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The peoples of the Lake Chad region who form the subject of this study are inhabitants of Bornu, today an administrative province of northeast Nigeria which includes the northern Cameroons, formerly one of the great empires of interior Africa. There were several reasons why this survey of abnormal haemoglobins was undertaken. It was an obvious consideration that nothing was known of their incidence in this area; indeed for the vast complicated ethnological patchwork that comprises the peoples of northern Nigeria there have been studied to date only general samples, predominantly Hausa. It should be regarded as a matter of urgency to ascertain gene frequencies in African peoples before their differences are completely obliterated with the breakdown of tribal patterns, and before the selection pressure differentials are readjusted with the arrival of modern medicine.
Another more cogent reason however lay in the historical information available for the area. Ancient tribal traditions are supplemented by the writings of early Muslim travellers and the written documents of the people themselves, and though many of the latter records were destroyed in the several invasions of Bornu, enough remain to enable the main outline of events over the last 1,200 years to be reconstructed. The story is of a succession of invasions and immigrations by peoples of different ethnic affinities, speaking different languages, possessing different customs, ways of life and outlook; the habitat into which they came is essentially uniform, a vast plain of scrub savana. It appeared of interest to enquire whether the demands of a uniform habitat had levelled out the genetic differences expected in peoples of such diverse orieins, and if not to examine the extent to which such differences had been retained.
