Origin of Human Bipedal Ism the Kunckle Walking Hypothesis Revisted
Trees first appeared during a plant diversity crisis, and the arrival of seed plants and ferns ended the dominance of the first trees, so the plant crises may have been more about evolutionary experiments than environmental conditions, although a carbon dioxide crash and ice age conditions would have impacted photosynthesizers. The that gave rise to trees and seed plants largely went extinct at the Devonian’s end. But what might have been the most dramatic extinction, as far as humans are concerned, was the impact on land vertebrates. During the about 20% of all families, 50% of all genera, and 70% of all species disappeared forever.
human evolution-WHY BIPEDALISM? | Yahoo Answers
Until the 20th century, people had no idea how their activities impacted a portion of their environment that may end up hastening humanity’s demise more than self-made deserts: the atmosphere. Agriculture and civilization meant deforestation, and there is compelling evidence that the Domestication Revolution began altering the composition of Earth’s atmosphere from its earliest days. The natural trend of carbon dioxide decline was reversed beginning about 6000 BCE. Instead of declining from about 260 PPM at 6000 BCE to about 240 PPM today, which would have been the natural trend, it began rising and reached 275 PPM by about 3000 BCE. At the beginning of the Industrial Revolution, atmospheric carbon dioxide concentrations were about 40 PPM higher than the natural trend would suggest. When a forest is razed and the resultant wood is burned, which is usually wood’s ultimate fate in civilizations, it liberated carbon that the tree absorbed from the atmosphere during . , and human activities began measurably adding methane to the atmosphere by about 3000 BCE, which coincided with the rise of the rice paddy system in China. In nature, methane is primarily produced by decaying vegetation in wetlands, both in the tropics and the Arctic, and human activities have increased wetlands even as they made other regions arid. Domestic grazing animals and human digestive systems also contribute to methane production. Atmospheric alteration by human activities has only come to public awareness in my lifetime, but human activities have had a measurable effect on greenhouse gases since the beginnings of civilization, even though the effects were modest compared to what has happened during the Industrial Revolution, as humans burn Earth’s hydrocarbon deposits with abandon.
Fertile Crescent civilizations are universally regarded as humanity’s first. In China, people began to domesticate millet around eight kya, which was about 3,000 years after . Some scientists are skeptical that Chinese domestication really developed without any Fertile Crescent influence, even if it was just the of domestication. Similarly, in Mesoamerica, and people domesticated . The potato could have begun domestication in Peru . Those are the primary places where plants were domesticated independently in the Western Hemisphere, and the practice spread. . Whether the of domestication passed between regions where it is thought to have appeared independently, where the pig, for instance, may have been domesticated independently in the Fertile Crescent and China, nearly all domesticated plants and animals were probably domesticated , and the idea/technique/offspring spread. The horse, , is an instance when , with a limited number of stallions, and wild mares were subsequently incorporated into domestic herds. Once a herd animal was domesticated in the Fertile Crescent, the of domesticating herd animals certainly made subsequent domestication events less innovative. The Domestication Revolution, even if it happened in as many as nine places independently, as with the previous two Epochal Events (/controlling , and that ), the people who initiated the Third Epochal Event were relatively few. Probably only a few hundred people were beacons of innovation, or maybe even only a few dozen or less, when they are added together, and the domestication of animals in the Fertile Crescent may have had a lone inventor, or handful of them, who initiated the process, and the domestication of plants may have had similarly few inventors.
The Origin of Bipedalism - James Q. Jacobs
The idea that the American mastodon was killed off by hunting was first proposed by in 1799, and , an early evolutionist, thought that humans exterminated the extinct ice age mammals. By 1860, wondered whether anything humans could have caused that mass extinction. Therefore, when first proposed his Overkill Hypothesis in 1966, it was by no means novel, but he started the modern debate and the controversy quickly focused on North America, beginning about 15 kya.
Origin of human bipedalism: The knuckle-walking hypothesis
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.