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Tuesday, October 18, 2005
The small hairy primate Dryopithecus, which served as ancestral stock for modern apes and man, lived about 36 million years ago and was controlled by a brain with a capacity of only 150 cubic centimeters, or the equivalent of about 9 heaping tablespoons of gray matter. By the time of the arrival of the family of man, or the hominid lineage, in the form of Ramaphitecus 15 million years ago, hominid size had doubled, but uts frowth was very slight over the next 10 million years. Once the ape-man began to make greater use of his nads to brandish weapons and fasion simple tools, however, the brain's expansion was rapid.

This seemingly sudden growth, after thousands of years of inertia, began about 4 million years ago with the dawn of Australopithecus a short, largely defenseless ape-man who live on the ground possessed the ingenuity to break antelope thighbones to legnths that made convenient clubs. In a "mere" 2 million years, from Australopithecus to Homo habilis, the first true man, brain capacity jumped from 450 cc to 750 cc. The tool-making industry of Homo habilis, or handy man, further stimulated brain development, so that by the time Homo erectus appeared, about 1.5 million years ago, the human brain had begun enlarging at the phenomeal rate of 20-odd centimeters, or 1 heaping tablespoon of gray matter, every hundred thousand years.

The evolution of speech also must have a profound effect on the human brain. About 500,000 years ago the rate of growth peaked when the brain expanded at an astonishing rate of more than 200 cubic centimeters every hundred thousand years. No other organ in the history of life is known to have grown as fast. When Homo sapiens emerged about 100,000 years agom, the brain already had reached its present size of 1400 cc, and changes since then had been insignificant.

The tapering off of grwoth, or stability of size, can be accounted for in two ways. One is that all the resources of the brain as it now exists have yet to be tapped, so no additional size is required. Second, from an anatomical standpoint, the fetal brain cannot be larger because of the narrow width of the female birth canal, itself a result of humans erect posture.

(abstracted from the book: The Browsers Book of Beginnings by:Charles Panati)
posted by infraternam meam @ 9:36 AM  
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Name: infraternam meam
Home: Chicago, United States
About Me: I am now at the prime of my life and have been married for the past 25 years. Sickly at times, but wants to see the elixir vita, so that I will be able to see my grandchildren from my two boys.
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