Lactase Deficiency: A Probable Ethnological Marker in East Africa

Abstract

Some writers of east African anthropology have been concerned with the problem of whether the Hima of Ankole and the Tutsi of Rwanda and Burundi, and the Iru and Hutu of the same kingdoms have different ethnic origins. It is widely held that the Hima and the Tutsi have a Hamitic ancestry (Thomas & Scott I949; Ingrams I960) whereas the Iru and Hutu are of a Bantu origin. Hiernaux (I966) has speculated that on the basis of morphology and climate, the Tutsi physique originated in a hot, dry area; he also considers (Hiernaux I966; I968) that there is a low rate of marriage between the Tutsi and the Hutu. On the basis of anthropometric data, ABO and MN blood groups and sickle cell trait, the Tutsi seem to constitute a separate group from the mass of other local sub-groups. Hiernaux (I966) has stressed the favourability of the Rwanda region of Africa for the study of this type of problem; its inhabitants display an extreme degree of intergroup diversity, it is a contact area ecologically between the equatorial forest and the eastern savannah, and it receives influences from the north along the Nile and from the south along the Great Lakes rift. Posnansky (I966) has reviewed the evidence for the distinction between the two subdivisions in Ankole, and considers that there are no clear-cut physical, anthropological or biochemical data to separate the Hima from the Iru; their physical appearances could be due to nutritional and social factors acting through natural selection. Such a situation would also apply to the groups in Rwanda and Burundi. Recent studies in Kampala suggest that two distinct ethnic groups can be delineated by the presence or absence of an intestinal enzyme-lactase-which is necessary for the digestion of the milk sugar lactose. The Hamitic tribes (the Hima and the Tutsi) possess the enzyme, as do most European and north American populations, but the Bantu tribes (including the Ganda, Iru and Hutu) are largely lactase-deficient (Cook & Kajubi I966; Cook I967; Cook et al. I967; Cook & Dahlqvist I968). Ideally, the level of the enzyme-lactase-in the cells of the jejunum is measured for the diagnosis to be established. As lactase hydrolyses lactose into glucose and galactose, oral tolerance tests which involve giving lactose (5o g. to the adult) and measuring the blood-glucose response are also of value in diagnosing this condition, and are easier to perform. In the initial study in east Africa (Cook & Kajubi I966), the following adults were tested for lactasedeficiency: twenty normal volunteers and ninety-five patients from a number of local tribes. They all had tolerance tests, and enzyme estimations were done in forty of the patients. An incidence of lactase-deficiency of approximately go per cent. was found in the Bantu subjects, but of the Hamites, ten of twelve Tutsi and ten of eleven Hima patients had normal enzyme levels. The Hutu and Iru patients