Starch grain and phytolith evidence for early ninth millennium B.P. maize from the Central Balsas River Valley, Mexico

TLDR

Maize origin and early dispersals remain unclear largely because the Balsas River Valley, home to its wild ancestor, lacks early historical data. The study aims to evaluate how early maize was used and to assess the tempo and timing of human selection on key domestication genes in Zea and Cucurbita using starch and phytolith evidence. Starch grain and phytolith analyses from the Xihuatoxtla shelter were employed to test these hypotheses. Starch and phytolith data show maize present by 8,700 cal.

Abstract

Questions that still surround the origin and early dispersals of maize (Zea mays L.) result in large part from the absence of information on its early history from the Balsas River Valley of tropical southwestern Mexico, where its wild ancestor is native. We report starch grain and phytolith data from the Xihuatoxtla shelter, located in the Central Balsas Valley, that indicate that maize was present by 8,700 calendrical years ago (cal. B.P.). Phytolith data also indicate an early preceramic presence of a domesticated species of squash, possibly Cucurbita argyrosperma. The starch and phytolith data also allow an evaluation of current hypotheses about how early maize was used, and provide evidence as to the tempo and timing of human selection pressure on 2 major domestication genes in Zea and Cucurbita. Our data confirm an early Holocene chronology for maize domestication that has been previously indicated by archaeological and paleoecological phytolith, starch grain, and pollen data from south of Mexico, and reshift the focus back to an origin in the seasonal tropical forest rather than in the semiarid highlands.