Chapter 4: Permavegan Jonathan Maxson’s investigation into Keith’s claims about australopith diets

Lierre Keith might be an interesting person with lots of life experience, but is not a nutritionist or a doctor with training in any school of either “western” or “nonwestern” medicine. She is not an anthropologist, palentologist, or biologist. This doesn’t mean she can’t have interests or even write about them; for instance, Chris of this blog has big-time interest in different ways to make pancakes and marathon running; Carolyn loves Bjork and is a huge geek for quantum physics; Alex is really into black metal and LARPing. But none of us (except maybe Alex with the black metal) would never even think to consider ourselves so well-established in the relevant information that we could map an entire history and science of these things. THEY ARE HOBBIES. Paleontology and nutrition are Keith’s hobby. She’s excited about it. We support excitement. But she has no credentials to make the kinds of claims she puts forth in this chapter, and almost none of her resources cited in are first-hand, peer reviewed research. Keith’s chapter 4, on “Nutritional Vegetarians”, arguably has more objective misinformation, much of it potentially dangerous, than anywhere else in the book.

Jonathan Maxson of the wonderful Permavegan Blog, a long-time vegan permaculture student, practitioner, and educator, has offered a critical analysis and much-needed perspective on chapter 4’s opening claims about the diets of our closest human ancestors. He analyzes the direct sources that Keith, it seems, cited only from 2nd and 3rd hand analyses. PLEASE READ THIS IF YOU ARE INTERESTED IN THE “PALEO DIET” DEBATE.

Does Carbon Isotope Analysis of Dental Enamel Prove Austhralopiths Ate Meat, Thereby Undermining Plant-Based Nutrition? by Jonothan Maxson

According to Lierre Keith – and she is by no means alone in her belief – it does.  Keith’s opening argument against plant-based nutrition in chapter four of The Vegetarian Myth [1] is that our Australopithecine ancestors were eating meat from the African savannah some four million years ago, and that meat consumption played a pivotal role in the evolution of our human brains and bodies.

The first scientific reference Keith cites in support of this assertion is a 1999 carbon isotope analysis of fossil dental enamel by Sponheimer and Lee-Thorp [2], which Keith treats as proof that Australopithecus ate meat.  (For a quick overview of how Australopithecus fits into our long-term evolutionary pathway, see the Wikipedia entry Timeline of Human Evolution).

It is not clear if Keith read the study by Sponheimer and Lee-Thorp herself, or merely read the interpretation of the study advanced by Eades and Eades [3], whom Keith cites as the source of the reference.  Nevertheless, the findings in the study do not, in fact, allow us to draw Keith’s conclusion, as the authors of the paper are the first to admit.  Here is the abstract [2]:

Current consensus holds that the 3-million-year-old hominid Australopithecus africanus subsisted on fruits and leaves, much as the modern chimpanzee does. Stable carbon isotope analysis of A. africanus from Makapansgat Limeworks, South Africa, demonstrates that this early hominid ate not only fruits and leaves but also large quantities of carbon-13 enriched foods such as grasses and sedges or animals that ate these plants, or both. The results suggest that early hominids regularly exploited relatively open environments such as woodlands or grasslands for food. They may also suggest that hominids consumed high-quality animal foods before the development of stone tools and the origin of the genus Homo.

An objective reading of the abstract, and especially the full text of the article, shows that Sponheimer and Lee-Thorp refrained from misinterpreting the results of their study as direct evidence of meat-consumption by Australopithecus. On the contrary, it is obvious they consider their results inconclusive about the exact nature of the the carbon-13 enriched foods consumed by this early hominid.  Looking exclusively at the isotope analysis, these foods may have been plant-based, or they may have been animal-based.  The authors admittedly lean slightly in the direction of meat, but they are careful to point out that this is only speculation on their part, and that further scientific investigation is required before the question can be settled.

Sponheimer and Lee-Thorp do not claim that bipedalism in Australopithecus was in any way related to the consumption of meat.  Nor do they assert that Australopithecus favored a grassland environment, but they seem equally open to the possibility of a predominantly woodland environment.  Indeed, in a 2008 paper almost ten years later, Sponheimer and Lee-Thorp together with first author de Ruiter [4] found that a predominantly woodland habitat seems more typical for Australopithecus:

Correspondence analysis of fossil assemblages reveals that the abundance profile of A. robustus is most similar to that of woodland-adapted taxa. In addition, fluctuations in the relative abundance of taxa assigned to the broad habitat categories reveal a significant negative correlation between A. robustus and open grassland-adapted taxa, indicating that the more grassland-adapted taxa there are in a given assemblage, the fewer hominins there tend to be.

In the discussion section of this 2008 paper, the authors generalize about the significance of their findings for hominins in general:

The likelihood therefore exists that the hominins were habitat generalists capable of living in a variety of environments, but perhaps preferring woodlands over the less-favored grasslands when conditions were sufficient.

Returning to the question of carbon isotope analysis of carbon-13 enriched foods in the diet of Australopithecus, it is true that in a 1994 paper [5], Lee-Thorp and co-authors lean toward an argument for the omnivory of Australopithecus, but this is tempered in the 1999 paper cited above, and again in a subsequent 2000 paper [6].

The latter paper, titled The Hunters and Hunted Revisited, is particularly intriguing, as it underscores the role of Australopithecus as prey, not predator, in African paleoecology – an understanding that fits rather well with the Australopith’s preference for protected woodlands.

Dart’s beliefs that australopithecines had played an active, leading role (Dart, 1949, 1956, 1957) in accumulating the considerable faunal bone assemblages in the Sterkfontein and Makapansgat Valley sites were overturned when Brain showed that the composition, damage, and state of preservation of the bones were due to activities of large predators rather than predation by hominids (Brain, 1970, 1981). The leopard Panthera pardus was first proposed as the predator most likely responsible for the primate accumulations in particular, an insight which effectively reversed the role of the hominids from that of dominant predator to that of victim (Brain, 1981). Indeed the leopard fang-sized impression in the cranium of a juvenile Paranthropus robustus, SK 54, shows convincingly that at least one hominid fell victim to a leopard.

Following the relegation of the australopithecines as prey rather than active hunters, their dietary niche began to be viewed from the perspective of a rather more chimpanzee-like diet, concentrating on plant foods. The role of more active meat-eater, as hunter or scavenger, was shifted to the shoulders of Homo habilis or early H. erectus (H. ergaster following Wood & Collard, 1999), appearing slightly later in the late Pliocene/early Pleistocene.

Significantly, the results of this 2000 study indicate no increase in the proportion of carbon-13 enriched foods in the diet of Homo ergaster relative to Australopithecus, providing no support for the hypothesis that the diet of Homo ergaster was any more meat-based than the diet of Australopithecus, thereby completely breaking a link in the idea that meat-eating is a distinctive attribute of Homo.

Lee-Thorp and Sponheimer worked together and with other coauthors on several subsequent papers exploring various aspects of this question in further detail [7][8][9][10][11][12].  None of these studies resolves the issue in favor of an omnivorous Australopith hypothesis, but the trend is rather consisently in favor of a plant-based interpretation of the evidence.

One of these studies may be pivotal.  In the 2005 paper Sr/Ca and early hominin diets revisited [9], Sponheimer, Lee-Thorp and their co-authors found that the strontium-calcium (Sr/Ca) ratios in the dental enamel of Australopithecus and Paranthropus were not consistent with the consumption of meat, but with some other source of carbon-13 enriched foods.  In her discussion of carbon-13 and Australopithecine dental enamel, Keith reduces the only other non-meat option to grass, but Sponheimer, Lee-Thorp and co-authors here speculate about two additonal non-meat sources of carbon-13 enriched foods: insects and tubers.

Sponheimer, Lee-Thorp, et al. consider all three of these options, but rule out grass and insects because the low barium/calcium (Ba/Ca) ratio also found in Australopithecus is inconsistent with either grass consumption or insectivory, as the Ba/Ca ratio is generally high among herbivores and insectivores.  Instead, they cite some exciting preliminary evidence in support of the tuber alternative:

We have noticed that among the modern fauna that have the unusual combination of high Sr/Ca and low Ba/Ca are warthogs (Phacochoerus africanus) and mole rats (Cryptomys hottentotus) (Sponheimer, unpublished data), both of which eat diets rich in underground resources such as roots and rhizomes. Thus, the possibility of greater exploitation of underground resources by Australopithecus compared to Paranthropus requires consideration. In addition, the slightly enriched Sr/Ca of Paranthropus compared to papionins might also be evidence of increased utilization of underground resources. Thus, the consumption of underground resources seems to be a reasonable hypothesis to explain the Sr/Ca of South African hominins in general, and the very high Sr/Ca of Australopithecus in particular. Indeed, Sillen et al. (1995) have argued that the consumption of underground resources (e.g., Hypoxis) led to relatively high Sr/Ca in early Homo. Underground resources are not consumed by either Pan or Gorilla to any significant degree (e.g., McGrew et al., 1982). It could be that the consumption of such foods, at least seasonally, was an important hominin adaptation that allowed exploitation of increasingly arid and seasonal environments so inimical to extant African apes (Hatley & Kappelman, 1980; Conklin-Brittain et al., 2002). We stress, however, that the consumption of underground foods is only one possible explanation for the Sr/Ca patterning observed herein.

This reasoning was good enough to get an outside research team to sit up and take notice, and within two years the Proceedings of the Royal Society published an isotopic analysis of the dental enamel in mole rats by Yeakel et al. [13] which supports the tuber alternative, known in the field as the underground storage organ (USO) hypothesis.  Here is the abstract of this important 2007 paper:

The diets of Australopithecus africanus and Paranthropus robustus are hypothesized to have included C4 plants, such as tropical grasses and sedges, or the tissues of animals which themselves consumed C4 plants. Yet inferences based on the craniodental morphology of A. africanus and P. robustus indicate a seasonal diet governed by hard, brittle foods. Such mechanical characteristics are incompatible with a diet of grasses or uncooked meat, which are too tough for efficient mastication by flat, low-cusped molars. This discrepancy, termed the C4 conundrum, has led to the speculation that C4 plant underground storage organs (USOs) were a source of nutrition for hominin species. We test this hypothesis by examining the isotopic ecology of African mole rats, which consume USOs extensively. We measured δ18O and δ13C of enamel and bone apatite from fossil and modern species distributed across a range of habitats. We show that δ18O values vary little and that δ13C values vary along the C3 to C4/CAM-vegetative axis. Relatively high δ13C values exist in modern Cryptomys hottentotus natalensis and Cryptomys spp. recovered from hominin-bearing deposits. These values overlap those reported for A. africanus and P. robustus and we conclude that the USO hypothesis for hominin diets retains certain plausibility.

It appears that carbon isotope, Sr/Ca, and Ba/Ca analysis are consistent with a plant-based USO hypothesis, not a meat-based hypothesis.  But what about the overall dental morphology of Australopithecus?  According to Teaford and Ungar (2000) [14], it is

clear that the dietary capabilities of the early hominids changed dramatically in the time period between 4.4 million and 2.3 million years ago. Most of the evidence has come from five sources: analyses of tooth size, tooth shape, enamel structure, dental microwear, and jaw biomechanics. Taken together, they suggest a dietary shift in the early australopithecines, to increased dietary flexibility in the face of climatic variability. Moreover, changes in diet-related adaptations from A. anamensis to A. afarensis to A. africanus suggest that hard, abrasive foods became increasingly important through the Pliocene, perhaps as critical items in the diet….

Interestingly, as suggested by Lucas and Peters (46), another tough pliant food they would have had difficulty processing is meat. In other words, the early hominids were not dentally preadapted to eat meat—they simply did not have the sharp, reciprocally concave shearing blades necessary to retain and cut such foods. In contrast, given their flat, blunt teeth, they were admirably equipped to process hard brittle objects….

In sum, Miocene apes show a range of adaptations, including folivory, soft-fruit eating, and hard-object feeding. This range exceeds that of living hominoids and especially the early hominids. Although studies of shearing crest length have been conducted on only some of the early hominids, all evidence indicates that the australopithecines had relatively flat molar teeth compared with many living and fossil apes. These teeth were well suited for breaking down hard, brittle foods, including some fruits and nuts, and soft, weak foods, such as flowers and buds; but again, they were not well suited for breaking down tough pliant foods such as stems, soft seed pods, and meat.

In summary, the scientific literature as of 2007 – two years before Keith published her book – is substantially in support of a plant-based diet for Australopithecus, and possibly for early Homo as well.  Keith’s reading of the 1999 paper by Sponheimer and Lee-Thorp is completely distorted, and neglects a review of subsequent papers by these very same authors.  In contrast to Keith’s narrative, the evidence suggests our Australopithecine ancestors favored woodlands over grasslands; they were prey, not predators; and they were uniquely adapted to harvest and metabolize tubers and a variety of other plant-based foods – not meat.

For those with a deeper interest in this topic, I would recommend starting with the excellent background on C3 versus C4 photosynthesis in plants provided by Ehleringer and Cerling [15], as well as the full text of the 2007 paper by Yeakel et al. [13] and the 2005 paper by Sponheimer et al. [9], each of which has been made freely available in PDF by the authors.

In my next post in this series, I will examine Keith’s second main evolutionary argument against plant-based nutrition: the expensive tissue hypothesis.

References

[1] Keith, L. (2009) pg. 140.
[2] Sponheimer, M. and Lee-Thorp, J. A., Science 283, 368 (1999).
[3] Eades, M.D. and Eades, M.R. (2001).
[4] de Ruiter, D.J., Sponheimer, M. and Lee-Thorp, J.A., J. Hum. Evol. 55, 1015 (2008).
[5] Lee-Thorp, J. A. et al., J. Hum. Evol. 27, 361 (1994).
[6] Lee-Thorp, J.A. et al., J. Hum. Evol. 39, 565 (2000).
[7] Lee-Thorp, J.A., Sponheimer, M., and van der Merwe, N.J. Int. J. Osteoarchaeol. 13, 104 (2003).
[8] Sponheimer, M. and Lee-Thorp, J.A., Comp. Biochem. Physiol. 136, 27 (2003).
[9] Sponheimer, M. et al., J. Hum. Evol. 48, 147 (2005).
[10] Sponheimer, M., Lee-Thorp, J.A., et al., J. Hum. Evol. 48, 301 (2005).
[11] Matt Sponheimer, et al., Science 314, 980 (2006).
[11] Sponheimer, M. et al., J. Hum. Evol. 51, 128 (2006).
[12] Sponheimer, M. et al., Am. J. Phys. Anthropol. 140, 661 (2009).
[13] Yeakel, J.D. et al., Proc. R. Soc. B 274, 1723 (2007).
[14] Teaford, M.F. and Ungar, P.S., PNAS 97, 13506 (2000).
[15] Ehleringer, J.R. and Cerling, T.E., The Earth System 2, 186 (2002).

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