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
History of Rwanda dominated by the majority Hutu under President Grégoire Kayibanda. Unsettled ethnic and political tensions were worsened when Juvénal Habyarimana, who was also Hutu, seized power in 1973. In 1990, the Rwandan Patriotic Front (RPF), a rebel group composed of 10,000 Tutsi refugees from previous decades of unrest, invaded the country, starting the Rwandan Civil War. The war ground on, worsening ethnic tensions, as the Hutu feared losing their gains. The assassination of Habyarimana was the catalyst for the eruption of the 1994 genocide, in which hundreds of thousands of Tutsis and some moderate Hutus were killed. The Tutsi RPF conquered