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␈↓ ↓H␈↓␈↓βS␈↓∧ Artificial Intelligence Laboratory, STANFORD UNIVERSITY, Stanford, California 94305

␈↓ ↓H␈↓∧Telephone 415 497-4430␈↓ 
≤May 26, 1978 




␈↓ ↓H␈↓Professor John Holdren
␈↓ ↓H␈↓University of California
␈↓ ↓H␈↓Berkeley CA

␈↓ ↓H␈↓Dear Professor Holdren:

␈↓ ↓H␈↓        In␈αa␈αrecent␈αpanel␈αdiscussion,␈αin␈α
response␈αto␈αsome␈αremarks␈αby␈αProfessor␈αPaul␈α
Ehrlich␈αabout
␈↓ ↓H␈↓what␈αthermodynamics␈αproved␈αabout␈αthe␈αpossibility␈αof␈αextraction␈αof␈αminerals␈αfrom␈αlow␈αgrade␈αores,
␈↓ ↓H␈↓I criticized the following statement taken from ␈↓↓Population, Resources and Environment␈↓:

␈↓ ↓H␈↓        "Thus␈α∞the␈α∞Laws␈α∞of␈α∂Thermodynamics␈α∞tell␈α∞us␈α∞why␈α∞we␈α∂need␈α∞a␈α∞continual␈α∞input␈α∞of␈α∂energy␈α∞to
␈↓ ↓H␈↓maintain␈αourselves,␈αwhy␈αwe␈αmust␈αeat␈αmuch␈αmore␈αthan␈αa␈αpound␈αof␈αfood␈αin␈αorder␈αto␈αgain␈αa␈αpound
␈↓ ↓H␈↓of␈αweight,␈αand␈α␈↓↓why␈αthe␈αtotal␈αweight␈αof␈αplants␈αon␈αthe␈αface␈αof␈αthe␈αEarth␈αwill␈αalways␈αbe␈αmuch␈αgreater
␈↓ ↓H␈↓↓than␈α
the␈α
weight␈α
of␈α∞the␈α
plant-eaters,␈α
which␈α
will␈α∞in␈α
turn␈α
always␈α
be␈α∞much␈α
greater␈α
than␈α
the␈α∞weight␈α
of
␈↓ ↓H␈↓↓∨esh-eaters␈↓".

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

␈↓ ↓H␈↓        It␈α∞seems␈α∂to␈α∞me␈α∂that␈α∞the␈α∞italicized␈α∂part␈α∞of␈α∂the␈α∞statement␈α∞does␈α∂not␈α∞follow␈α∂from␈α∞the␈α∂laws␈α∞of
␈↓ ↓H␈↓thermodynamics,␈αand␈αindeed␈αis␈αnot␈αuniversally␈αtrue.␈α Namely,␈αif␈αa␈αpredator␈αeats␈αprey␈αthat␈αreaches
␈↓ ↓H␈↓at␈α∂an␈α∂average␈α⊂age␈α∂less␈α∂than␈α⊂approximately␈α∂twice␈α∂the␈α∂time␈α⊂it␈α∂takes␈α∂the␈α⊂predator␈α∂to␈α∂eat␈α⊂its␈α∂own
␈↓ ↓H␈↓weight,␈α
then␈αthe␈α
biomass␈α
of␈αthe␈α
prey␈α
can␈αbe␈α
less␈α
than␈αthat␈α
of␈α
the␈αpredator.␈α
 For␈α
example,␈αa␈α
python
␈↓ ↓H␈↓in␈α
a␈αhen␈α
house␈α
that␈αeats␈α
its␈α
own␈αweight␈α
in␈αabout␈α
a␈α
year␈αcould␈α
live␈α
on␈αchickens␈α
that␈αreach␈α
maturity
␈↓ ↓H␈↓in␈α7␈αto␈α8␈αweeks.␈α Imagining␈αthe␈αchickens␈αto␈αaverage␈αhalf␈αtheir␈αmature␈αweight,␈αthe␈αmass␈αof␈αpython
␈↓ ↓H␈↓could␈α
be␈αabout␈α
12␈α
times␈αthe␈α
biomass␈α
of␈αits␈α
prey.␈α
 Even␈αpeople␈α
or␈α
dogs␈αliving␈α
on␈α
chickens␈αwould
␈↓ ↓H␈↓exceed them in biomass.

␈↓ ↓H␈↓        In␈α⊂view␈α∂of␈α⊂the␈α⊂above␈α∂would␈α⊂you␈α⊂like␈α∂to␈α⊂modify␈α∂your␈α⊂statement␈α⊂about␈α∂what␈α⊂the␈α⊂laws␈α∂of
␈↓ ↓H␈↓thermodynamics show?


␈↓ ↓H␈↓Sincerely,



␈↓ ↓H␈↓John McCarthy
␈↓ ↓H␈↓Director
␈↓ ↓H␈↓Professor of Computer Science
␈↓ ↓H␈↓αProfessor John Holdren␈↓ ¬tMay 26, 1978␈↓ 
nPage 2␈↓ 


␈↓ ↓H␈↓cc: Paul Ehrlich