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Old 11-26-2008, 06:02 AM   #1
Darryl Shaw
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Default Roots and Tubers in Diet of Early Human Ancestors.

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In pondering human origins, Dominy said, anthropologists have long been stumped by the sudden, nearly simultaneous increases in our brain size, body size, and geographic range, while other apes changed little. Early humans simply must have found some source of better nutrition to make it all possible, they reasoned.

"That's the big mystery of paleoanthropology," Dominy said. "What changed? Why did our earliest human ancestors deviate from the pattern we see in living apes to evolve this incredibly large brain, which is very energetically expensive to maintain, and to become a much more efficient bipedal organism?"

For years, the answer was thought to be the growing importance of meat in the diet, as early humans learned to hunt. But, Dominy pointed out, "Even when you look at modern human hunter-gatherers, meat is a relatively small fraction of their diet. They cooperate with language, use nets; they have poisoned arrows, even, and still it's not that easy to hunt meat. To think that, two to four million years ago, a small-brained, awkwardly bipedal animal could efficiently acquire meat, even by scavenging, just doesn't make a whole lot of sense."

Some anthropologists have begun to suspect the new source of food consisted of starches, stored by plants in the form of underground tubers and bulbs--wild versions of modern-day foods like carrots, potatoes, and onions. Once early humans learned to recognize tuber-forming plants, they opened up a food source unknown to other apes.

"It's kind of a goldmine," Dominy said. "All you have to do is dig it up."
http://press.ucsc.edu/text.asp?pid=1553

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The flat, thickly enameled molars of early humans have led scientists to infer that their diet consisted primarily of hard, brittle foods, such as seeds. But in light of recent findings, researchers speculated that a diet of corms, bulbs, rhizomes, and tubers of plants that use a form of photosynthesis that produces the same isotopic signature as grasses and sedges, could resolve the conundrum.

The UCSC team tested the hypothesis by analyzing stable carbon and oxygen isotopes of the bone and tooth enamel of African mole rats, small tunneling rodents that eat primarily corms, bulbs, rhizomes, and tubers, otherwise known as plant underground storage organs (USOs). The team also analyzed the fossil remains of mole rats recovered from the same locations where Australopithecus africanus and Paranthropus robustus were discovered and found sufficient overlap between the isotopic signatures to support their contention that early human ancestors, like African mole rats, ate a diet rich in USOs.

"This study certainly adds to the body of evidence that the diet of early hominins included bulbs and corms, and possibly tubers," said Nathaniel J. Dominy.
http://press.ucsc.edu/text.asp?pid=1251

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In the new paper, entitled "Mechanical Properties of Plant Underground Storage Organs and Implications for Dietary Models of Early Hominins," Dominy tested USOs, which plants use to store water and carbohydrates. His data establish rhizomes as the toughest, followed by tubers, corms, and bulbs (familiar examples of which include Bermuda grass, potatoes, iris, and onions, respectively). Corms and bulbs emerged as the most plausible hominin foods, according to Dominy, because their physical qualities match up with dietary inferences based on dental morphology and modern chemical isotopic analysis.

The new data also allowed Dominy to correlate plant characteristics with the dental morphology of different species of hominins. The teeth of Australopithecus, for example, appear well-suited to process bulbs, while the teeth of Paranthropus appear well-adapted to process hard and brittle corms.

Finally, prompted by his own observations of Hadza hunter-gatherers in northern Tanzania, Dominy also conducted a pilot field study of the effects of roasting by Hadza on the toughness of five tuber species. The results, that roasting lessens the work of chewing and thereby enhances digestibility, add to the plausibility of relatively tough tubers in the diet of hominins.
http://www.cbse.ucsc.edu/news/article.php?ID=1680

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.......the real revolution came once human ancestors tasted a tuber baked in a lightning-sparked grass fire and realized the value of cooking, Wrangham asserts. Heat turns hard-to-digest carbohydrates into sweet, easy-to-absorb calories. Using the protein, fat, and carbohydrate makeup of modern fruits, seeds, meats, and tubers, Wrangham's team calculated the caloric value of diets containing various proportions of these foods, assuming a constant total amount of food dry matter. A diet of 60% cooked tubers, about the proportion used in modern native African diets, and no meat boosts caloric intake by about 43% over that of humans who ate nuts, berries, and raw tubers, says Wrangham. A 60% meat diet offers just a 20% advantage.

"There seems to be a genuine energetic advantage in cooking food," agrees Yale's Hill. "This could lead to a shift in human behavior" as well as physical changes such as smaller teeth. "Tubers have a lower fiber content [than other plant foods], and that would fit very nicely with this [idea]," adds Leslie Aiello, an anthropologist at the University College in London. "And cooking would just accentuate this."
http://cogweb.ucla.edu/Abstracts/Pennisi_99.html
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Old 11-26-2008, 06:56 AM   #2
Scott Kustes
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Good information Darryl. In the book The Old Way: A Story Of The First People, Elizabeth Marshall Thomas discusses the diet of the !Kung. She describes a diet heavily focused on roots and tubers brought home by the women. However, meat was what was prized and celebrations were held when there was a kill (which wasn't all that uncommon). Tubers no doubt played an important role in the evolution of humans.
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Old 11-26-2008, 07:15 AM   #3
Emily Mattes
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This is not surprising--for most of human history, evolutionary advantage did not think of diet in terms of nutrients but in terms of calories. That is, whomever could get the most calories survived Not that people didn't get vitamin deficiencies (e.g. scurvy), but that you ate whatever you could get your hands on. This would be especially the case in hunter-gatherer societies, where each new food source discovered would offer another chance to increase calorie intake. The switch to agriculture essentially revolutionized civilization because at its base it provided for massive amounts of calories for a population.

The luxury of wide sections of the population being in the position of having a caloric surplus and having the option of picking and choosing their foods is a relatively recent one. Now the question is no longer what can we eat, but what should we eat. I think viewing food in the "Paleo" model can be helpful, but sometimes somewhat misleading: the Paleolithic man would have eaten Snickers bars if he could get his hands on them because to him calories are precious items and not to be discarded because they're considered to be less nutritious than other calories.
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Old 11-26-2008, 10:52 AM   #4
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But the Paleo model isn't based on what "would" Paleolithic man have eaten. You're right, he'd have eaten Snickers and Twinkies. The Paleo model is built on what DID Paleolithic man eat, i.e., what foods shaped the human animal throughout evolution. Under that guideline, Snickers, Twinkies, and other highly processed foods do not fit. Only meat, vegetables, fruits, tubers, nuts, and seeds fit that model.
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