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A large set of measurements were taken on 512 women and 425 men belonging to ten populations of the Niger bend area, some of which live in the Sahelian, the other in the Sudanian climatic zones about 200 km apart. The two zones differ chiefly by a two-fold higher annual rainfall in the Sudanian zone. The pattern of differences in body weight, skinfold and limb circumferences suggests that the Sahelians allot proportionally more food and/or less physical work to women than the Sudanians . In one or both sexes, Sahelians have significantly longer lower limbs and forearms, larger hands and ears, a narrower face, and a higher and narrower nose. Sexual dimorphism of the shoulder-hip-width proportions is lower in the Sahelians , resulting from the Sahelian males, but not females, having wider hips, whereas Sahelians of both sexes have narrower shoulders. Multivariate analysis using D2 distances shows Sahelian and Sudanian populations forming two separate clusters, with the exception of the Dogon . In the male sex, nose width and sitting height account for the total multivariate interpopulational variation; nose width alone separates the two zonal groups, again with the Dogon as an exception. The position of the Dogon near to Sudanian populations while living in the Sahelian zone is explained by their migration from the Sudanian zone a few centuries ago. Adaptative genetic response to climate is proposed as a partial explanation of the evidence presented.