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and a group of about 300 leave Africa and colonize the rest of Earth

Out of Africa or Out of Eden?

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crosses the southern tip of Africa.

Perhaps a few hundred million years after the first mitochondrion appeared, as the oceanic oxygen content, at least on the surface, increased as a result of oxygenic photosynthesis, those complex cells learned to use oxygen instead of hydrogen. It is difficult to overstate the importance of learning to use oxygen in respiration, called . Before the appearance of aerobic respiration, life generated energy via and . Because oxygen , aerobic respiration generates, on average, about per cycle as fermentation and anaerobic respiration do (although some types of anaerobic respiration can get ). The suite of complex life on Earth today would not have been possible without the energy provided by oxygenic respiration. At minimum, nothing could have flown, and any animal life that might have evolved would have never left the oceans because the atmosphere would not have been breathable. With the advent of aerobic respiration, became possible, as it is several times as efficient as anaerobic respiration and fermentation (about 40% as compared to less than 10%). Today’s food chains of several levels would be constrained to about two in the absence of oxygen. Some scientists have and oxygen and respiration in eukaryote evolution. is controversial.

The 'Out of Africa' hypothesis has no comment on this. It simply follows the fossil trail.

In the mid-Miocene cooling’s early stages, beginning about 14 mya, apes were richly spread across Eurasia and were adapted to the hardier diets that less-tropical biomes could provide, and one from Spain 13 mya . It largely lived on the ground and had a relatively upright posture. Its discovery threw previously accepted ideas of ape evolution into disarray. The idea of apes ancestral to humanity living beyond Africa is a recent one, but is gaining acceptance. Important new fossils are found with regularity, as with all areas of paleontology, but the most plentiful funding is for investigating human ancestry. A , with features common to both orangutans and African apes, led to questioning whether some key ape features are ancestral or . One early finding is still highly controversial as to where it fits into the evolutionary tree, as it had ape and monkey features but lived 10 million years after the hypothesized ape/monkey split. The great ape lineages are the subject of considerable controversy today, and the human ancestral tree is regularly shaken up with new findings.

New Research Confirms 'Out Of Africa' Theory Of …

The skull of the smallest individual was the smallest, most primitive hominin skull found outside Africa.

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.

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.

Out of Africa or Out of Eden: Does Science Contradict …

Analysis in support of the Out of Africa model, by Dr. Donald Johanson.

But Thorne argues that such dramatic change is unlikely over such a short period and that fossils from the only environmentally comparable region - southern Africa - show that people have remained gracile over the past 100,000 years. Moreover, Thorne maintains, "there is nothing in the evidence from Australia which says Africa" - not even the Mungo fossil's modern features, which he believes look much more like those of contemporaneous Chinese fossils. And Thorne observes that living indigenous Australians share a special suite of skeletal and dental features with humans who inhabited Indonesia at least 100,000 years ago.

As evolutionary biologists have pointed out, any of the experiments designed to test Darwin and Wallace's theory of natural selection since it was first proposed could have proven the hypothesis wrong. None of those tests did. So evolution is "just a theory" the same way that the theory of plate tectonics and the germ theory of disease are just theories. And gravity.

Out-of-America vs. Out-of-Africa Families of Hypotheses
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    Out of Africa or Out of Eden

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The "Out of Africa" ("OA") Hypothesis ..

From the Permian extinction’s devastation arose a reptilian sheep called . Fossil hunters of early Triassic sediments have been frustrated for many years, as nearly are , because it was about the Permian extinction’s only land animal survivor. There has been about why it survived when almost nothing else did. No single animal ever dominated Earth’s land masses as thoroughly as did during the early Triassic. was probably a burrower (many have likened to a pig because of that burrowing), which may have provided the shelter needed to survive the Permian holocaust. It may also have been a and could eat most surviving plants. But some think that its survival, when almost every other species died, was due to luck. Luck is a surprisingly common proposed explanation for evolutionary events and outcomes, and some creatures seemed to be in the right place at the right time while others were in the wrong place at the wrong time. The spread of was also aided by two other facts: the land masses , so could simply walk to dominance of Earth; and few predators capable of eating a survived. One (being semi-aquatic may have also helped species survive the Permian extinction), as did , but not much else did. was a , as were the dominant land animals before the Permian extinction.

Out Of Africa Hypothesis Essay - …

The grew , and there were no more island barriers on the Tethys’s east end. The was finally squeezed out of existence by islands that became part of Eurasia. The shallow margins of the Tethys became the greatest oil source in Earth’s history. The and Paleo-Tethys oceans also formed oil deposits, but about initially formed during the Mesozoic’s anoxic events, primarily along the Tethys’s margins. In the Middle East, Caspian Sea, Western Russia, North Africa, Gulf of Mexico, and Venezuela virtually all of the oil deposits were laid down by dying and preserved organisms along Tethyan shores. In the early Triassic, along the west end of what became North America, oceanic plate subduction under continental plates that continue to this day. The foundations of the Sierra Nevada mountain range were formed then. I have spent .

Origins of Modern Humans: Multiregional or Out of Africa

Artists have been depicting Carboniferous swamps for more than a century, and the . That represents a key Carboniferous issue and perhaps why the period ended. That , and others like it, appeared in the fossil record about 300 mya, when oxygen levels were Earth’s highest ever, at somewhere between 25% and 35%. The almost universally accepted reason for that high oxygen level is that for the entire Carboniferous Period removed carbon dioxide from the atmosphere in vast amounts. Today, the estimate is that carbon dioxide fell from about 1,500 PPM at the beginning of the Carboniferous to 350 PPM by the end, which is lower than today’s value. That tandem effect of sequestering carbon and freeing oxygen not only may have led to huge arthropods and amphibians, but also intensified . The idea that high oxygen levels led to those giants was first proposed more than a century ago and dismissed, but has recently come back into favor. Flying insects have the highest metabolisms of all animals, but they do not have diaphragmatic lungs as mammals have, or air sac lungs as birds have, and although they may have some way of actively breathing by contracting their tracheas, it is not the bellows action of vertebrate lungs. The for early insect gigantism is that high oxygen, as well as a denser atmosphere (the nitrogen mass would not have fallen, so increased oxygen would have added to the atmosphere’s mass), would have enabled such leviathans to fly, and the other is that flying insects got a head start in the arms race and could grow large until predators that could catch them evolved. The late Permian had an even larger dragonfly, when oxygen levels had crashed back down. The evolution of flight is another area of great controversy, and insects accomplished it long before vertebrates did. The general idea is that flight structures evolved from those used for other purposes. For insects, wings appear to have evolved from aquatic “oars,” and gills became lungs. Reptiles did not develop flight until the Triassic, and .

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