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Did Animal Protein Bring Dogs and Humans Together?

By Raphael Sirtoli, M.Sc., Science Writer
March 25, 2021
Did Animal Protein Bring Dogs and Humans Together? image

In East Africa between 50,000 and 70,000 years ago, humans were already expert large game hunters. It characterized their optimal foraging strategy (OFS) and was remarkably profitable.

They earned tens of thousands of calories per hour in return. Humans took every edible morsel of food from the carcass thanks to technological advances such as stone tools to crack open skulls for the brain and bones for the marrow.

Controlled use of fire also helped unlock calories and nutrients. Humans were virtually free to select whichever ‘cut’ on the carcass they desired, and would usually stalk the fatter and larger (i.e. older) prey, all else being equal. Humans protected their kill from other predators as a coordinated band ready to exert ‘violence at a distance’ with spears and atlatls.

Human apex predation is to the human species what mathematics is to physics: unreasonably successful. [1] Hominin brain expansion took off 250,000 to 500,000 years ago, resulting in the large, energy-hungry brains we carry with us today. [2]

This incredible brain expansion would have only been possible with access to many more fat calories. And, those extra calories played an important role in the close relationship humans developed with dogs, as we’ll explore now.

Did Animal Protein Bring Dogs and Humans Together? image

Enter Canis lupus familiaris

There is evidence to suggest humans began domesticating dogs 13,000 to 17,000 years ago in the late Pleistocene. [4, 5] Dogs resemble their masters in many respects. They’re hypercarnivores in the carnivore guild, getting approximately 70 percent of their calories from animals. [6]

They also share guild characteristic behaviors like food sharing, cannibalism, surplus killing, interspecies intolerance, and pack hunting of large prey. Dogs became a hunting technology for humans, in some respects, just like bows. They helped humans adapt to hunting smaller fleeing prey (higher in protein).

Humans had to adapt in this way because they hunted large fatty game to extinction. This also drove a decline in prey size and adiposity in the Late Quaternary Megafauna extinction [7]. As Ben-dor explains, “Large animals contain around 50 percent fat calories,” which is typically five times more than smaller ones. [8]

Despite similarities, dogs and humans also differ physiologically in several relevant ways, namely their ability to enter nutritional ketosis, their body fat levels, their physiological protein ceiling, and dietary protein requirements during growth. It can be argued that these differences are conducive to allyship.

First, dogs find it harder to enter ketosis [9] or go deeply into it without supplemental medium chain triglycerides. [10] Secondly, the body fat of free-ranging female wolves is 3.3 to 15 percent [11] in comparison to the 12.4 - 27.7% percent of the average healthy adult female hunter-gatherer. [12]

Third, and most pertinently, dogs have a higher protein ceiling than humans. Dogs can’t crack bones open to access the fattier parts of the carcass and are limited to the leaner parts and to fewer calories.

What’s available to them is approximately >70 percent of calories from protein when going by the amount of edible meat in wild game. [13] We’d also predict higher urea synthesis and excretion rates in dogs, resulting from a higher dietary protein intake.

And, in fact, we see this in humans, as they share a very similar physiology and diet. The dog’s dietary protein ceiling is likely ≥70 percent, a figure derived from benchmarking it to the human protein ceiling of 30 to 50 percent [14, 15, 16, 17], factoring in wild game carcass macronutrient ratios, as well as the substantial protein requirement dogs have during growth. [18]

Dog behavior also provides a clue in this regard. When given free access over 10 days to either a high-fat, high-carb, or 58-percent high-protein diet, dogs self-select the higher protein diet more often, increasing their proportional protein intake from 29 percent to 44 percent. [19]

So, although humans and dogs competed for some of the same prey, they also shared differences that set them up for an allyship. In 2021, Dr. Lahtinen and colleagues argued that protein is what brought humans and canines together in their paper entitled, “Excess protein enabled dog domestication during severe Ice Age winters.” [20]

Should you feed your pet The Paleo Diet?
By Johnathan David

Did “excess protein” allow humans to domesticate dogs?

The argument made by the research team hinges on three claims.

  1. Harsh Pleistocene winters made for leaner prey creating an excess of protein.
  2. Humans aren’t fully adapted to a carnivorous diet because of their lower protein ceiling.
  3. Pleistocene archaeological sites were analogous to subarctic and arctic environments that are most conducive to dog domestication.

First, harsh Pleistocene winters do make for leaner prey. The authors go further, saying “that even with a higher lipid content, our hypothesis still works.” What they mean is that humans would still have come up against their protein ceiling.

However, this only holds on the assumption that the whole carcass represents what was actually eaten. It downplays the ability of cut selection to change dietary macronutrients, and the extent to which the brain and marrow were uniquely available to humans with stone tools.

Brains and marrow are also more calorically invariant from season to season compared to highly variable subcutaneous fat stores. Furthermore, the degree of successful herd hunting of elephants, for example, meant having lots of extra calories (especially muscle meat). [21] That could go to the dogs.

Second, it is incorrect to state that humans are not adapted to a carnivorous diet because they encountered an excess of protein relative to fat or carbohydrate. Humans were hypercarnivores throughout the Pleistocene and avoided coming up against their protein ceiling thanks to significant amounts of fat calories from large game. [22]

If fatty animals were scarce but the local environment was hospitable to plant life, humans could also fall back on their remarkable omnivorous ability—in combination with cooking—and so exploit dietary carbohydrates.

Additionally, the ease with which human physiology enters nutritional ketosis signals a strong reliance on dietary (animal) fat, as well as the aforementioned high physiological body fat levels.

The voluminous human brain requires a substantial energy reservoir, for which subcutaneous fat stores are preferred. Dietary fat is the macronutrient with priority uptake in fat cells. [23] The fattiest parts, like the brain and marrow, were uniquely accessible to humans thanks to the aforementioned stone tool technologies.

Did Animal Protein Bring Dogs and Humans Together? image

The third claim is correct: Subarctic and arctic environments host little plant life compared to milder climates. This increases the odds of interaction between both dog and human predators who share similar prey. However, dog domestication happened in warmer climates as well. [25]

When fat animals were scarce there, plant carbohydrates were more available as a fallback food. The authors recognize the proficient omnivory but don’t connect it to how warmer climates can offer more carbohydrate-rich fallback foods helping stay below the protein ceiling.

Did Animal Protein Bring Dogs and Humans Together? image


More research is needed to answer the question of what brought dogs and humans together. Even very basic questions like who domesticated whom is yet to be fully addressed. [27] The ‘trades’ between both species were extensive. Dogs were an early warning alarm system, body guards, beasts of burden, even companions. In exchange they got meat and possibly heat and shelter. The social intelligence characterizing both species seems inextricably linked to the degree of domestication and to the depth of the emergent social relationship.

The aforementioned research paper rightfully explores how central animal protein was to both dogs and humans throughout evolution. It also identifies the evolutionary ‘trade’ opportunities emerging from the gap between the protein ceilings.

Evolutionarily, incentives aligned. However, the authors set the human protein ceiling too low and underestimate how consequential human prey and cut selection are for retaining access to fat year round (even in prey with depleted subcutaneous fat stores).

Neither do they put weight on cooking carbohydrate fallback foods in warmer climates. Overall, the authors present an interesting thesis on protein as the evolutionary commodity with which dogs and humans developed a relationship.

Big Brains Do Not Need Carbs


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