Were the dramatic changes in a result of cooked food, or was Turkana Boy as his species became hunters instead of hunted, and the stone tools softened up the meat and plant foods so that he did not need to chew as much? Wrangham co-authored a that began with . It concluded that food processing, cooking in particular, accounted for the effect. Cooked food versus raw food and the number of neurons that can be supported in a brain has been . The primary reason why Wrangham’s hypothesis was initially dismissed was that archeological evidence for fires that long ago is almost nonexistent. When was published, the earliest evidence with wide acceptance only supported fires , where Israel is today, which is more than a million years after Wrangham’s estimated timeframe. Wrangham did what all bold scientists do: he made falsifiable predictions. If it turned out that no evidence of early fires was ever found, his hypothesis could begin looking shaky.
People and animals universally prefer the taste of cooked food over raw, except for fruit, which was designed by the plant to be eaten by animals; no other foods were designed to be eaten and digested (except nectar, blossoms, and mother’s milk). The toxins created by cooking, such as , can cause health problems in humans, including chronic diseases. But cooking also destroys some toxins, making otherwise inedible food palatable. Cooking also reduces , which makes meat tough, to gelatin (called the protein, when it falls apart), and converts raw starch to a far more digestible form. However, , humans only have to live long enough to produce offspring. The degenerative diseases (especially artery disease, cancer, and diabetes) that shorten human lives today would have been irrelevant in the ancient past, when virtually nobody lived long enough to die of old age and they could reproduce long before the deleterious effects of cooked food caught up with them. Many detriments of cooking and food processing have only become important to human welfare with the advent of civilization. Cooking would have been an undisputed advantage long ago.
If habilines began to control fire two mya, one thing is certain: the australopithecine Tesla who banged the first rocks together that fashioned a stone tool, and who was able to continue doing it and eventually taught others, probably via active demonstration and their observation, could not have imagined that his/her invention would lead to a relatively giant descendant (or cousin of a descendant) that slept on the ground, controlled fire, and would quickly migrate to the ends of Earth and traverse distances that were incomprehensible in australo-Tesla’s time. That relatively quick series of innovations, never before seen on Earth, gave birth to a creature that would have simply been unrecognizable to that ; it would have appeared magical. There have only been a few subsequent Epochal Events in the human journey, and like the first one(s), they were all energy events above all else, and were all dependent on humans gaining the technological prowess and social organization that enabled them to exploit a new energy source, which was dependent on their increasing mental feats. Each time, the human reality after the Epochal Event was to the humans who lived immediately before it (, , ). Also, the events and their aftermaths became far more dramatic each time, in shrinking the event’s timeframe and shortening the time until the next Epochal Event, and the energy levels greatly increased each time, and by an order of magnitude for the most recent event.
The energy from controlled fire allowed humans to , , and socially organize in new ways. Humans commandeered energy that otherwise and used it for immediate human benefit. It was also the first great human robbery. All heterotrophs “” energy from other life forms to live. The primary exception is the symbiosis that . But no animal had ever robbed energy from ecosystems on that scale before. By making fires, humans were liberating many times the energy that their biological processes used - energy that could have fed forest ecosystems. While humans were only using deadwood, it was the least destructive to forest ecosystems. But when humans began burning forests to flush out animals to kill and make biomes suitable for animals to hunt, they were destroying and altering ecosystems on a vast scale. A cord of wood provides about four years of the calories that fuel a human adult’s body, and one hectare can provide a sustainable annual harvest of about ten years of human calories. A family of four using a hectare for firewood on a sustainable basis would be using more than twice their caloric intake for burning wood. Very little of that released energy would benefit humans if they burned it over a campfire, as humans did for the entire epoch of the hunter-gatherer; that liberated energy largely went straight into the sky. The direct benefit to humans would be the energy that went into cooking food, what warmed human flesh, what was used to make tools, and the benefits of scaring off predators and providing light at night. More indirect benefits would have been ecosystem changes to provide human-digestible calories, such as American Indians burning the woodlands and plains to make environments conducive to animals that they could easily hunt. In , the earliest epochs are the most uncertain, but saying that hunter-gatherer humans used 2.5 times their dietary calories in their economy is probably, perhaps greatly, understating the case. That 5% efficiency number is also a rough estimate, and both numbers could be refined by a scientifically performed effort. Maybe somebody has already done it. The numbers in that table for subsequent epochs are more accurate, and the most accurate of all are those for , and I live in one. The increases in efficiency became more modest with each epoch as the limits of were approached.
Did the control of fire to , ? Or did merely use it to begin dominating the world? Was cooking the seminal event in the appearance of humans? Those questions may not be definitively answered in my lifetime, and led to the somewhat uncertain title of this chapter. Highly transformative developments coincided with the appearance and dispersal of , which was a radical break from all that came before – biologically, technically, and culturally – and strongly implies great cognitive enhancements. I believe that the control of fire and cooking would leave deep cultural and biological impacts on the human journey, and because barely changed during its nearly two-million year tenure on Earth, both in biology and in Acheulean artifacts, I favor Wrangham’s hypothesis, at least until the Next Big Finding. Just as Einstein said that and that his theories would one day become obsolete, but that their best parts would survive in the new theories, I suspect that significant aspects of Wrangham’s hypothesis will live on in successor hypotheses, and other scientists have been following Wrangham’s lead.
What is fire? That may seem too-elementary a question, but understanding what it is and where it came from is vitally important for understanding the human journey. The first fires were the quick release of stored sunlight energy that life forms, plants in that instance, had used to build themselves as they made their “decisions,” and it was from vegetation that recently died and was dry enough to burn. The energy was released from burning so fast that it became far hotter (because the molecules were violently "pushed" by the reaction that also released photons) than the biological process of making animals warm-blooded. Hot enough in fact that the released photons' (energetic enough) so that human eyes could see them, in a phenomenon called flames. Flames are visible side-effects of that intense energy release. The rapid movement of the molecules as they rocketed due to that great release of energy is the motion that powers the industrial age. Those rocketing molecules move pistons in automobile engines and , and are behind the damaging explosions of bombs and the propulsive explosions of rockets. For more than one million years, all human fires were made by burning vegetation, and wood in particular. What was fire doing? Energy stored by plants, trees in particular, was violently released by controlled fires for human-serving purposes of warmth, light, food preparation (to obtain more energy from food) and protection from predation, and it also became the heart of social gatherings. Humans have stared into fires for a million years or more.
In summary, becoming bipedal had great portent for evolving protohumans, and the suspicion is strong among scientists that it led to feedback loops in which tool use became advanced, which allowed for a richer diet, which helped lead to larger and more complex brains, which led to more advanced thinking and behaviors, which led to more advanced tools, which led to more acquired energy, better protection, and larger brains, and so it went. But the control of fire was a watershed event. Although better tools improved the viability of early humans, on Earth could challenge fire-wielding humans. With the control of fire, humans never had to worry again about being preyed on, nor as a threat to species viability, except by other humans. Naturally, fire was eventually used for offense instead of defense.
Apes make poor carnivores and are adapted for eating fruit as their staple, and fruit is the ideal human food. The dietary shift to meat, probably out of necessity, came with a price. If humans get more than half of their calories from protein, they will die from protein poisoning. Chimpanzees get about ten percent of their calories from protein today, which is about the same level that humans seem to need, but it is not necessary to get that protein from meat. I have not .
But even though they were “regular” on the geologic time scale, driven by , there would have been nothing “regular” about them to evolving humans. When ice sheets advanced, global climate became cooler and dryer; rainforests shrank and deserts expanded. Human adaptations to those changes, which could even be discerned in one human lifetime, must have had profound impacts on the human journey. In short, humans had to readily adapt to rapidly changing conditions, and rapid adaptation would have had selective effects on burgeoning human intelligence and problem-solving ability; those that adapted, survived. Also, scientists think that the rapidly oscillating climate resulted in migrations and pockets of isolated members of species that then underwent rapid evolutionary adaptation, the kind that leads to speciation. This may have been partly responsible for the relatively rapid evolution of the human line, particularly in the past million years.
Growing the human brain was about more than energy. There is speculation that meat protein helped human evolutionary brain development, and there is also evidence that oils help. There are surely nutritional requirements besides calories, but calories comprise the vast majority of nutrition. About 80% of what is called human nutrition consists of calories. If animals can obtain enough energy, the other dietary constraints are usually minor issues.
Although our species, (named if we consider that Neanderthals and an are subspecies of but I will use in this essay to denote today’s humans), is the only survivor of the past several million years of human-line evolution, many of our cousins and ancestors were recognizably human. When did language begin, especially spoken language? Language certainly predated the appearance of . All great apes readily learn sign language, and even when monkeys chatter, the , and there is plenty of evidence that great ape vocalizations can . The and their corvid cousins can be hard to believe; they can solve some problems better than great apes can, and birds do not have a neocortex, but seems to function like the neocortex does. Becoming that began to . If fossils are sufficiently preserved, important anatomical features can provide key evidence for human abilities and behaviors. Turkana Boy, for instance, had his inner ear, which is responsible for balance, preserved well enough so that it provided more evidence that he did not spend time in trees (it is larger in primates that regularly climb). Similarly, the , which succeeded , apparently enabled keener hearing than its predecessors were capable of, and may have reflected the beginnings of spoken language. There is strong evidence that . As with many other human traits, the potential for language seems to have existed with monkeys (), and it kept developing more sophistication over vast stretches of time, and structural and cognitive changes interacted as human language developed into today’s version.