Origins of Hutu, Tutsi and Twa of neighboring people, it was almost non-existent among Rwandan Tutsi. Presence of the sickle cell trait is evidence of survival in the presence of malaria over many centuries, suggesting differing origins. Regional studies of the ability to digest lactose are also supportive. The ability to digest lactose among adults is widespread only among desert-dwelling nomadic groups that have depended upon milk for millennia. Three quarters of the adult Tutsi of Rwanda and Burundi have a high ability to digest lactose, while only 5% of the adults of the neighboring Shi people of eastern Congo can. Among Hutu, one in three
Ethnic groups in Burundi declared a presidential republic; however peace did not ensue as a result. Even after 1966, the subsequent dictatorial regimes of Michel Micombero (1966–76), Jean-Baptiste Bagaza (1976–87), and Pierre Buyoya (1987–93) were dominated by Tutsi elites which often consciously marginalized and discriminated against the Hutu majority. The first Hutu to become head of state was Melchior Ndadaye in 1993, although he was assassinated shortly after taking power. Ethnic violence peaked in 1972 when 100,000 people, mainly Hutu, were killed by the Tutsi regime in the Burundian Genocide. Twa have also been targeted, specifically in violence directed against the Tutsi with whom