In the meantime - and because it sounded unbelievable that the clan members don't have difficulties to change the clan, and that their is no opression among clan members of different clans - we googled a bit and found out what the professor didn´t know:
"The Somali untouchables"
http://www.africamasterweb.com/AdSense/SomaliUntouchables.html
an Artikel of Bashir Goth
If you think that Dalits (untouchables) exist only in India think again. We have them in Somalia. But what makes the situation of ours even worse is that unlike India where people belong to different races, languages and colours; Somalia is the most homogenous country in Africa with people belonging to a single race and sharing a common language, a common religion and a common skin complexion.
To find a dehumanised group of people in a third world country may look normal, despite its gravity, but the real tragedy is when international human rights organisations ignore the plight of such people.
One such blunder that went unnoticed appeared in the March 2007 report of the Minority Rights Group International (MRG), which placed Somalia above Iraq as the world’s most dangerous country for minority groups. For anyone familiar with Somalia, this assessment will conjure up images of clans who suffered for centuries from sub-human treatment. We Somalis know them; UN organisations on the ground know them and anyone with Internet access will have no difficulty to find them.