diet

Joseph Ferraro and colleagues have done some neat analyses of the faunal remains from Kanjera South, Kenya [1]. Kanjera South is an archaeological assemblage of Oldowan artifacts and associated animal bones from around 2 million years ago. The site was once a plain next to a lake, and gradually built up clay and silt sediments over years and years of flooding and soil formation. Stone tools and bones stand out in the sediments, representing recurrent activities of ancient humans over a few hundreds or thousands of years. As a result, the site has a good statistical representation of fauna that were hunted by early humans, relatively early in the evolution of our genus.

This is not the earliest site with evidence for meat acquisition by stone toolmakers. We know that people were butchering animals with stone tools around 2.6 million years ago. But the first really good evidence for hunting strategies is much more recent -- around 1.8 million years ago at Olduvai Gorge. There are actually very few Oldowan-era faunal assemblages large enough to study hunting behaviors. Kanjera South shows that the activities documented at Olduvai Gorge were happening a bit earlier, and the site helps to clarify the kind of context in which we might expect to find more evidence of hunting behavior.

Hunting versus scavenging is the tiredest chestnut in anthropologists' Oldowan arsenal. Were early hunters really competent enough to bring down a duiker on their own? Or did they steal away pieces of half-eaten zebra carcases when the lions took a break?

In reality, there is no contradiction here. Undefended meat doesn't last a day in the open, whether on the plains or near waterholes. So scavenging meat from other carnivores usually means facing them down -- not a job for an incompetent killer. Meanwhile, present-day peoples who hunt and gather rely quite a lot on "power scavenging", or taking advantage of other carnivores' successes. The present value of a dead carcass is higher than that of a live animal, as long as it may still escape you. Whether the hunter has to predict prey behavior, or the scavenger has to predict competitors' behavior, both strategies require a depth of planning. So, when it comes to Oldowan-era sites, we should expect to see a mixture of hunted and scavenged remains.

In that context, we can make some inferences about hominin hunting practices by assessing which kinds of animals they hunted, and which they scavenged. Looking at tooth mark and cutmark evidence is not a perfect way of sorting hunting and scavenging -- because both kinds of marks are rare on faunal elements in archaeological contexts. But sometimes those comparisons lead to clear results. For example, here is the chart showing the number of tooth-marked midshaft fragments from long bones at Kanjera South, in comparison to experimental bone assemblages:

Figure 3 from Ferraro et al. 2013. Original caption: Tooth-marked mid-shaft fragments: results from experimental assemblages and excavations at KJS. Figure follows a published model [26]. Hominin-first assemblages refer to remains initially defleshed and demarrowed by hominins, then subsequently exposed to large-bodied carnivores (primarily hyenas). Carnivore-first assemblages refer to remains initially defleshed and/or demarrowed by large-bodied carnivores (primarily hyenas and/or lions). Data for body sizes 1–4 [21]. Modern data (with single standard deviations where available) derived from the literature [23]–[26], [56]–[58]. KJS frequencies are from Table 2 and Table S1. Multiple symbols for KJS indicate the results of multiple analysts. X’s indicate minimum and maximum estimates of damage (see Table S1). doi:10.1371/journal.pone.0062174.g003

These are cool data. Carnivores who get to chew on bones for a while tend to leave the middle of them covered in tooth marks. If humans get access to the carcass early, they will strip off the meat from those midshafts, break them into bits, and otherwise prevent the taphonomic pathway to carnivore tooth marking. And in the graph we see that the Kanjera South faunal assemblage looks like cases where humans were the agents of defleshing and butchering.

If humans had primary access to the carcasses, then the transport decisions of ancient hunters should have shaped the bone assemblage at Kanjera South. It is very common in analyses of the fauna from African Oldowan-era sites to divide the prey animals into three size classes -- small, medium and large. The majority of prey species were bovids, ranging from small antelopes to water buffalo, although most were in the small and medium size categories at Kanjera South. Ferraro and colleagues show that for medium-sized bovids, the hominins were taking two strategies. These bovids were too big to carry wholesale to a central place for sharing. So the hunters disarticulated the animals and carried back the legs, leaving the axial skeleton for the most part behind.

Except for the heads:

But why acquire, transport, and process an abundance of medium-sized heads? In living animals, these remains contain a wealth of fatty, calorie-packed, nutrient-rich tissues: a rare and valuable food resource in a grassland setting where alternate high-value foodstuffs (fruits, nuts, etc.) are often unavailable [2], [3], [29], [49], [52], [63], [76]–[78]. Medium-sized heads are also relatively dense and durable elements, and their internal contents are generally inaccessible to all but hyenas and tool-wielding hominins [63], [79], [80]. As a result, they are often seasonally-available as scavengable resources in East African grasslands [63], [76], [79]–[83]. Additionally, bone surface modification studies at KJS clearly demonstrate that hominins accessed internal head contents: several cranial vault and mandibular fragments bear evidence of percussion striae. Considered in sum, the presumed availability of these isolated remains across the landscape, the relative abundance of these remains in the KJS assemblages, and unambiguous material evidence that hominins exploited their contents on-site is most parsimoniously interpreted as reflecting very early archaeological evidence of a distinct hominin scavenging strategy – one that included a strong focus on acquiring and exploiting fatty, nutrient-rich, energy-dense within-head food resources (e.g., brain matter, mandibular nerve and marrow, etc.) [e.g., 24,63,76,82,84–86].

This is John Speth's scenario for fat acquisition from lean animals. The brain is the last part of the body to become fat-depleted during times of stress. If hunters are energy-limited, further lean meat is not going to be valuable to them because protein takes energy to digest. What they need most is fat, and the most ready source of fat is the brain. Accumulation of head elements, whether from hunted or scavenged sources, is an effective behavioral strategy in those circumstances. It's one that we think Neandertals pursued at the end of winter in some parts of Europe, and a strategy followed by hunters in ethnographic and historic contexts as well.

The paper's conclusion is well-framed as a summary of the overall value of evidence from Kanjera South.

With regard to evolutionary ecology, the relative uniformity of hominin activities documented through the KJS sequence indicates an evolved foraging adaptation well-tuned to local ecological contexts. This point implies that hominin involvement with, and their presumed consumption of, animal remains had substantial fitness implications. In turn, sufficiently strong selective pressures are implicated as having favored the evolution of persistent hominin carnivory no later than 2.0 million years ago. This date is approximately 200,000–500,000 years earlier than previously documented [11], [20], [33], [45], and increases the known time depth of this adaptation within the hominin lineage (range of dates reflects varied interpretations of faunal materials from Olduvai [20]–[42]).

This one was fun to read, because the data being built up at Kanjera South are really capable of testing hypotheses about hunting behavior in a way that some of the Oldovai Gorge assemblages have done up to now. Putting the faunal exploitation together with the stone tool evidence, we see a really interesting picture. As I reported a few years ago ("Plant processing with early Oldowan tools"), Kanjera South is one of the locations where we have good evidence of plant exploitation of some kind by Oldowan peoples. The site has also provided evidence about stone material transport decisions and the planning depth of stone flaking ("Technological sophistication of the earliest toolmakers". It is a good illustration of how deep knowledge of a single site, with teams returning to excavations over multiple seasons, can yield a richness of statistical information about hominin behavior.

References

During the past couple of years, new evidence has really shifted our view of Neandertal diet. Even three years ago, it was not unusual to hear Neandertals described as "hypercarnivores", more heavily reliant upon meat than any living hunter-gatherers, except possibly for Inuit who live on seal meat and whale blubber.

The idea that Neandertals had diets with a very high fraction of meat -- maybe as high as 90-95% meat -- came from analyses of stable isotopes. I reviewed some of the stable isotope work on Neandertal diet in 2005 - "Neandertals noshed on mammoth meat?", "Neandertals: gone fishin' or not?". Here at the beginning of 2013, stable isotopes are well worth another review here on the blog.

The extreme view of Neandertals as hypercarnivores has been softened by new evidence from several sources. Phytoliths and starch grains from Neandertal dental calculus have shown a wide variety of plants were consumed by Neandertals at least occasionally. Meanwhile, the starch grains have not only documented consumption of grains and tubers, but have also shown that Neandertals were cooking those plant foods. I wrote about the phytolith and starch granule discoveries by Amanda Henry and colleagues [1] last year ("Tartar control and Neandertal plant use").

A new article by John Speth in Before Farming reconsiders the archaeological record of game exploitation by Neandertals and early modern humans in the Near East [2]. Speth begins with a short review of how Neandertals gradually came to be known as hypercarnivores -- in spite of many archaeologists' insistence that they must have been incompetent in various ways. After some discussion of the limits of the archaeological record, he notes that the zooarchaeological record doesn't tell us about the quantitative contribution of meat to the diet. In short:

Lots of gazelle bones doesn’t necessarily mean lots of gazelle meat per capita per day.

He illustrates this point with a historical case, the excavation of trash heaps from Fort Ligonier, Pennsylvania, occupied by the British during the French and Indian War. There, the total meat yield represented by animal bones was estimated at only 4,000 pounds, a tiny fraction of the meat ration known to have been issued to soldiers. The point of the example is that many biases prevent the accumulation and discovery of animal bone, even in historic contexts. The Paleolithic record of faunal exploitation can represent only the merest fraction of animal carcasses that were actually handled or consumed by ancient peoples. Biases guarantee that this record will be unrepresentative in ways that we may be poorly able to assess.

Speth addresses the idea that Middle Pleistocene people consumed a very high fraction of meat by emphasizing that a diet of lean meat is unsustainable at such a level. If Neandertals' animal consumption was as high as Inuit peoples, then they must have been eating a high fraction of fat somehow:

The Inuit or Eskimos provide a classic example of peoples whose traditional sustenance was provided almost entirely by meat, the diet commonly envisioned for cold-climate Neanderthals. But when looked at quantitatively, Inuit diet was actually composed primarily of fat, not lean meat, with the protein contribution seldom surpassing about 35 per cent of their calories, and usually lower, closer to 25 per cent. Pemmican, the traditional mainstay of Native Americans and First Nation peoples (‘Indians’) inhabiting the Great Plains of mid-continental North America, was a mixture of rendered fat and dried, pulverized lean meat, the mix carefully prepared so that the pro- tein component did not exceed 25–30 per cent of total energy (eg, Stefansson 1956; Speth 2010). In habitats where plant foods are neither abundant nor available for long periods of the year, and particularly for foragers in such habitats who do not store foods, fat becomes the principal non-protein macronutrient for much of the year. Foragers in the northern latitudes did obtain some carbohydrates by consuming fermented stomach contents of reindeer and ptarmigan, and sometimes inner bark (cambium), as well as small quantities of berries during the summer months (Eidlitz 1969; Gottesfeld 1992; Östlund et al 2009; Sandgathe & Hayden 2003; Zackrisson et al 2000). Until fairly recently, stomach contents were actually considered a delicacy (often referred to as ‘Eskimo ice cream’), not an emergency resource resorted to only when all else failed (Starks 2007; Speth 2010). Unfortunately, we lack quantitative data on the actual amounts that were consumed, how those amounts varied over the year, and whether men and women had comparable access. Did Neanderthals also con- sume fermented stomach contents? If so, would such a practice have had any detectable impact on their unusually high nitrogen isotope values?

Through the middle of the article, Speth provides a detailed account of the biases due to taphonomy and ancient behavior that apply to faunal collections in Middle Paleolithic contexts. Many of these factors, such as biases in transport of different size animals, are well-known to archaeologists, but Speth's review will be useful for those who may not have studied the issue. The value of this part of the article is in its application of prey transport and landscape use to the unique geography of the Near East. Here, Middle Paleolithic peoples hunted amid water scarcity and temperature regimes that were very different from those found in Southwestern Europe. Yet by several indicators, the Middle Paleolithic population in both areas was relatively dense and successful.

Speth reminds us that ancient hunters were active agents who made choices in their hunting strategies. Some of those choices may have been influenced by landscape use and prey abundance, but others are less easily predictable in such terms:

The Hadza, one of the most thoroughly documented modern foraging populations, offer another interesting example. Wildebeest are one of the most abundant prey available to Hadza hunters, but they commonly avoid wildebeest in favour of zebras. Why? According to Hadza informants, the fat from wildebeest is hard and sticks to one’s teeth and palate,while zebra marrow and back-fat, especially the yellow subcutaneous deposits near the rump, are far more desirable (Oliver 1993:217; Selous 1907:220; Speth 2010:66–70). Were we to assume that Hadza hunters took prey in direct proportion to their availability on the landscape, our conclusions would be very wide of the mark.

Back to the problem of lean meat: Hunter-gatherers in ethnographic and historical records have used boiling to degrease bone. This allows the use of the fat from inside the cancellous structure of the bone, which is a key resource supporting the use of lean wild animal meat. Boiling or slow-cooking using heated stones has been applied by many peoples around the world, and tends to leave a very distinctive archaeological trace -- the heated rocks, lined pits dug to enclose the slow-cooking mass, all show up in the archaeology. These techniques were not used by Middle Paleolithic people, or if such people used heated rocks, they did not use them terribly extensively. Stone boiling became common only later in the Upper Paleolithic of Europe.

But Speth discusses other means of boiling, including the use of skin and bark containers. These are expedient and perishable, yet filled with water will effectively contain boiling liquid over hot coals or indirect flame. Whether such techniques were used by Neandertals remains speculative. The suggestion is latent in the identification of cooked starches within Neandertal dental calculus. If they were capable of cooking grains in moist heat, they must at least have been using bark packets or some other style of slow-cooking. The rendering of fat from bone by boiling in perishable containers would not take much additional innovation, and would have been energetically and nutritionally very advantageous.

As I was discussing this with friends a couple of weeks ago, it occurred to me that the combination of cooked grains and meats within an animal bladder is a recurrent feature of the cuisine of Northern Europe. Neandertal haggis.

References