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 president, followed by a command to kill Tutsi. The Hutu population, which had been prepared and armed during the preceding months, and maintained the Rwandan tradition of obedience to authority, carried out the orders without question. In Kigali, the genocide was led by the Presidential Guard, the elite unit of the army. They were assisted by the Interahamwe and Impuzamugambi, who set up road blocks throughout the capital; each person passing the road block was required to show the national identity card, which included ethnicity, and any with Tutsi cards were slaughtered immediately. The militias also initiated searches of houses