Humans Have Multiple Copies of AMY1, a Salivary Enzyme

Nate Dominy was hired into the anthropology department of my undergraduate university during my last year there, and while I was ecstatic that my department finally picked up a physical anthropologist that was into genetics and ecology, I was bummed that I wouldn’t have any classes with him… unless of course I purposefully flunked, dropped or postponed my graduation, which was not an option. His research seemed to always interest me, and the latest one to come out from his lab, “Diet and the evolution of human amylase gene copy number variation,” is no exception.Razib clued me into this new paper, published in Nature Genetics, and it seems like the web is just beginning to build some major buzz about this. Why? Because, it is one of the few papers that I know about which tie the mysteriousness of our genome and the functions of our genes to a behavior so tangible, and so common across cultures… eating starchy foods.The title of the paper is pretty descriptive and explains the jist of the paper, but here’s some more information on what and how Dominiy and crew did. After sampling populations, they discovered people carry extra copies of a gene, called AMY1, which is essential for making the salivary enzyme amylase that digests starch. Often carrying extra copies of a sequence means there is some sort of positive selection or benefit to having multiples. Of course, extra copies of sequences can disrupt normal cell functions and ultimately induce tumor formation or cell death, but that usually prevents the sequence from persisting. In this particular case, extra copies of AMY1 means our bodies make more of the enzyme…. Perhaps to deal with the abundance of starches we consume. Explained in the abstract,

“Higher AMY1 copy numbers and protein levels probably improve the digestion of starchy foods and may buffer against the fitness-reducing effects of intestinal disease.”

This is a pretty phenomenal correlation.They next extended their research, by screening populations with different diets like those in the North who eat mostly meat. They found out that those who subsided on high-starch diets tended to have more copies of AMY1 than individuals from populations with low-starch diets. Here’s a summary of some of the populations:

  • The Yakut of the Arctic, whose traditional diet centres around fish, had fewer copies than the related Japanese, whose diet includes starchy foods like rice.
  • The Hadza of Tanzania who rely heavily on tubers and other root vegetables, have 6.7 copies of amylase, on average.
  • The Mbuti, pygmy rain forest hunter-gatherers from central Africa who eat little starch, have 5.4 copies on average.

At the some point in the evolution of our lineage, our ancestors were eating a lot of starches… it coulda been around the Neolithic when people were see the explosion of agriculture and the domesticating grains, rices, etc. or it coulda been even earlier when our australopithecine brethern were digging up tubers. Whenever it was, extra amylase gene copies was more valuable trait… one that was ultimately incorporated into our genomes throughout evolutionary time.

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