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
Rwandan genocide between Hutu, Tutsi, and Twa. The systematic destruction of the judicial system during the genocide and civil war was a major problem. After the genocide, over one million people were potentially culpable for a role in the genocide, nearly one-fifth of the population remaining after the summer of 1994. After the genocide, the RPF pursued a policy of mass arrests for the genocide, jailing over 100,000 in the two years after the genocide. The pace of arrests overwhelmed the physical capacity of the Rwandan prison system, leading to what Amnesty International deemed "cruel, inhuman, or degrading treatment". The country's nineteen