If intra-clan marriage was the cause of all these ailments, Arab nations would be at the top of the list. They all marry their first cousins from their fathers side, talk about genetically warped people.
I know of no Somali married to their cousins -- first, second or third. If you are from the north, marry a girl from the south, and vice versa. We will also eliminate clannism with this approach.
Afars

though they hate us. Oromo, only the Afaan Qaalo, rest look like their Amhara bantu cousins.