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.
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.
By understanding the various aspects of chemistry, you can understand many things about the world around you. You can also understand about how things work and what you can do to solve simple problems related to your home environment. For example, if you have a stain on your white shirt; you can use lime or baking soda to remove the stain. These are some of the chemical formulae or properties that you can apply in your daily life.
Here is how chemistry is used in everyday life:
The way a plastic wrap protects your food and how it is extracted from polymers is all part of chemistry. In fact, polymers is the next biggest industry to textiles in the United States.
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From about 32 kya to 22 kya, prevailed in Europe. That culture produced the and art such as the . By 20 kya, . But as far as human expansion is concerned, the Gravettian (and related cultures) are most notorious as mammoth hunters extraordinaire for those that lived on the near the ice sheets. To , they could not swim to Sahul, but flourished everywhere else they could get to. At , they were the ultimate hunter-gatherer kill. Also, near the ice sheets, meat could be stored in the ground. Cro-Magnons did just that, and that “freezer” full of meat led to the first seasonally sedentary humans. It long predated the Domestication Revolution when people could be sedentary year-round, but while the megafauna lasted, the first signs of what came later appeared as Cro-Magnons created villages around frozen mammoth meat. Gravettians hunted along migration routes and set traps and ambushes for mammoths. For thousands of years, mammoths were the primary focus of Gravettian hunters, and many scientists believe that humans at least . Gravettians probably used the bow and arrow, and using poisoned arrows on mammoths would have been child’s play, not a hazardous undertaking. They also tended to focus on the easy meat: the young, relatively defenseless, tender mammoths. Killing the offspring alone would have driven the slowly reproducing mammoths to extinction, and as the interglacial period began around 15 kya, there would have been new pressures on mammoths. One of them was that fewer mammoths meant that they were not terraforming their environments like they used to, and the warming climate probably reduced their range. For a mammoth facing humans, there was literally no place to hide (except maybe in the living room), and there is little reason to think that hunters would have eased up when mammoth numbers dwindled. If anything, their efforts would have to get the last ones, as they competed and fought over the final mammoths. In one lifetime or even several, the changes would have been barely noticeable, if at all. There was simply no way out for mammoths, and they went extinct south of the European ice sheets under the ministrations of Cro-Magnon hunters. More evidence of their fate is some mammoths surviving in refugia: islands where humans did not arrive until thousands of years later. mammoths survived on in the chain off of Alaska until less than six kya, and went extinct when humans arrived. Several hundred apparently full-sized mammoths survived on near Siberia and went extinct less than five kya, when humans arrived. In today's France and Spain, Gravettians also semi-settled along the migration routes of reindeer and red deer. From Spain across Europe, into today's Russia, Gravettians hunted migrating herds, and not only the mammoth was driven to extinction, but also the wooly rhino, the Irish elk, the musk ox, and steppe bison were driven to extinction as the ice sheets retreated. Neanderthals had been ambush hunting in similar fashion, and those animals, like the African megafauna, grew wary of humans, and killing those animals probably took planning and guile.
The closer the timeline of life on Earth gets to the appearance of humanity, the less our ancestry is doubted among scientists, and there is virtual certainty that is humanity’s direct ancestor. Their brains were nearly the size of modern humans and they inherited from their ancestors and used them for hundreds of thousands of years. There is plenty of evidence that migrated to Western Eurasia about 800 kya. But there is evidence that somewhere around 500 kya that began to change; there is evidence of in today’s South Africa. in today’s Germany, along with butchered horses, dated to about 400 kya. Scientists today are confident that was also the direct ancestor of , and the split began around 500 kya. The range of was Africa, West Asia, and Europe, but the advancing and retreating ice sheets of Eurasia, Europe in particular, kept driving southward, and during one of the retreats, it seems that the ancestors of Neanderthals stayed. Neanderthals became a cold-adapted species that specialized in hunting big game. As the evidence demonstrates today, life was a brutal proposition in humanity’s early days, and was particularly harsh for Neanderthals. They probably could not throw very well and relied on ambush predation. Scientists have studied Neanderthal bones and , but a , partly in light of recent evidence that Neanderthals may have also developed wooden throwing spears. But whether Neanderthals had to stab their prey in close quarters or eventually learned to throw weapons at them, the studies of early human bones describe a grim existence. Breaking bones were regular events, particularly skull fractures, and that was for trauma survivors.
Anthropologists and primate researchers , but relatively recent scientific findings have disproven that notion. , and it is more sophisticated with great apes. It took a few million years after the human/chimp split for our ancestors to learn to , and that culture then spread widely in Africa. The , , and were probably all closely related and at least partly interdependent, but little seemed to change . Then the and possessed a larger brain, and new tools and behaviors are evident . The timeframes continually shrank between major events in the human journey. Only 200 thousand years later, and , and new behaviors are in evidence. Only 100 thousand years after that, anatomically modern humans appeared. Only 30 thousand years after that, about 170 kya, , probably due to necessity, where life once again was eked out on the margins, and those humans may have decorated their bodies. About 100 kya, innovation seems to have accelerated again, and by 75-60 kya there is evidence of . Needles and perhaps even arrowheads first appeared about 60 kya. There is no doubt among scientists that members of made those advances, and their artifacts provided evidence of increasing cultural and technical sophistication, which soon left Neanderthals and all other land animals far behind. About 75-70 kya, a , and there is controversy today whether that eruption was partly responsible for the that passed through not long afterward. What became today’s humanity seems to have nearly gone extinct at that bottleneck.
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.
I am taking some liberties in calling Turkana Boy a ; he is technically a member of , which is often considered ancestral to , which is the Asian variant’s name. There is great debate regarding how the human family tree branches between and . Some call the various -type species all subspecies of , while others argue for several distinct species. I will not stray far from the orthodox narrative here, for good reason. The reconstructed early human tale is based on very limited evidence, but that evidence will only grow over time, and the tools and techniques for using them will become more sophisticated. Although there may be some upcoming radical changes in the view of the early human journey, efforts of countless scientist and fossil hunter lifetimes support the narrative that this essay sketches, and I respect their findings and opinions, even though I acknowledge many limitations. The human ego, it seems, becomes more involved as the story of life on Earth moves closer to its human chapters.