When the first prehistoric people trekked into South America toward the end of the Ice Age, they found a wondrous, lush continent inhabited by all manner of strange creatures like giant ground sloths and car-sized armadillos. But these hunter-gatherers proceeded to behave like an "invasive species," with their population surging then crashing as they relentlessly depleted natural resources. Only much later did people muster exponential population growth after forming fixed settlements with domesticated crops and animals... The researchers identified two distinct colonization phases: the first unfolding about 14,000 to 5,500 years ago, with the human population hitting around 300,000; the...