Trade-offs and human adaptation at the extremes.

Despite being genetically homogeneous compared with other animals, humans are geographically diverse and have evolved to meet the demands of local environments, pathogens, and diets (1). In 1962, James Neel proposed that genes that predispose people to metabolic diseases may have been advantageous in the evolutionary past (2). Yet empirical support for his hypothesis remains limited. On page 1246 of this issue, Lea et al. (3) report genomic analyses of samples from the Turkana people in northwest Kenya that reveal a more nuanced narrative. The Turkana have practiced nomadic pastoralism (raising and herding of livestock) in extreme arid environments for ~5000 to 8000 years. The authors analyzed 367 genomes and discovered adaptations to ecological pressures, particularly chronic water scarcity. They identified physiological compromises in kidney function that improved water retention but mildly increased the amounts of urea in the blood. This context-specific trade-off may become pathological as Turkana populations urbanize. [ABSTRACT FROM AUTHOR]