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The Evolutionary Approach

Human evolution occurred over 2.5 million years. During that span of time, the foods available to us have been inextricably linked to who we are genetically. Yet, 70 percent of the foods comprising our modern diet were introduced in the last 10,000 years. There simply hasn’t been ample time for evolution to keep pace with our rapidly changing diet. The Paleo Diet® helps us return to eating the foods we were designed to eat.

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Law of the bell-shaped curve.

Evolution is based on the law of the bell-shaped curve, meaning that while there is large genetic variability between individuals, most of us fit within a narrow range—the bell of the curve. In scientific terms, 95 percent of us are within two standard deviations of that peak.

Take height, for example. There is much individual variance in height, but most of us are still between about 5’4” and 6”1”. That’s the peak of the curve. Of course, there are people who are shorter than 4-feet and taller than 7-feet, but they’re the genetic outliers.

Just as with height, there is individual variance as to our optimal diet. Still, most of us exist within a tight range—the peak of the curve. Comprising that peak are the foods that were available to us throughout our evolution: unprocessed foods including fruits, vegetables, lean meats, fish, eggs, nuts, and seeds.

Certainly, we’ve all heard of someone who ate only hamburgers and candy bars, smoked a pack of cigarettes per day, and lived into his nineties. He or she is the outlier. And just as you don’t want to design door frames around the tallest or shortest people in history, you don’t want to base a diet on dietary outliers either.

When we talk about evolutionary change, we are referring to a shift in the curve. Generally, some change in the environment gives outliers on one side of the curve a genetic advantage that causes them to flourish. And over time the curve moves:

So, yes, that theoretically means that after enough time, pizza could become the optimal human food. But evolution is slow moving, measured in millennia. For the curve to shift, those of us at the center of the original curve must die off—so don’t hold your breath waiting for that shift to take place.

Of course, the problem has to do with more than just pizza. Seventy percent of the foods that comprise the modern diet—grain products, vegetable oils, dairy, refined sugar, and alcohol—were introduced in the past 10,000 years and are completely out of line with the center of the curve.1 Importantly, 10,000 years is not nearly enough time for evolution to shift the curve. In fact, many of the foods we now eat only appeared in any significant quantity in the last 200 years. (Refined flour, for example, only appeared after the invention of steel roller mills in the late 1800s.)

As a result, many people now eat a diet that is, in effect, an outlier on the dietary bell-shaped curve. Because of that, we now have chronic illnesses collectively referred to as the Diseases of Civilization.

Some have argued against this evolutionary view of diet, pointing out that epigenetic changes allow adaptations within a single generation. However, while epigenetics allows us to slightly shift our position on the curve, they don’t shift the curve. And it can even be argued that epigenetic changes can work against us. Unprocessed grains are normally poisonous to humans. It’s possible that epigenetic changes have allowed us to tolerate them, but not without long-term consequences.

The Paleo Diet is based on this evolutionary approach to diet. As Theodosius Dobzhansky, a well-known Ukranian evolutionary biologist said,Nothing in biology makes sense, except under the light of evolution.”

At the center of the bell-shaped curve are the foods we evolved to eat. That doesn’t mean there is a single Paleo Diet—our Paleolithic ancestors ate different foods depending on where they lived. The optimal human diet is a range, not a point, and most of us sit within the two standard deviations of the peak of that curve.

Our recommendation is to start with the foods at the center and then find which side of the curve you’re more suited to—more or less fruit, more plant-based or more animal-based. The one thing we can tell you for certain: Grains, refined sugar, vegetable oils, dairy, and alcohol, in any regular quantity, are the outliers.

  1. Eaton, S.B., M. Konner, and M. Shostak, Stone agers in the fast lane: chronic degenerative diseases in evolutionary perspective. Am J Med, 1988. 84(4): p. 739-49.
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