We summarize what is known about Archaic period occupation of southeastern Mesoamerica and Central America as background for presenting new paleoenvironmental evidence of pre-Early Formative human impacts on the landscape of Pacific coastal Guatemala. Our evidence comes from sediment cores in three locations, all of which are in the mangrove-estuary zone of the lower coast. Pollen and phytoliths from the cores document increased burning, decreased forest cover, the appearance of domesticates, and increased disturbance indicators at various times during the Archaic period, the earliest being around 3500 cal B.C. The available evidence demonstrates that shifting horticulture was an early and widespread adaptation to the southeastern Mesoamerican deciduous tropical forest and constituted the base from which later adaptations, including that of early Maya farmers, differentiated. Early Formative adaptive innovations may have been favored by shifts in return rates from various estuarine and terrestrial resources during a dry and variable interval 2000 and 1500 cal B.C.