Reason for crossed projections in the nervous system?
rubinsnk at is2.nyu.edu
Fri Nov 17 11:12:09 EST 1995
: A hypothesis I came across last night, attributed to Marcel Kinsbourne by
: Steven Pinker in his book "Language as Instinct", runs as follows:
: bilaterally symmetrical invertebrates have an uncrossed nervous system,
: their spinal cords (or the invert. equivalent) ventrally and their hearts
: etc. dorsally, whereas vertebrates have a crossed nervous system, their
: spinal cords dorsally and their internal organs ventrally. Kinsbourne
: speculates that sometime during invert-vert evolution, the head was
: twisted around 180 degrees so that it points the other way (sort of like
: what happened to flatfish only worse). I thought that was a kind of cute
: idea. I have no idea whether it has any merit or not.
That makes the assumption that there is a direct lineage between the two
which I regard as unlikely.
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