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Subject: Re: acorns as food
From: (Jay Mann)
Date: Sep 04 1996

B. Keith Ryder ( wrote:
: Jay Mann ( wrote:
: : Consider the remarkable fact that so many poisonous chemicals made by
: : plants taste bitter to us. Why?  Are the tastebuds early-warning systems
: : that react biochemically to poisonous chemicals? Or (my preference) is it
: : a "choice" by plants to select for easily detectable poisons?  There is no
: : shortage of undetectable plant-made toxins, but the trouble is that the
: : ultimately dead or ill animal will already have consumed the plant. 
: : Whereas a bitter chemical gives a warning to the animal, and eventually
: : many animals will learn to associate a bad taste with a subsequent bout 
: : of illness.
: Doubt it -- very little of nature is so altruistic.  Consider that when
: an animal eats, for example, a strawberry, most of the seeds pass
: through the digestive tract unharmed, thereby potentially spreading
: the seed around.  Therefore, a good-tasting strawberry entices the animal
: to eat more and spread the seed.  A good thing.
: Conversely, eating an acorn destroys the seed, stopping any chance that
: seed might have to make a new tree.  A bad thing.  Therefore, oak trees
: with good-tasting acorns would have fewer chances of successful propogation,
: and may, in the extreme, become extinct (and would at least not have
: as many "offspring" as a bad-tasting variety).
: The tree cares far more about self-preservation than it does about
: protecting animals from poisoning themselves.

I never implied any altruistic motivation on the part of plants, merely 
the observation that bitterness usually is associated with toxicity.  
There are lots of acorns on an oak tree, so even a nondetectable but 
lethal poison might suffice to reduce the local population of 
acorn-eaters.  Perhaps the "choice" between detectable and indetectable 
poison is dictated by the size of the seed-eating population.  If there 
is in effect an inexhaustible supply of seed-eaters, then a bitter toxin 
is far better for the tree than an indetectable one.  

Contrast this with the lectins of dried common beans, which are quite 
indetectable (at least to humans).  They seem to be entirely satisfactory 
in reducing the number of bean-eating insects to a tolerable level.

Jay D Mann  <>
Christchurch, New Zealand

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