<P> The Americas are thought to have been first inhabited by people from eastern Asia who crossed the Bering Land Bridge to present - day Alaska; the land separated and the continents are divided by the Bering Strait . Over the course of millennia, three waves of migrants spread to all parts of the Americas . Genetic and linguistic evidence has shown that the last wave of migrant peoples settled across the northern tier, and did not reach South America . </P> <P> The first evidence for the existence of agricultural practices in South America dates back to circa 6500 BCE, when potatoes, chilies and beans began to be cultivated for food in the Amazon Basin . Pottery evidence suggests that manioc, which remains a staple foodstuff today, was being cultivated as early as 2000 BCE . </P> <P> South American cultures began domesticating llamas and alpacas in the highlands of the Andes circa 3500 BCE . These animals were used for both transportation and meat; their fur was shorn or collected to use to make clothing . Guinea pigs were also domesticated as a food source at this time . </P> <P> By 2000 BCE, many agrarian village communities had developed throughout the Andes and the surrounding regions . Fishing became a widespread practice along the coast, with fish being the primary source of food for those communities . Irrigation systems were also developed at this time, which aided in the rise of agrarian societies . The food crops were quinoa, corn, lima beans, common beans, peanuts, manioc, sweet potatoes, potatoes, oca and squashes . Cotton was also grown and was particularly important as the only major fiber crop . </P>

When did north and south america become isolated from the world's other continents