Contrary to what our calendars seem to tell us, Columbus did not discover America. There's a lot of dispute over who did actually find the continent, with theories ranging from the Vikings to the Chinese, but the most common belief is that tribes migrated into Northern Canada from Russia.
Back then, North America and Asia were connected by a thin strip of land at the Bering Strait in Alaska. The details on the migration have always been slim, since it took place so long ago (waaaay before things like recorded history). For instance, one thing scientists have always debated over is the actual logistics of the migration -- we're talking about a long, frigid trek made entirely on foot. And there's also the question of why.
We can only theorize.
The answer may be, you guessed it, poop.
First, you have to picture what this migration would have looked like. Northern Canada, after all, isn't really known for its lush forests and fertile lands, but rather its magnificent amount of snow and devastating, remorseless cold. Consequently, there really isn't much wood or coal in ready abundance that could have been burned for everyday tasks like cooking food and not freezing to goddamn death. However, something they do have in abundance is yaks, and their accompanying igloo-sized mounds of colonic eruption.
Don't let the colors fool you. He will poop the skin off of your face.
Scientists now believe that the migrating tribes' source of fuel for their fires -- and the very fuel that allowed them to migrate to America -- was yak poop. The idea is that, just as certain tribes of American Indians would follow the buffalo across the country because they depended so heavily on the animals, so would these earlier tribes follow the yak. They'd use the yaks for food and clothing, and burn their shit to prepare their meals and stay warm as they moved across continents.
Which is to say, the humans didn't even want to migrate -- they just went where the poop took them. There were almost no other sources of fuel for the tribes to use, essentially forcing them to survive entirely on flaming yak turds. So, they followed the yak, as it was essentially their one-stop shop for every aspect of daily life. And, as the yak wandered into North America, so did the humans, following a brown trail right into world history.
"Do you mind? I can't go when you're staring at me like that."