GENOMICS: A Little Gene Xeroxing Goes a Long Way

Researchers studying the evolution of starch digestion have uncovered evidence of a surprising adaptation: Rather than relying on mutations in a particular gene to help us digest roots and tubers better, the human genome simply made more copies of the gene in question. The finding is one of the strongest examples yet of evolution affecting gene copy number in humans and sheds light on how our diet split us apart from other primates.

An enzyme called salivary amylase--encoded by the AMY1 gene--helps humans digest starchy food. In a typical evolutionary scenario, natural selection would favor random mutations in AMY1 that caused it to churn out more of the enzyme or a more effective version of it in people who ate a high-starch diet.

But a study published online 9 September in Nature Genetics contends that something else happened. Nathaniel Dominy, an evolutionary anthropologist at the University of California, Santa Cruz, and George Perry at Arizona State University in Tempe analyzed AMY1 in high-starch eaters such as Americans of European descent, Japanese, and Hadza from Tanzania, hunter-gatherers who eat many roots and tubers, as well as groups that eat little starch, such as the Biaka of the Central African Republic and the Mbuti from Congo, both rainforest hunter-gatherers, and Tanzania's Datog and Siberia's Yakut pastoralists. In all, the researchers studied samples from more than 200 people.

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