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
Origins of Hutu, Tutsi and Twa area may have assimilated some South Cushitic pastoralists. In general, the Tutsi appear to share a close genetic kinship with neighboring Bantu populations, particularly the Hutu. However, it is unclear whether this similarity is primarily due to extensive genetic exchanges between these communities through intermarriage or whether it ultimately stems from common origins: [...]generations of gene flow obliterated whatever clear-cut physical distinctions may have once existed between these two Bantu peoples – renowned to be height, body build, and facial features. With a spectrum of physical variation in the peoples, Belgian authorities legally mandated ethnic affiliation in the 1920s, based