While this captive gorilla noshes on fibrous veg such as kale, in the wild, the animals' diets vary seasonally, as does their microbiome. (Credit Wikimedia Commons/Ltshears) Researchers analyzing the gut microbes of gorillas and other primates found seasonal shifts that underscore just how much is missing from the modern human diet — and why it matters. Right now, you're hosting your own special ecosystem. Millions of microbes live out their lives on your skin and in every nook and cranny, especially in your gut, where they perform a multitude of essential tasks. Sort of like tiny houseguests who actually cook and clean. The microbiome — particularly the mini-cities in your gut — has been a popular research focus of late as scientists investigate what it can tell us about health, behavior and even human evolution. Researchers probing the poop of 87 wild western lowland gorillas in the Republic of Congo over three years found that the apes' gut microbiome population fluctuated seasonally based on resource availability. Though the animals' diet typically consisted of leaves and bark, in the dry season they chowed down on abundant fruit, and their microbiomes changed accordingly. A similar seasonal shift has been observed previously in our own species, in members of traditional hunter-gatherer societies, such as the Hadza of Tanzania. It's not the case, however, for the average human living in an industrialized environment where a global industry serves up the same produce year-round to restaurants and grocery store shelves, whether it's snowing or sweltering in your neck of the woods. The researchers sequenced the genetic material of the different microbes present in the gorillas' fecal material to find that the seasonally-shifting bacterial populations did different things. Bacteria that helped the apes break down bark and other fibrous material were replaced annually by different microbes when fruit was in season: These fruity fellows fed on a protective layer of mucus in the gut itself. In turn, the arrival of bark season (mmm!) sent the mucus-nibblers packing and brought back the bacterial breakdown team. Given how close Homo sapiens are on the Tree of Life to gorillas and other primates included in the study, it's not crazy to compare gut microbiomes and see that ours may be falling short in terms of optimal health. The average human in an industrialized society with a season-less diet — especially one that favors animal protein over veggies — is likely living a fiber-deficient life and has the unbalanced microbiome to prove it. With our microbiomes already less diverse than those of our nearest primate kin, the lack of seasonal fluctuation may mean the ever-present mucus-eaters and other potentially harmful bacteria in the gut can nibble away at us year-round, increasing intestinal inflammation and even potentially raising the risk of colon cancer and other disease. The research appears in Nature Communications and is open access, so take a read for yourself.