 There are three broad theories about evolution and food. One is that humans have become adapted to the products of the agricultural revolution over the last 10,000 years. Two is the paleo view, that 10,000 years is a blink of an evolutionary eye, and that humans have adapted to paleolithic diets with lots of lean meat. But why stop there? The last 200,000 years as mostly stone age humans represents just the last 1% of 20 or so million years we've been evolving since our common great-ape ancestor. During our truly formative years, the first 90% of our existence, one might say, our nutritional requirements reflect an ancestral past in which we ate mostly leaves, flowers, and fruits, with some bugs thrown in thanks to wormy apples to get our vitamin B12. For this reason, another approach that might improve our understanding of the best dietary practices for modern humans is to focus attention not on the past, but rather on the here and now. That is on the study of the foods eaten by our closest living relatives, given the bulk of our ancestral diets and the lack of evidence supporting any notable diet-related changes in human nutrient requirements, metabolism, or physiology compared to our fellow great-apes. This could explain why fruits and vegetables are not only just so good for us, but vital to our survival. We're actually one of the few species so adapted to a plant-based diet that we could actually die from not eating fruits and vegetables from the vitamin C deficiency disease, scurvy. Most other animals just make their own vitamin C. But why would our body waste all that effort making vitamin C when we evolved hanging out in the trees just eating fruits and veggies all day long? It's presumably not a coincidence that the few other mammals unable to synthesize their own vitamin C like guinea pigs and bunny rabbits and fruit bats are all, like us great-apes, strongly herbivorous. Even during the Stone Age, we may have been getting up to 10 times more vitamin C than we get today, and 10 times more dietary fiber, based on essentially rehydrated human fossilized feces. The question is, are these incredibly high nutrient intake simply an unavoidable byproduct of eating whole plant foods all the time, or might they actually be serving some important function like antioxidant defense? Plants create antioxidants to defend their own structures against free radicals. The human body must defend itself against the same types of pro-oxidants, and so we have also evolved an array of amazing antioxidant enzymes, which is effective but not infallible. Free radicals can breach our defenses, cause damage that accumulates with age, leading to a variety of disease causing, and ultimately, fatal changes. That's where plants may come in. Plant-based antioxidant-rich foods traditionally form the major part of our diet, and so we didn't have to evolve that great of an antioxidant system. We could just let the plants in our diet pull some of the weight, like the not bothering to make vitamin C thing, let the fruit do it. Using plants as a crutch may well have relieved the pressure for further evolutionary development of our own defenses, meaning we'd become dependent on getting lots of plant foods in our diet, and when we don't, we may suffer adverse health consequences. Even during the Stone Age, this may not have been a problem. Only in recent history did we start giving up on whole plant foods. Even modern-day paleo and low-carb advocates may be eating more vegetables than those on standard Western diets. There's this perception that low carbers are chowing down on the three B's, beef, butter, and bacon, but that's just a small minority. And what they are eating more of is salad. The number one thing an internet low carb community said they were eating more of was vegetables. Great! If people want to cut their carb intake by swapping junk food for vegetables, that's not the problem. The concern is the shift to animal-sourced foods. Greater adherence to a low carb diet high in animal sources of fat and protein was associated with higher mortality, for example after a heart attack, meaning they cut their lives short. If there's one takeaway from our studies of ancestral diets, perhaps it's that diets based largely on plant foods promote health and longevity.