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Advantage: Starch

New genetic evidence supports the controversial notion that the lowly tuber propelled humans to the top of the evolutionary heap.

Human saliva is rich in amylase, an enzyme that breaks starch into glucose before it's swallowed. People carry more copies of the amylase gene than their ape relatives do and in turn make more of the enzyme, according to a report in the October Nature Genetics.

Nathaniel Dominy, an anthropologist at the University of California, Santa Cruz who coauthored the report, says that the findings add to other evidence that starch from tubers, corms, and bulbs provided crucial calories in the early human diet.

The study found that people carry up to 15 copies of the amylase gene. Chimpanzees, whose diets contain little starch, carry just two copies.

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