So far in this essay, mammals have received scant attention, but the mammals’ development before the Cenozoic is important for understanding their rise to dominance. The , called , first , about 260 mya, and they had key mammalian characteristics. Their jaws and teeth were markedly different from those of other reptiles; their teeth were specialized for more thorough chewing, which extracts more energy from food, and that was likely a key aspect of success more than 100 million years later. Cynodonts also developed a secondary palate so that they could chew and breathe at the same time, which was more energy efficient. Cynodonts eventually ceased the reptilian practice of continually growing and shedding teeth, and their specialized and precisely fitted teeth rarely changed. Mammals replace their teeth a . Along with tooth changes, jawbones changed roles. Fewer and stronger bones anchored the jaw, which allowed for stronger jaw musculature and led to the mammalian (clench your teeth and you can feel your masseter muscle). Bones previously anchoring the jaw were no longer needed and . The jaw’s rearrangement led to the most auspicious proto-mammalian development: . Mammals had relatively large brains from the very beginning and it was probably initially . Mammals are the only animals with a , which eventually led to human intelligence. As dinosaurian dominance drove mammals to the margins, where they lived underground and emerged to feed at night, mammals needed improved senses to survive, and auditory and olfactory senses heightened, as did the mammalian sense of touch. Increased processing of stimuli required a larger brain, and . In humans, only livers use more energy than brains. Cynodonts also had , which suggest that they were warm-blooded. Soon after the Permian extinction, a cynodont appeared that may have ; it was another respiratory innovation that served it well in those low-oxygen times, functioning like pump gills in aquatic environments.
Wrangham’s hypothesis is more robust and subtle than this essay can do justice to, but I will survey some of the findings, implications, and controversy. Raw food has various nutritional properties that are superior to cooked food, such as vitamins, but because cooked food provides more digestible calories for humans than raw food, it represented an evolutionary advantage. Meat, starches, and seeds are far more digestible when cooked, and are much easier to chew. Today, chimps in will not eat raw seeds of trees, but when a fire passes through the savanna, they search the ground below the trees and eat their cooked seeds.
But the branch of the that readers might find most interesting led to humans. Humans are in the phylum, and the last common ancestor that founded the Chordata phylum is still a mystery and understandably a source of controversy. Was our ancestor a ? A ? Peter Ward made the case, as have others for a long time, that it was the sea squirt, also called a tunicate, which in its larval stage resembles a fish. The nerve cord in most bilaterally symmetric animals runs below the belly, not above it, and a sea squirt that never grew up may have been our direct ancestor. Adult tunicates are also highly adapted to extracting oxygen from water, even too much so, with only about 10% of today’s available oxygen extracted in tunicate respiration. It may mean that tunicates adapted to low oxygen conditions early on. Ward’s respiration hypothesis, which makes the case that adapting to low oxygen conditions was an evolutionary spur for animals, will repeatedly reappear in this essay, as will . Ward’s hypothesis may be proven wrong or will not have the key influence that he attributes to it, but it also has plenty going for it. The idea that fluctuating oxygen levels impacted animal evolution has been gaining support in recent years, particularly in light of recent reconstructions of oxygen levels in the eon of complex life, called and , which have yielded broadly similar results, but their variances mean that much more work needs to be performed before on the can be done, if it ever can be. Ward’s basic hypotheses is that when oxygen levels are high, ecosystems are diverse and life is an easy proposition; when oxygen levels are low, animals adapted to high oxygen levels go extinct and the survivors are adapted to low oxygen with body plan changes, and their adaptations helped them dominate after the extinctions. The has a pretty wide range of potential error, particularly in the early years, and it also tracked atmospheric carbon dioxide levels. The challenges to the validity of a model based on data with such a wide range of error are understandable. But some broad trends are unmistakable, as it is with other models, some of which are generally declining carbon dioxide levels, some huge oxygen spikes, and the generally relationship between oxygen and carbon dioxide levels, which a geochemist would expect. The high carbon dioxide level during the Cambrian, of at least 4,000 PPM (the "RCO2" in the below graphic is a ratio of the calculated CO2 levels to today's levels), is what scientists think made the times so hot. (Permission: Peter Ward, June 2014)
The was merely the latest in a over several millennia, which likely influenced Amazonian cultures. While the markets in Aztec-run Tenochtitlán were incomparable and conquering Spaniards had an appreciation for the materialistic and greedy aspects of Aztec culture, Incan culture was another matter entirely. There were no vast markets in Incan society, but it was run more like a communist regime, with central planning of the economy. The Incas had ornate rituals combined with feasts and festivals, in which religion, warfare, economic reciprocity, and an elite-justifying ideology were inextricably linked, which formed the social cohesion of the empire. They naturally had human sacrifice to appease the gods in their Sun-worshipping imperial religion. The Incan Empire, which was the Western Hemisphere's largest, by far, stretched along the Andes Mountains for thousands of kilometers and was continually subjected to El Niño's vagaries. The Incas had novel means of dealing with it, including forming a vast network of storage facilities along the Incan "highway" on the Andes's high Western slopes, which like those took advantage of the "freezer effect" (and drying) of preserving food, and the Incas advertised their ability to provide for their subjects. The empire's taxation was often more in the form of services than food. Those peoples were arguably the greatest agricultural experimenters of pre-industrial peoples, getting the most out of their challenging environments.
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The human ability to think abstractly was exploited by social managers from civilization’s earliest days. Fixating people on irrational symbols, and then manipulating those symbols for elite benefit, is arguably a universal trait of civilized peoples. Even today, a great deal of politics is the ; as with the earliest religion, the neocortex is bypassed in favor of , and people are easy prey to the cynical manipulation of emotionally charged symbols. The effects of can last for the victim’s lifetime. When people mistake symbols for reality, they are easily manipulated. Large-scale ideological indoctrination probably began in Sumer, as the priesthood concocted and promoted various beliefs. Symbology replaced reality, including the acceptance of the secular elite as deific, getting slaves to accept their status, and getting commoners to give food to the priesthood to fulfill some divinely ordained obligation. Religion passed from experience to belief with the rise of civilization. I am not suggesting that pre-civilized religions were necessarily enlightened. They had shamanic intermediaries too, but with the rise of civilization, the priest class had to work hard to justify the obviously unfair social organization that accompanied stratified populations. Direct religious experience was disparaged and suppressed while the priesthood’s religious indoctrination was promoted.
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The genetic testing that has been performed on humanity in the past generation has shown that the founder group’s pattern of migration was to continually spread out, and once the original settlement covered the continents, people did not move much at all, at least until Europe began conquering the world (and there were some ). There is little sign of warfare in those early days of migration, and the leading hypothesis is that people moved to the next valley rather than be close enough to fight each other. Any conflict would have been easily resolved by moving farther out, where more easily killed animals lived. Also, in those virgin continents, people need not have roamed far to obtain food. Today, an !Kung woman will carry her child more than 7,000 kilometers before the child can walk for himself/herself. If an !Kung woman bears twins, it is her duty to pick which child to murder, because she cannot afford to carry two. That demonstrates the limitations of today’s hunter-gatherer lifestyle, but in those halcyonic days of invading virgin continents (which had to be the Golden Age of the Hunter-Gatherer), those kinds of practices probably waned and bands grew fast. When they they split, and the new group moved to new lands where the animals, again, never saw people before. Unlike the case with humans, there would not have been a grapevine so that animals told their neighbors about the new super-predator. The first time that those megafauna saw humans was probably their last time. It is very likely, just as with all predators for all time, and as can be seen with historical hunting events such or , that those bands soon took to killing animals, harvesting the best parts, and moving on. To them it would not have been a “blitzkrieg,” but more like kids in candy stores. After a few thousand years of grabbing meat whenever the fancy took them, or perhaps less, those halcyonic days were over as the far coasts of Australia were reached and the easy meat was gone. When that land bridge formed to Tasmania about 43 kya, people crossed and were able to , until all the megafauna was gone on Tasmania. They also may have worked their way through the food chain, in which the first kills were the true mother lode. Nobody even deigned to raise a spear at anything less than a until they were gone. Then they started killing smaller prey, which eventually did wise up and were harder to kill, so humans had to work at it again and the brief golden age was over. The as they shaped the new continent to their liking, maybe recreating the savanna conditions that they left in Africa, may have also been used to flush out animals if they began to avoid humans.
Effects of Fast Food Consumption essay
When humans began to raze forests and use the resultant soils to raise crops, they were working their way down through the food chain, no longer harvesting ecosystem detritus but destroying entire ecosystems literally at their roots for short-term human benefit. That practice eventually turned forest ecosystems into deserts. As this essay will survey, that was a rampant problem in all early civilizations. Eventually, humans learned to reach even further back into the ecological horizon as they began burning energy stores that were hundreds of millions of years old; was first and second. They were burned a million times as fast as they were created. In all instances, humans were releasing sunlight energy that had been captured and stored by organisms. In the 20th century, when humans began using nuclear fission, they were going even further back in time and harvesting energy stored via billions of years ago. With each new energy source, humans were harvesting older, more concentrated energy sources, which released far more energy than the previously used source. In each instance, humans plundered the energy source to exhaustion. Humans have not lived in “harmony” with nature since they learned to control fire.