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∂AIL Professor John Holdren↓University of California↓Berkeley CA∞

Dear Professor Holdren:

	In a recent panel discussion, in response to some remarks
by Professor Paul Ehrlich about what thermodynamics proved about
the possibility of extraction of minerals from low grade ores,
I criticized the following statement taken from %2Population,
Resources and Environment%1:

	"Thus the Laws of Thermodynamics tell us why we need a
continual input of energy to maintain ourselves, why we must eat
much more than a pound of food in order to gain a pound of weight,
and %2why the total weight of plants on the face of the Earth
will always be much greater than the weight of the plant-eaters,
which will in turn always be much greater than the weight of
flesh-eaters%1".

	In the ensuing somewhat heated discussion, Professor
Ehrlich attributed the statement to you and defended its truth
even though stating that "inverted ecological pyramids" can exist.
Your authority as a physicist was appealed to.

	It seems to me that the italicized part of the statement
does not follow from the laws of thermodynamics, and indeed is not
universally true.  Namely, if a predator eats prey that reaches
at an average age less than approximately twice the time it takes
the predator to eat its own weight, then the biomass of the prey
can be less than that of the predator.  For example, a python in
a hen house that eats its own weight in about a year could live
on chickens that reach maturity in 7 to 8 weeks.  Imagining the
chickens to average half their mature weight, the mass of python
could be about 12 times the biomass of its prey.  Even people or
dogs living on chickens would exceed them in biomass.

	In view of the above would you like to modify your statement
about what the laws of thermodynamics show?

.sgn

cc: Paul Ehrlich