Some groups, like the Pima Indians and Nauruans, might have genes that store energy more efficiently because of past famines and being cut off from others — which helped them survive back then, but now makes them more likely to get type 2 diabetes when eating modern diets full of carbs.

Some groups, like Europeans, might be less likely to get type 2 diabetes because their ancestors started eating farm-based, high-carb diets thousands of years ago—giving their bodies more time to adapt—while other groups, like the Pima or Nauruans, started later and may not have had as much time to adjust.

Some groups, like the Pima Indians and Australian Aborigines, are seeing more type 2 diabetes because their bodies may be genetically used to handling sugar differently, and today’s processed, high-sugar diets could be overwhelming their systems over time.

Back when humans were hunters during the Ice Age, their bodies might have adapted to use less insulin so their brains and babies could keep getting enough sugar — and that same trait might still be common in people whose ancestors lived that way.