Our Vegetarian Past? : 13.7: Cosmos And Culture Should a healthy human diet be based on the almost-entirely vegetarian habits of ancestral monkeys and apes? Or should we accept that no evolutionary time period is a helpful guide to making good eating choices in today's world?

Gut Check: Should You Embrace Our (Mostly) Vegetarian Past?

Phil Walter/Getty Images
Fresh fruit and vegetables at the Wesley Market in Auckland, New Zealand, on September 2, 2011.
Phil Walter/Getty Images

We humans evolved to eat meat. How many times have you read or heard some version of this statement?

Even when the evolutionary importance of plant foods to the human diet is acknowledged, assertions about the naturalness of meat-eating retain immense power over conversations about diet and health in our society (see examples here, here and here).

Now a Scientific American blog post, "Human ancestors were nearly all vegetarians," offers a different origins story.

In the post, biologist and science writer Rob Dunn suggests that when healthy eating is calibrated to the past, it's too often to a relatively recent period of time. More helpful, he believes, would be 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." This means looking back at monkeys and apes of the past, our primate relatives who, Dunn says, ate a great deal of fruits, leaves, nuts and vegetables, with the occasional protein snack (insects or small animals) thrown in.

In other words, with a tweak of the evolutionary time scale, a primate past comes into focus that is essentially vegetarian.

A few responses spring to mind right off. Isn't it misleading to talk about monkeys and apes as our ancestors? Not the way Dunn means. He knows we share common ancestors with today's monkeys and apes — indeed, it's those ancestors he's talking about.

Next, what about chimpanzee hunting? Males chimpanzees famously band together to bring down and eat colobus monkeys and other prey, and presumably have been doing so for millions of years. Chimpanzees are exceptional, though, and Dunn notes that their diet is, by mass, only 3 percent meat.

Most pressingly, how come the ancestral monkey-and-ape diet doesn't pale in significance compared to the more recent Homo ancestral diet, which did include meat from hunting or scavenging?

The conservative nature of the human gut across millions of years is the critical point for Dunn. Compared to other primates, he says, we modern humans have unique hands and unique brains, but even though our Homo forebears ate meat, our guts are pretty much primate-average, not adapted for a meat diet.

I noticed that Dunn doesn't much discuss teeth, but dental analysis suggests our Homo ancestors were able to eat a broad spectrum of foods, so he'd be right to say that our dentition isn't adapted for a meat diet either.

"Plants were our paleo diet for most of the last thirty million years," Dunn concludes.

So what's the take-home message here? It's not, I think, that we're meant to be vegetarian (nor does Dunn claim this). Rather, it's that ancestral diets don't aid us in making food choices today, any more than our ancestors' mating patterns help us in establishing healthy partnerships and families.

Last week, two friends remarked that I'm a pescetarian — a term I hadn't known, meaning someone who eats vegetarian foods plus fish. That diet works for me, taking into account my health needs, animal-welfare needs and environmental issues combined.

I don't know if there's a good pescetarian evolutionary model to be found. But then again, I don't need one.

You can keep up with more of what Barbara is thinking on Twitter: @bjkingape