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Growing Up is Hard

28 Eliezer_Yudkowsky 04 January 2009 03:55AM

Terrence Deacon's The Symbolic Species is the best book I've ever read on the evolution of intelligence.  Deacon somewhat overreaches when he tries to theorize about what our X-factor is; but his exposition of its evolution is first-class.

Deacon makes an excellent case—he has quite persuaded me—that the increased relative size of our frontal cortex, compared to other hominids, is of overwhelming importance in understanding the evolutionary development of humanity.  It's not just a question of increased computing capacity, like adding extra processors onto a cluster; it's a question of what kind of signals dominate, in the brain.

People with Williams Syndrome (caused by deletion of a certain region on chromosome 7) are hypersocial, ultra-gregarious; as children they fail to show a normal fear of adult strangers.  WSers are cognitively impaired on most dimensions, but their verbal abilities are spared or even exaggerated; they often speak early, with complex sentences and large vocabulary, and excellent verbal recall, even if they can never learn to do basic arithmetic.

Deacon makes a case for some Williams Syndrome symptoms coming from a frontal cortex that is relatively too large for a human, with the result that prefrontal signals—including certain social emotions—dominate more than they should.

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