Posted by: fireandstone | April 26, 2010

On Isotopes, Meat and Goal Posts

I recently alluded in a comment to an upcoming post that’s in the works regarding my nutritional philosophy, but since it’s becoming something of a mini-dissertation, I thought I could roll something really quickly in the meantime that’s actually a component of my current research on the matter. This is that…

During one of my feverish bouts of skim research I recently combed out an abstract to an article titled “What do Stable Isotopes tell us about Hominid Dietary and Ecological Niches in the Pliocene?”, from the International Journal of Osteoarchaeology, which synthesizes the results of carbon and oxygen isotope analyses from a wide variety of Pliocene/Pleistocene deposits in South Africa for hominids and related fauna. The full article can be accessed here at no cost:

http://www3.interscience.wiley.com/journal/102528305/abstract

The purpose of the study was to characterize carbon isotope values that distinguish between forest and grassland consumption patterns, as well as distinguishing oxygen isotope values that are widely understood to characterize carnivorous consumption patterns, and compare those values against data collected from the isotope analyses of a variety of fossilized bone samples collected from the aforementioned deposits.

The study forwarded two major conclusions:

  • All of the fossil sample groups analyzed showed significant reliance on foods originating from grasslands, with the caveat that it would be impossible to distinguish whether the isotopes were contributed by the consumption of animals that ate the grass, or from the grass itself. Dental wear analysis however showed none of the characteristic patterns related to grass consumption.
  • Oxygen isotope values for all sample groups were consistent with carnivore values, but with the caveat that the mechanism for oxygen isotope deposits was poorly understood.

These conclusions are in fact at odds with previous analyses based on classical sources for dietary modeling, including craniodental anatomy, dental wear, tool association and, of course, educated guesstimation. Not coincidentally or insignificantly it also moves back the hominid transition to grassland lifestyles by about a million years from previous estimates based on environmental models. The authors were certainly not overreaching in their conclusions beyond the grassland transition hypothesis due to the existence of alternative explanations for each of the values, but it must be said that when multiple threads of data intersect on the same conclusion, that conclusion is likely a pretty safe bet. All early hominids deriving from Australopithicene lines were significantly predating/scavenging on grass consumers. To what these values don’t enlighten us in regard to the forest dwelling component of their diet, I would venture comfortably to say that meat consumption was equally significant if it can be assumed that consumption patterns are illustrative of behavioral patterns.

There’s a moral to this story (blog post) of course: even our very earliest bipedal ancestors weren’t merely scraping by on leaves, roots, occasional fruits and fortuitous carcasses, distracted by fear or incapacity, but were actively carnivorous to a very significant degree, which implies success in predation and in competition with other grassland predators. Every time we move the goal post back on when exactly it was that we were soft, weak and vulnerable, we find that the post needs to be moved back even further. Maybe the reason is that we actually never were any of those things. That’s food for *my* thoughts anyway.

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