> @ucl.ac.uk wrote:
> : 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.
And we're talking about left/right crossing, not dorsal/ventral
crossing. Also the mammalian brain DOES bulge ventrally, but the spinal
cord (where things are crossed) is still the same. Nice ideas though.
sandraw at U.Arizona.EDU