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Date: Wed, 18 Aug 1999 09:15:12 -0500
Subject: Re: Cooking veggies and human evolution
From: "Don and Rachel Matesz" <[log in to unmask]>
To: Paleolithic Diet Symposium List <[log in to unmask]>
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Don Matesz <[log in to unmask]>
Next Generation Nutrition. (419) 476-2967


Ray Audette wrote on  "Cooking veggies and human evolution":
>
>This is also the time that many other species increased in size to take
>advantage of vast areas of steppe-tundra.  These species were collectively
>known as the Pleistocene Megafauna.  Hominids had to evolve into a mega form
>to take advantage of this new enviroment.

I am pretty sure Ray did not mean this the way it reads.  The species in
question did not "increase in size [in order] to take advantage of vast
areas of steppe-tundra", they increased in size BECAUSE they took advantage
of the resources of those areas.  The increase in size was not intentional
(Hey, lets increase in size then we can take advantage of these vast
areas....), but was a natural consequence of taking advantage of the
increased nutrients available from those areas.

In my post April 17 1999 I wrote:

>Brains are higher in fat, so they are almost twice as energy dense as lean
>meat; the fat content
>of brains is not affected by feeding practices--the brains of wild game are
>just as rich in fat as are the brains of domesticated cattle.   Further, the
>EFA profiles of brains of all species so far studied are identical (Crawford
>and Marsh, Nutrition and Evolution, p. 125)

To clarify, although the %fat content of brains is fixed, the EFA content
actually is variable within limits based on the food the animal eats.  For
example, on a DHA-rich diet, human have more DHA in their cerebral neurons
than on a DHA poor diet, although the total fat content of the brain will
remain the same.  According to professor Michael Schmidt, Dr. C.D. Stubbs
has stated "when cells are deprived of sources [of DHA] in the diet the cell
wil tend to produce the neraest fatty acid (in terms of unsaturation and
chian length) that is possible, even if the faty acid is from the omega-6
series."  The nearest "substitute" for DHA is DPA (omega-6), which is far
inferior to DHA with regard to neural activity.  ( Stubbs CD,  The structure
and function of docosahexaenoic acid in membranes, in Sinclair A, Gibson R,
eds, Essential Fatty Acids and Eicosanoids, Champaign Ill, American Oil
Chemists' Society 1992: 116 cited in Schmidt M, Smart Fats, North Atlantic
Books, 1997, p. 47).

Since it seems that some would like to take issue with it, I would like to
drive home the point that as a matter of fact, not all animals make AA and
DHA from vegetable precursors, and of those that do, the
amount they make is insufficient to support development of a sophisticated
nervous system.  There are some animals, including humans, who are incapable
of converting the "precursors" into the longer chains in amounts required
for nervous system development, maintenance and health.  I quote from
Nutrition and Evolution (Keats, 1995) Marsh and Crawford, who has done much
of the relevant research:

"Were all species able to make the neural fatty acids from the starting
point in plants?  In all small mammals like mice, rats and tree shrews,
there was evidence of ample conversion.  However, in the large herbivores
like cows, buffaloes and giraffes, which eat leaves and seeds, we could find
plenty of the original linoleic and alpha-linolenic acids in their tissues,
but the conversion process to the neural fatty acids was not completed; it
seemed to peter out. The production of the most polyunsaturated fatty acid,
docosahexaenoic acid (22:6, n-3) was most affected.  The tissues of the
large herbivores accumulated  only small amounts of these neural fatty
acids, whereas the big cats which ate them had many more.

"This was interesting because carnivores have more sophisticated nervous
systems and presumably a higher demand for neural fatty acids.  Were they
perhaps better at making them?  Surprisingly, we found the opposite.  John
Rivers and Andrew Sinclair reported another peculiarity of cats in 1975:
cats did not convert plant EFAs into neural fatty acids (Rivers, Sinclair &
Crawford, 1975).  Others have found that this same principle operated in
carnivorous fish.  This inability is similar to the inability of the cat to
make vitamin A from the carotenoids in plants.  It relies on the efforts of
its prey!

"Once again the economy of this method is clear.  The process of building up
these long-chain fatty acids is tedious.  Any animal that can bypass even a
part of it can switch off the mechanism, save on effort and time and
possibly on genetic 'disk space'.  The same argument applies as with vitamin
A:  the direct supply of preformed nerual fatty acids could alow the
development of biological systems dependent on or stimulated by these
nutrients.

"The ready availability of preformed neural acids and vitamin A in the flesh
the carnivores eat offers nutrients needed specifically to suport more
sophisticated brains, nervous and optical systems.  They can afford the
luxuries of widely adjustable irises in their eyes, along with the nerves
and central control systems they demand.  The herbivores cannot."
(Nutrition and Evolution, p. 126 - 128)

In short--by skipping the step of making all the neural fats from scratch,
humans like other carnivores are able to divest themselves of biological
investments in the hard- and softwares required for producing neural fats
from 'scratch', and instead invest their biological resources in making new
structures from neural fats--'hardwares' like the kinds of supersensitive
eyes, peripheral nerves, and cerebral developments that allow me to type
this post.

Don Matesz