While the existence of conclusive data on how and when Mesoamerica was first populated is still wanting in substance, it is generally accepted that the first people to arrive in the New World did so around 18,000 years ago. Occasionally data will surface that suggests that pre-modern humans may have come to the Americas prior to 16,000 BCE, but these conclusions are largely speculative, or based on data that cannot be corroborated. It is unknown if the migration played out as a single event, or if it happened in a succession of waves. Regardless, there are a few prominent theories on how genetically modern humans were able to make the last great migration from the Old World into the Americas. In any case, despite our murky understanding of how humans arrived in Mesoamerica, it is clear that once there, human civilization and culture was not only able to subsist, but thrive under a set of conditions that were unique to the region.
The most widely understood theory of human beginnings in the Americas involves a land bridge that would have “extended over what is now the Bering Strait and linked north-eastern Siberia to Alaska.” A migration of this sort would have necessarily occurred prior to 9,500 BCE during the last of Earth’s glacial maximums. During this glacial period the sea levels would have been relatively low, exposing the areas of Beringia that are currently underwater. This land bridge — as it is often referred — would have supported large herds of several species of megafauna, such as mammoth, bison, and horses. Paleolithic hunters and gatherers could have easily followed these herds out of the Eurasian tundra and into North America.
An alternative theory suggests that humans may have traveled to the Americas by sea. They would likely have followed along the coast of the Baring Straight, and could potentially have traveled along the west coast of the Americas all the way to the tip of South America. This theory allows for the possibility of a slightly more recent migration, but only just. All of the data suggests that by 9,500 BCE (the end of the Pleistocene era) genetically modern humans - Homo sapiens — had populated “every habitable continent of the world.” As such, even under this theory, humans were settled in Mesoamerica no later than about 12,000 years ago.
Following the migration of humans into Mesoamerica, the slow shift from Paleolithic hunter-gatherer to settled Neolithic agricultural society began. This shift started around 7000 BCE, and by 1500 BCE “agricultural village societies were established all over Mesoamerica.” This period of “incipient agriculture” — as Richard E. W. Adams refers to it — saw a period of prolific experimentation in the practice and application of cultivation. The melting of the glaciers (and possibly the effects of human hunting) resulted in the extinction of many of the species of megafauna that these people relied upon for food. In the absence of these animals (whom...