In _Wonderful Life_, Stephen J. Gould makes a brief comment about
plant evolution, to the effect that because plants are far less
picky about crossing between species than animals are, the metaphor
of a "tree" ironically may not be appropriate to plant phylogeny as
it is to animal phylogeny.  The "tree" works for animals because
the ancestry of any natural animal can be traced down one twig,
down the branch that twig split off of, etc., a single path.  For
plants this is supposedly not as clear cut.  Is this true?  I 
thought that the phenomenon of genes "jumping" from one species
of plant to another was documented.

The context this came up in:  I was at a Cafe Scientifique in Denver
where a researcher was defending the benefits of genetically
engineered crops.  She mentioned the possibility of increasing the
efficiency of photosynthesis, and this seemed to me to be a fundamental
change compared to things like pesticide resistance or changing 
nutritional composition of crops.  I asked her if a gene for improved
photosynthesis wouldn't benefit pretty much any plant it ended up
in, and unlike the other modifications she had been talking about,
have a strong tendency to survive and spread once it had "jumped"
out of the crop species.  She replied that genes do not "jump"
between plant species, that there are reproductive barriers for
plants just as for animals:  Chromosome number, size of pollen 
grains, etc.  I doubt that chromosome number is as big a deal for
plants as for animals--aren't healthy polyploids common?

So, are plant genes "promiscuous" or not?  One one hand, the researcher
speaking at the Cafe was on the defensive from the very beginning
of her talk (understandable, given the subject matter) and may
have seen my question as an attack, on the other, I get the 
impression that some biologists think Gould is a hack.  Do plant
genes jump?

-- 
Please reply to:               | "Evolution is a theory that accounts
pciszek at panix dot com       |  for variety, not superiority."
Autoreply has been disabled    |                   -- Joan Pontius
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