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10/23/12 3:41 PMRaw Food Not Enough to Feed Big Brains - ScienceNOW
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ENLARGE IMAGE
Raw material. Gorillas don’t get enough
calories from their raw food diet to grow
bigger brains.
Credit: (left) Julielangford; (right)
Stockbyte/Thinkstock
Eating a raw food diet is a recipe for disaster if you're trying to boost your
species' brainpower. That's because humans would have to spend more
than 9 hours a day eating to get enough energy from unprocessed raw
food alone to support our large brains, according to a new study that
calculates the energetic costs of growing a bigger brain or body in
primates. But our ancestors managed to get enough energy to grow brains
that have three times as many neurons as those in apes such as gorillas,
chimpanzees, and orangutans. How did they do it? They got cooking,
according to a study published online today in the Proceedings of the
National Academy of Sciences.
"If you eat only raw food, there are not enough hours in the day to get
enough calories to build such a large brain," says Suzana Herculano-
Houzel, a neuroscientist at the Federal University of Rio de Janeiro in Brazil who is co-author of the report. "We can
afford more neurons, thanks to cooking."
Humans have more brain neurons than any other primate—about 86 billion, on average, compared with about 33
billion neurons in gorillas and 28 billion in chimpanzees. While these extra neurons endow us with many benefits,
they come at a price—our brains consume 20% of our body's energy when resting, compared with 9% in other
primates. So a long-standing riddle has been where did our ancestors get that extra energy to expand their minds as
they evolved from animals with brains and bodies the size of chimpanzees?
One answer came in the late 1990s when Harvard University primatologist Richard Wrangham proposed that the
brain began to expand rapidly 1.6 million to 1.8 million years ago in our ancestor, Homo erectus, because this early
human learned how to roast meat and tuberous root vegetables over a fire. Cooking, Wrangham argued, effectively
predigested the food, making it easier and more efficient for our guts to absorb calories more rapidly. Since then, he
and his colleagues have shown in lab studies of rodents and pythons that these animals grow up bigger and faster
when they eat cooked meat instead of raw meat—and that it takes less energy to digest cooked meat than raw
meat.
In a new test of this cooking hypothesis, Herculano-Houzel and her graduate student, Karina Fonseca-Azevedo,
now a neuroscientist at the National Institute of Translational Neuroscience in São Paulo, Brazil, decided to see if a
diet of raw food inherently put limits on how large a primate's brain or body could grow. First, they counted the
number of neurons in the brains of 13 species of primates (and more than 30 species of mammals). The researchers
found two things: One, that brain size is directly linked to the number of neurons in a brain; and two, that that the
number of neurons is directly correlated to the amount of energy (or calories) needed to feed a brain.
ScienceNOW. ISSN 1947-8062
Raw Food Not Enough to Feed Big Brains
by Ann Gibbons on 22 October 2012, 4:08 PM | 20 Comments
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10/23/12 3:41 PMRaw Food Not Enough to Feed Big Brains - ScienceNOW
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After adjusting for body mass, they calculated how many hours per day it would take for various primates to eat
enough calories of raw food to fuel their brains. They found that it would take 8.8 hours for gorillas; 7.8 hours for
orangutans; 7.3 hours for chimps; and 9.3 hours for our species, H. sapiens.
These numbers show that there is an upper limit on how much energy primates can get from an unprocessed raw
diet, Herculano-Houzel says. An ape's diet in the wild differs from a modern "raw food diet," in which humans get
sufficient calories from processing raw food in blenders and adding protein and other nutrients. In the wild, other
apes can't evolve bigger brains unless they reduce their body sizes because they can't get past the limit of how
many calories they can consume in 7 hours to 8 hours of feeding per day. But humans, she says, got around that
limit by cooking. "The reason we have more neurons than any other animal alive is that cooking allowed this
qualitative change—this step increase in brain size," she says. "By cooking, we managed to circumvent the limitation
of how much we can eat in a day."
This study shows "that an ape could not achieve a brain as big as in recent humans while maintaining a typical ape
diet," Wrangham says.
Paleoanthropologist Robert Martin of The Field Museum in Chicago, Illinois, agrees that the new paper does
"provide the first evidence that metabolic limitations" from a raw food diet impose a limit on how big a primate's brain
—or body—can grow. "This could account for small brain sizes of great apes despite their large body sizes." But "the
jury is still out" on whether cooking was responsible for the first dramatic burst of brain growth in our lineage, in H.
erectus, Martin says, or whether our ancestors began cooking over a fire later, when the brain went through a
second major growth spurt about 600,000 years ago. Hearths show up in the archaeological record 800,000 years
ago and the regular use of fire for cooking doesn't become widespread until more recently.
But to Herculano-Houzel's mind, our brains would still be the size of an ape's if H. erectus hadn't played with fire:
"Gorillas are stuck with this limitation of how much they can eat in a day; orangutans are stuck there; H. erectus
would be stuck there if they had not invented cooking," she says. "The more I think about it, the more I bow to my
kitchen. It's the reason we are here."
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20 comments • 8 reactions
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DiscussionDiscussion CommunityCommunity
• Reply •
There is new research that suggests that the brain prefers lactose over glucose in some
metabolic processes. I really wonder what the role cooking, dairy, human milk production, and had
a brain level. Awesome stuff.
Matt Lewis • 3 hours ago
 2 1 
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10/23/12 3:41 PMRaw Food Not Enough to Feed Big Brains - ScienceNOW
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• Reply •
But if this is true, ancient human must first clever enough to produce or maintain fire,
which seems not as easy as something that a simple brain like chimps' can achieve. Thus the
cooked food should not be the crucial factor in our evolution.
Swkjd • 7 hours ago
 2 1 
• Reply •
Homo Erectus had already perfected stone tools. They weren't simple chimps
allbuss84 • an hour ago • parent
 0 1 
• Reply •
WRONG! WRONG! WRONG!
HUMANS DID NOT COME FROM MONKEYS AT ALL AND COOKING HAD NOTHING TO DO WITH
IT IT IS TOTAL STUPIDITY TO EVEN SAY THIS AND THE FACT IS THAT THE EARTH IS 6000
YEARS OLD AND MADE BY GOD WHO MADE THE APES AND ALL OTHER BEASTS AND THEN
MADE MANKIND IN HIS IMAGE AND MADE ADAM AND EVE FROM THE DUST OF THE EARTH
AND ALLTHIS EVOLUTION NONSENSENSE IS PROVEN WRONG BECAUSE I READ A BOOK
THAT SHOWED MANY PROOFS THAT THE EARTH IS ONLY 6000 YEARS OLD BUT OF COURSE
YOU "SCIENTISTS" BEING DECEIVED BY THE DEVIL WILL NOT PUBLISH THE TRUE SCIENCE
AND RESEARCH THAT PROVES THE EARTH IS 6000 YEARS OLD AND THAT THERE WAS A
FLOOD!
BIRDFISH • 16 minutes ago
 1 
• Reply •
Yes Mr. Birdfish you are very much correct. It is a proven scientific fact that the earth
is 6000 years old and created by God. The evidence is overwhelming.
For you NONBELIEVERS out there here is a link with six proofs that the Earth is only 6000
years old
http://www.christiananswers.ne...
praisejesus • 8 minutes ago • parent
 1 
• Reply •
It isn't difficult to visualize our ancestors during the 150,000 years that we were able to live
in a habitat rich in plant nutrients, stuff we only needed to grab and eat. I can imagine a life of 9-
hour-a-day food taking. Why not? However, when the superb and rich habitat is gone —volcano,
Indonesia, circa 70,000 years ago— then we needed to find a different way to feed our brains. I
don't think brains are the result of food taking; I think food taking WAS the result of a large brain. A
large brain is a successful mutation, that has prevailed—just like others, with even larger brains,
didn't prevail. Also, what we know today as «raw nutrients» is probably a sub-sample of what our
species once had at its disposal for a paradise-like life. Also, raw food did not pose the health
problems that intense food has brought to our species, cancer included, but not limited.
Franz J Fortuny Loretdemola • 18 hours ago
 2 3 
• Reply •
I do see a correlation here between brain size and cooking; but, do not see any reason to
believe that cooking caused increase in brain size, the impression that we get from this article. Can
a scientist here help me understand?
Sam • 7 hours ago
 1 1 
Absolutely right, Sam -- separating correlation and causation is a notoriously sticky
task. What the PNAS article suggests is that the energy required to maintain a modern human
(Homo sapiens) brain based on our body size should have placed an evolutionary limit on
how large the brains of our ancestors could have become without somehow getting more
calories. To get up to the levels of energy use in our current brains, the author suggests that
d.r. • 5 hours ago • parent
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10/23/12 3:41 PMRaw Food Not Enough to Feed Big Brains - ScienceNOW
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• Reply •
cooking foods, which makes the calories in those foods more readily digestible and available
for use, was the technology that allowed the fairly rapid expansion from the Homo erectus
size brain to the Neanderthal and modern human sized brain. However, this does not account
for the other earlier expansion from Australopithecus and Panthropus to the roughly doubled
brain size in Homo antecessor and Homo erectus. Presumably that sudden rise in brain size
came along with other advances over early simians -- in that case, I would speculate that
social and communicative developments may have allowed for more efficient collection of
foods or for harvesting of higher energy foods (nuts, meats, etc.). Bottom line: we may not be
able to say with certainty that the second increase from Homo erectus to modern human
relied on cooking, but it is a bit of coincidence that development of cooking seems to
precede the rapid increase in brain size to a degree that should otherwise be extremely
difficult to maintain.
 6 
• Reply •
It would seem more likely that an increase in calories was a result of large scale
migration and diet change as you alluded to.
Michael Maher • 2 hours ago • parent
 0 1 
• Reply •
"our ancestors ... evolved
from animals with brains and bodies the size of chimpanzees?"
Umm... evolution is only a theory...
Bob • 20 hours ago
 3 18 
• Reply •
Science isn't a belief system Bob, it's evidence based. All the evidence is
overwhelmingly in support of evolution. I don't know who you can be so blind to such
compelling evidence. I think some psychologists really need to study people like you to see
what's wrong.
Theorist • 13 hours ago • parent
 9 1 
• Reply •
Gravity is also only a theory.
I suggest you check the definition of "scientific theory" vs. the popular definition of "theory",
Bob.
I also suggest that you gather some background knowledge on the subject before you
embarrass yourself.
greek.fire • 13 hours ago • parent
 10 4 
• Reply •
All the elements heavier than hydrogen, up to iron, were created by fusion processes
in stars. All the elements heavier than iron were created in supernovas. Of course it's only a
theory but it allows nuclear bombs. Just as theories of evolution explain all life on Earth.
A Noyed • 20 hours ago • parent
 5 4 
• Reply •
Rather human use evolution to explain all life on Earth, all the life on Earth keep
showing to human that they are evolving. Even human drop the ideas of Charles
Darwin, they can always re-invent them from their observations.
He L • 16 hours ago • parent
 2 1 
I agree is only a theory. but what does that say? what about gravity dude? isn't this
alex • 9 hours ago • parent
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10/23/12 3:41 PMRaw Food Not Enough to Feed Big Brains - ScienceNOW
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• Reply •
"only" a theory?
 1 1 
• Reply •
great article. That actually explains why orcas and dolphins with such a unique calamari
based diet are having the brains they have.
alex • 9 hours ago
 0 3 
• Reply •
but maybe this is just a mammal association between brain-size and diet because larger
fish eat a lot of other fish but they do not look clever
alex • 9 hours ago
 0 2 
• Reply •
This article is pretty ridiculous. When you live in the non-seasonal tropics and there is fruit
year round all over the place, it would be easy as hell to live a foraging live and get the amount of
energy you need from you're food. Me and many others live on a raw food plant-based diet and i
get well over 2,000 calories a day..and you can bet that i'm not spending 9 hours eating!
Mrs. Doubtfire • 40 minutes ago
 0 1 
• Reply •
While cooking might increase the availability of energy found in plant food sources, it likely
also destroys many beneficial phytochemicals. Humans seem to struggle more with internal
parasites and bacterial diseases than wild primate populations. The whole concept of "medicine" is
based on adding back those protective chemicals (also found in some raw food sources) that help
to cure and prevent infections. Cooking with herbs and spices may have evolved to strike this
balance.
caveman • 2 hours ago
 0 1 
• Reply •
Corn syrup created the internet?
I still like raw Pecans, popular in China as brain food.
Check Engine • 3 hours ago
 0 1 
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