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
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