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
Origins of Hutu, Tutsi and Twa the importance of the pastoralist migrations. Still other studies point out that cultural transmission can occur without actual human migration. This raises the question of how much of the changes around the fifteenth and sixteenth centuries was the result of an influx of people as opposed to the existing population being exposed to new ideas. Studies that approach the subject of racial purity are among the most controversial. These studies point out that the pastoralist migrants and pre-migration Rwandans lived side by side for centuries and practiced extensive intermarriage. The notion that current Rwandans can claim exclusively Tutsi or Hutu