Scientific American 2003 Human Evolution Special
Re: “Food For Thought” William R Leonard

Short version:
Leonard raises some interesting points about evolutionary theory. He
certainly has succeeded in giving us “food for thought” but he has left me
with an intellectual stomach ache. His discussion of various aspects of
bioenergetics was very enlightening but he leaps to a number of unjustified
conclusions about the effect of diet on the health of modern man.

He gives examples at length, but I think the principle he is driving at
could be stated as “the carrying capacity of an area of land for a species
is directly related to the amount of energy the species can procure from the
land”. Leonard attempts to refute the role of other dietary factors in human
health and thus leap to the convenient but unjustified conclusion that
excess energy intake is the cause of diseases of civilisation.
<SNIPPED for brevity>

On the last page he indicates he views the human as a great garbage-guts
capable of eating anything and inter-converting it at will. He correctly
asserts “our species was not designed to subsist on a single optimal diet.
What is remarkable is the extraordinary variety of what we eat” and
attributes this dexterity to evolution. One is then left to subliminally
insert an unwritten dogma of modern science- that evolution is always
perfect (to do otherwise would presumably be to become a heretic or a
flat-Earther) and ipso facto we must be perfectly suited to all these diets.
More dangerously, Leonard implies that if we are suited to so many diets,
then we must be suited to virtually every diet.

However over 99.5% of our evolution was moulded entirely under the influence
of the Paleolithic food groups, present since time immemorial, (and still
eaten by modern hunter-gatherers), and not under the influence of the
Neolithic food groups of grains beans, potatoes, and more recently of
alcohol, sugar, salt, MSG, and a large variety of other foods and
substances. Thus Leonard has presented no evidence to justify the hypothesis
that we have evolved to eat the Neolithic food groups with impunity.
Therefore to bundle off our health problems as being entirely due to
bioenergetic factors is unjustified.

He also overlooks the physiological impact of diet- there are undeniable
physiological effects from omega 6/3 balance, trans fats, glycemic load, and
acid-base balance etc, that go far beyond the impact of the energy intake
and expenditure. Furthermore, diseases of modern man go far beyond mere
obesity, and most cannot be explained by energy balance, although this makes
a contribution in many, particularly in conjunction with elevated levels of
insulin and free IGF-1.

Compared to modern diets of equal energy, hunter gatherer diets tend to have
much higher vitamin and mineral levels, more omega-3 fat, less omega-6, no
trans-fat, low salt, negative acid load, more protein, less carbohydrate,
more antioxidants, far more phytosterols etc. These attributes make them
much less likely to cause disease. Neolithic foods generally introduce
changes that are acknowledged as unhealthful. Many so-called advances of
modern nutritional science have done nothing more than reverse-engineer
features of Paleolithic diets.

Diet has many dimensions, and all are important. There are very generous
inbuilt evolutionary tolerances to variation in many of these dimensions, as
Leonard clearly recognises. But once the boundaries of evolutionary
tolerance are exceeded, health must be affected. This is the basis of modern
discussions on this list. This is corroborated by the absence of many common
Western diseases in scientifically studied populations who eat Paleolithic
food groups i.e. hunter-gatherer populations. Energy may be the most
important of these dietary dimensions in evolutionary theory, but this does
not excuse one from ignoring the impact of other dietary factors on the
health problems of modern man.

Neolithic farmers have managed to dominate the world and nearly eliminate
hunter-gatherers, partly or entirely because of their bioenergetic
advantages. But they have paid a terrific cost in terms of disease burden,
and many of these diseases are due to the quality of the food rather than
the quantity of energy.

Yours faithfully
Ben Balzer
Dr Ben Balzer General Practitioner [log in to unmask]
Beverly Hills Medical Service
109 Morgan St
Beverly Hills 2209 NSW Australia
Tel (02) 9502 3355 Fax (02) 9502 4243 Int'l prefix (+612)

Further reading:
1. Cordain, Loren. Cereal Grains, Humanity's Double Edged Sword. PDF
available from www.thepaleodiet.com
2. Cordain, Loren. The Paleo Diet.
3. Liener, Irvin, ed. Toxic Constituents of Plant Food Substances, 2nd ed
1980 Academic Press- See Introduction
4. Diamond, Jared, Guns Germs and Steel


Long Version (Insert at SNIP above)

He is quick to point out that the success of our species has been greatly
assisted by the large variety of foodstuffs (and therefore energy) in our
diets- being not merely omnivorous but also eating a very large variety of
plant foodstuffs. He also points to our ability to use tools to eat the
brain and marrow of prey- a wonderful bonus of energy for little extra
effort- energy that is mostly wasted by other carnivores. Digging for roots
provides another source of energy. The use of fire for cooking can increase
the energy yield of many plants and also make some toxic roots/tubers edible
(eg potatoes), and similarly make some toxic seeds edible(cereal grains and
lentils/beans). Liener 1980 concludes that the cooking of toxic plants
doubled the available plant food energy available to a forager. Farming goes
even further to increase available food energy enormously (10-100 times
according to Jared Diamond) by removing inedible species from the land.

I would agree that the procurement of energy is easily the single most
important role of diet for all species. All else in diet is secondary.
Seasonal variation is also critical and earlier correspondence on this list
confirms that winter starvation has been an important bottleneck for our
species. By crude example, I think Leonard’s view would imply that in a
forest if the chimps all ate bananas and the forest could support one
hundred chimps- that if they learnt to also eat apples then the forest could
support two hundred chimps (assuming the apples could supply as much energy
as the bananas).

Leonard further points out that bipedal locomotion is energetically
efficient, and reduces energy consumption, and clearly this will assist to
increase the carrying capacity of the land for the species. Perhaps some of
the energy requirements of our large brain are directly offset by the energy
savings of bipedal locomotion- large parts of the brain being devoted to
balance and locomotion. While our large brain may consume 25-30% of resting
energy needs, bipedalism saves energy. It seems likely bipedalism is
dependent upon a larger brain, and that even larger brains probably are
required for even better balance and locomotion. Leonard states that
bipedalism was immediately followed by an expansion of the brain. Given the
large amount of energy the brain devotes to balance and locomotion, perhaps
the energy expended by intellectual and abstract thought isn’t as big as one
might assume- besides which planning and cunning etc can save much energy,
particularly when hunting, and so can be justified on bioenergetic grounds
in their own right.

One is left wondering whether the brain evolved because it was efficient and
gave us a competitive advantage or whether merely our energetic prowess made
sufficient energy available to splurge on more brain matter

There are limits on the energy equation for success of a species. If our
success depends (as it has for over 10,000 years) upon the cooking of toxic
plants in order to detoxify them (e.g. grains, beans, potatoes), we must
obtain wood for fires. Obtaining wood can be environmentally destructive and
reduce the carrying capacity of the land for our species. I presume that the
work required to obtain wood and cook has been included in discussions of
optimal foraging theory.

If a species causes significant environmental destruction, the carrying
capacity can decrease. An example of this is the elephant whose tree
destroying activities are so environmentally destructive that culling
programs are needed. Farming may increase available food energy but
sustainability needs to be considered.

Leonard uses humans’ large day range of foraging to explain their rapid
spread. Their immense success in procuring energy and locomotive efficiency
would seem better reasons.

In the area of brain evolution, Leonard has concentrated on energetics,
including a discussion of Wrangham’s hypothesis that the energy from tubers
made sufficient energy available to splurge on more brain matter. There is
no direct discussion of the role of micronutrients in brain evolution, which
many workers see as critical. The issues of energetics are important and
perhaps micronutrients are better considered another day. The article was
really about energetics and evolution rather than