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Noam Chomsky: A Critical Review - Russil Wvong
and noted that Eurasia was spread along an east-west axis, while Africa and the Americas were north-south, which made Old World diffusion easier, but that idea also has problems, as Fertile Crescent crops did not spread to East Asia due to rainfall timing differences (winter rains in the west and summer monsoons in the east). Mesoamerican and Andean civilizations had dramatic geographic limitations, which was their greatest contrast with Eurasian civilizations. However, like the migration of or the exchange when , it was easier for cultural innovations to spread along the same latitude, as they would move through similar biomes. North-south diffusion is far more difficult, as it moves through different biomes, such as tropical forests and . Eurasia's geography was more conducive to communicating innovations, which made it more cosmopolitan than sub-Saharan Africa or the Americas, which helped them technologically advance at a faster pace. Isolated peoples are usually culturally and technologically backward compared to nearby peoples who are more cosmopolitan, and people isolated by mountainous geography, such as those of the Scottish Highlands, Balkans, Appalachia, and Southeast Asia were relatively primitive compared to those around them. and are classic instances of isolated peoples keeping their cultures intact, which provided a window into the human past, but their cultures also did not "progress," which included their technology.
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The (c. 5.3 to 2.6 mya) began warmer than , but was the prelude to today’s ice age, as temperatures steadily declined. An epoch of less than three million years reflects human interest in the recent past. Geologically and climatically, there was little noteworthy about the Pliocene (although the was created then), although two related events made for one of the most interesting evolutionary events yet studied. South America kept moving northward, and the currents that once in the Tethyan heyday were finally closed. The gap between North America and South America began to close about 3.5 mya, and by 2.7 mya the current land bridge had developed. Around three mya, the began, when fauna from each continent could raft or swim to the other side. South America had been isolated for 60 million years and only received the stray migrant, such as rodents and New World monkeys. North America, however, received repeated invasions from Asia and had exchanges with Europe and Greenland. North America also had much more diverse biomes than South America's, even though it had nothing like the Amazon rainforest. The ending of South America’s isolation provided the closest thing to a controlled experiment that paleobiologists would ever have. South America's fauna was devastated, far worse than European and African fauna were when Asia finally connected with them. More than 80% of all South American mammalian families and genera existing before the Oligocene were extinct by the Pleistocene. Proboscideans continued their spectacular success after leaving Africa, and species inhabited the warm, moist Amazonian biome, as well as the Andean mountainous terrain and pampas. The also invaded and thrived as a mixed feeder, grazing or browsing as conditions permitted. In came cats, dogs, camels (which became the ), horses, pigs, rabbits, raccoons, squirrels, deer, bears, tapirs, and others. They displaced virtually all species inhabiting the same niches on the South American side. All large South American predators were driven to extinction, as well as almost all browsers and grazers of the grasslands. The South American animals that migrated northward and survived in North America were almost always those that inhabited niches that no North American animal did, such as monkeys, (which survived because of their claws), and their small cousins (which survived because of their armor), , and (which survived because of their quills). The opossum was nearly eradicated by North American competition but survived and is the only marsupial that made it to North America and exists today. One large-hoofed herbivore survived: the . The (it weighed one metric ton!) survived for a million years after the interchange. , that , also survived and migrated to North America and lasted about a million years before dying out. In general, North American mammals were , which resulted from evolutionary pressures that South America had less of, in its isolation. They were able to outrun and outthink their South American competitors. South American animals made it past South America, but none of them drove any northern indigenous species of note to extinction.