Ever wonder why Eurasia developed agriculture and thus early civilization before the New World? Well, according to author Jared Diamond, a big part of the answer may be simple geography. If you look at a map of the two hemisphere one gross difference immediately stands out: the Americas are long and skinny and Eurasia is fat and wide. The Americas stretch across latitude, almost form pole to pole connected by a tiny, narrow isthmus in Panama, and Eurasia flops sideways crossing many lines of longitude. So what you ask, what's the big deal?
Well, let's say you are a member of a neolithic community in Eurasia, and over time your ancestors have, more or less unconsciously, selected for a traits in a particular set of plants of animals that are useful to hungry hominids. Those organisms can move east or west with relative ease because, as long as the altitude and rainfall remains within survivable limits, the climate is similar enough that the proto-domesticated new strains of grain or herd animals can thrive, carried by traveling bands or simply springing from farming and ranching city-states maintained by the people that depend on them for food. But if you're in a late stone-age tribe in North America about 12,000 years ago, and live on the ancestor of what would one day be called corn, or hunt buffalo, those organisms are limited by much more dramatic changes in seasonal variation as they try to expand south, and are funneled through that tiny isthmus to boot. Shaggy buffalo, hairy mammoth, and grain adapted to the Great Plains aren't likely to trudge down through Texas and cross Central American rain-forests no matter how much the lush, distant plains of South America beckon. And incidentally, the same applies to innovations such as metal working or writing.
Now, run that forward, for a couple of hundred human generations. In Eurasia the best strains and breeds are being passed back and forth over thousands of miles, each community contributing its best versions and management techniques, plus there's larger populations distributed in a greater range of climates, more diversity for artificial selection to work on. It wouldn't be surprising if, at the biological nexus of the Eurasian exchange, say for example the Middle East in a fertile region between two river that flood every year depositing rich, fresh sediment, the domesticated plants and animals would become so well adapted for human consumption that those folks could settle down and actually cultivate them. As opposed to chasing down their wild cousins. Viola, civilization is born.
Native Americans may have been limited by geography, but they didn't sit on their laurels. North and South Americans got a later start, and they didn't have the benefit of migrating hunter-gatherers spreading useful, edible plants around Eurasia for fifty-thousand years before hand. But they were every bit as ingenious as Eurasians. They also developed robust, high yield domesticated subspecies. It's also not surprising that the most advanced pre-Colombian city-states that did manage to crank up did so at the geographic nexus of their respective biological sanctuaries: Central America. Given a few millennia, it's entirely likely that their civilizations, based on their versions of domesticated plants and animals, would have spread north and south, just as it had spread east and west thousands of years earlier on the other side of the world.
No one reading this should think that these early civilizations were better than neighboring hunter-gatherer societies. In fact I'd argue the opposite; even without concentrated wealth and organized warfare, they were freaking miserable for the vast majority of have-nots compared to their free ranging relatives. Analysis of remains shows that, on average, people in early agricultural societies were significantly less healthy over all. The advantage wasn't in standard of living, size, infant mortality, or life expectancy, at least not at first, it was in population density. There were ten times, a hundred times, in some cases a thousand times, as many per unit area. Ten strapping big hunter-gatherers with stone tools wouldn't have had a prayer against a thousand sword-wielding runts.
One big reason they weren't as healthy: the diseases carried by the new animals, and pests like rats and insects, that come along with agriculture and ranching. In the long run, during the same time they're seeding the Old World with all these artificially selected subspecies, Eurasians developed resistance to a multitude of diseases that crossed over to humans. The surviving Eurasians become a sort of super resistant kind of human, no doubt at great cost and misery to millions of unknown and unlucky non-survivors (Perhaps with a suite of auto-immune conditions and genetic adaptations that let them run the disease gauntlet even in the midst of plagues, at least long enough for a few to reproduce, although that's an essay for another day). And so it remained for thousands of years ...
Then all of the sudden, in the blink of an eye on evolutionary time-scales, one group of Eurasians develop technology that allowed them to travel to the New World, and they brought along their nifty domesticated plants and animals, and the diseases they carry. Native American communities had little resistance to the Old World microbes, they don't know how to manage the domesticated plants and animals, and they have little experience with civilization. They were devastated, in every way, biologically, as well as agriculturally and technologically. That's also an essay for another day, a dark, sobering one.
But the Native Americans weren't without any useful proto-domesticated plants. Tobacco and chocolate are two that come to mind. The latter helped build the western version of the New World way more than the gold and spices promised to Old World monarchs who initially footed the bill. And of course, this week, we enjoy another of those legacies, the humble and so-called wild turkey, which was well on its way to being domesticated by meso-Americans and had spread all the way to the eastern seaboard long before Plymouth Rock. A roasted variant of that bird, Meleagris gallopavo, will grace millions of tables this week. And its sliced, atrophied flight muscles will soon play the leading role in yummy turkey and mayonnaise sandwiches sitting next to my PC!