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
Rwanda Nziza under the presidencies of Gregoire Kayibanda and Juvénal Habyarimana, were marked by continued cycles of violence, culminating in the 1990s with the launch of the Rwandan Civil War by exiled Tutsi led by Paul Kagame, the assassination of President Habyarimana, and the 1994 Rwandan Genocide, in which between 500,000 and 1,000,000 Tutsi and politically moderate Hutu were killed by Hutu extremists, on the orders of the interim government, in the space of just 100 days. The genocide was ended when Kagame's rebel army took control of the country in July 1994. A period of reconciliation began, as a unity government