Contact: Katherine Unger Baillie
University of Pennsylvania
Caption: Penn's Sarah Tishkoff administers a lactose tolerance test to a group of Maasai people in Tanzania. The test measures the ability to digest milk -- a trait that Tishkoff and other researchers link with the practice of pastoralism.
Credit: University of Pennsylvania
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Related news release: Penn team links Africans' ability to digest milk to spread of cattle raising