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The Overkill Hypothesis: Why Eating Antelope is Preferable to 500 Squirrels

By Loren Cordain, Ph.D., Professor Emeritus, Founder of The Paleo Diet
March 19, 2015
The Overkill Hypothesis: Why Eating Antelope is Preferable to 500 Squirrels image

I recently had the pleasure of speaking with Eric Edmeades, author and Founder of WildFit, the fitness methodology training program informed by evolution. The grandson of Professor T.F. Dreyer who discovered the early hominid Florisbad skull in 1932, 1 Eric’s interest and business ventures in evolutionary biology were shaped by his grandfather’s exploration and research.

Together we discussed geoscientist Paul Martin of the University of Arizona “Overkill Hypothesis” which argues the Pleistocene extinction of large mammals worldwide was caused by overhunting by humans.2

We’ve made a contribution to this concept by developing 3rd order polynomial equations which allow one to predict total body calories of any mammal, if their weight is known. This procedure also allows for the calculation of total body fat calories and total body protein calories if one knows body weight. Hunter-gatherers must have intuitively known this phenomenon. In light of the hypothesis and optimal foraging theory, a large body of evidence indicates that larger and fatter animals generally were preferred by hunter-gatherers to smaller, leaner animals. We believe these physiological dictums are the reasons our Stone Age hunters frequently risked life and limb to kill very large mammals with nothing more than wooden spears.

A corollary to this phenomenon was originally written about extensively by my colleague and co-author, John Speth, a noted anthropologist from Michigan who is also a colleague of Martin.3 Speth's idea has come to be known as "rabbit starvation" or "protein poisoning." In the ethnographic and historical literature it was recognized that sole consumption of only lean protein without fat caused sickness and nausea to rapidly develop. The phenomenon was dubbed "rabbit starvation" because in the far North, both hunter-gatherers and frontiersmen (Lewis and Clark documented this phenomenon) knew that if small animals like rabbits were the sole food source, nausea, disease, weight loss and eventual death would result.4 Our research group has outlined the physiological mechanism involved and the dietary levels at which protein becomes toxic. It ranges between 35-40% of normal daily calories for most people.

This begs the question as to whether the Hadza, East Africa's last remaining true hunter-gatherers, prefer a single Kudu or Gemsbok antelopes to 500 ground squirrels and why? The Hadza, unlike more northerly hunter-gatherers would generally always have had access year round to plant foods. Hence, sufficient dietary carbohydrate could in effect "dilute" excessive protein from small lean animals, so that small lean mammals could be consumed right up to the physiological protein ceiling without developing protein toxicity. This would provide the balance of calories stemming from either a fat or carbohydrate source. Except for some nuts and seeds, plant foods are generally poor sources of fat. Animal foods are poor sources of carbohydrate and are mixtures of protein and fat which scale to body weight via the 3rd order polynomial equations we developed.

So, the second question to ask the Hadza would be, what would happen if they could only eat ground squirrels without access to plant foods? Have they experienced the nausea of excessive protein intake? I can tell you from personal experience that the phenomenon is real. In an experiment I performed upon myself, I ate only water packed tuna and skinless chicken breasts. After only two days I started to become nauseous and stopped the experiment on day three.

An interesting archaeological caveat to this concept comes from the fossil record of Neanderthals who almost exclusively targeted large mammals. Perhaps, it was because of the seasonal unavailability of plant foods (carbohydrates) in more northern latitudes and the protein toxicity of smaller animals. Plunging a wooden spear between the ribs of rhinos, mammoths, aurochs, and other animals alike becomes a much more sensible proposition if your life depends upon the higher fat/protein composition of large mammals.

Further, the best available most recent evidence indicates Neanderthals could not produce fire at will, but rather could control it only by gathering naturally occurring fire. This inference comes from European Neanderthal cave sites demonstrating the absence of fire during some winter periods in which the caves were occupied. Further no archaeological evidence exists showing that Neanderthals drilled objects -- a first, foremost and necessary step involved in the accidental discovery of the technology required to make fire at will using a fire drill. Without the ability to make fire at will, entire groups (cereals, legumes, many underground storage roots and structures) of plant food (ergo carbohydrate) become unavailable, thereby physiologically forcing Neanderthals to become reliant upon large animals.

So, with this background information, I wonder if there could be confirmation by the Hadza that protein toxicity occurs in their world, or perhaps a year-round carbohydrate source that prevents "rabbit starvation.”

Cordially,

Loren Cordain, Ph.D., Professor Emeritus


References

[1] "Florisbad Skull." Wikipedia. Wikimedia Foundation, n.d. Web. 1 Mar. 2015.

[2] "Paul S. Martin." Wikipedia. Wikimedia Foundation, n.d. Web. 1 Mar. 2015.

[3] Cordain L, Miller JB, Eaton SB, Mann N, Holt SH, Speth JD. Plant-animal subsistence ratios and macronutrient energy estimations in worldwide hunter-gatherer diets. Am J Clin Nutr. 2000;71(3):682–692.

[4] Seidensticker, John. "Human Problems from a Rabbits Viewpoint." Rabbits: The Animal Answer Guide. By Susan Lumpkin. N.p.: Nature, 2011. 185. Print.

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