The first complex society in Mesoamerica was the Olmec civilization, which emerged around 2000 BCE during the Early Preclassic. It is documented that around this time many Mesoamerican languages adopted loanwords from the Mixe–Zoquean languages, particularly loanwords related to such culturally fundamental concepts as agriculture and religion. This has led some linguists to believe that the carriers of Olmec culture spoke a Mixe–Zoquean language and that words spread from their language into others because of their potential cultural dominance in the Preclassic period, though the relationship between the Olmec and other Preclassic groups is still debated (see Olmec influences on Mesoamerican cultures). During this time the Oto-Manguean languages diversified and spread into Oaxaca and central Mexico. In the Valley of Oaxaca, the Oto-Manguean Zapotec culture emerges around c. 1000 BCE. The splitting of Proto-Mayan into the modern Mayan languages slowly began at roughly 2000 BCE when the speakers of Huastec moved north into the Mexican Gulf Coast region. Uto-Aztecan languages were still outside of Mesoamerica during the Preclassic, their speakers living as semi-nomadic hunter-gatherers on the northern rim of the region and co-existing with speakers of Coracholan and Oto-Pamean languages.