How burning biomass made us human


[ This is a book review of Wrangham’s “Catching Fire: How cooking made us human”.

Fire enabled us to have larger brains from the increased calories in cooked food, held carnivores at bay, killed bacteria, and gave us many other advantages.

But it was burning coal, oil, and natural gas that briefly allowed us to become Homo Giganticus, conquering more than half of the world’s land mass for our crops and animals, driving hundreds of thousands, if not millions of species extinct already or within the next few hundred years.  Fossil fuels exploded the human population from 1 billion to 7.5 billion people, each of us equivalent to hundreds of locusts, devouring the majority of the bounty created by solar energy to grow plants and animals.

We stand on the precipice of descent now that the peak of conventional oil, 90% of our oil supplies — over half of it from just 500 giant oil fields discovered over 50 years ago — is behind us (2005).  Within 50 years or less, those who survive will go back to the past (there’ll still be a trickle of oil, coal, and natural gas obtainable in politically stable areas that haven’t drained their reserves so much that a technologically simpler society can’t reach them.  Once again we will rely on muscle and biomass power as we always have, and always will after the extremely brief age of fossils, which some scientists propose to name the Anthropocene.  We’re more than on the way in some places: biomass is over half of Europe’s renewable power

Since agriculture was invented, the energy that came from using trees to build and burn to melt metals out of ores, ceramics, glass, bricks, steel, and other objects requiring heat.  Biomass in the past is what made civilizations rise to never-before-seen heights, and then fall after deforestation and consequent topsoil loss that drastically lowered crop production (1).

And hundreds of thousands of years before that, burning biomass enabled us to become human (2).  Our brains never could have gotten as large eating raw food all day.

Alice Friedemann  author of “When Trucks Stop Running: Energy and the Future of Transportation”, 2015, Springer and “Crunch! Whole Grain Artisan Chips and Crackers”. Podcasts: Practical Prepping, KunstlerCast 253, KunstlerCast278, Peak Prosperity , XX2 report ]

Richard Wrangham. 2009. Catching Fire: How cooking made us human.  

I’ve always loved creation myths.  How we came to be is a question all cultures ask and religions try to answer.  The Iroquois believed we were created by the Sky People. The Australian Aborigines by the Sun Mother, the African Bushmen that we emerged from the depths of the earth, and the Christian Bible believes in a God that made the universe in seven days and humans began with Adam and Eve.

It was only with the invention of science, which is basically a method of testing reality, that we have finally solved our true origin mystery of how the universe began and our own evolutionary history.  Wrangham adds to this evolving story by making the case that we couldn’t have evolved our large brains without fire.

Fire played a role in our evolution in many ways.  We could have never become the “Naked Ape” without fire, or we would have died of cold at night.

Becoming a naked ape opened a new niche. We became the best creature on earth at running long distances, and more importantly, could do this mid-day in heat that would kill furry creatures from overheating, and catch them (2).

Fire also kept dangerous animals at bay, killed bacteria so they didn’t sicken or kill us, made otherwise indigestible or poisonous food edible, reduced spoilage, dried our clothes, and signaled friends.  Cooked food tastes much better than raw food –just ask Koko the gorilla, who signed that she preferred cooked over raw food.  Children can be weaned earlier and grow faster. All of the above led to longer lives, which greatly shaped human societies.

A new and major finding of this book is that of all the ways fire has helped us, the most important may be cooked food, which has more usable calories that our body can digest fully than raw food, and that cooked food can be consumed much faster. So instead of spending over six hours a day chewing fruit and leaves like our chimpanzee relatives do, we only spend about an hour a day chewing.

Not only that, but you get more calories from cooked food than raw food.  This was only discovered recently when tests were done on people who’ve had their large intestines removed.  Food was taken out after the small intestine, which is where most of our ability to get nutrition takes place. After that, the bacteria in our large intestine steals most of the remaining food for themselves.

When you ask people what’s essential to survival, they’ll usually say food, water, and shelter.  But by the end of this book, most will add fire to the list.  And the soon to be 9 billion of us depend on fire far more than our ancestors did to stay alive, we are utterly dependent on the “fire” of the fossil fuels we burn to power transportation, the electric grid (coal and natural gas provide two-thirds of our electricity in the U.S.), heat and cool our homes, cook with, to make every product around us — try to think of anything in your life that doesn’t depend on energy.
For example, your body can digest 94% of the protein in cooked eggs, but only 65% raw.  This is because heat increases the digestibility of protein.  Besides heat, proteins are more digestible if denatured in acids like lemon juice – think of ceviche, pickling, marinades, salt, or drying.

If you’re a food geek, you’ll love all the details Wrangham has about what cooking does to food, why we get more calories from cooked than raw food, or the minutiae of your digestive system.  Perhaps you’ll even become a better cook learning how heat breaks down starches and protein, at what temperatures meat is most tender, food safety, and so on.

Wrangham makes the case we’re adapted and dependent on cooked food in the first few chapters showing how we’ve lost the ability to survive on raw food alone.  Although more studies need to be done, the current scientific consensus is that a strict diet of raw food does not provide an adequate energy supply.  Dieters take note!  Yes, there are raw food consumers who are alive and well, so you’ll need to read the details to find out why their food is quite different from what our ancestors would have found in the wild.

Rumors that tribal people like the Inuit ate their food raw turned out not to be true.  Certainly some food is eaten raw, especially the softer organs like liver or stomach, but most of the calories the Inuit eat are cooked.  Women use twigs in summer, and seal oil or blubber to boil meat in the winter.

All species of mammals digest cooked food easier.  Farmers like to give cooked swill to their animals because they gain weight much faster.  That’s why your pets get so fat, all pet food is cooked.

Our anatomy shows that we’ve adapted to cooked food.  We have weak jaws, and really small mouths and lips compared to our closest relatives, the chimpanzees, who need big mouths, lips, and strong jaws to digest leaves and fruit.

We use 20% of our energy to fuel our brains, which are only 2.5% of our body weight.  The average primate uses 13% and mammals 8 to 10% of their energy to fuel their brains.

That energy came from smaller guts, because with cooked food we didn’t need to have a large digestive system.  Birds also evolved a small gut system, but they put their extra energy into wing muscles.  We used the extra energy for brain power, because social intelligence helped people survive longer.

The shorter gut, bigger brain theory is far from proven, so stay tuned to whether this ends up being completely, or partially true, as an explanation of how we evolved.

The average human diet is two-thirds starchy food.  The finer the flour, the more it’s digested, and modern white flour is basically a starchy powder, which is why so many Americans are overweight.  Worse yet, these calories are empty since wheat and corn flour has been stripped of protein, essential fatty acids, vitamins, and minerals.

The scientific human origin story unfolds like a mystery novel as each riddle is solved. One riddle that needs to be figured out is when humans first used fire. Unfortunately the evidence of the most ancient fires hasn’t survived, but archeologically there is good evidence of fires going back for 790,000 years.

Another riddle is when did we first control fire?  We couldn’t have depended on cooked food until we could make fire from scratch, which probably happened first in a place where both flint and pyrite rocks existed.  When struck together, they make excellent sparks and this method is used by hunter gatherers from the Arctic to Tierra del Fuego.

We can also look at the skeletons of our ancestors going back 2 million years to see what and when changes in our anatomy happened.  We know from the Grant’s study of finches in the Galapagos and other research that evolution can happen very fast.   It’s likely that we evolved quickly once we became dependent on cooked food.

There have only been three times in the past 2 million years when evolution was so fast that our ancestor species names changed.  Atello and Wheeler believe that cooking was responsible for the transition from Homo erectus to homo heidelbergensis 800,000 years ago, but Wrangham believes this transition was much earlier, when Homo erectus emerged over 1.5 million years ago, and explains why and alternative theories for the other times we evolved quickly.

Years ago         Species    Brain size  (cubic inches)      Weight (lbs)

2,300,000     Homo habilis                    37                   70- 81

1,800,000     Homo erectus                   53                123-145

800,000        Homo heidelbergensis       73

200,000        Homo sapiens                  85

It’s the social ramifications of eating cooked food that may be of the most interest.  A division of labor between men and women dramatically changed how we lived and related to one another, freed up time to pursue cultural activities, and made a much higher standard of living possible.

But the dark side is that men used their larger size to get out of the most boring chores.  In 98% of all societies, past and present, women do most or all of the cooking.  Even in the most egalitarian societies that have ever existed, like the Vanatina of the South Pacific, women did the cooking, washing dishes, fetching water and firewood, sweeping, and so on.  Meanwhile the men sat on verandahs chewing betel nuts.

It may have all started as a protection racket – men protected women from being robbed of their food by hungry groups of men in exchange for women cooking their meals.

Bonobo females form fighting alliances to protect themselves from male bullying, but in all other great ape species, including ours, women lose out to men.  Although Wrangham says that women can try to use their cooking as a form of empowerment by threatening to leave or not cooking if their husband is too abusive.

In Inuit societies, wives made warm, dry hunting clothes, and spent many hours cooking.  A man didn’t have time to hunt, make clothes, and cook, so a wife was essential to survival.  Desperate bachelors often tried to steal other men’s wives, usually killing the husband.  So men killed strangers on sight to prevent their wives from being stolen.

In the Tiwi culture, old men got the young wives, so 90% of men’s first marriages were to widows as old as sixty.  But the young men didn’t mind, because the wives cooked for them.  In most societies, bachelors are miserable.

In the end, Wrangham unravels far more than some of the riddles of the mystery of our creation, but also why we are getting so fat today, and the way that cooking and eating created how humans live and how men and women relate to each other.


(1) John Perlin. 2005. A Forest Journey: The Story of Wood and Civilization.

(2) Jared Diamond. 2006.The Third Chimpanzee: The Evolution and Future of the Human Animal“.

(3) Nina Jablonski.  2006. Skin, A Natural History.  University of California Press.


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