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(Humanity's Evolutionary Prehistoric Diet and Ape Diets--continued, Part G)

P O S T S C R I P T :   S I G N I F I C A N T   R E S E A R C H   U P D A T E S   ( c o n t .)

(EDITORIAL NOTE: Triple-asterisked items in boldface below refer to passages in the interview as originally published, which are followed by updated comments based on additional observations or more recent scientific research.)

Corrected anthropological survey data shows
meat averages over 50% of hunter-gatherer diets

*** "No text I have yet read ventures any sort of percentage figure from this time period [the historical period of Homo erectus' existence], but it is commonly acknowledged that plants still made up the largest portion of the subsistence."

The most significant correction to Part 1 of the interview series here involves newer Paleodiet analysis of the amount of plant vs. animal food in modern hunter-gatherer diets, which--in conjunction with optimal foraging theory and knowledge of ancient habitats--can be used as a basis for extrapolating backward to estimate what that of our hominid ancestors may have been. The widely quoted figures of Richard Lee (in his Man the Hunter, 1968) that stated an average of 65% plant and 35% animal food for modern hunter-gatherers have, upon review by other researchers, been discovered to have been somewhat flawed. (Lee's 65%/35% ratio was in turn repeated in the research sources I used for this interview, but I had not traced the figures to their ultimate source at the time.)

Previous meta-analysis of Ethnographic Atlas survey data on hunter-gatherer diets was performed incorrectly. As noted by Ember [1978], it turns out that in calculating his averages, Lee somewhat arbitrarily threw out a portion of the North American hunter-gatherer cases (who often had higher rates of meat consumption); plus he classified shellfishing as a "gathering" activity (normally used to categorize plant-food gathering). Taken together, these skewed the resulting average considerably. Reanalysis correcting for Lee's analytical errors shows a more likely average of somewhere between 50-65% meat consumption in modern hunter-gatherer diets. (For a brief enumeration of the reanalysis that researcher Loren Cordain's group has done, see the first section or two of Metabolic Evidence of Human Adaptation to Increased Carnivory.)

Modern hunter-gatherer diets vis-a-vis optimal foraging theory and reconstructed prehistoric diets. An important issue worthy of mention here is the reliability of backward extrapolations from behaviorally modern hunter-gatherers to more primitive hominids. The phrase "behaviorally modern" generally refers to the time horizon of approximately 40,000 B.C., during and after which humans began exhibiting behaviors we think of as modern: such as ritual burials, cave paintings, body ornamentation, other expressions of art, and most importantly for our purposes here, more sophisticated tool design, use, and techniques where hunting is concerned (eventually culminating in the bow-and-arrow, for example) which would presumably have increased hunting success.

In light of this, critics have questioned how reliable the backward extrapolations may be. Proponents, in justification, note that well-established "optimal foraging theory" (which, reduced to its bare essentials, says that all creatures tend to expend the least foraging effort for the greatest caloric and/or nutritional return) can be used as a basis to make reasonable predictions. The kind of food intake that optimal foraging theory predicts for a particular species (modern or ancient) is in turn dependent on the surrounding environment and foods prevailing at the time (i.e., savanna habitat, generally, in the case of humans), along with what is known about the kind of foods their digestive physiology would likely be able to efficiently process.

Based on this approach, proponents believe even with less sophisticated hunting technologies--given what is now known about ancient environments and availabilities of ancient plant and animal resources--the level of animal food in the diet beginning with erectus, at least, probably would have been in the 50% range with variations for local habitat. The increasing encephalization quotient (brain volume relative to body size) of Homo and particularly the jump in brain size with Homo erectus at 1.7 million years ago also tends to corroborate the suggestion of increasingly large amounts of meat in the diet at this time.

Meat consumption levels
in early Homo species

*** "based on the fact that the diet of modern hunter gatherers...has not been known to exceed 40% meat in tropical habitats like habilis evolved in, we can safely assume that the meat in habilis' diet would have been substantially less than that."

As just discussed above regarding earlier analyses of anthropological data that have since been corrected, the average percentage of meat eaten by all modern hunter-gatherers studied to date who have been described in the Ethnographic Atlas (an anthropological compendium and database of hunter-gatherer data)--has now been shown to be in the 50-65% range, looking at the entire range of habitats studied. There are tropical hunter-gatherers eating in this range of meat consumption as well. Therefore, the percentage of meat in habilis' diet becomes an even more interesting question than before.

As the diet of habilis' precursor Australopithecus would presumably have been higher in meat than modern chimps (who are in the 2% range of meat consumption) at some undetermined level, while habilis' successor erectus is now thought to have been near the range of modern hunter-gatherers (perhaps 50%), the question of where in between those wide endpoints habilis' meat consumption fell is not something I am prepared to guess. However, when we note that habilis was the first known hominid tool user--and that those tools were specifically used for processing meat--it seems logical to suggest that the amount must have jumped well above that of Australopithecus.

*** "1,500,000 to 230,000 B.C.: Evolution of Homo habilis into the 'erectines'..."

New and controversial reanalysis of previous fossil discoveries in Java has suggested erectus' span of existence may possibly have extended to as late as 30,000-50,000 B.C. in isolated areas, although the new analysis is still undergoing intensive debate. [Wilford 1996]

*** "There were also physical changes in response to the colder and darker [more northerly] areas that were inhabited [by erectus after 700,000 years ago], such as the development of lighter skin color that allowed the sun to penetrate the skin and produce vitamin D, as well as the adaptation of the fat layer and sweat glands to the new climate."

To avoid confusion here, it should be mentioned that these adaptations are believed to have evolved a second time in modern homo sapiens 100,000-200,000 years ago once they began migrating out of Africa--after having evolved from a group of erectines that would have remained behind in Africa during the earlier migrational wave during which other erectines had spread northward 700,000 years ago.


(Diet and Health Late in Human Evolution / Chimp Diet Clarifications)

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GO TO PART 2 - Fire and Cooking in Human Evolution


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