On Mar 17, 8:28 pm, Sir Frederick fuzzysys.com> wrote:

I think this supports the article;

PART 4:
Intelligence, Evolution of the
Human Brain, and Diet

Introduction: Claims of the Comparative "Proofs"

Human intelligence ignored or rationalized. One of the key systematic
restraints on the alleged comparative anatomy/physiology "proofs" that
promote particular diets is such proofs generally do not consider the
many important features that make humans unique in nature. In
particular, human intelligence is usually ignored or dismissed (via
rationalizations) in such "proofs." For example, Fit Food for Humanity
asserts (p. 14):

But merely having a superior brain does not alter our anatomy and
physiology which, according to natural law, remain characteristic of a
total-vegetarian mammal, meant to eat a variety of vegetables, nuts
and seeds.

Brain size discounted. Le Gros Clark is sometimes quoted by those
advocating comparative "proofs" of vegetarian diets. He also appears
to minimize the importance of large brains in humans (the term is
"encephalization," discussed later herein). From Le Gros Clark [1964,
pp. 4-5]:

In Homo the large size of the brain relative to the body weight is
certainly a feature which distinguishes this genus from all other
Hominoidea, but it actually represents no more than an extension of
the trend toward a progressive elaboration of the brain shown in the
evolution of related primates.

The attitudes stated in the quote from Fit Food for Humanity reflect
an underlying denial of the importance of human intelligence, in
particular its impact on behavior (and, ultimately on morphology via
evolution). The attitude one finds in some raw/veg*n circles is that
human intelligence is suspect because it allows us to "make errors,"
i.e., to eat foods different from those promoted by dietary advocates
(who often behave as if they are absolutely 100%% certain that they
know better than you what foods you should eat).

Hidden, contradictory views on the value of intelligence. An irony
here is that there is a contradiction in the logic of the attitudes of
certain dietary advocates regarding intelligence. Some fruitarian
extremists promote the alleged naturalness of fruitarian diets via the
"humans are naked apes, without tools" myth discussed in the last
section. This falsehood is often presented as actual science (needless
to say, it is crank science) by those who promote it. Inasmuch as the
advanced use of tools is an evolutionary characteristic of human
intelligence, we can observe that those promoting the myth are saying
that you should reject tool use in seeking your "natural" diet (this
nonsense may even be presented as being scientific or logical).
However, the preceding is equivalent to telling you to reject your
intelligence, and even reject your status as a human being, in order
to select the (allegedly) optimal diet.

The argument made by fruitarian extremists is thus contradictory; the
argument can be stated as: Use your intelligence to agree with the
extremist that humans are "naked apes, without tools," and thus
reject, in the future, your use of intelligence in food choices.
Another irony here is that some of the extremists promoting this false
myth present themselves as "scientific." Crank science (or science
fiction) is a more accurate description for such myths, however. The
contradictory logic of the "naked ape" myth is a good example of the
ambivalent, confused attitude toward intelligence displayed by some
dietary advocates.

Recent evolutionary research now emphasizes the interaction of diet
and brain development. Further, recent research has rendered the
quotations above outdated. The remarks of Milton [1993] on the
interaction between brain evolution and diet provide a brief
introduction to a more modern perspective (p. 92):

Specialized carnivores and herbivores that abound in the African
savannas were evolving at the same time as early humans, perhaps
forcing them [humans] to become a new type of omnivore, one ultimately
dependent on social and technological innovation, and thus, to a great
extent, on brain power.

This section will review some of the research on the human brain,
specifically:

Its evolution,

How our brains compare to other animals (especially primates--using a
comparative anatomy approach), and

The dietary/metabolic factors required to support the large human
brain.

We begin our review with the topic of encephalization, or brain size.

Encephalization

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Introduction

The most significant features that make humans unique in all of nature
are our high intelligence and "large" brains. Here "large" means the
brain is large relative to body size. Encephalization, or the relative
size of the brain, is analyzed using a measure known as the
encephalization quotient.

"Expected" vs. actual brain size. In order to measure encephalization,
statistical models have been developed that compare body size with
brain size across species, thereby enabling the estimation of the
"expected" brain mass for a given species based on its body mass. The
actual brain mass of a species compared to (divided by) its "expected"
brain mass gives the encephalization quotient. Higher quotients
indicate species with larger-than-expected brain sizes. Thus, a
quotient greater than 1 indicates an actual brain mass greater than
predicted, while quotients less than 1 indicate less-than-expected
brain mass.

The encephalization quotient is important because it allows the
quantitative study and comparison of brain sizes between different
species by automatically adjusting for body size. For example,
elephants, which are folivores, and certain carnivorous marine mammals
have larger brains (actual physical mass) than humans. However, after
adjusting for body size, humans have much "larger" brains than
elephants or marine mammals. Additionally, the complexity of the brain
is significant as well (and, of course, encephalization does not
directly measure complexity--it only measures size).

Kleiber's Law. Kleiber's Law expresses the relationship between body
size--specifically body mass--and body metabolic energy requirements,
i.e., RMR (resting metabolic energy requirements), also known as BMR
(basal metabolic energy requirements). The form of the equation is:

RMR = 70 * (W0.75)

where RMR is measured in kcal/day, and W = weight in kg. (The above is
adapted from Leonard and Robertson [1994].) An understanding of
Kleiber's Law is important to several of the discussions in this
paper.

Brain and digestive system compete for limited share of metabolic
energy budget. A key observation to note about relative brain size
when averaged across species is that the equation for how brain size
varies in proportion to body size uses an exponential scaling factor
almost identical to the one used in the equation for how an organism's
basal metabolic rate (BMR) varies with body size, i.e. Kleiber's Law.
(The exponential scaling coefficient used in the equation for how
brain mass varies in relation to body mass is 0.76 [Foley and Lee
1991]; the analogous scaling coefficient for BMR is 0.75; Kleiber
[1961] as cited in Foley and Lee [1991].) This is important because it
directly implies that brain size is closely linked to the amount of
metabolic energy available to sustain it [Milton 1988, Parker 1990].

This point will become central as we proceed. For now it is enough to
observe that the amount of energy available to the brain is dependent
on how the body's total energy budget has to be allocated between the
brain and other energy-intensive organs and systems, particularly the
digestive system. Further, how much energy the digestive system
requires (and thus how much is left over for the brain and other
"expensive" organs) is a function of the kind of diet that a species
has developed to handle during its evolution. As we proceed, we will
return to the ramifications of this for human diet as it relates to
the evolution of the large human brain.

For more information on the derivation of encephalization quotients,
Kleiber's Law, and the statistical fitting procedures used, consult
Appendix 2.

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A comparative anatomy analysis of primate brains

Stephan [1972] provides a comparative anatomy analysis of primate
brains, including modern humans, non-human primates, and our
prehistoric ancestors. Below is a summary of the important points made
in Stephan [1972]. Note here that the Stephan paper was done before
the Martin research cited above; thus Stephan uses a slightly
different measure of encephalization.

Humans at top of primate scale. Using measures of encephalization
based on the encephalization of insectivorous primates, Stephan [1972]
reports that humans are at the very top of the index (with an
encephalization quotient, or EQ, of 28.8), while Lepilemur is at the
bottom (EQ=2.4).

Large gap between humans and great apes. There is a large gap between
the encephalization of modern humans and all extant (present-day) non-
human primates, including our closest relatives, the great apes. This
large gap is filled, however, by analysis of the encephalization of
our prehistoric hominid ancestors.

Brain enlargement disproportional. The enlargement of the human brain
vs. non-human primates is not proportional (thereby possibly
contradicting the earlier quote from Le Gros Clark). Stephan [1972, p.
174] notes:

The enlargement of the brain is not proportional; that is, all parts
do not develop at the same rate. The neocortex is by far the most
progressive structure and therefore used to evaluate evolutionary
progress ( = Ascending Primate Scale).

Also of interest here is the additional remark in Stephan [1972],
regarding comparative anatomy in this context (p. 174): "It must be
stressed, however, that because our scientific approach is indirect,
it can provide only inferences, not proofs."

Factors in Encephalization: Energy (Metabolism) and Diet

The reality of encephalization--the relatively large human brain--with
its correspondingly high intelligence, is readily apparent. The object
of current research and debate, however, is the examination of what
evolutionary factors have driven the development of increased human
encephalization. Such research provides insight into our evolutionary
diet, and also reveals why any comparative "proof" that ignores
intelligence and the significant impact of brain size on metabolic
requirements is logically dubious.

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Life cycle and energy requirements

Parker [1990] analyzes intelligence and encephalization from the
perspective of life history strategy (LHS) theory, a branch of
behavioral ecology. LHS is based on the premise that evolutionary
selection determines the timing of major life-cycle events--especially
those related to reproduction--as the solution to energy optimization
problems.

Extensive energy required for brain growth. Parker discusses the life
history variables in non-human primates, and then examines how life
history events relate to large brain size, gestation period, maturity
at birth, growth rates and milk consumption, weaning and birth
intervals, age of puberty, and other events. The motivation for
studying such events is that the brain is the "pacemaker of the human
life cycle" [Parker 1990, p. 144], and the slow pace of most human
life history events reflects the extensive energy required for brain
growth and maintenance.

Foley and Lee [1991] analyze the evolutionary pattern of
encephalization with respect to foraging and dietary strategies. They
clearly state the difficulty of separating cause and effect in this
regard; from Foley and Lee [1991, p. 223]

In considering, for example, the development of human foraging
strategies, increased returns for foraging effort and food processing
may be an important prerequisite for encephalization, and in turn a
large brain is necessary to organize human foraging behaviour.

Dietary quality is correlated with brain size. Foley and Lee first
consider brain size vs. primate feeding strategies, and note that
folivorous diets (leaves) are correlated with smaller brains, while
fruit and animal foods (insects, meat) are correlated with larger
brains. The energetic costs, both daily and cumulative, of brains in
humans and chimps, over the first 1-5 years of life are then compared.
They note [Foley and Lee 1991, p. 226]:

Overall the energetic costs of brain maintenance for modern humans are
about three times those of a chimpanzee. Growth costs will also be
commensurately larger.

Then they consider encephalization and delayed maturation in humans
(compared to apes), and conclude, based on an analysis of brain
growth, that the high energy costs of brain development are
responsible for the delay in maturation.
Dietary shift beginning with Homo. Finally, they consider the dietary
shifts that are found in the fossil record with the advent of humans
(genus Homo), remarking that [Foley and Lee 1991, p. 229]:

The recent debate over the importance of meat-eating in human
evolution has focused closely on the means of acquirement... but
rather less on the quantities involved...
In considering the evolution of human carnivory it may be that a level
of 10-20%% of nutritional intake may be sufficient to have major
evolutionary consequences...

Meat-eating, it may be argued, represents an expansion of resource
breadth beyond that found in non-human primates...

Homo, with its associated encephalization, may have been the product
of the selection for individuals capable of exploiting these energy-
and protein-rich resources as the habitats expanded (Foley 1987a).

The last sentence in the preceding quote is provocative indeed--it
suggests that we, and our large brains, may be the evolutionary result
of selection that specifically favored meat-eating and a high-protein
diet, i.e., a faunivorous diet.

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How dietary quality relates to the brain's share of total metabolic
budget

The research of Leonard and Robertson [1992, 1994] provides an in-
depth analysis of brain and body metabolism energy requirements.
Relevant points from their research:

Dramatic changes in last 4 million years. Leonard and Robertson [1992,
p. 180] note:

Evidence from the prehistoric record indicates that dramatic changes
have occurred in (1) brain and body size, (2) rates of maturation, and
(3) foraging behavior during the course of hominid evolution, between
four million years ago and the present. Consequently, it is reasonable
to assume that significant changes in metabolic requirements and
dietary changes have also occurred during this period.

Human brain's metabolic budget significantly different from apes. They
point out that anthropoid primates use ~8%% of resting metabolism for
the brain, other mammals (excluding humans) use 3-4%%, but humans use
an impressive 25%% of resting metabolism for the brain. This indicates
that the human "energy budget" is substantially different from all
other animals, even our closest primate relatives--the anthropoid
apes.

In contrast, total human resting metabolism not significantly
different. In order to understand the relationship between metabolism
(energy budget) and body size, Leonard and Robertson collected
relevant data on metabolism and body size in primates, humans, and
other mammals. Some of the data collected included body size, brain
size, resting metabolic rate (RMR), brain metabolic rate (brain MR),
total energy expenditure (TEE), etc. They also collected activity and
energy expenditure data on a few hunter-gatherer societies, and select
non-human primates. Statistical analysis of the data showed that:

[L]arge-brained anthropoids [great apes], as a group, do not depart
from the general mammalian metabolism/body size relationship. Several
individual species, however, do deviate markedly from the RMRs
predicted by the Kleiber relationship.

To summarize, they found that the RMR (resting metabolic rate) for
humans--that is, the overall total energy budget--as predicted by body
size, did not deviate significantly from that predicted by the Kleiber
relationship; that is, resting metabolic rate for humans is comparable
to that for other animals (based on body mass).

Human brain MR 3.5 times higher than apes. However, in marked
contrast, they found that humans have a radically different brain
energy metabolism than the other animals. From Leonard and Robertson
[1992, p. 186]:

The human brain represents about 2.5%% of body weight and accounts for
about 22%% of resting metabolic needs...
At 315 kcal (1318 kJ), humans use over 3.5 times more of RMR to
maintain their brains than other anthropoids (i.e., a positive
deviation of 255%%). Clearly, even relative to other primate species,
humans are distinct in the proportion of metabolic needs for the
brain.

Important changes in diet of Homo erectus. Leonard and Robertson
[1992] also applied their statistical models to our prehistoric
ancestors. Their analysis points to important changes in diet. From
Leonard and Robertson [1992, p. 191]:

The clear implication is that the diet of Homo erectus [note: Homo
erectus evolved roughly 1.7 Mya] was not simply an australopithecine
diet with more meat; rather there were important changes in both
animal and vegetable components of the diet...
What made meat an important resource to exploit was not its high
protein content, rather, its high caloric return...

In short, the early hunting-gathering life-way associated with H.
erectus was a more efficient way of getting food which supported a
35-55%% increase in caloric needs (relative to australopithecines)...

In a followup paper, Leonard and Robertson [1994] expanded the
analysis of their 1992 paper by looking at the relationship of dietary
quality to body size and metabolic rates. Important points from their
1994 paper:

Body size and dietary quality (DQ). When the relationship between body
size and dietary quality (i.e., the energy and nutrient content of the
diet) was analyzed, the general relationship found was that larger
primates, e.g., gorillas, have low-quality diets (gorillas are
folivores), while the smaller primates have higher-quality
(insectivorous) diets. Leonard and Robertson [1994, p. 78] note:

In general, there is a negative relationship between diet quality (the
energy and nutrient density of food items) and body size (Clutton-
Brock and Harvey, 1977; Sailer et al., 1985).

Humans depart from normal DQ/body-weight relationship. Next, they
calculated dietary quality (DQ) indices for 5 hunter-gatherer groups,
and 72 non-human primate species, relative to body weight. The
observed DQ values for the hunter-gatherer groups were higher than
predicted for a primate that weighs as much as a human. Leonard and
Robertson [1994, p. 79] comment that:

Humans, however, appear to depart substantially from the primate DQ-
body weight relationship (Fig. 1)...

[T]he diets of the five hunter-gatherer groups are of much higher
quality than expected for primates of their size. This generalization
holds for most all subsistence-level human populations, as even
agricultural groups consuming cereal-based diets have estimated DQs
higher than other primates of comparable size...

[E]ven in human populations where meat consumption is low, DQ is still
much higher than in other large-bodied primates because grains are
much more calorically dense than foliage.

Availability of grains vs. animal food. A note here regarding cereal
(i.e., grain) consumption: Prior to the development of agriculture,
grains would only have been a miniscule fraction of the human diet due
to lack of technology to farm, harvest, and store them. In some
locations they may have been available seasonally, but the low level
of harvesting, storing, and processing technology would necessarily
have sharply limited their consumption. Hence prior to the development
of agriculture 10,000 years ago (a tiny fraction of the 2.5-million-
year existence of the Homo genus), grains were not a feasible option
to increase DQ.

DQ and RMR. Another statistical comparison was run to analyze the
relationship between dietary quality and RMR, or resting metabolic
rate. (The previous comparisons just discussed were based on body
weight.) While the model fit was not very good, the data plot suggests
that human DQ may also be higher than expected when using RMR as the
yardstick for comparison in lieu of body weight. (As the model fit is
not good, the preceding is a hypothesis only.)

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The paradox: Where does the energy for the large human brain come
from?

In any event, as we have seen, what begs explanation is that humans
"spend" far more energy on the brain than other primates: 20-25%% of
RMR vs. roughly 8%% in the great apes. Yet the total human RMR remains
in line with predictions based purely on body size. This presents a
paradox: where do humans get the extra energy to "spend" on our large
brains? As we will see later in the research of Aiello and Wheeler,
the most feasible hypothesis is that the answer lies in considerations
of dietary efficiency and quality. Leonard and Robertson [1994, p. 83]
conclude:

These results imply that changes in diet quality during hominid
evolution were linked with the evolution of brain size. The shift to a
more calorically dense diet was probably needed in order to
substantially increase the amount of metabolic energy being used by
the hominid brain. Thus, while nutritional factors alone are not
sufficient to explain the evolution of our large brains, it seems
clear that certain dietary changes were necessary for substantial
brain evolution to take place.

In other words, while the evolutionary causes of the enlarging human
brain themselves are thought to have been due to factors that go
beyond diet alone (increasing social organization being prime among
the proposed factors usually cited), a diet of sufficient quality
would nevertheless have been an important prerequisite. That is, diet
would have been an important hurdle--or limiting factor--to surmount
in providing the necessary physiological basis for brain enlargement
to occur within the context of whatever those other primary selective
pressures might have been.

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To summarize:

The significance of Leonard and Robertson's research [1992, 1994] lies
in their analysis of energy metabolism, which reveals the paradox: How
do humans meet the dramatically higher energy needs of our brains,
without a corresponding increase in RMR (which is related to our body
size)? They argue that the factor that allows us to overcome the
paradox is our higher-quality diet compared to other primates. Of
course, prior to the advent of agriculture and the availability of
grains, the primary source of such increased dietary quality was the
consumption of faun