We Are What We Ate

Was ancient man a vegetarian? Robb Dunn reviews the evidence. 
First published in Scientific American. This edited and updated extract reprinted with their kind permission.

Rob Dunn

‘Right now, one half of all Americans are on a diet. The other half just gave up on their diets and are on a binge. Collectively, we are overweight, sick and struggling. Our modern choices about what and how much to eat have gone terribly wrong. The time has come to return to a more sensible way of eating and living, but which way? An entire class of self-help books recommends a return to the diets of our ancestors. Paleolithic diets, caveman diets, primal diets and the like, urge us to eat like the ancients. The idea that we might take our ancestral diet into consideration when evaluating the foods on which our organs, cells and existence thrive, makes sense. But there are big questions to be answered before we do. The first is which paleo diet we should consider? The one from twelve thousand years ago? A hundred thousand years ago? Forty million years ago?

What is your ancestral diet, the one our ancestors ate when most of the features of our guts were evolving? If you want to eat what our ancestors spent the most time eating during the largest periods of the evolution of our guts, you should eat fruits, nuts, and vegetables – especially fungus-covered tropical leaves. A new paper suggests even Neanderthals – our north country cousins and mates – may have eaten much more plant material than previously suspected. (See Neanderthal Medics in News Briefs in this issue.)

But didn’t the guts of our ancestors evolve as their diets later changed? Yes, some. But these changes, at least the ones we know about so far, seem to have had as much to do with the shift to processed and agricultural foods as they did with the shift to meat per se. Some of the changes that occurred along with the shift to processed (burned, mashed) foods and later agriculture happened to everyone. Our guts shortened, for example. But others were stories not of humans but of individual human or hominid lineages. With agriculture, some human populations evolved extra copies of amylase genes, arguably so as to better be able to deal with starchy foods. The case of agriculture is the most clear. With agriculture, several human populations independently evolved gene variants that coded for the persistence of lactase (which breaks down lactose) so as to be able to deal with milk, not just as babies but also as adults. Drinking milk of another species as an adult is weird, but some human populations have evolved the ability. With agriculture, the species in our guts seem to have evolved too. Some populations of humans in Japan have a kind of bacteria in their guts which appears to have stolen genes for breaking down seaweed, a foodstuff that became popular along with the post-agricultural Japanese diet. With agriculture, human bodies changed so as to cope with new foods. Our bodies bear the marks of many histories. As a result, if you want to eat what your body ‘evolved to eat’ you need to eat something different depending on who your recent ancestors were.

We already TAKE our individual histories into account in our diets to some extent. If your ancestors were dairy farmers, you can drink milk as an adult without trouble, you’ve ‘got lactase.’ But if they were not, you tend to get diarrhea when you drink milk and so you probably avoid the stuff (lest your friends avoid you). Yet, the truth is, for most of the last twenty million years of the evolution of our bodies, through most of the big changes, we were eating fruit, nuts, leaves and the occasional bit of insect, frog, bird or mouse. And so while some of us might do well with milk, some might do better than others with starch and some might do better or worse with alcohol, we all have the basic machinery to get fruity or nutty without trouble.

Interestingly, if our gut bacteria responded rapidly to shifts in diets toward more meat during the stone age, they might be expected to have shifted again when we began to farm, at least for those of us with ancestors who began to farm early. When our gut bacteria met up with our agricultural diets, beginning twelve thousand years ago or so, they would have begun to compete with new microbial species that kicked ass at living off wheat, barley, corn, rice or any of the other grasses that have come to dominate the world, sometimes at our expense. This may even mean that which diet is best for you depends not only on who your ancestors were, but also who the ancestors of your bacteria were.

In this light, the second question is what should we eat? One might hope that the answer would be that we could simply point to an ancestor in one place or time and eat what they ate. Our historic diets should inform what we eat today. But they are not an answer, not on their own, for what we should eat today. The past was not idyllic. It was difficult. Our ancestors died younger than we do. They suffered many fates we would not wish upon ourselves or upon our children. If our ancestors looked into the future and saw us they would ask, “How do we get what they have?” In a way, our problems actually stem from our ancestors. We have become better and better at producing more and more of those foods that our ancestors would have craved (but could not get in excess). Our ancestors had taste buds that called out for sweets, but they only found the rare and dangerous honey of bees. Our ancestors had taste buds that called out for salt, but they had to search out salt licks or the salty blood of animals. Our ancestors had bodies that cried out for the quick energy of easy to digest foods but they had, for most of our history, the harder to digest food of raw fruits, nuts and vegetables. The great success and difficulty of humanity in terms of our diets is that we have been able to produce each thing our bodies crave in excess; we have met our ancient paleo cravings in spades. The trick is to figure out what would make our bodies most healthy, based on the insights of modern nutrition and ancient context of our ancestral diets (plural). It is no great insight that many of us would be healthier if we ate more fruit and nuts like our earlier ancestors, but this is not because they had everything so right. It is because in trying to make everything our ancient bodies crave we have gotten it so wrong.  

Rob Dunn is a biologist and writer in the Department of Biology at North Carolina State University. His writing has appeared in Natural History, BBC Wildlife Magazine, Scientific American, Smithsonian Magazine, National Geographic and other magazines. You can read his articles on his website:

Rob’s latest book, The Wild Life of Our Bodies, examines the long human relationship with other species (be they tapeworms or tigers) and how changes in those relationships are affecting our health and well being. You can buy it HERE.