Human Ancestors Were Nearly All Vegetarians
By Rob Dunn | July 23, 2012 | 39

Paleolithic diets have become all the rage, but are they getting our ancestral diet all wrong?

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. Taken too literally, such diets are ridiculous. After all, sometimes our ancestors starved to death and the starving to death diet, well, it ends badly. Yet, 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 what did our ancestors eat?

Here is where the trouble starts. Collectively, anthropologists have spent many a career attempting to hone in on the diets of our most recent ancestors. Typically, they focus on our stone age (AKA Paleolithic) human ancestors or our earlier pre-human, hominid ancestors. Even if we just consider our stone age ancestors—those folks whose stories span the time between the first stone tool and the first agriculture—the sides of the debate are polarized. If you listen to one camp, our ancestors got most of their nutrition from gathered fruits and nuts; successful kills of big mammals may have been more of a treat than an everyday reality. A paper out just this month suggests even Neanderthals–our north country cousins and mates– may have eaten much more plant material than previously suspected. Still, the more macho camps paint a picture of our ancestors as big, bad, hunters, who supplemented meaty diets with the occasional berry “chaser.” Others suggest we spent much of our recent past scavenging what the lions left behind, running in to snag a half-rotten wildebeest leg when the fates allowed. Although “Paleolithic” diets in diet books tend to be very meaty, reasonable minds disagree as to whether ancient, Paleolithic diets actually were. Fortunately, new research suggests answers (yes, plural) to the question of what our ancestors ate.

The resolutions come, in part, from considering the question of our diets in a broader evolutionary context. When we talk about “paleo” diets, we arbitrarily tend to start with one set of ancestors, our most recent ones. I want to eat like Homo erectus or a Neanderthal or a stone age human, my neighbors testify. But why do we choose these particular ancestors as starting points? They do seem tough and admirable in a really strong five o’ clock shadow sort of way. But if we want to return to the diet our guts and bodies evolved to deal with, perhaps we should also be looking our earlier ancestors. In addition to understanding early humans and other hominids, we need to understand the diet of our ancestors during the time when the main features of our guts, and their magical abilities to turn food into life, evolved. The closest (albeit imperfect) proxies for our such ancestral guts are to be found in the living bodies of monkeys and apes.

I should start by explaining what the “gut” is and does; I use the term too loosely. What I really mean is the alimentary canal and all of its gurgling bells and whistles. This canal is the most important and least lovely one on Earth. It takes you from the mouth through the body all the way down to the anus. But while most canals take the shortest course between two points, the one inside you takes the longest. The longer the canal, the more area over which digestion can occur. Food enters the canal through the mouth, where it is chewed and slimed with saliva. It then hits the stomach, where much of the digestion of proteins occurs. Next, it is on down to the small intestine where simple sugars are absorbed. If you have just eaten a twinkie, the process essentially ends there. Everything worth consuming has been absorbed. But if you have eaten broccoli or an artichoke, things are just beginning. It is in the large intestine, where harder to break down carbohydrates (such as cellulose, the most common plant compound on Earth) are torn asunder. This system evolved so as to provide us with as many calories as possible (long to our benefit) and, also, as many of the necessary but hard to produce nutrients. The alimentary canal is, evolutionarily speaking, a masterwork1.