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By 4000 years ago, people had introduced maize to the southwestern United States; full agriculture was established quickly in the lowland deserts but delayed in the temperate highlands for 2000 years. We test if the earliest upland maize was adapted for early flowering, a characteristic of modern temperate maize. We sequenced fifteen 1900-year-old maize cobs from Turkey Pen Shelter in the temperate Southwest. Indirectly validated genomic models predicted that Turkey Pen maize was marginally adapted with respect to flowering, as well as short, tillering, and segregating for yellow kernel color. Temperate adaptation drove modern population differentiation and was selected in situ from ancient standing variation. Validated prediction of polygenic traits improves our understanding of ancient phenotypes and the dynamics of environmental adaptation.

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Archaeological excavations carried out during the past five years along the Pacific coast of Mexico, Guatemala, and El Salvador have recovered 79 new 14C dates for the Late Archaic and Early to Middle Formative periods. We analyze these new dates along with 25 previously published dates to refine a sequence of 10 archaeological phases spanning almost three and a half millennia, from ca. 4000 to 650 B.C. The phases are summarized with a brief description of their most salient characteristics. We include illustrations of the Early Formative period ceramics and figurines from the Mazatan region. The sequence of phases reveals a trajectory of cultural evolution beginning in the Archaic period with the mobile hunting, fishing, and gathering Chantuto people. By 1550 B.C., the first ceramic-using sedentary communities appeared on the coast of Chiapas. They were hunter-fisher-gatherers who supplemented their food supply with cultivated plants, including maize and beans. We suggest that by the Locona phase (1400–1250 B.C.) in Chiapas, they began the transition from egalitarian sociopolitical organization to simple chiefdoms, leaving behind evidence of large-scale architectural constructions, long-distance imports such as obsidian and jade, and elaborately crafted prestige goods. Also in Chiapas, during the Cherla phase (1100–1000 B.C.), ceramic and figurine styles, nearly identical to those found at San Lorenzo Tenochtitlan on the Gulf Coast, made their first appearance. Many of the local artifact styles were gradually replaced by styles that became increasingly widespread in Mesoamerica. The chronology presented here shows that these changes were roughly contemporaneous with similar ones in neighboring regions of Mesoamerica.

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