Can you digest bone?
If you like shrews, especially if you like them parboiled, you'll want to devour a 1994 study published in the Journal of Archaeological Science. Called Human Digestive Effects on a Micromammalian Skeleton, it explains how and why one of its authors – either Brian D Crandall or Peter W Stahl; we are not told which – ate and excreted a 90mm-long (excluding the tail, which added another 24mm) northern short-tailed shrew (Blarina brevicauda).
This was, in technical terms, "a preliminary study of human digestive effects on a small insectivore skeleton", with "a brief discussion of the results and their archaeological implications". Crandall and Stahl were anthropologists at the State University of New York in Binghamton. The shrew was a local specimen, procured via trapping at an unspecified location not far from the school. For the experiment's input, preparation was exacting. After being skinned and eviscerated, the report says, "the carcass was lightly boiled for approximately 2 minutes and swallowed without mastication in hind and fore limb, head, and body and tail portions".
Here's how Crandall and Stahl handled the output: "Faecal matter was collected for the following 3 days. Each faeces was stirred in a pan of warm water until completely disintegrated. This solution was then decanted through a quadruple-layered cheesecloth mesh. Sieved contents were rinsed with a dilute detergent solution and examined with a hand lens for bone remains." They then examined the most interesting bits with a scanning electron microscope, at magnifications ranging from 10 to 1,000 times.
A shrew has lots of bony parts. All of them entered Crandall's gullet, or maybe Stahl's. But despite extraordinary efforts to find and account for each bone at journey's end, many went missing. One of the major jawbones disappeared. So did four of the 12 molar teeth, several of the major leg and foot bones, nearly all of the toe bones, and all but one of the 31 vertebrae. And the skull, reputedly a very hard chunk of bone, emerged with what the report calls "significant damage".
The vanishing startled the scientists. Remember, they emphasise in their paper, that this meal was simply gulped down: "The shrew was ingested without chewing; any damage occurred as the remains were processed internally. Mastication undoubtedly damages bone, but the effects of this process are perhaps repeated in the acidic, churning environment of the stomach."
Chewing, they almost scream at their colleagues, is only part of the story. In each little heap of remains from ancient meals, there be mystery aplenty. Prior to this experiment, archaeologists had to, and did, make all kinds of assumptions about the animal bones they dug up, especially what those partial skeletons might indicate about the people who presumably consumed them. Crandall and Stahl, through their disciplined lack of mastication, have given their colleagues something toothsome to think about.
The human stomach was more capable at digesting bones than they expected. This isn't terribly surprising to me, as many cultures consume whole bone-in animals and there is plenty of archaeological evidence for this. Here's a bit from John Speth's book:
Well-preserved prehistoric human coprolites (feces) recovered in large numbers from dry caves throughout western North America are full of pulverized bone fragments, including pieces of broken skulls, as well as fur and feathers, indicating that rodents, rabbits, birds, lizards, snakes, and amphibians were often cooked whole, pounded in a wooden mortar or on a milling stone, and then consumed in their entirety – bones, fur, feathers, and all, including the precious DHA in the brains (Reinhard et al. 2007; Sobolik 1993; Yohe et al. 1991).
It would appear that the Desha people at Dust Devil Cave ate rabbit legs more-or-less whole, then pounded the rest of the carcass before eating it... The consumption of wood rats (Neotoma spp.), also known as pack rats, has been noted ethnographically. They were regarded as good food by the Yaqui (Spicer, 1954: 49), constituted a staple for all tribes along the lower Colorado River (Castetter & Bell, 1951: 217), and many were eaten by the Tohono O’Odham. The Cocopah set fire to their nests, clubbing the rats as they emerged, undoubtedly fragmenting some bone in the process.
In the past, there was perhaps more focus on big game hunting. And while big game bones are nice, they are harder to process than little animal bones. Primates have probably been digesting little bones for much longer than they have been breaking open larger bones for marrow. Excessive focus on big game has led to ignoring the contribution of small game to human nutrition, which has also led to the misconception that women don't hunt since some anthropologists classified small game hunting as gathering.
It would be interesting to know if other primates can also digest bone. Chimpanzees seem to degrade the bones of other primates they hunt and consume (PDF). Salad lovers might be interested to know that when chimpanzees consume a meal of meat, they consume it with leaves.
It would also be fascinating to know if humans process the same ability as some other carnivores to use animal parts as de-facto fiber and ferment it into SCFA.
At some point in human evolution, humans developed technology to extract nutrients from bones more efficient than their own stomaches, which is referred to as "grease processing" in many archaeological papers, but is close to what we do in making broths today. It is understandable why humans developed this, considering a meaty meal for a chimpanzee can take nearly the entire day to consume. Frankly, while I like a 6-hour tasting menu sometimes, I don't have time for that very often.
But today, could many humans handle bone? With dietary and medical factors like widespread use of proton pump inhibitors reducing acidity of the digestive tract, are we losing this capability?
For the record, I have never eaten a whole rodent bones and all, though I have eaten many small whole bony fish. There is some indication that humans degrade fish bones more completely, leading to their relative scarcity in coprolites and underestimation of their importance in diet.
Perhaps whole rat eating is becoming trendy again though, a posh rat dinner was featured in the New York Times recently.