Origins of Hutu, Tutsi and Twa adults has a high capacity for lactose digestion, a surprisingly high number for an agrarian people, which Mamdani suggests may be the result of centuries of intermarriage with Tutsi. Bethwell Ogot in the 1988 UNESCO "General History" further notes that the number of pastoralists in Rwanda increased sharply around the fifteenth century. Although Luis et al. (2004) in a more general study on bi-allelic markers in many African countries found a statistically significant genetic difference between Tutsi and Hutu, the overall difference were not large. Modern-day genetic studies of the Y-chromosome generally indicate that the Tutsi, like the Hutu, are
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