If you're relying on an Arab sheik to fill in the blanks of your family history, make sure he cites his sources.
"They will tell you these enormously fanciful genealogical stories that trace everyone back to one guy who was the ancestor of them all," said retired Col. Patrick Lang, formerly the Defense Intelligence Agency's regional director for the Middle East. "Sometimes they just invent these things. Sometimes families get associated with a tribe and convince themselves that they, too, are descended from this original ancestor."
A tribe is formally defined as a "segmentary lineage," a kinship network organized by branching lines of descent from a common ancestor, with the most-direct male-line descendants holding the greatest prestige. But anthropologists are quick to note that such kinships are often hazy or even fictitious, projected onto the past to justify practical arrangements in the present. [Link]