divided the Arab communities into three categories, according to the birth pattern of human generations.
1.Back up
These are those ruined ancient communities who have become absolutely clear from the world. There is no reliable information available about them. These are 'Aad, Thamud, Tasam, Zadis, Amalika etc. They have been lost in history in such a way that there is no other sign of emergence after their fall.
2.Arab 'Ariba'
These are those tribes - who are descendants of Yarub bin Yashajub bin Qahtan. These are called kahtani arabi.