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March 24, 2004
Freaks of nature
If you aren't familiar with the work of Stephen Jay Gould and other modern evolutionary scientists, this might come as a surprise to you, but the development of human intelligence was not the inevitable result of evolution. It turns out it was more of a random occurence, that was possible but certainly not a preordained outcome of natural law. People often confuse the word evolution with the word progress, or development. In fact, the historical record does not show that evolution favors increasing complexity among organisms. It's just that with so much abundance of life, and a left wall of the simplest single cell, the range of life is more like an L-shaped curve than a bell curve or normal distribution. Bacteria are still over 90% of all biomass on earth. Complex organisms like us are the exception to the rule.
Now, it turns out that the development of human intelligence can be traced to the mutation of a single gene. So much for our long historical procession towards greater intelligence, directed by pure natural selection. On a geological time scale at least, we went from apes to artists overnight:
Early humans swapped bite for brain
18:00 24 March 04
NewScientist.com news service
Humans owe their big brains and sophisticated culture to a single genetic mutation that weakened our jaw muscles about 2.4 million years ago, a new study suggests.The slack muscles relaxed their hold on the human skull, giving the brain room to grow. Other primates remained stuck with mighty muscles that squeezed the skull in a vice-like grip.
The finding is "pretty amazing", says Peter Currie, an expert on skeletal muscle development at the Victor Chang Cardiac Research Institute in Darlinghurst, Australia: "Changes in muscle anatomy are well known to alter the bones to which they attach. The exciting part of this is the mutation in the gene dates to exactly when this transition occurs in the fossil record."
Over the past 2.5 million years, human brains have grown enormous compared to those of other primates. Human brains are now roughly three times the size of those of chimps or gorillas.
One possible reason is that changes in the environment forced early humans to invent tools, and those with the biggest brains had greatest manual dexterity, which led to yet more sophisticated tool use. Alternatively, selection may have favoured larger brains because they permitted more complex cultures.
But why did this process occur in humans and not in other primates? According to Hansell Stedman, an expert on muscle disorders at the University of Pennsylvania in Philadelphia, it was a simple mutation in a gene found in our jaw muscles.
Posted by Mike at March 24, 2004 02:05 PM
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