The nose-to-tail fallacies

This post is about the commonly held, but deeply mistaken idea that pre-agricultural humans must have eaten liver in proportion to its hunted carcass weight, and that therefore we should, too. Some of this material was presented at KetoCon 2019.

Although the implications of the nose-to-tail narrative extend beyond the hypervitaminosis A question, it's deeply relevant, since many advocates for the idea that regular doses of liver are essential on Carnivore rely heavily on this reasoning.

As I mentioned in Hypervitaminosis A: a brief introduction there are many components to the full picture about hypervitaminosis A on Carnivore, and I intend to address them only a piece at a time, even though it probably won't all make sense until all the pieces are in place (with luck it will at that point!). One particularly thoughtless correspondent made an entire X post criticising my introduction for the absence of arguments I specifically said I would get to later. But I know my regular audience is more astute than that. Thank you for your patience! This topic was not on that original list, but belongs there.

Contents

Nose-to-tail entails bad assumptions
The human predatory pattern is unique
Co-evolution with dogs affected proportions
Modern livestock is higher in vitamin A
Conclusions
End-to-end citations

Nose-to-tail entails bad assumptions

The basic idea of "nose-to-tail" is that pre-agricultural humans must have eaten everything edible they had access to. The two main bad assumptions typically rolled into this logic include are

1. "Until recently, humans were constantly on the brink of starvation."
2. "Because we are omnivores, we have no food selectivity."

Let's first address these and then re-examine the nose-to-tail idea in light of an evolutionary lens.

We were not constantly almost starving

The idea that until very recently humans were constantly on the brink of starvation is so commonly believed as to feel practically intuitive, but in fact it is neither logical nor concordant with evidence. We can tell it is widely believed because it is assumed in two other commonly told stories: the erroneous idea used to argue for fasting that humans are adapted to frequent famines, and the hypothesis that the modern obesity epidemic is a result of an unprecedentedly abundant food environment.

As I have described in the second chapter of Facultative Carnivore, many believe that humans are only recently facing obesity problems because never in our past did we have access to enough food to have become obese. This is silly for several reasons. One is that it assumes our satiation processes don't work properly. It's the mirror image of the trope about thirst—"Drink more than you think you need, because by the time you get thirsty, you're already dehydrated!" In this case: "Don't eat as much as you think you need to, because by the time you get satiated, you've already overeaten!" Poor, stupid humans. Hundreds of millions of years of evolution and we still can't get basic biological signalling down.

Most versions of this idea entail the existence of a genetic override to satiation, which is otherwise functionally adaptive. But we know this genetic override doesn't exist. I've pointed to the basic evidential problems with this "thrifty gene hypothesis" in the chapter linked above, so I'll direct the interested reader there. And in the absence of some special fattening gene, the normal pattern for a species faced with food supply changes is to shrink and expand in population, not to become too fat.

Another problem is that we have many examples of abundance without obesity, including not only long modern periods without famines, but examples like the Pima before the colonization of the Americas by Europeans. In Gary Taubes' opus Good Calories, Bad Calories [1] he uses the Pima as an example of how obesity is typically correlated with poverty—not abundance!—in the modern world. Specifically he notes that historical accounts of the Pima describe them both as very fit and as having a huge abundance of food availability. Now, in poverty, they are renowned for extreme rates of diabetes and obesity. This does not appear to be an outlier.

As to the stereotype that humans were regularly subject to famines before agriculture, this seems to be based on a naive and uncharitable notion of a "stupid caveman" archetype; people who would be in the habit of hunting only what is needed immediately and then eating it until it ran out and then having to starve until the next successful kill. Given that even Neanderthal had massive "fat factories"[2], that our target prey were megafauna providing weeks to months of food at a time if preserved [3][4][5][6], that meat preservation through fermenting is so common as to probably account for our vulture-like stomach pH [7][8], and that we survived at all, the idea that we would have just let ourselves run out of food routinely seems rather unlikely. On top of that, comparisons of bone evidence of hunter-gatherer societies with contemporary agriculuralists suggest that famines are far more characteristic of the latter [9]. In other words, it may have been less common before agriculture.

If it is not true that humans were so desperate for food on a regular basis that they would simply have eaten everything it was possible to eat, then it stands to reason that like every other species we would have developed preferences and standards. And of course we have [10].

Just because you can, doesn't mean you should

The notion that omnivores "eat everything" is another one of those ideas that sounds logical on its face but falls apart almost immediately upon inspection. In another chapter of Facultative Carnivore, Carnivores, Herbivores, and Boars. Oh my., I describe in detail the fundamental problem with the lay understanding of what it means to be an omnivore: that if the definition is not carefully constructed, almost all animals on earth would be classified as omnivores, including felines and bovines, canonical carnivorous and herbivorous species. A definition of omnivore that does not render the whole classification system meaningless must admit that: flexible eating alone does not an omnivore make; physiological adaptations make some foods better than others for each species, even if nutritional needs can be met to some degree by lesser choices.

In the absence of frank starvation, all species will eat the preferred parts of what is available even if it means throwing away or ignoring possible choices, for example as wild primates discard thick peels, and spit out "wadges" of the parts they don't want once they've extracted juice [11]. In microeconomics there is a concept of an inferior good -- the higher one's income, the less it is bought. The canonical example of this is a food: cabbage. But in fact even in the presence of starvation, food with the wrong characteristics will not be eaten. In my talk linked above, I picture a racoon hat to drive home the point that there are limits to "eat the whole carcass" and we all have some agreement about what's clearly over the line. But it should not be assumed that bones and fur are the only components one might try to eat only in the worst possible circumstances.

As an example of what might not be eaten even if starving we have the phenomenon of rejecting hunted carcasses having inadequate fat [12]. This lean meat rejection is due to the inability of humans to derive adequate energy from protein alone, partly because of the inability to handle the byproducts of protein metabolism over a certain threshold (see eg. [13]). Similarly, there are plants that animals will eat, but only in limited quantities or in the presence of other detoxification substrates. For example, cattle will eat less of a high kale mix diet than they would otherwise [14], and generally speaking employ strategies of altering diet selection to deal with plant secondary compounds [15]. Cedar waxwings will eat the fruit of the European cranberrybush, but not until they also have access to adequate protein from cottonwood catkins to counterbalance the toxicity [16].

In these cases, the animal is motivated to eat certain foods when their bodies are in a ready state, but motivated against eating the same foods when resultant toxicity levels would be too high. Presumably this is mediated in part by taste. For this reason, I consider it extremely unwise to eat something that tastes bad to you just because you think rationally that it would be good for you. Many people don't like the taste of liver, and part of this could simply be enculturation! However, my own experience with liver, and one I've heard echoed in many others, is that it can taste absolutely delicious from time to time, but after a large portion it becomes unappetizing or even revolting for a long period after. This seems quite clearly to me reminiscent of the cattle-kale relationship, and strongly suggests toxicity that it would be the height of foolishness to circumvent via pill swallowing.

Evolutionary adaptation is an interaction, not just a response

I think that a lot of people have the idea that the process of natural selection involves a basically stable environment that an organism becomes more and more adapted to. But this misses the critical realisation that organisms change the environment as they go. As an organism specializes to use some resources, leaving others behind as waste, other organisms step in to fill the newly created niche. That means that it is not a given that humans would just naturally use up resources in "whole" parts. We use what we want, and this creates opportunties. We'll discuss one of those below.

The human predatory pattern is unique

Humans are facultative carnivores, but we have a different lineage than others, resulting in different possibilities, optimizations, and requirements.

Things the "Carnivore Diet" is not

In the early 2010's when I and a couple others started calling the "Zero Carb" (ZC) diet many of us were doing a Carnivore diet, it was because the name ZC gave many newcomers the wrong impression. While we were in fact still minimising carb intake, the primary difference between the "very low carb" / "ketogenic" diet that most of us had first come from was not carb count, but "kingdom source". The most accurate first pass at a description of ZC was that we ate food only from Kingdom Animalia. This was not the whole story--for example, liver was discouraged, and coffee was considered "ok" (for reasons I've discussed elsewhere). Nonetheless, it seemed to me at the time that "carnivorous" was a much less confusing description than "zero carb". I was wrong.

Or at least, while it may have been less confusing in the ways ZC was confusing, it created a great deal of confusion of its own. You see, the Carnivore Diet was a protocol with specific rules and guidelines, but of course, when these rules and guidelines began to be described in oversimplified terms, newcomers mistook them for a definition of the protocol instead of a roughly summarised description.

Specifically, among other distortions, the Carnivore Diet is not defined by trying to mimic the eating patterns of other animals known to be carnivorous. We are not trying to eat like wolves, lions, or polar bears. While they may be inspirational icons, each of those animals has physiological differences from humans that make their diets necessarily different. We aren't even trying to replicate the diet of some idealised early man, carnivorous as he may have been!

Humans are Lipivores

As I have discussed extensively elsewhere, the provenance of humans compared to other carnivorous species came with constraints that limited us to a much higher reliance on fat than species traditionally acknowledged as carnivorous. For this reason, I have suggested a classification view of humans as not just carnivorous from the animal-plant spectrum aspect, but as lipivores from a macronutrient perspective.

I will defer this discussion, as I'm currently writing a great deal more about that with another scholar. However, if you accept this as a premise for now, or have been persuaded of it based on my previous work, then you can see why I think it's an important part of the evidence that we didn't just eat "whatever we could find".

Co-evolution with dogs affected proportions

Dog domestication probably started before agriculture, with hunter-gatherers near the end of the Ice Age. Domesticating an ecological competitor is not easy to explain, but it has been argued that the higher protein-to-fat ratios of hunted game in this era provided humans with more protein than we could use [17]. This unused surplus could have been the intial attractant, and something of value to eventually exchange with dogs for their labour.

This is consistent with many ethnographic reports of modern hunter-gatherer societies feeding dogs excess lean. Moreover, reports often include preferential feeding of organ meats to dog. While people certainly do and did eat liver at times, the proportion must have been affected by this practice. Examples from Speth [18] include:

The Indian feeds his dog on tenderloin, sirloin, the meat of the legs and the heart, lungs, liver and kidneys. He confines his own activities to the head, bones, intercostal muscles, fat, intestines, unborn calf and afterbirth. [...] Meat straight is an unsatisfactory diet unless the Indian custom is followed. If one is to keep in condition he should use a great deal of raw smoke-dried fat. Well cooked fat is more palatable but more cloying. (Wheeler 1914: 58)

It is seldom among the Alaska and Mackenzie River Eskimos that caribou hams are eaten when there is enough of other meat. The hams, some of the entrails, the lungs and liver, the outside meat from the neck and brisket, and the tenderloin are the food of the dogs (Stefansson 1921: 232)

If a family of three Eskimos has a team of six dogs, then on the average the people eat half of each caribou, the team the other half. And the halves are always the same. The dogs, for instance, get all the livers and the people get all the heads; the dogs get all the tenderloins and most of the ham meat, the people get all the briskets and most of the rib meat. (Stefansson 1944: 2)

But also quoted!:

I found the Indians putting great emphasis upon the eating of the organs of the animals, including the wall of parts of the digestive tract. Much of the muscle meat of the animals was fed to the dogs. (Price 1939: 260)

Similarly in Fat of the Land, Stefansson repeatedly emphasises giving caribou and other liver to dogs, but also notes that seal liver in particular was often eaten preferentially by people. There may be particular components of individual sources that make them more or less preferred or tolerable. For example, seal liver on average has about half the vitamin A as caribou (but variability is enormous) [19], and it also probably has a lot of taurine, which may be a mitigating factor in hypervitaminosis A [20] (perhaps relevant to the observation that it was often eaten raw when eaten, as taurine is very heat-sensitive).

Regardless, even if liver were only given to dogs part of the time, it could have a large effect on the total intake, and it's even plausible that liver not consumed was part of the original draw of canines to the human doorstep. Evidence of this kind puts serious doubt on even the upper bound calculation of eating liver in proportion to the animal we eat other parts of that it came from.

Modern livestock is higher in vitamin A

Another component often missed I learned from Matthew Dalby on his sadly abandoned blog The Call of the Honey Guide. In a post preserved on the Wayback Machine, he wrote about his findings showing that because of modern farming supplementation practices, liver we buy today may have significantly higher levels of vitamin A than previously -- potentially by a factor of 3-9!

Moreover, as a result of higher quality feed and practices, it is the opinion of Oklahoma State University forage experts that in recent years, "vitamin A has probably been overfed, and in many cases, drastically overfed."

Even if you reject all of my previous arguments about how much liver intake Paleolithic humans regularly participated in, this ought to give you pause.

In sum

"Nose-to-tail" advocacy is based on romantic and incoherent notions about starving humans who ate everything indiscriminately (like no other creature on Earth), and who hadn't the wherewithal to stock food (contrary to the evidence). It ignores ethnographic evidence about food partitioning, and wrongly assumes that the modern food supply matches ancient nutritional profiles.

On top of this, it encourages ignoring real physiological signals of potential harm, such as taste adaptation, and ignores the collective wisdom of people practicing the Carnivore diet who subjectively or objectively have better outcomes when they consume organs rarely or not at all. As supplementation is one of the only ways to make money from a Carnivore Diet, this advocacy becomes even more suspect.

End-to-end citations

1 “Good Calories, Bad Calories" by Gary Taubes https://archive.org/stream/GoodCaloriesBadCaloriesGaryTaubesViny/Good Calories%2C Bad Calories - Gary Taubes-viny_djvu.txt

The problem with this version of the Pima history is that obesity and overweight had been evident a century ago, when the relevant nutrition transition was from relative abundance to extreme poverty. From
November 1901 to June 1902, the Harvard anthropologist Frank Russell lived on the Pima reservation south of Phoenix studying the tribe and its culture. Many of the older Pima, Russell noted in a report of
the Bureau of American Ethnology, “exhibit a degree of obesity that is in striking contrast with the ‘tall and sinewy’ Indian conventionalized in popular thought.”

Obesity among the Pima is not a new phenomenon, as demonstrated by this photo of “Fat Louisa” taken in 1901 or 1902 by the Harvard anthropologist Frank Russell.

Russell’s assessment of the Pima’s relative corpulence was then confirmed by the anthropologist and physician Ales Hrdlicka, who visited the Pima reservation in 1902 and 1905. “Especially well-
nourished individuals, females and also males, occur in every tribe and at all ages,” Hrdlicka reported, “but real obesity is found almost exclusively among the Indians on reservations.”

For perhaps two millennia, the Pima had lived as both hunter-gatherers and agriculturalists. Game was abundant in the region, as were fish and clams in the Gila River. When the Jesuit missionary
Eusebio Kino arrived among the Pima in 1787, the tribe was already raising corn and beans on fields irrigated with Gila River water. In the decades that fol owed, they took to raising cattle, poultry, wheat,
melons, and figs. They also ate mesquite beans, the fruit of the saguaro cactus, and a mush of what Russel later cal ed “unidentified worms.” In 1 846, when a U.S. Army battalion passed through Pima
lands, the battalion’s surgeon John Griffin described the Pima as “sprightly” and in “fine health.” He also noted that the Pima had “the greatest abundance of food, and take care of it wel , as we saw many
of their storehouses ful of pumpkins, melons, corn etc.”

Life began to change dramatical y the following year, when a wagon route was opened to California “by way of Tucson and the Pima villages.” This became the southernmost overland route for the
California gold rush that began in 1849; tens of thousands of travelers passed through the Pima villages on the way west over the next decade. They relied on the Pima for food and supplies.

With the arrival of Anglo-American and Mexican settlers in the late 1860s, the prosperity of the Pima came to an end, replaced by what the tribe referred to as “the years of famine.” Over the next quarter-
century, these newcomers hunted the local game almost to extinction, and the Gila River water, on which the Pima depended for fishing and irrigating their own fields, was “entirely absorbed by the Anglo
settlements upstream.” By the mid-1890s, the Pima were relying on government rations to avoid starvation, and this was stil the situation when Hrdlicka and Russell arrived in the early 1900s.

2 Kindler, Lutz, Sabine Gaudzinski-Windheuser, Fulco Scherjon, et al. “Large-Scale Processing of within-Bone Nutrients by Neanderthals, 125,000 Years Ago.” Science Advances 11, no. 27 (2025): eadv1257. https://doi.org/10.1126/sciadv.adv1257.

In this area, Neanderthals practiced bulk harvesting of a wide range of animal resources including forest elephants, the largest terrestrial mammals of the Pleistocene (26). Here, we focus on one of the richest locales, Neumark-Nord 2/2 (NN2/2). We present data showing that body parts from a minimum of 172 large mammals (mainly bovids, horses, and deer) were brought to NN2/2 for intensive lipid processing, an activity that took place over a comparatively short period within a very small water-edge location. This processing entailed marrow extraction, as well as the creation of tens of thousands of small bone fragments for the production of grease.”

3 Ben-Dor, Miki, and Ran Barkai. “A Bioenergetic Approach Favors the Preservation and Protection of Prey, Not Cooking, as the Drivers of Early Fire.” Frontiers in Nutrition 12 (May 2025): 1585182. https://doi.org/10.3389/fnut.2025.1585182.

Hunting large prey (>100 kg) yielded significantly higher energetic returns (16,269 ca/h) than plant gathering (1,443 ca/h), with megaherbivores like hippopotamus providing sustenance for up to 22 days for a group of 25.

4 Ben-Dor, Miki, and Ran Barkai. Supersize Does Matter: The Importance of Large Prey in Palaeolithic Subsistence and a Method for Measuring Its Significance in Zooarchaeological Assemblages. April 14, 2021. https://doi.org/10.15496/publikation-55587.

[A]round 50% of the caloric estimation they present, or a million calories of the elephant energetic resources, are in the form of fat (Ben-Dor et al., 2011; Guil‐Guerrero et al., 2018), which does not require smoking for preservation, for the most part. Likewise, a Pleistocene elephant was more likely to supply double the calories estimated in their paper (Ben-Dor et al. 2011), thus providing the hunting group with essential calories and fatty acids for weeks (Guil‐Guerrero et al., 2018) and thus a surely prized food package (see Ichikawa, this volume; Lewis, this volume; Yasuoka, this volume).”

5 Barkai, Ran. Chapter 11 - An Elephant to Share: Rethinking the Origins of Meat and Fat Sharing in Palaeolithic Societies (Towards a Broader View of Hunter-Gatherer Sharing). McDonald Institute for Archaeological Research, 2019. https://doi.org/10.17863/CAM.47189.

The effect of the unprecedented enormous quantities and qualities of the fat and meat provided by the hunting of a single elephant, accompanied by the humans’ reciprocal behaviour towards their non-human counterparts, may have led to the human behavioural pattern of sharing that was aimed at resolving this dissonance. Sharing the fat and meat of the hunted probiscidean was directed at treating the carcass with respect by distributing the edible parts among group members as well as neighbouring groups, and most probably also by using the inedible parts as replicas of tools or even as practical tools, as pendants and figurines etc.

6 Blasco, R., J. Rosell, M. Arilla, et al. “Bone Marrow Storage and Delayed Consumption at Middle Pleistocene Qesem Cave, Israel (420 to 200 Ka).” Science Advances 5, no. 10 (2019): eaav9822. https://doi.org/10.1126/sciadv.aav9822.

Marrow consumption has been linked to immediate consumption following the procurement and removal of soft tissues. Here, we present the earliest evidence for storage and delayed consumption of bone marrow at Qesem Cave, Israel (~420 to 200 ka). By using experimental series controlling exposure time and environmental parameters, combined with chemical analyses, we evaluated bone marrow preservation. The combination of archaeological and experimental results allowed us to isolate specific marks linked to dry skin removal and determine a low rate of marrow fat degradation of up to 9 weeks of exposure.

7 Speth, John D. Putrid Meat and Fish in the Eurasian Middle and Upper Paleolithic: Are We Missing a Key Part of Neanderthal and Modern Human Diet? n.d., 29.

This paper begins by exploring the role of fermented and deliberately rotted (putrefied) meat, fish, and fat in the diet of modern hunters and gatherers throughout the arctic and subarctic. These practices partially ‘pre-digest’ the high protein and fat content typical of northern forager diets without the need for cooking, and hence without the need for fire or scarce fuel. Because of the peculiar properties of many bacteria, including various lactic acid bacteria (LAB) which rapidly colonize decomposing meat and fish, these foods can be preserved free of pathogens for weeks or even months and remain safe to eat.

...

In the second part of the paper, I extend these arguments to suggest that putrefied meat, fish, and fat are likely to have been equally important to the lifeways and adaptations of Eurasian Paleolithic hominins inhabiting analogous environments. If such food practices were in fact widespread during the mid- to late Pleistocene, they may help account for aspects of the archaeological record that are presently difficult to comprehend, such as the ‘on again, off again’ evidence for fire use (and hence cooking) during the Eurasian Middle Paleolithic.

8 Beasley, DeAnna E., Amanda M. Koltz, Joanna E. Lambert, Noah Fierer, and Rob R. Dunn. “The Evolution of Stomach Acidity and Its Relevance to the Human Microbiome.” PLoS ONE 10, no. 7 (2015). https://doi.org/10.1371/journal.pone.0134116.

It is interesting to note that humans, uniquely among the primates so far considered, appear to have stomach pH values more akin to those of carrion feeders than to those of most carnivores and omnivores. In the absence of good data on the pH of other hominoids, it is difficult to predict when such an acidic environment evolved. Baboons (Papio spp) have been argued to exhibit the most human–like of feeding and foraging strategies in terms of eclectic omnivory, but their stomachs–while considered generally acidic (pH = 3.7)–do not exhibit the extremely low pH seen in modern humans (pH = 1.5) [38]. One explanation for such acidity may be that carrion feeding was more important in humans (and more generally hominin) evolution than currently considered to be the case (although see [39]).

9 Berbesque, J. Colette, Frank W. Marlowe, Peter Shaw, and Peter Thompson. “Hunter–Gatherers Have Less Famine than Agriculturalists.” Biology Letters 10, no. 1 (2014). https://doi.org/10.1098/rsbl.2013.0853.

The idea that hunter–gatherer societies experience more frequent famine than societies with other modes of subsistence is pervasive in the literature on human evolution. This idea underpins, for example, the ‘thrifty genotype hypothesis’. This hypothesis proposes that our hunter–gatherer ancestors were adapted to frequent famines, and that these once adaptive ‘thrifty genotypes’ are now responsible for the current obesity epidemic. The suggestion that hunter–gatherers are more prone to famine also underlies the widespread assumption that these societies live in marginal habitats. Despite the ubiquity of references to ‘feast and famine’ in the literature describing our huntergatherer ancestors, it has rarely been tested whether hunter–gatherers suffer from more famine than other societies. Here, we analyse famine frequency and severity in a large cross-cultural database, in order to explore relationships between subsistence and famine risk. This is the first study to report that, if we control for habitat quality, hunter–gatherers actually had significantly lessnot more—famine than other subsistence modes. This finding challenges some of the assumptions underlying for models of the evolution of the human diet, as well as our understanding of the recent epidemic of obesity and type 2 diabetes mellitus.

10 Marlowe, Frank W., and Julia C. Berbesque. “Tubers as Fallback Foods and Their Impact on Hadza Hunter-Gatherers.” American Journal of Physical Anthropology 140, no. 4 (2009): 751–58. https://doi.org/10.1002/ajpa.21040.

The Hadza are hunter-gatherers in Tanzania. Their diet can be conveniently categorized into five main categories: tubers, berries, meat, baobab, and honey. We showed the Hadza photos of these foods and asked them to rank them in order of preference. Honey was ranked the highest. Tubers, as expected from their low caloric value, were ranked lowest. Given that tubers are least preferred, we used kilograms of tubers arriving in camp across the year as a minimum estimate of their availability. Tubers fit the definition of fallback foods because they are the most continuously available but least preferred foods.

11 Nakamura, Michio, and Noriko Itoh. “Seeds from Feces: Implications for Seed Dispersal and Fecal Analyses.” In Mahale Chimpanzees: 50 Years of Research, edited by Kazuhiko Hosaka, Koichiro Zamma, Michio Nakamura, and Noriko Itoh. Cambridge University Press, 2015. https://www.cambridge.org/core/books/mahale-chimpanzees/seeds-from-feces-implications-for-seed-dispersal-and-fecal-analyses/5FDAE8A4124E97393491063E87F3F500.

There are several fruit species at Mahale that are not swallowed immediately but are, instead, eaten by “wadging” in the mouth (Figure 19.3). Typically, when wadging, a chimpanzee puts mouthfuls of fruit between the lips and incisors, and, without biting, squeezes out the juice (Goodall, 1986). The fruit parts (i.e. skin, seeds, and fibers) that remain after extracting the juice are called a wadge, and this is often discarded. However, occasionally, chimpanzees will eat and swallow the wadge.

12 Ben-Dor, Miki. “Use of Animal Fat as a Symbol of Health in Traditional Societies Suggests Humans May Be Well Adapted to Its Consumption.” Journal of Evolution and Health: A Joint Publication of the Ancestral Health Society and the Society for Evolutionary Medicine and Health 1, no. 1 (2013). https://doi.org/10.15310/2334-3591.1022.

There is ample ethnographic evidence for human dependence on and preference for animal fat as a food source. Kelly (32) writes: “...although ethnographic accounts abound with references to the importance of meat they equally convey the importance of fat...”. He adds: “It therefore may be fat rather than protein that drives the desire for meat in many foraging societies”. Lee (33) writes about the !Kung of the Kalahari: “Fat animals are keenly desired, and all !Kung express a constant craving for animal fat”. About the James Bay Cree, Rockwell (34) writes: “The Cree considered fat the most important part of any animal. One reason they valued bears above other animals was because of their body fat and because the fat rendered down into a high quality grease”. The essentiality of fat is best demonstrated in Tindale’s account of the Pitjandjara of Australia (35). He writes: "When killing the animal they immediately feel the body for evidence of the presence of caul fat. If the animal is njuka, fatless, it is usually left unless they are themselves starving”. Coote and Shelton (36) report a similar attitude among the Yolngu of Arnhem, Australia, saying that "Animals without fat may indeed be rejected as food". In summary, ethnographic evidence corroborates archaeological evidence of the prominent role of animal fat in human nutrition and behavior.

13 Rudman, Daniel, Thomas J. DiFulco, John T. Galambos, Robert B. Smith, Atef A. Salam, and W. Dean Warren. “Maximal Rates of Excretion and Synthesis of Urea in Normal and Cirrhotic Subjects.” Journal of Clinical Investigation 52, no. 9 (1973): 2241–49.

A B S T R A C T When normal individuals eat 0.33 g protein N/kg body weight (BW)3' per day, they excrete 10-15 mg urea N/h per kg BW3'4. If they now ingest (at 0 h) 0.27 (dose A), 0.40 (dose B), 0.53 (dose C), 0.94 (dose D), or 1.33 (dose E) g protein N/kg BW3' (in the form of casein, ovalbumin, or lactalbumin), the rate of urea N excretion accelerates within 4 h. At dose C a maximal rate of urinary urea N excretion (MRUE) is reached, which averages 55 mg urea N/h per kg BW3' and which persists for 16 h. Higher doses of protein do not further accelerate urea excretion, but prolong the duration of MRUE to 28 h (after dose E). Blood urea N (BUN) rises by 7-20 mg/100 ml during the first 8 h after dose C to E, and remains stable within ±5 mg/100 ml during the ensuing 8-28 h of MRUE. Each increment of protein above dose C causes a further increment in plasma a-amino N. During infusion of free amino acids at a rate of 110 or 165 mg amino acid N/h per kg BW3' for 12 h, rate of urea excretion increases to the MRUE value produced by dose C-E of oral protein. These findings indicate that MRUE corresponds to a period of maximal rate of urea synthesis (MRUS).

14. Keogh, B., P. French, J. J. Murphy, et al. “A Note on the Effect of Dietary Proportions of Kale (Brassica Oleracea) and Grass Silage on Rumen pH and Volatile Fatty Acid Concentrations in Dry Dairy Cows.” Livestock Science 126, no. 1 (2009): 302–5. https://doi.org/10.1016/j.livsci.2009.06.010.

Offering dry cows K100 relative to K0 reduced dry matter intake by 17.5% (7.32 vs. 8.87 kg DM day−1, respectively) which may be associated with the presence of S-methyl-L-cysteine sulphoxide which can cause haemolytic anaemia and depressed DM intake. The results suggest that increasing the dietary proportion of kale was associated with a progressive decrease in dry matter intake but with minimal effects on rumen pH, total volatile fatty acid concentration and individual volatile fatty acid proportions.

15. Estell, R. E. “Coping with Shrub Secondary Metabolites by Ruminants.” Small Ruminant Research 94, no. 1 (2010): 1–9. https://doi.org/10.1016/j.smallrumres.2010.09.012.

Ruminants cope with PSM through integrated behavioral and physiological mechanisms that involve both pre-ingestive (sensory) and post-ingestive processes. Behavioral strategies to cope with PSM include reduced consumption, avoidance (especially bitter compounds), cautious sampling to attain familiarity with consequences, selecting plants/parts with lower concentrations, temporary intake cessation, changing pattern of feeding, altering diet composition, increasing dietary breadth/diet mixing, regulating PSM intake below a critical threshold, consuming dietary constituents to counter PSM, and consuming soil (Boyle et al., 2005; Dziba et al., 2006; Freeland and Janzen, 1974; Marsh et al., 2006a; Wiggins et al., 2003; Wink, 1998).

16. Levey, Douglas J., and Carlos Martínez del Rio. “It Takes Guts (And More) to Eat Fruit: Lessons from Avian Nutritional Ecology.” The Auk 118, no. 4 (2001): 819–31. JSTOR. https://doi.org/10.2307/4089834.

The interplay between fruit secondary metabolites and protein use and availability is well illustrated by Witmer’s (2001) study of springtime consumption of Viburnum opulus fruit by Cedar Waxwings. The fruits of V. opulus ripen in the fall but remain uneaten through the winter. In the spring, flocks of waxwings rapidly strip the fruit from bushes. After carefully falsifying a series of previous hypotheses to explain this curious pattern, Witmer (2001) demonstrated in the field that waxwings only ingested V. opulus fruit when they could also ingest supplemental protein from cottonwood (Populus deltoides) catkins, which are only available in the spring. In the laboratory, he demonstrated that waxwings maintained body mass and a positive protein balance only when they fed on both V. opulus fruit and the protein rich catkins. They lost mass when they were provided with only fruit or only catkins. Viburnum opulus fruit contain sufficient energy to satisfy the waxwings but contain little protein and high levels of chlorogenic acid, a toxic phenolic compound.

17. Lahtinen, Maria, David Clinnick, Kristiina Mannermaa, J. Sakari Salonen, and Suvi Viranta. “Excess Protein Enabled Dog Domestication during Severe Ice Age Winters.” Scientific Reports 11, no. 1 (2021): 7. https://doi.org/10.1038/s41598-020-78214-4.

How could humans possibly have domesticated a competitive species? Here we present a new hypothesis based on food/resource partitioning between humans and incipient domesticated wolves/dogs. Humans are not fully adapted to a carnivorous diet; human consumption of meat is limited by the liver’s capacity to metabolize protein. Contrary to humans, wolves can thrive on lean meat for months. We present here data showing that all the Pleistocene archeological sites with dog or incipient dog remains are from areas that were analogous to subarctic and arctic environments. Our calculations show that during harsh winters, when game is lean and devoid of fat, Late Pleistocene hunters-gatherers in Eurasia would have a surplus of animal derived protein that could have been shared with incipient dogs. Our partitioning theory explains how competition may have been ameliorated during the initial phase of dog domestication.

18. Speth, John D. “Rethinking Binford’s Utility Indices: Interpretive Problems in Northern Environments and Their Pleistocene Analogs.” PaleoAnthropology, October 17, 2022, Vol. 2022 No. 2 (2022): PaleoAnthropology. https://doi.org/10.48738/2022.ISS2.113.

19. Egeland, Grace M., Peter Berti, Rula Soueida, Laura T. Arbour, Olivier Receveur, and Harriet V. Kuhnlein. “Age Differences in Vitamin A Intake Among Canadian Inuit.” Canadian Journal of Public Health / Revue Canadienne de Sante’e Publique 95, no. 6 (2004): 465–69.

Table III

Liver	Median vitamin A, µg/100 g	Reported range
Ringed seal	5,490	195–15,000
Caribou	9,640	4,122–32,000

20. Yeh, Yen-Hung, Ya-Ting Lee, Hung-Sheng Hsieh, and Deng-Fwu Hwang. “Effect of Taurine on Toxicity of Vitamin A in Rats.” Food Chemistry 106, no. 1 (2008): 260–68. https://doi.org/10.1016/j.foodchem.2007.05.084.

Accumulation of vitamin A is the net consequence of uptake, biotransformation and elimination processes within an individual. Once vitamin A is absorbed, taurine exerts synergistic actions in scavenging it to form vitamin-thionein. Although the half-life of vitamin-thionein in the liver and kidney is not known exactly, it is many years (Sakamoto et al., 2001) and with continued retention, there is progressive accumulation in these tissues. The accumulated amount of vitamin A in the tissue was effectively reduced by taurine. Taurine is a special amino acid, which possesses an amino group and a sulfonate group. These functional groups might bind with vitamin A, and then stimulate the excretion of such compounds. In this study, it was also found that the amount of vitamin A in the serum of rats fed with the supplement of taurine was slightly increased. There is no evidence that taurine directly reduces the production of free radicals but it may well operate by binding vitamin A which is then not absorbed or is more rapidly excreted. In other words it may act by reducing the overall bioavailability of vitamin A or the intracellular availability of absorbed vitamin A. Hence, dietary taurine may play a role to reduce the toxic effect of vitamin A in the liver and kidney of rats.