Food For Thought: Dietary Change
Was A Driving Force In Human Evolution
By: William R. Leonard
Professor of Anthropology at Northwestern University
Laurie Forti, Reviews Professor Leonard’s Article:
Professor Leonard: We humans are strange primates. We walk on two legs,
carry around enormous brains and have colonized every corner of the globe.
Anthropologists and biologists have long sought to understand how our
lineage came to differ so profoundly from the primate norm in these ways, and
over the years all manner of hypotheses aimed at explaining each of these
oddities have been put forth.
Laurie Forti: Simple: culture. The other species are driven by instincts, thus
can function only in harmony with Nature, not destroy it and themselves
through misuse of intellect as humans do as a result of cultural conditioning.
Some of the primates, such as the chimp, are starting to develop culture as
shown by their limited flesh eating.
Professor Leonard: But a growing body of evidence indicates that these
miscellaneous quirks of humanity in fact have a common thread: they are
largely the result of natural selection acting to maximize dietary quality and
Laurie Forti: Natural selection made our species into the self- and omni-
destructive plague that is currently destroying our planet? This is, indeed, a
perverted view of evolution. "Quirks" of behavior are not the slightest bit
related to evolution, which occurs in the physical body, only. "Quirks" of
behavior exist only in the domain of culture/consciousness, which is totally
independent from, and different than, genetic processes.
Professor Leonard: Changes in food availability over time, it seems, strongly
influenced our hominid ancestors. Thus, in an evolutionary sense, we are very
much what we ate.
Laurie Forti: Here, the false and long-abandoned 18th Century Lamarckian
view of evolution, that personal behavior in one generation influences the
physical evolution of the species in the next, is invoked.
If we really "are what we ate" then the human species would show some
signs of "adapting" to a flesh-oriented diet; however, we have developed no
physiological or biochemical tools to do so successfully. Further, the current
epidemiology of degenerative diseases proves otherwise, also.
Professor Leonard: Accordingly, what we eat is yet another way in, which
we differ from our primate kin.
Laurie Forti: Much to our own detriment, as epidemiology shows.
Professor Leonard: Contemporary human populations the world over have
diets richer in calories and nutrients than those of our cousins, the great apes.
Laurie Forti: Thus, humans are the only ape species to suffer rampant acute
and "degenerative diseases".
Professor Leonard: Scientific interest in the evolution of human nutritional
requirements has a long history.
Laurie Forti: Yet, evolutionary theory provides no known mechanism whereby
any species can adapt to a diet different than the one prescribed by its own
biochemistry. The "nutritional requirements" of the human ape has not
changed over time, and that is the reason cultural diets inevitably produce
disease profiles characteristic of their local chemistry.
Professor Leonard: But relevant investigations started gaining momentum
after 1985, when S. Boyd Eaton and Melvin J. Konner of Emory University
published a seminal paper in the New England Journal of Medicine entitled
They argued that the prevalence in modern societies of many chronic diseases--
obesity, hypertension, coronary heart disease and diabetes, among them--is
the consequence of a mismatch between modern dietary patterns and the type
of diet that our species evolved to eat as prehistoric hunter-gatherers.
Laurie Forti: The glaring error in the whole Paleolithic Diet mythology,
conveniently and uniformly overlooked by its proponents, is that there is no
way our species could have "adapted" to it, as opposed to our original tropical
The claimed successes of adopting a Paleo diet is an effect due only to the
fact that it is somewhat closer, chemically, to the original than the modern,
processed, low-fiber flesh, dairy, grain, junk food cultural diets.
Thus, reducing some of the modern dietary perversions will produce some
improvement; however, reducing them further by adopting a frugivorous ape
diet will obviously produce better results, and this is born out in practice.
The Paleo diet propagandists ignore the fact that there is no mechanism
espoused in modern evolutionary theory that will allow any species to
"adapt" to a diet radically different, chemically, from its natural one.
Note that we do not see any other species changing its diet radically over time,
only the human does this due to culture and choosing to live in an
environment not its natural ecological niche.
Professor Leonard: Since then, however, understanding of the evolution of
human nutritional needs has advanced considerably.
Laurie Forti: Is there any evidence that any other species demonstrated any
"evolution of nutritional needs"? Do we see the diet of any other species
changing over time?
Professor Leonard:... thanks in large part to new comparative analyses
of traditionally living human populations and other primates--a more
nuanced picture has emerged.
Laurie Forti: Major error: "traditionally living human populations" also eat
unnatural, culturally driven flesh-including diets that necessitate tools and fire.
This "Noble Savage" paradigm falsely assumes that such tribes are eating the
natural diet for our species, and that is simply not true if tools and fire are
necessary to secure or consume any element in that diet.
Professor Leonard: We now know that humans have evolved not to subsist on
a single, Paleolithic diet but to be flexible eaters, an insight that has important
implications for the current debate over what people today should eat in order
to be healthy.
Laurie Forti: Nonsense: We simply do not see any other species "evolving" to
eat as "flexible eaters" since animals eat as a function of their instincts which
obviously do not change over time or as a function of cultural whim (except in
those species "advanced" enough to be exhibiting cultural behavior).
Professor Leonard: To appreciate the role of diet in human evolution....
Laurie Forti: We should look at current evolutionary theory and discover
that there are no mechanisms elucidated by which any species' inherent
biochemistry changes as a function of its dietary input. Humans do not
have this magical ability, either.
Professor Leonard: Thus, by looking at the way animals go about obtaining
and then allocating food energy, we can better discern how natural selection
produces evolutionary change.
Laurie Forti: One does not find this in contemporary evolutionary theory. This
implies that behavior influences evolution, the long-abandoned Lamarckian
Professor Leonard: Chimps, gorillas and orangutans evolved in and continue
to occupy dense forests where only a mile or so of trekking over the course of
the day is all that is needed to find enough to eat. Much of early hominid
evolution, on the other hand, took place in more open woodland and grassland,
where sustenance is harder to come by.
Laurie Forti: So, the human apparently abandoned its natural ecological niche,
which resulted also in its abandoning its natural diet.
Professor Leonard: Indeed, modern human hunter-gatherers living in these
environments, who provide us with the best available model of early human
subsistence patterns, often travel six to eight miles daily in search of food.
Laurie Forti: Here is another fundamental error. Once our species abandoned
its proper ecological niche and the plants therein, and thus also abandoned its
natural, biologically correct diet, any diets chosen in a different ecosystem
cannot be used as any valid indication of human nutritional needs.
That is, our inherent digestive and assimilative biochemistry did not change to
accommodate any new, cultural diet; there is nothing in current evolutionary
theory that supports this even as a possibility, and certainly not as a fact.
By conveniently ignoring this fundamental fact, the Paleo Diet propagandists
blithely, dishonestly, and without the slightest bit of credible support, claim it
Professor Leonard:... bipedalism can be viewed as one of the first strategies in
human nutritional evolution ...
Laurie Forti: Strategy implies conscious decision; evolution occurs
mechanically, without the slightest bit of participation of the intellect of the
individual or the evolving gene pool.
Professor Leonard: Across all primates, species with bigger brains dine on
richer foods, and humans are the extreme example of this correlation, boasting
the largest relative brain size and the choicest diet.
Laurie Forti: This allegedly "choicest diet" of cultural humans has led directly
to all the currently popular "degenerative diseases" not seen in the wild.
Some real data, however, clearly indicate that largest primates eat no "richer
foods", i.e. animal flesh, but conversely the smallest primates consume the
Professor Leonard: According to recent analyses by Loren Cordain of
Colorado State University, contemporary hunter-gatherers derive, on average,
40 to 60 percent of their dietary energy from animal foods (meat, milk and other
Laurie Forti: Cultural diets, hunter-gatherer or couch potato, are not the
slightest bit useful for developing an understanding of the optimally healthy
human diet. Bringing in factual, but totally irrelevant, data to create the illusion
of credibility is a common, reprehensible tactic among propagandists.
Professor Leonard: Modern chimps, in comparison, obtain only 5 to 7 percent
of their calories from these comestibles. Animal foods are far denser in
calories and nutrients than most plant foods.
Laurie Forti: True, and that is a reason that eating them leads to obesity, heart
disease, cancer, and toxin-producing putrefactive bacteria in the colon.
Professor Leonard: For example, 3.5 ounces of meat provides upward of 200
kilocalories. But the same amount of fruit provides only 50 to 100 kilocalories.
And a comparable serving of foliage yields just 10 to 20 kilocalories.
Laurie Forti: So what?? With 65% of Americans being overweight, obese,
or morbidly obese what is the point of "evaluating" the desirability or
appropriateness of "foods" based on calorie content alone?
Would he recommend coal or petroleum based on their calorie content alone?
There is an unstated and quite erroneous assumption in Professor Leonard’s
irrational pro-meat propaganda, and that is that all ingested dietary calories are
efficiently and totally converted to usable calories, and that is simply not true.
The body muscles and brain uses glucose, blood sugar, as a source of
energy, and it is a lot easier to convert fruit sugars, and less easy to convert
starches, to glucose than animal protein or fat.
Nuts have a calorie density comparable to meat, and there is no cholesterol,
cooking-induced carcinogens, artery-clogging animal fats, denatured protein,
farm-chemical residues, bacterial contamination, antibiotics, or other hazards
inherent in meat consumption.
Professor Leonard: It stands to reason, then, that for early Homo, acquiring
more gray matter meant seeking out more of the energy-dense fare.
Laurie Forti: No, there is no "reason" here; this "meat-eating caused brain
growth in humans" theory is commonly touted in Paleo propaganda, yet
strangely, obligate carnivores did not produce large brains as a result of their
only-flesh-consumption, and conversely the large brains of the elephant and
gorilla do quite well on plant-based diets.
Professor Leonard: Fossils, too, indicate that improvements to dietary quality
accompanied evolutionary brain growth.
Laurie Forti: There is no way to "improve dietary quality" since the proper
optimum diet for any species is fixed at the genetic level and manifested by
each individual species' inherent physiology, biochemistry, and instincts.
There is no way to "improve" on the original design by cultural diets, and
the profusion of cultural diet-caused degenerative diseases is proof of that.
I am always amused by such pseudoscientific claims regarding the great
wonders conferred to our species by flesh-eating, when the proponents of
such claims can not explain just why the human did not evolve the sharp,
pointy tools seen among all natural flesh-eaters, and especially why we
did not evolve instincts to capture, kill, and eat flesh raw.
In fact, there is a strong anti-instinct to do so, and no proponent of these
nonsensical theories will test their beliefs by killing and eating raw any small
animal, using only their natural equipment.
Professor Leonard: This is not to say that australopithecines never ate meat.
They almost certainly did on occasion, just as chimps do today.
Laurie Forti: Strangely, people who bring this trivial fact up never indicate that
this is strictly a cultural practice among chimps, and certainly not a nutritional
imperative. Shouldn't anthro-apologists be able to distinguish between
culture and Nature?
Professor Leonard: As to what prompted Homo's initial shift toward the higher-
quality diet necessary for brain growth….
Laurie Forti: There is no evidence that any "higher-quality" diet exists; the
proper diet for any species is dictated at the genetic level. Similarly, there is
no evidence that different diets are necessary for small or large brains.
Professor Leonard: The continued desiccation of the African landscape limited
the amount and variety of edible plant foods available to hominids.
Laurie Forti: True, but irrelevant to any discussion of the natural/optimum diet
for our species, as these groups had left their proper ecological niche and the
plant communities therein.
Professor Leonard: As it turns out, the spread of grasslands also led to an
increase in the relative abundance of grazing mammals such as antelope and
gazelle, creating opportunities for hominids capable of exploiting them.
Homo erectus did just that, developing the first hunting-and-gathering economy
in which game animals became a significant part of the diet and resources were
shared among members of the foraging groups.
Signs of this behavioral revolution are visible in the archaeological record,
which shows an increase in animal bones at hominid sites during this period,
along with evidence that the beasts were butchered using stone tools.
Laurie Forti: True, but irrelevant, since the use of tools and fire is absolutely
and unquestioningly not necessary with our biologically correct diet;
conversely, their use proves that the items for which they are necessary
are not part of our natural diet.
It is insightful that anthro-apologists conveniently obfuscate or ignore the
profound differences between Nature and culture to support their hollow
Will the evidence of pesticide pollution in our corpses some 10,000 years from
now convince those future anthro-apologists that we somehow "adapted" to
Professor Leonard:... the addition of modest amounts of animal foods to the
menu ... would have significantly increased the quality and stability of hominid
Laurie Forti: No evidence is presented that links animal foods and "quality" of
diets. In fact, there is none; however, there is abundant and convincing data
that all the currently popular "degenerative diseases" are linked with the
consumption of "animal foods".
This false link is simply assumed as a result of Professor Leonard’s cultural
programming and superstition; clearly, he has not any personal experience
with plant-based diets, or such foolishness would not be presented as fact.
Insightfully, people who tout human flesh-oriented diets, or disparage human
plant-based diets, generally have not had any personal experience with the
Professor Leonard: The impetus behind this newfound wanderlust again
appears to be food. What an animal eats dictates to a large extent how much
territory it needs to survive. Carnivorous animals generally require far bigger
home ranges than do herbivores of comparable size because they have fewer
total calories available to them per unit area.
Laurie Forti: But, wait. Weren't we told that a flesh-oriented diet was "better"
since it was more calorie-dense and thus necessitated less locomotion?
Carnivores do not have "home ranges" they follow herbivore herds, or hang
out at watering holes, and have an incredibly-populous food sources available
at all times.
Professor Leonard: Large-bodied and increasingly dependent on animal foods,
Homo erectus most likely needed much more turf than the smaller, more
vegetarian australopithecines did.
Using data on contemporary primates and human hunter-gatherers as a guide, .
I have estimated that the larger body size of Homo erectus, combined with a
moderate increase in meat consumption, would have necessitated an eightfold
to 10-fold increase in home range size compared with that of the late
Laurie Forti: Weren't we told above that a "better" more calorie-dense diet
necessitated less locomotion to obtain it?
Professor Leonard: -- enough, in fact, to account for the abrupt expansion of
the species out of Africa. Exactly how far beyond the continent that shift would
have taken Homo erectus remains unclear, but migrating animal herds may
have helped lead it to these distant lands.
Laurie Forti: And, moving out of our natural ecological niche also was
responsible for the "addiction" our species developed to tools and fire, with the
logical diminution of health resulting from using such.
Professor Leonard: As humans moved into more northern latitudes, they
encountered new dietary challenges. The Neanderthals, who lived during the
last ice ages of Europe, were among the first humans to inhabit arctic
environments, and they almost certainly would have needed ample calories to
endure under those circumstances.
Hints at what their energy requirements might have been come from data on
traditional human populations that live in northern settings today.
The Siberian reindeer-herding populations known as the Evenki, which I have
studied with Peter Katzmarzyk of Queen's University in Ontario and Victoria A.
Galloway of the University of Toronto, and the Inuit (Eskimo) populations of the
Canadian Arctic have resting metabolic rates that are about 15 percent higher
than those of people of similar size living in temperate environments.
The energetically expensive activities associated with living in a northern
climate ratchet their caloric cost of living up further still.
Indeed, whereas a 160-pound American male with a typical urban way of life
requires about 2,600 kilocalories a day, a diminutive, 125-pound Evenki man
needs more than 3,000 kilocalories a day to sustain himself.
Using these modern northern populations as benchmarks, Mark Sorensen of
Northwestern University and I have estimated that Neanderthals most likely
would have required as many as 4,000 kilocalories a day to survive. That they
were able to meet these demands for as long as they did speaks to their skills
Laurie Forti: Interesting as these comments are, they completely ignore the
negative health consequences of living is such unnatural environments and
consuming the unnatural diets; that is, why do these types of "analysis"
always ignore the poor health and shortened life spans of these tribes?
Professor Leonard: Just as pressures to improve dietary quality influenced
early human evolution, so, too, have these factors played a crucial role in the
more recent increases in population size.
Laurie Forti: Where do we see these supposed, "pressures to improve dietary
quality" elsewhere in Nature? Nowhere. They did not exist.
Professor Leonard: Innovations such as cooking, agriculture and even aspects
of modern food technology can all be considered tactics for boosting the quality
of the human diet.
Laurie Forti: There is no rational argument that suggests that cooking and/or
modern food technology "boosts" the "quality of the human diet" in fact, the
opposite is true.
Professor Leonard: Cooking, for one, augmented the energy available in wild
Laurie Forti: The cooking of starchy plants, such as roots and tubers,
increases the availability of starch for digestion because the cell walls are
broken, thus cell contents are more readily available to digestive enzymes.
However, the creation of carcinogens, mutagens, teratogens, Maillard reaction
chemicals, cross-linked protein-sugar complexes, various toxic and foreign
species of chemicals, and the reduction of the nutritional efficacy of many
nutrients by cooking are all conveniently ignored.
Professor Leonard: With the advent of agriculture, humans began to
manipulate marginal plant species to increase their productivity, digestibility and
nutritional content-- essentially making plants more like animal foods.
This kind of tinkering continues today, with genetic modification of crop species
to make "better" fruits, vegetables and grains.
Similarly, the development of liquid nutritional supplements and meal
replacement bars is a continuation of the trend that our ancient ancestors
started: gaining as much nutritional return from our food in as little volume and
with as little physical effort as possible.
Laurie Forti: Conveniently, the ongoing reduction in nutritional quality of
commercial products over time as a result of this continuing "progress" and
the coming horrors related to genetically-modified organisms being released
into the wild are ignored.
Professor Leonard: Overall, that strategy has evidently worked: humans are
here today and in record numbers to boot.
Laurie Forti: When did quantity relate to quality? The health of people who are
victims to this "tinkering" is rapidly decreasing, as seen in the ever-increasing
Professor Leonard: But perhaps the strongest testament to the importance of
energy- and nutrient-rich foods in human evolution lies in the observation that
so many health concerns facing societies around the globe stem from
deviations from the energy dynamic that our ancestors established.
Laurie Forti: Here, the false concept that our ancestors' misguided nutritional
perversities somehow affected our genes in a way such as to require our
continuing their mistakes is propagated again.
Professor Leonard: For children in rural populations of the developing world,
low-quality diets lead to poor physical growth and high rates of mortality during
In these cases, the foods fed to youngsters during and after weaning are often
not sufficiently dense in energy and nutrients to meet the high nutritional needs
associated with this period of rapid growth and development.
Although these children are typically similar in length and weight to their U.S.
counterparts at birth, they are much shorter and lighter by the age of three,
often resembling the smallest 2 to 3 percent of American children of the same
age and sex.
Laurie Forti: Could the growth hormones, both natural and artificial, in animal
products be responsible for this excessive growth? When did bigger mean
better? Especially with the global epidemic of obesity rapidly following the
introduction of "modern civilized foods"?
Professor Leonard: In the industrial world, we are facing the opposite problem:
rates of childhood and adult obesity are rising because the energy-rich foods
we crave--notably those packed with fat and sugar.
Laurie Forti: Hmm, animal and junk "foods" exactly what was touted as
Professor Leonard: Obesity has also appeared in parts of the developing world
where it was virtually unknown less than a generation ago.
Laurie Forti: As traditional diets, somewhat closer to our nutritional needs, are
abandoned in favor of "tinkered foods" including more animal foods.
Professor Leonard: We are victims of our own evolutionary success.
Laurie Forti: What an incredibly stupid thing to say. It is "evolution's" fault for
the current state of degenerate health existing only in the human species.
Professor Leonard: The magnitude of this imbalance becomes clear when we
look at traditionally living human populations. Studies of the Evenki reindeer
herders that I have conducted in collaboration with Michael Crawford of the
University of Kansas and Ludmila Osipova of the Russian Academy of
Sciences in Novosibirsk indicate that the Evenki derive almost half their daily
calories from meat, more than 2.5 times the amount consumed by the average
Yet when we compare Evenki men with their U.S. peers, they are 20 percent
leaner and have cholesterol levels that are 30 percent lower.
Laurie Forti: The dietary practices of people living so far from our natural
ecological niche have no relevance to our optimally healthy diet. What is the
life span and health profile of these people? This important data is always
ignored in "the noble savage" paradigm.
Professor Leonard: These differences partly reflect the compositions of the
diets. Although the Evenki diet is high in meat, it is relatively low in fat (about
20 percent of their dietary energy comes from fat, compared with 35 percent in
the average U.S. diet), because free-ranging animals such as reindeer have less
body fat than cattle and other feedlot animals do.
The composition of the fat is also different in free-ranging animals, tending to
be lower in saturated fats and higher in the polyunsaturated fatty acids that
protect against heart disease. More important, however, the Evenki way of life
necessitates a much higher level of energy expenditure.
Laurie Forti: So, he admits that such "apple and orange" comparisons are
Again, we see that anthro-apologists have abandoned real science, facts, and
logic in their fanciful creative writing efforts.
By: Laurie Forti
WILLIAM R. LEONARD is a professor of anthropology at Northwestern
University. He was born in Jamestown, N.Y., and received his Ph.D. in
biological anthropology at the University of Michigan at Ann Arbor in 1987.
The author of more than 80 research articles on nutrition and energetics
among contemporary and prehistoric populations, Leonard has studied
indigenous agricultural groups in Ecuador, Bolivia and Peru and traditional
herding populations in central and southern Siberia.