Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!mnetor!uunet!husc6!hao!ames!ptsfa!well!wcalvin From: wcalvin@well.UUCP (William Calvin) Newsgroups: comp.ai,comp.cog-eng,sci.misc Subject: Re: Genesis of language (was: Why can't my cat talk, and a bunch of others) Message-ID: <4627@well.UUCP> Date: Fri, 4-Dec-87 21:52:39 EST Article-I.D.: well.4627 Posted: Fri Dec 4 21:52:39 1987 Date-Received: Thu, 10-Dec-87 06:14:10 EST References: <1987Dec2.182753.622@mntgfx.mentor.com> Reply-To: wcalvin@well.UUCP (William Calvin) Organization: Whole Earth 'Lectronic Link, Sausalito, CA Lines: 19 Xref: mnetor comp.ai:1195 comp.cog-eng:352 sci.misc:669 Apropos cell death in brains, the old saw about losing 10,000 neurons every day is now being challenged by the people that work on cerebral cortex; they seem to think that there is little neuron loss there during most of postnatal life. Some subcortical areas like substantia nigra do lose 50% of cells by age 70, while adjacent regions in midbrain may lose less than 2%. But there is a LOT of synapse death -- or, as I like to phrase it, withdraw of axon collaterals, breaking synapses. Synaptic density in neocortex peaks at 8 months after birth (in humans; 2 months in monkey) -- and then drops by 30-50% during childhood. After puberty, the data gets too noisy to interpret. So there is a lot of opportunity for Darwinian editing of randomly-made synaptic connection, achieving information storage by carving (rather like photographic development removes unexposed silver grains). I review a variety of Darwinian selection stories in my piece in the 5 November 1987 NATURE 330:33-34, entitled "The brain as a Darwin Machine." William H. Calvin University of Washington NJ-15, Seattle WA 98195 206/328-1192 wcalvin@well.uucp