In this case, though, pups born to mice on American-type diets — no fiber, lots of sugar — failed to acquire the full endowment of their mothers’ microbes.

There has been a rise in studies discussing the importance of the microbes that live in our gut and their primary food source: fiber. The “Burkina Faso microbiota produced about twice as much of these fermentation by-products, called short-chain fatty acids, as the Florentine [citizens]. That gave a strong indication that fiber, the raw material solely fermented by microbes, was somehow boosting microbial diversity in the Africans.”

This biodiversity of microbes in our gut can wax and wane depending on what we eat so that “[e]ven after weeks on this junk food-like diet, an animal’s microbial diversity would mostly recover if it began consuming fiber again.” That said, as quoted above, if a child does not eat the right diet at birth, she is at risk of never recovering the full biodiversity of her mother’s gut. Over generations, you have disparities in gut health from region to region across the globe that may not be recoverable.

N.b: In May 2016 there has been additional reporting on the gut by FiveThirtyEight.