Importance of Fat
Abstract
The worldwide association of H. erectus with elephants is well documented and so is the preference of humans for fat as a source of energy. We show that rather than a matter of preference, H. erectus in the Levant was dependent on both elephants and fat for his survival. The disappearance of elephants from the Levant some 400 kyr ago coincides with the appearance of a new and innovative local cultural complex – the Levantine Acheulo-Yabrudian and, as is evident from teeth recently found in the Acheulo-Yabrudian 400-200 kyr site of Qesem Cave, the replacement of H. erectus by a new hominin. We employ a bio-energetic model to present a hypothesis that the disappearance of the elephants, which created a need to hunt an increased number of smaller and faster animals while maintaining an adequate fat content in the diet, was the evolutionary drive behind the emergence of the lighter, more agile, and cognitively capable hominins. Qesem Cave thus provides a rare opportunity to study the mechanisms that underlie the emergence of our post-erectus ancestors, the fat hunters.
The physiological ceiling on plant food intake. The intake of plant foods can conceivably be limited due to a physiological ceiling on fiber or toxins intake, limited availability, or technological and time limitations with respect to required preconsumption preparations, or a combination of these three factors. A significant contribution to the understanding of the physiological consequences of consuming a raw, largely plant-based diet was made by Wrangham et al. [17,18]. A physiological limitation seems to be indicated by the poor health status of present-day dieters who base their nutrition on raw foods, manifested in subfecundity and amenorrhea [17,18]. Presumably this limitation would have been markedly more acute if pre-agriculture highly fibrous plant foods were to be consumed. Limited availability is manifested by the travails of the obligated high-quality diet consumer of the savanna, the baboon. Baboons are somewhat similar to humans with respect to their ratio of colon to small intestine rendering the quality requirements of their diet comparable to an extent to that of humans. Baboons have been documented at times as devoting ‘‘almost all of their daylight hours to painstakingly seeking out small, nutritious food items….[the] adult male baboon (Papio cynocephalus) may pick up as many as 3000 individual food items in a single day’’ ([59]:103). Nuts, or other high-quality foods of decent size appear only seasonally above ground in the savanna and such is the case in the Levant, too. But not only are they seasonal, they also require laborious collection and most of them contain phytic acid that inhibits the absorption of contained minerals. These foods also contain anti-nutrients and toxins such as trypsin, amylase and protease inhibitors as well as tannins, oxalate, and alkaloids the elimination of which can only be achieved (sometimes only partially) by pre-consumption processing like drying, soaking, sprouting, pounding, roasting, baking, boiling and fermentation. While these technologies are extensively used, mostly conjointly, in present day pre-consumption preparation of many plant foods, some were probably not practiced by H. erectus, especially those requiring accumulation and storage of produce for weeks (see, for example, [60]:173 with respect to Mongongo nuts, or [61]:31 regarding Baobab seeds). Comparing food class foraging returns among recent foragers, Stiner ([62]:160) has found the net energy yield of 3,520–6,508 kj/hour for seeds and nuts compared to 63,398 kj/hour for large game. Roots and tubers returns are not better, ranging from 1,882 kj/hour to 6,120 kj/hour. These numbers point to the substantial time investment required in gathering and preparing plant foods for consumption.
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The Importance of Fatty Meat
Humans have a pronounced desire for meat, and especially fatty meat. Even where plant food provides the bulk of calories, foragers still refer to the lack of meat in camp as a time of hunger and starvation (see Silberbauer 1981b: 494; Shostak 1981). Even though hunting frequently provides meager returns (Table 3-6), all foragers value meat highly (Dwyer 1985b). Despite the importance of plant foods to Bushmen diet, for example, the Ju/’hoansi “eat as much vegetable food as they need, and as much meat as they can” (Lee 1968: 41; Figure 3-7). In some Australian societies, young men acquire religious knowledge from older men by exchanging meat for it. This gives them considerable motivation to hunt because men cannot become full-fledged adults and marry if they do not acquire sufficient ritual knowledge. Hunting success correlates with quantity of ritual knowledge as well as with secular status in Australia (Sackett 1979; Altman 1984, 1987). Gunwinggu men are divided into maihmak (men good for animal flesh) or maihwarreh (men rubbish for animal flesh; Altman 1987). In fact, hunting among many foragers often takes on strong symbolic meanings since it takes the life of beings that are, as the Cree point out, “like humans” (Tanner 1979). An ecological approach to diet, however, must initially assume that an activity’s value is related to its material consequences. Why is meat so highly desired in all hunter-gatherer societies? One obvious reason is that meat contains high-quality proteins, the nine essential amino acids that the human body cannot synthesize. High-quality proteins are essential for normal metabolic function. (Meat is also more nutrient-dense than plant food, providing essential minerals, such as iron and zinc, vitamins such as B12, and glucose in an easily digestible form. ) However, although ethnographic accounts abound with references to the importance of meat, they equally convey the importance of fat in assessing the quality of game ( Jochim 1981: 78–87; Hayden 1981b; Speth and Spielmann 1983; Abrams 1987). Among the Kaska, for example: Meat itself is ranked in order of preference . . . Fat is greatly relished and all meat is improved if it contains fat. From October, when the moose begins to run, and throughout the winter, bulls are tough and their meat contains little fat. They then are regarded as “no good eating,” in comparison to the cow, which is rich and succulent with fat. (Honigmann 1949: 104; see Speth 2010: 70–72 for more accounts) Animals that generally have little body fat are often considered secondary resources or even starvation food. During a time when no large, fat-rich game was available in the Canadian subarctic, for example, a Hare man wearily moaned that it was “back to choking rabbits” (Savishinsky 1974: 25). It may therefore be fat rather than protein that drives the desire for meat in many foraging societies. Animal fat is important as a source of linoleic acid (although not as good a source as oil-rich seeds) and is important for the absorption, transportation, metabolism, and storage of fat-soluble vitamins. There is, therefore, a physiological reason for humans’ preference for fatty foods. But do foragers desire meat for protein and fat or for calories? Protein and fat are both a source of energy. At 4 kcal/gm, the protein in meat provides the same amount of energy as carbohydrates, and fat provides even more – 9 kcal/gm. To derive energy from protein, however, the human body must raise its metabolic rate by 10 percent over that required to process energy from carbohydrate or fat (Noli and Avery 1988: 396). The rate of oxygen uptake by the liver limits the proportion of an individual’s energy need that can be derived from protein to about 50 percent – about the maximum seen in hunter-gatherer diets (Cordain et al. 2000; the Ache, e.g., derive about 39 percent of their energy from protein; Hill 1988). Experimental studies show that consuming large amounts of lean meat leads to clinical symptoms of protein poisoning, signs that the kidneys and liver are overloaded: nausea, a sense of uneasiness, dehydration, and diarrhea. In extreme cases, this can lead to death (through what is known as “rabbit starvation” among explorers of the north: eat all the rabbits you want in the spring – you will still die because rabbits at that time are extremely lean). Excessive use of protein as an energy source can also lead to toxic levels of ammonia in the blood, calcium loss, and lean-tissue loss, even over the short term, and it may be especially damaging to pregnant women (see Speth and Spielmann 1983; Spielmann 1989; Speth 1990, 2010). Lean meat is not only a problem in the Arctic but also at any time that animals go through a lean season that requires them to metabolize their own fat deposits (Speth 2010: 72). In addition, human energy needs must be met before protein needs. A diet high in protein and low in carbohydrates or fat results in the body using protein as energy, rather than as protein, meaning that a diet high in lean meat could result in protein deficiency (Speth and Spielmann 1983: 13). Carbohydrates and fat spare protein from being used as a source of energy. All things being equal, wise foragers will want a certain amount of carbohydrate or fat in their diet to free up the protein in the meat they consume. We could be justified in using calories as the only currency in foraging models if the caloric and protein contents of foods are correlated, as Hawkes and O’Connell (1985) show to be true for the foods consumed by the Ju/’hoansi. This perspective on calories, protein, and fat makes some sense out of several practices of foraging societies. It accounts for the so-called fat and grease “obsessions” of maritime huntergatherers, such as those of the Northwest Coast, where eulachon fish oil was highly prized (see Noli and Avery 1988). It also accounts for meat gorging among Plains hunter-gatherers (Speth and Spielmann 1983) and the trading of meat for carbohydrates between foragers and horticulturalists (as noted in Chapter 1; see also Spielmann 1991). And it sheds light on the nature of tropical-forest subsistence. Anthropologists have attributed village warfare and hunting taboos in the tropical forests (especially the Amazon) to the difficulty of acquiring sufficient animal protein (see review in Sponsel 1986).19 However, some studies suggest that tropical foragers acquire a substantial proportion of calories from meat; for example, 68 percent for the Hiwi (Hurtado and Hill 1990). Tropical hunter-gatherers may have an excess of protein but be deficient in carbohydrates (Milton 1985; Sponsel 1986; Hill et al. 1987). The Efe, for example, trade meat for Lese agricultural produce containing two to five times the meat’s caloric content (Hart 1978; Bailey and Peacock 1988). Tropical horticulturalists, however, may have a surfeit of carbohydrates but inadequate protein (e.g., Keegan 1986). Foragers may need the carbohydrate resources of neighboring horticulturalists, and hunting may be the most cost-effective means of acquiring them.
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Conclusion: In line with evidence for the importance of dietary animal fat in prehistoric and traditional societies, the studied traditional societies perceived animal fat as a vital component of their diet and a profound source of health rather than an impediment to health as it is presented in many dietary recommendations today.
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