"Ahem."
Charlie cleared his throat softly while tapping the podium table with his fingertip, signaling to the entire class that their casual question-and-answer session had come to an end.
"Alright, I think the introduction and question-and-answer session have been more than enough."
"Now, it is time for us to shift to our main purpose here, which is starting the lesson material."
"Since this is Sensei's first time working as a teacher in a formal school, I hope you can understand if my teaching later might be slightly short of your expectations."
Charlie turned around, picked up a fresh piece of chalk, and wrote a single large word in the center of the blackboard: COOKING.
He faced his students once again, resting both of his hands on the podium table, and then looked at them one by one with a deep gaze.
"Tonight, after you return to your respective homes, most of you will probably turn on the stove. You will heat something up for dinner. And, you won't think twice about that activity. To you, it is just a boring daily routine, isn't it?"
The students appeared to nod slowly, including Amane, who watched lazily from his desk, while Mahiru listened with a straight back.
"But..." Charlie raised one index finger into the air, "Not a single animal on this planet does what you just did."
"Not chimpanzees, not dolphins, not even crows—which by scientists today are considered to be among the smartest animals to ever exist on earth. Only you. Only humans. And strangely, most people actually take that ability completely for granted."
Charlie walked slowly to the right side of the podium, letting his words settle in his students' minds.
"But it is not an ordinary thing. It is one of the strangest, most radical things to ever happen in the long history of life on this earth. Because for our species, cooking is not merely a habit or a culinary art. Cooking is the primary reason why all of you can sit comfortably inside this classroom right now."
Charlie stopped his steps, then cast a challenging look toward the rows of students.
"Let us start with a question that might sound foolish to your ears. Can anyone give me an opinion as to why other animals do not cook?"
"..."
The classroom atmosphere fell silent for a moment. Itsuki, Amane's best friend, raised his hand hesitantly. "Is it because they do not have minds and flexible hands like ours, Sensei?"
"Good question, Akasawa-kun. But unfortunately, the fact is not that simple." Charlie answered while shaking his head slowly. "Chimpanzees can use tools exceptionally well. They can crack hard nuts with stones."
"They can dip tree twigs into ant nests to get food instantly."
"They even possess a hand structure that is almost exactly identical to the hands you have right now."
"But not a single one of them has ever, in the entire history of human scientific observation, cooked its own food."
A female student in the back row chimed in, "Perhaps because animals are afraid of fire, Sensei?"
"That is a logical assumption, but also not quite correct." Charlie countered gently. "In fact, fire is not an unfamiliar thing to them."
"In 2015, a researcher named Jill Pruetz from Iowa State University documented something extraordinary in the field. She observed a group of chimpanzees in Senegal when a massive savanna fire occurred. And do you know what happened?"
"Those chimpanzees did not run in panic like wild animals in movies. Instead, they stood still, observing the direction of the wind and the movement of the fire."
"They predicted where the fire would move, then waited very calmly until the fire died out on its own. As soon as it went out, they immediately entered the freshly burned area and searched for charred fruits or tubers to eat."
The students began to show a great amount of interest; even Amane, who had been propping up his chin lazily, now began to straighten his posture, feeling that this material was far more alive than his usual biology lessons.
"They understand fire. They are not afraid of it." Charlie continued with a faint smile. "But they still do not cook. And this is what makes the question even stranger in the realm of biology. If even chimpanzees can understand the nature of fire, why hasn't a single one of them been able to make the evolutionary leap to start cooking?"
He returned to the podium, tapping the blackboard.
"The answer is far deeper than you think."
"Richard Wrangham, a renowned anthropologist from Harvard, proposed a hypothesis in 1999 that at the time was considered nearly insane by his fellow scientists. He called it the cooking hypothesis. His argument was simple, but its implications were extraordinary for our history."
"Wrangham argued: Humans did not start cooking because their brains were large. On the contrary, the human brain became large precisely because humans started cooking."
That sentence successfully caused several students, including Mahiru, to furrow their brows, trying to digest a concept that completely flipped common logic on its head.
"It wasn't stone tools that made us intelligent. It wasn't complex verbal language. Nor was it a high social life." Charlie emphasized. "Fire. Cooked food. That is the single solitary factor that changed everything in human biology."
"And this is how it works biologically." Charlie began to explain the anatomical mechanism. "Your body requires an extraordinarily large energy budget just to think. Your brain, whose mass is only about 2% of your total body weight, voraciously consumes around 20% of all the calories you eat every day. That is a highly absurd figure for an organ that small."
"And the main problem, for a very long time in the evolutionary history of living creatures, we could not afford a brain that large. Our ancestors, Australopithecus, lived around 3 to 4 million years ago. They ate everything entirely raw. Hard fruits, leaves, tubers, and occasionally raw meat left over from predatory animals' hunts."
"To digest all that raw food, they needed a very large and long gut organ. If you look at gorillas today, their protruding bellies are not because they are fat or have a lot of adipose tissue, but because their midsections are full of a giant digestive system that must work hard, processing raw food fibers all day long without stopping."
"The problem is, a large gut also requires a very massive supply of energy. And the law of biology dictates that energy which has already been used by the gut can never be used by the brain."
Charlie wrote a new term on the blackboard: Expensive Tissue Hypothesis.
"This is called the Expensive Tissue Hypothesis. A scientific idea that the body of a living creature only has a limited energy budget, and large organs within the body must compete intensely with one another to obtain that energy."
"So for millions of years, our ancestors were trapped in an evolutionary vicious cycle. Their brains remained small because all of the body's energy was completely drained in the gut. Meanwhile, their guts had to remain large because raw food is highly difficult to digest."
"Then..." Charlie smiled faintly, "Fire came. Cooking did something that the strongest teeth and any stomach in this world could never do."
"The heat from the fire breaks down the molecular structure of food even before that food enters your mouth. Hard and rigid starches become soft and easy to absorb by the stomach walls. Tightly bound and complex proteins become opened up, ready to be digested instantly. Tough plant cell walls are destroyed by heat before your gut has to struggle to break them down."
"The result? Your body obtains far more calories from the exact same portion of food, yet with much less digestive effort."
"Wrangham and his team performed laboratory calculations and discovered that cooked food provides about 30% to 40% more energy that can be absorbed by the body compared to identical raw food. Thirty to forty percent." Charlie repeated with emphasis. "That is not a small figure for a metabolism. That is a biological revolution!"
"Suddenly, our ancestors possessed a massive energy surplus that had never existed before in history. And the biological body knew exactly where to send that energy surplus. Around 1.8 million years ago, a massive leap occurred in the human lineage. The species Homo erectus emerged onto the surface of the earth. And it was completely different from all of its ancestors."
Charlie looked at the students, drawing their focus.
"Its characteristics? Its legs became longer. Its body was perfectly upright. Its gut shrank drastically. Its teeth grew smaller. Its jaw became weaker. And most astonishingly, its brain size surged to nearly twice the size of the Australopithecus brain."
"For decades, scientists were left utterly bewildered. What exactly triggered an anatomical change this large and this extreme in a span of time that on an evolutionary scale is considered highly brief?"
"Wrangham argued the answer lies absolutely within the fire. The oldest evidence regarding the controlled use of fire by human ancestors was found in Wonderwerk Cave in South Africa, dating back to around 1 million years ago. But, there are strong indications of a much earlier use that to this day continues to be debated by experts, perhaps nearing the 1.5 million-year mark."
"The timeline pattern fits too perfectly to be simply ignored." Charlie tapped his fingers on the desk. "Homo erectus appeared. Its body changed drastically. Its gut shrank, its brain enlarged. All of those anatomical changes are highly consistent with one thing: a diet of cooked food. Their guts shrank and grew smaller because they no longer needed to work as hard as before to ferment raw food. Their teeth and jaws shrank because food had already become soft before entering the mouth. And their brains enlarged because there was excess energy that could now be fully invested into the cranium."
"So in conclusion." Charlie glanced at Mahiru briefly before circulating his gaze across the whole class, "Cooking is not the result or product of human intelligence. Cooking is the primary cause of why humans were able to become intelligent."
The classroom atmosphere was completely hypnotized by the narrative delivered by Charlie. However, Charlie was not finished yet.
"But there is an important part of this grand story that is almost never talked about inside your school textbooks. And this is perhaps the most crucial part for our civilization. Cooking did not only alter our biological structure physically. It also completely changed the way we live together as social creatures."
"Think about this. If you had to eat the way a chimpanzee does, you would spend around 6 hours a day merely chewing food."
"Remember, not searching for or hunting food, but purely just sitting and chewing. Raw food is highly tough and takes a long time to be broken down by saliva. An adult chimpanzee chews for an average of 5 to 6 hours per day to meet their caloric needs. Meanwhile, modern humans like us? We only need about 1 hour in a day to chew all of our food."
"Five hours that were lost every single day for millions of years suddenly became free. Anthropologist Richard Wrangham refers to this as one of the greatest transformations in human history that is most frequently overlooked by many people."
"The 5 hours of time that used to be spent entirely just on chewing could now be used by our ancestors for other things that were far more useful. Talking to one another. Thinking. Crafting better hunting tools. Teaching their children how to survive. All the way to building closer social bonds."
"And there is one more thing that is often forgotten by us: fire requires constant guarding. You cannot simply light a giant campfire and then just walk away from it into the forest."
"Fire must be tended to carefully. It requires a constant supply of dry wood. It requires full attention because if you are careless for even a moment, it can die out or instead burn down the entire living space. And this condition created something that had never existed before in the entire animal kingdom: a powerful reason to stay together in one place."
"Groups of humans who shared the same fire were forced to begin coordinating and cooperating. There had to be members who went to search for firewood, while other members stayed behind to guard the fire so it wouldn't die. There had to be someone tasked with cooking the catch, while others went out to hunt."
"Fire indirectly created the first division of labor system in human history."
"Fire created a dependence on one another."
"Fire created a community."
Charlie paused his sentence, putting emphasis on this point.
"In 2012, a scientific study published in the prestigious journal Proceedings of the Royal Society analyzed the social life patterns of various primate groups in the world."
"The conclusion highly surprised the researchers. No strong correlation was found between brain volume size and the level of social complexity in non-human primates. But in the human species, both of those graphs exploded upward simultaneously."
"The researchers finally concluded that there is something highly unique in human ecology that drove our brain and social development concurrently. And the strongest candidate is none other than: the activity of cooking together around the fire."
"Because for the first time in the long history of evolution, there was a 'center of social gravity'. Not merely a herd of animals moving together for reasons of safety from predators, but rather a close-knit group gathering because there was something warm to be shared together."
"Warm food. The same fire. And a night that felt far safer from the darkness."
Charlie smiled faintly. "The first dining table in this world, children, was not made of neat wooden planks at all. It was made from mounds of earth, piles of stones, and a blazing fire."
"And this is the part that is most difficult for our logic to accept today. We frequently think that technology is something that changes humans only from the outside. We invent computers, we use them, and then our lifestyle changes. But the activity of cooking does not work in that external way. Cooking changes humans biologically from the inside."
"Literally, your gut organs today are far shorter than the guts of your ancestors millions of years ago. Your teeth are smaller. Your jaws are much weaker. Even the enzymes contained within your saliva at this moment have already been optimized by nature to digest cooked food, no longer raw food."
"In other words, your physical body right now was built by evolution with an assumption that you will cook your food."
"If any among you tries to recklessly live entirely off raw food alone—remember, not as a lifestyle choice or an occasional aesthetic diet, but as the sole life-sustaining food source for a lifetime—then your body will struggle intensely and suffer."
"Modern medical research shows that humans who undergo a purely raw food diet consistently will experience highly drastic and significant weight loss, as well as experience great difficulty maintaining normal biological reproductive functions."
"Why? Because you are not chimpanzees. Your body is no longer designed by nature for that. All of you, without exception, are products of millions of years of co-evolution with fire."
"So, returning to our initial question." Charlie stepped slowly into the center of the class, halting his explanation. "Why do no other animals cook?"
"The answer is not because they are not intelligent enough to understand the function of fire, because the chimpanzees earlier already proved that they can predict it. Nor is it because they do not possess hand organs that can hold or manipulate objects, because many other animals possess them."
"The answer is far simpler and at the same time more surprising than all of that: Not a single other animal on this planet needs the activity of cooking simply to survive."
"Their biological bodies to this day are still highly capable and efficient at processing raw food. Their gut organs are still large enough and strong enough to break it down. They have never made an 'evolutionary bet' that is as equally extreme as the bet which has been made by your ancestors millions of years ago."
"When the ancestors of early humans began deciding to rely entirely on cooked food, their bodies began to change completely to accommodate that new diet. And that anatomical change is a one-way street that absolutely cannot be reversed ever again."
"We deliberately surrendered our body's natural ability to digest raw food efficiently. Yet in return, we obtained a far larger brain size, a vast amount of more free time, and a much more complex social community structure."
"It was a massive gamble that proved successful. But regardless, it remains a biological gamble."
Charlie stood straight once again behind his podium, looking at the entire biology class students who were now staring at him with gazes full of admiration and a profound new understanding.
The classroom atmosphere that was previously boisterous with gossip had now completely shifted into an academic space full of deep respect.
"Tonight, when you return to your respective apartments or houses, and you stand in front of the kitchen to turn on the stove in order to heat something up... remember this: that activity is not merely a trivial daily habit. It is a legacy from millions of years of evolutionary decisions that have shaped every single strand of cell that exists inside your body right now."
"Every time you cook, you are actually performing a biological ritual that first began on the expanses of the African savanna millions of years ago."
"A unique act that will never be able to be performed by a single other animal upon this planet earth. Not because you are creatures stronger than a lion, not because you run faster than a cheetah. But because at some point in that highly long and silent history of evolution, someone among your ancestors decided not to eat something raw. And since that very second, this world would never, ever be the same again."
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