Arctodus simus by Sergiodlarosa via Wikimedia Commons

North and South America were the last continents to be conquered by humans. We have been in Africa since we first evolved, Europe and Asia for over a million years, in Australia for about 60,000 years, but in the Americas for only about 15,000. Considering that reaching Australia required a treacherous ocean voyage but you could walk to Alaska without getting your feet wet via the flat, treeless, mammoth steppe of Beringia (with plenty of game to hunt en-route), why did it take people so long to reach the promised land? Some researchers have suggested that perhaps people did reach Beringia much earlier, but what they met there prevented them from penetrating any further. Along with the mammoths, cave lions, bison, and horses, Beringia had something else. Something that would have been completely unfamiliar to the humans who encountered…