South America was the last habitable continent to be colonized by humans . Researchers have just identify two trenchant phase angle in the demographic account of South Americans : rapid cattle farm with low universe sizes , followed by sedentary lifestyle with exponential growth . The study , published inNaturethis week , compared the universe increment of prehistoric South Americans to that of encroaching species .
The first Americans were descendants of Siberians that crossed the ancient land bridge circuit that connected Asia with Alaska some 15,000 to 30,000 year ago . They arrive at southerly South America pretty speedily , by at least 14,500 days ago . Unlike most other continents , South America was peopled during a unmarried undulation of encroachment over a minute prison term physical body . However , the human universe kinetics during colonization , subsequent expansions , and domestication remain unclear .
To restore spaciotemporal normal of human population growing in South America , a Stanford squad led by Amy Goldberg compiled a database of 5,464 radiocarbon appointment from 1,147 archaeological sites . These various areas of human occupation pair 14,000 to 2,000 years ago . Rather than a steady elaboration , the team rule that the demographic history of South Americans is characterise by two distinguishable phases .
The first phase occurred between 14,000 and 5,500 year ago . Initial growth was rapid , with the universe doubling every 19 to 21 genesis . ( Generation time was about 26.5 years . ) And the former and in high spirits population growth patterns occurred along the Pacific coastline in Peru , Chile , and Ecuador . Though they spread rapidly throughout the continent , they stayed at humble population sizes . universe sizes stayed relatively changeless from 9,000 to 5,500 years ago . Even with boom - and - bust rhythm , the population saw no net growth .
The combination of the rapid spread with low universe sizes is similar to the population size dynamics of a typical invasive species : rapid initial expansion and resource - limited growth over fourth dimension . Supplementing hunting with domesticated animals and crops ( like squash , peppers , and corn ) had small impact on the carrying capacity of the universe .
The second demographic phase began around 5,500 years ago , with the shift to a sedentary and agricultural subsistence . Stable nutrient sources and the need for human labor in one spot meant that parents were more uncommitted , the interval between birth became shorter , and populations became big .
During this time , the population increase threefold , and by 2,000 years ago , there were as many as a million people in South America .
