This is not a practice compatible with any strict interpretation of Islam. One of the most fundamantal doctrines of Islam is that all believers are equal (and superior to all unbelievers). The very idea that one tribe is "higher" than another is flatly incompatible with Islam.
As others have pointed out, in some parts of the Muslim world, pre-Muslim beliefs such as caste still have a strong hold. There are some "Christian" tribes in parts of Africa with some pretty weird holdovers, too. Doesn't say anything at all about Christianity as such.
On the thread that I began, I went to Yahoo and did a search on the Muslims. The references that I cited occurred in different countries, but the acts were done by Muslims. These practices are not isolated.