Amadeus Schmidt writes:

>Summary: density in terms of metabolic energy is *not* given with
>animal carcasses (meat), except when only minor parts were used
>(only the fatty brain and marrow or adipose).
>Density *is* given in the form of fatty foods. Fatty foods in
>paleo-africa are - nuts (about 300 g per day enough).
>Tubers and roots (maniok e.g.) may also be a reasonable dense food.
>
>Speaking of comparative anatomy therefore i find that
>the increased metabolic energy needed by the bigger brain
>and smaller gut may point to a denser food
>but not to animal carcasses.
>I see a hint towards an increased usage of nuts and roots.
>
>Does this sound logical to you?
>I'd be looking forward to some counterarguments.

Nice try, but unfortunately there are two huge holes in this view of what
fueled the bigger human brain:

1. Paleo humans couldn't just drive to the grocery store to get all those
nice bananas, nuts, and tubers. They had to expend a lot of energy
(calories) to get them, crack them, dig them, etc., assuming they were in
season in the first place and even available certain parts of the year.
Whereas animals are available more or less all-year-round, and contrary to
vegetarian rumors, take less energy expenditure to get based on net energy
return. Optimal foraging theory shows that on a NET CALORIC RETURN basis
(i.e., available energy from a food minus the energy expended to obtain
it), in a paleo environment, animal foods are more efficient to hunt/forage
and would have provided the bulk of the calories. (This has been
demonstrated to a high level of detail with modern hunter-gatherers: see
for instance Hawkes K, Hill K, O'Connell JF (1982) "Why hunters gather:
optimal foraging and the Ache of eastern Paraguay." American Ethnologist,
vol. 9, pp. 379-398.)

2. Carbs, nuts, roots, etc., don't provide DHA, which is essential in
building brains, especially bigger brains. Since humans are relatively
inefficient in synthesizing DHA from the precursor available in plant foods
that can be used for this (mainly alpha-linolenic acid) it is highly
doubtful sufficient DHA could have been synthesized from plant foods
available in a paleo environment compared to what can be gotten preformed
in animal foods. (And while one might contend that EPA is a better
precursor than ALA from which to generate more sufficient levels of DHA,
unfortunately there were no flaxseed oil bottles lying around in paleo
times from which to get plant-based EPA which is a better precursor than
alpha-linolenic acid, though likely still not ideal. For more on this
issue, see http://www.beyondveg.com/billings-t/comp-anat/comp-anat-7h.shtml
and http://www.beyondveg.com/billings-t/comp-anat/comp-anat-7h.shtml.)

There is also the problem that human brain size has decreased by 11% in the
last 35,000 years and 8% in the last 10,000 (Ruff CB, Trinkaus E, Holliday
TW (1997) "Body mass and encephalization in Pleistocene Homo." Nature, vol.
387, pp. 173-176), which--since animal consumption has plummeted during the
transition at the end of paleo times and the inception of
agriculture--doesn't bode well for plant-based theories of human brain
evolution.

--Ward Nicholson <[log in to unmask]>