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  #1   ^
Old Sun, Jul-14-02, 22:00
Voyajer's Avatar
Voyajer Voyajer is offline
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Plan: Protein Power LP Dilletan
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Default The human brain: dependent on meat

Why bigger brains?

Theories about the origin of the large human brain have focused on many aspects of behavior that were supposed to have driven this change...

Scholars have tended to assume that the reason that brains did not get larger earlier is that they were not needed. A new theory, the "expensive tissue hypothesis" has argued instead that brains could not become larger earlier, because they used up too much of the body's energy -- ounce for ounce, the mammalian brain uses nine times as much energy as the rest of the body, on average. Leslie Aiello and Phillip Wheeler point out that five major organs or organ systems use up 60-70% of the body's energy at rest, although they account for only 7% of the body's total mass. These "expensive" organs are the gut, the heart, the liver, the kidney and the brain. (Lungs are also quite "expensive.") Unless the animal eats a lot more high calorie foods (very unlikely in the case of humans, to judge from the teeth) or one of these organs gets smaller, there is no energy budget left to feed a larger brain.

What got smaller around 2 mya that allowed the brain size to finally increase? The heart, liver and kidney are scaled to body size (mass); they cannot get smaller unless you do. The only remaining possibility is the gut, which could become smaller if foods were either higher quality or partially "digested" outside the body by tools.

Babies, Brains and Bone Marrow
(continued)

In many ways, humans have guts like other apes. Food travels slowly through the intestines to allow time to absorb nutrients from fibrous plant foods. The human gut differs from those of other apes in one important way - it is far shorter. Mammals with short guts tend to be carnivores, because animal foods are easily digested. With meat, the nutrition comes in smaller, low fibre packages, which means less processing time is needed in the gut. Eating meat may also help to reduce the effects of undigestible or poisonous substances in the plant foods that are eaten.

Modern humans have smaller guts than would be expected if we were ordinary apes, which supports the archaeological evidence that our ancestors embarked on a meat-rich diet. There are even more important repercussions connected with this fundamental change in dietary strategy. The evolution of a smaller gut freed up energy that could be used elsewhere. The most obvious place to benefit from an increased share of the body's energy budget is the brain. The fossil record shows that Homo erectus brains were about twice as big as those of the australopithecines.

So, meat in the diet also allowed the evolution of a larger brain.

http://www.mc.maricopa.edu/~refflan...rney/root2.html

http://www.bbc.co.uk/science/apeman...rticle_8b.shtml
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  #2   ^
Old Mon, Jul-15-02, 08:47
razzle razzle is offline
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Thought the gut-brain theory is quite controversial, I enjoy it. I also like the theories about the connection between brain size and hunting larger animals.

Higher brain functions have to evolve in order to be successful hunters for a couple of proposed reasons:

- Throwing accuracy
- Communication with other hunters
- (there may be others that I'm spacing out!)
William Calvin has a long chapter from a book about the throwing accuracy issue and a new look at the so-called "hand ax" It's on his UW website page.
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  #3   ^
Old Mon, Jul-15-02, 12:21
Voyajer's Avatar
Voyajer Voyajer is offline
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Plan: Protein Power LP Dilletan
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Thanks Razzle. I always like to read your comments.

Yes, it is said even in these links above that hominids needed a larger brain for hunting strategies, etc as you pointed out. The point they are making however was that it was impossible to get this larger brain even though we needed it because the brain uses up so much energy. Evolution, mutations, and natural selection couldn't make the body grow a larger brain until we changed our nutrition to get enough energy for the brain to grow. In other words, we had to eat enough meat first in order for the evolutionary process to have enough materials to make the larger brain that we so needed.
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  #4   ^
Old Mon, Nov-03-03, 16:38
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johns johns is offline
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Or the code for a larger brain could have been there for some time, awaiting the energy to produce it. It could be that over many generations, there were always hominids with the potential for bigger brains, of which only a few attained it.
Going way out on a theoretical limb here, that could help to explain the complex dominance behaviors and strategies that developed in humans. The one with the bigger brain becomes chief, and demands tribute from the others. His offspring are better fed and continue the tradition of demanding tribute. They could naturally be killed in their sleep, so those who developed rules and enforced them and rewarded loyalty would be likeliest to survive.
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  #5   ^
Old Mon, Nov-03-03, 16:42
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johns johns is offline
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A significant use of the large brain for the hunter gatherer, as alluded to by razzle, is communication. Ecologically, humans seem to hunt as pack animals, like wolves. The ability to fan out across an open plain and chase fleeter but less durable prey would be much enhanced by the ability to communicate plans across the space.
Some research (again I lack the references) that I read over the past year indicated that the upright posture and hairlessness were adaptations to hunting by chasing prey across an open grassy plain (upright posture to see and run, and hairlessness to shed heat while running).
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  #6   ^
Old Tue, Nov-04-03, 10:41
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catfishghj catfishghj is offline
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I will put out a theory that people on this WOE are and become much more intellegent than high carb eaters.
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  #7   ^
Old Tue, Nov-04-03, 10:48
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adkpam adkpam is offline
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I'm sure EATING a lot smarter now!
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  #8   ^
Old Mon, Nov-10-03, 07:58
haycreek haycreek is offline
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Hey you all: I've got some ornery Highland cattle up here with with about a 3 foot horn spread. What say you sharpen up those hand axes and chuckin spears , bone up on your tactics and chase 'em around an 80 acre bottomland to see who drops first? I'll bet one thing: you'll quickly discover humans have devolved in certain ways!
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  #9   ^
Old Mon, Nov-10-03, 12:27
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Lissette Lissette is offline
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Plan: ALOT of salads,veggies ec
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Quote:
Originally Posted by haycreek
Hey you all: I've got some ornery Highland cattle up here with with about a 3 foot horn spread. What say you sharpen up those hand axes and chuckin spears , bone up on your tactics and chase 'em around an 80 acre bottomland to see who drops first? I'll bet one thing: you'll quickly discover humans have devolved in certain ways!


Ah just think how fast they would run if the cattle was chasing them??? Especially during calving season!!! I have found that I can be quite agile even at 3 in the morning whilst being chased by an angry and protective momma!!
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