For more than half a century, the prevailing story of how the first humans came to the Americas went like this: Some 13,000 years ago, small bands of Stone Age hunters walked across a land bridge between eastern Siberia and western Alaska, eventually making their way down an ice-free inland corridor into the heart of North America. Chasing steppe bison, woolly mammoths and other large mammals, these ancestors of today’s Native Americans established a thriving culture that eventually spread across two continents to the tip of South America.
In recent years, however, that version of events has taken a beating, not least because of the discovery of archaeological sites in North and South America showing that humans had been on the continent 1,000 or even 2,000 years before the supposed first migration. A subsequent theory, known as the “Kelp Highway,” came closer to the mark: As the massive ice sheets covering western North America retreated, the first humans arrived on the continent not only by foot but by boat, traveling down the Pacific shore and subsisting on abundant coastal resources. Supporting that idea are archaeological sites along the West Coast of North America that date back 14,000 to 15,000 years.
Civilizations are intimately associated with and often further defined by other socio-politico-economic characteristics, including centralization, the domestication of both humans and other organisms, specialization of labour, culturally ingrained ideologies of progress and supremacism, monumental architecture, taxation, societal dependence upon farming and expansionism.
Historically, civilization has often been understood as a larger and "more advanced" culture, in contrast to smaller, supposedly primitive cultures. In this broad sense, a civilization contrasts with non-centralized tribal societies, including the cultures of nomadic pastoralists, Neolithic societies or hunter-gatherers, however sometimes it also contrasts with the cultures found within civilizations themselves. Civilizations are organized in densely populated settlements divided into hierarchical social classes with a ruling elite and subordinate urban and rural populations, which engage in intensive agriculture, mining, small-scale manufacture and trade. Civilization concentrates power, extending human control over the rest of nature, including over other human beings.
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