Just as the reason why our may have and why may have , that founder group may well as an act of desperation, driven to the margins by their neighbors. If they left about 60-50 kya, as seems the most likely timeframe in light of today’s evidence, by 10 kya the entire planet had been conquered. Behaviorally modern humans were atop all terrestrial food chains outside of Africa, and in Africa megafauna avoided them, so there was nothing on Earth that threatened human existence except for other humans. Like the way in which the australopithecine Tesla who made the first stone tool the that emerged from his/her act a half-million years later, by 10 kya (about a tenth as long as the previous epochal innovative interval). Several million descendants of that founder group were spread across the planet, from tundra to desert to rainforest, and they filled all inhabitable continents. The people existing 10 kya would have been anatomically recognizable and all had , as they do today. However, with , versus what the founders left Africa with (several million people versus ), the immensely diverse climates and the tools used to survive in them, as well as their mutually unintelligible languages, the founder group’s members would not have comprehended a tour of their descendants’ world. The founder’s descendants even began to look different as evolution marched onward, and many racial differences would have been noticeable, although the bizarre had yet to appear in . Some people of 10 kya even had companions called (first domesticated as long as 33 kya, wolves were domesticated more than once, and the modern dog was domesticated about 15 kya), which would have seemed a miracle, terror, or strange beyond imagining. The world’s large animals paid the ultimate price for fueling that expansion, and the thus began.
People are usually surprised to hear that grass is a relatively recent plant innovation. and only became common in the late Cretaceous, along with flowering plants. With grass, some , and grazers have been plentiful Cenozoic herbivores. According to , carbon dioxide levels have been falling nearly continuously for the past 150-100 million years. Not only has that decline progressively cooled Earth to the point where we live in an ice age today, but is currently considered the key reason why complex life may become extinct on Earth in several hundred million years. In the Oligocene, between 32 mya and 25 mya some plants developed a during photosynthesis known as . It allowed plants to adapt to reduced atmospheric carbon dioxide levels. C4 plants became in the Miocene, and grasses are today’s most common C4 plants and . The rest of Earth’s photosynthesizers use or , which is a water-conserving process used in arid biomes.
92910 9 17 The Pleistocene Overkill Hypothesis …
Importantly, the expectation of a north to south spatiotemporal extinction trend across the Western Hemisphere should be largely unique to the overkill hypothesis. There is no single climatic (, ) or catastrophic () extinction hypothesis that shares this prediction. Therefore, this kind of analysis is not only capable of testing the overkill hypothesis, but of posing legitimate challenges to other extinction hypotheses, with the possible exception of multifactor models that also invoke “first contact” effects, such as the keystone herbivore (), habitat modification (), and hyperdisease hypotheses ().